Cerebral Time-of-Flight MRI in Third Trimester Fetuses: Visibility of the Circle of Willis, Diameter of the Middle Cerebral Artery, and Tolerability of the Technique Compared with Ultrasound

Cerebral Time-of-Flight MRI in Third Trimester Fetuses: Visibility of the Circle of Willis, Diameter of the Middle Cerebral Artery, and Tolerability of the Technique Compared with Ultrasound | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Cerebral Time-of-Flight MRI in Third Trimester Fetuses: Visibility of the Circle of Willis, Diameter of the Middle Cerebral Artery, and Tolerability of the Technique Compared with Ultrasound Davy Vanderweyen, Kassem Seifeldine, Maude Philibert, Christine Wilk, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7715526/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background: The evaluation of the fetal intracranial arteries remains a challenge. A potential solution could be non-contrast enhanced MRI. Objectives: Evaluating the visibility and size of major intracranial arteries by time-of-flight (TOF) MRI in third trimester pregnancies and evaluate the acceptability and tolerability of MRI in third trimester pregnancies. Materials and methods: Cross-sectional observational study with ten healthy monofetal pregnancies. Participants underwent 3T fetal MRI and Doppler ultrasound to visualize the fetal cerebral vasculature and completed comfort and tolerability questionnaires. The visibility of the arteries forming the fetal circle of Willis (CoW) was evaluated on TOF MRI. Diameters of the middle cerebral arteries (MCA) were compared between MRI and ultrasound. Results: Median maternal age was 30 years, and median gestational age was 37 +1 weeks. The internal carotid arteries and the MCA were visible in all patients. The anterior cerebral arteries were visible in more than 75% of the cases and the posterior cerebral artery in 87.5%. Average MCA diameter was 2.36 mm (± 0.30) for grayscale ultrasound, 2.53 mm (± 0.33) for Doppler, and 1.56 mm (± 0.22) on TOF. Participants expressed high satisfaction levels regarding both examinations. Conclusions: Even if ultrasound is the most used fetal imaging modality, TOF MRI could become an additional tool to visualize and measure the fetal intracranial vasculature and to evaluate vascular anomalies in-utero. Vessel diameter measurements by TOF MRI were on average 1 mm smaller than their ultrasound counterparts. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction The fetal brain is a rapidly developing organ throughout gestation. Because of this longitudinal development and important metabolic needs, which are supported by a constantly adaptative vasculature, the developing brain is highly susceptible to ischemic insults that can lead to long term consequences[ 1 , 2 ]. The milestones of fetal intracranial vasculature development are generally well understood[ 3 ], but their intrauterine evaluation is limited due to the small size of the vessels and their location within the abdominal cavity. Yet, intrauterine imaging of the intracerebral vessels could provide useful early information to clinicians, especially in cases of fetal brain anatomic malformations or fetal stroke[ 4 ]. While Doppler ultrasound can visualize fetal intracranial arteries[ 5 , 6 ], its effectiveness is user dependent and limited by factors such as maternal obesity, abnormal fetus position, and ossified structures[ 7 ]. MRI can address some of these limitations[ 8 ], but MRI-based intrauterine diagnosis of cerebral pathology is typically based on sequences depicting brain parenchyma rather than vessel-focussed Magnetic Resonance Angiography (MRA). This is due to challenges including the small size of blood vessels, the distance between fetal arteries and the MRI’s radiofrequency coils, fetal movements, and the relative contraindication of gadolinium injection during pregnancy. One promising way to visualize intracranial arteries is using a non-contrast-enhanced, flow-sensitive sequence such as Time-of-Flight (TOF). This method has previously been used to image the main fetal vessels such as the aorta, the carotid and vertebral arteries, and the basilar artery and middle cerebral arteries. However, it has shown limited effectiveness in the evaluation of the entire circle of Willis (CW) and intracranial arteries[ 9 , 10 ]. The primary objective of this study was to assess the feasibility of using non-contrast enhanced TOF MRI to visualize not only the major intracranial vessels making up the fetal CW but also to compare lumen diameter measurements obtained with TOF MRI to those acquired through more conventional ultrasound-based methods. A secondary objective was to evaluate the tolerability and acceptability of MR imaging of the fetal CW compared to Doppler Ultrasound. Methods a) Study design This was a prospective cross-sectional unicentric observational study. b) Participants Eligible participants included pregnant women between the ages of 18 and 40 years old with a monofetal pregnancy between the week 36 and 40 of gestational age (GA). Exclusion criteria included contra-indications to MRI, obstetrical complications (such as preterm labour, preterm premature rupture of membranes, etc.), and known fetal malformations. Participants were initially approached during routine obstetrical ultrasound (US) appointments and formally recruited via telephone calls for the participants who accepted to be contacted with further information. Written informed consent was obtained from all participants prior to their involvement. c) Procedure All participants were scheduled for two imaging sessions on the same day. One session was a fetal MRI with TOF sequences, while the other was a Doppler ultrasound. Both exams aimed to assess the fetal cerebral vasculature and evaluate patient acceptability and tolerability of the examinations. Participants were free to discontinue the imaging session at any time. Participants were asked to complete several questionnaires throughout their participation in the study. Sociodemographic data was collected at first contact, as well as postnatally. Before each imaging session, participants completed the State-Trait Anxiety Inventory, Form Y-1[ 11 ]. The comfort and tolerability questionnaires were completed immediately following each exam. d) Ultrasound exam Patients underwent a routine third trimester fetal ultrasound exam (GE Voluson E10) with an additional 2D and color Doppler assessment of the main fetal intracranial arteries. Four different ultrasonographers participated in the project and were instructed to perform an axial view of the fetal brain at the level of the CW with an optimal 75% screen zoom and the lowest gain and power doppler levels needed to adequately visualize the vascular walls of the middle cerebral artery (MCA) in its first originating segment (M1). Three different measures of the inner diameter of the M1 segment of the MCA that was closest to the probe at 1 cm from its origin on the CW were collected, both with and without doppler imaging (Fig. 1 ). The final diameter value for each technique was determined by averaging these three measurements (in mm). The mean duration of the ultrasound exam (including both routine US and intracranial artery evaluation) was 29.9 minutes. e) MR Imaging Fetal MRI was performed on a 3T Ingenia Phillips scanner. Participants were accompanied by a member of the research team throughout the process. They were placed in a left lateral decubitus position to avoid compression of the inferior vena cava by the gravid uterus. Their positioning was adjusted using various wedge pillows to maximise comfort. A body coil was placed over the gravid abdomen, and auditory protection was provided. Routine fetal brain anatomical scans using an axial 2D T2-weighted sequence was followed by an axial 2D MRA sequence for imaging the fetal intracranial vessels. For the TOF-MRA acquisition, the following imaging parameters were used: repetition time/echo time 20/7.6 ms, flip angle 50 degrees, slice thickness 2 mm, number of slices 46, flow direction feet to head, field of view 180 x 180 x 101 and voxel size 0.46 x 0.46 x 2.2 mm. The total scan time for the TOF sequence was under 4 minutes. A fetal functional MRI sequence was also performed for other research purposes not discussed here. f) MRI image processing and measurements An example of an unprocessed TOF image is shown in Fig. 2 a. To improve visibility of the fetal CW, we manually segmented the fetal brain from the T2-weighted image (Fig. 2 b) using FSLeyes[ 12 ] and used it as a mask to suppress maternal vessels on the unprocessed TOF (Fig. 2 c). Next, intracranial arteries in the CW were visually inspected using 3D Slicer[ 13 ]: internal carotid artery (ICA), A1 segment of anterior cerebral artery (A1-ACA), M1 segment of middle cerebral artery (M1-MCA), P1 segment of posterior cerebral artery (P1-PCA), and basilar artery (BA). M1-MCA diameters were measured by digital calipers on 3D Slicer[ 13 , 14 ] at 1cm from the CW by two authors (DV and MP). The average of the two measurements was considered the true diameter and inter-observer agreement was computed. g) Questionnaires Participant’s anxiety prior to each imaging modality was assessed using the State-Trait Anxiety Inventory (STAI), Form Y-1. The STAI is one of the most commonly used questionnaires to measure anxiety in pregnant women[ 11 ], with the Y-1 form being specific to current levels of anxiety. To evaluate tolerability and comfort, participants completed a questionnaire which contained various visual analogue scales of perceived discomfort immediately after each imaging session. The questionnaire was adapted from the one developed by Heilmaier et al.[ 15 ] for evaluating the perception of discomfort in adults, modified to include additional MRI side effects that have been reported in the literature. A slightly modified version was administered after the ultrasound exam, as not all MRI-related side effects are applicable to ultrasound. The discomfort scale ranged from 0 to 100, with 0 = no discomfort and 100 = unbearable discomfort. If the exam was discontinued, the specific reason was detailed. Any other sources of discomfort not included in the scale were also documented. The questionnaire further assessed the overall perceived acceptability of the exam and whether participants would be willing to undergo the exam again. Recall bias was minimized by administering questionnaires immediately before and after each examination. h) Statistical Analysis Analysis was performed using MATLAB and Excel. Socio-demographic and clinical variables are presented with frequencies and percentages for nominal variables. Continuous variables are presented as medians and interquartile ranges considering the small sample size. Two-sided tests and a 5% significance level were used. The Wilcoxon Signed Rank test for paired data was performed to compare vessel diameters and STAI scores obtained before each exam, to determine if anxiety levels differed between modalities, as well as to compare the scores for each of the potential side effects, when applicable. Spearman correlation coefficients were used to calculate significance of correlation between continuous variables. Inter-rater reliability was assessed in accordance with Shrout and Fleiss[ 16 ], using a one-way intraclass correlation coefficient[ 17 ]. Data sharing is available upon request to the corresponding author. i) Ethical approval The study received both ethical and scientific approval from the university hospital’s ethical review board. Results a. Demographical data Between December 2020 and October 2021, approximately 100 potential participants were approached, of which 42 accepted to be contacted for further information. Ultimately, 10 participants met inclusion/exclusion criteria and desired to participate in the study. Sociodemographic characteristics of the participants are presented in Table 1 . Median maternal age at imaging was 30 years old. Median gestational age was 37 +1 weeks at both ultrasound and MRI examination. Medical conditions and tobacco and drug use are also displayed. Table 2 illustrates demographical information about the fetuses and their mode of delivery. Head biometrics and fetal weight were within normal range and all newborns were delivered free of complications. b. Imaging sessions The average duration of MRI examination was 50.8 minutes (standard deviation (SD)=15.7), including the TOF as well as structural and functional MRI sequences (acquired for research purposes, not discussed here). In comparison the entire ultrasound examination had an average duration of 29.9 minutes (SD=6.7). MRI and ultrasound were done on the same day for all but two patients, who needed to reschedule one of the exams for personal reasons; one patient underwent MRI the day after their ultrasound, while the other had MRI five days prior. Patient characteristics Participants (n = 10) Gestational age at MRI 37 +1 (36 +5 – 37 +5 ) weeks Gestational age at ultrasound 37 +1 (36 +5 – 38) weeks Maternal age 30 (26.5 – 33.25) years Number of prior deliveries 0 2 (20%) 1 4 (40%) 2 2 (20%) 3 2 (20%) Ethnicity Caucasian 10 (100%) Country of birth Canada 9 (90%) France 1 (10%) Mother tongue French 9 (90%) English 1 (10%) Pre-pregnancy BMI 1 24.5 (20.1 – 27.3) Diabetes (pre-existing or gestational) 3 (30%) Hypertension (chronic or gestational) 1 (10%) Hypothyroidism (pre-existing or gestational) 1 (10%) Anemia 1 (10%) Medication use in pregnancy 2 (20%) Tobacco use 1 (10%) Cannabis use 1 (10%) Alcohol use 0 Drugs (other) 0 Table 1: demographic data for study participants. Continuous variables are presented with medians and interquartile ranges (IQR). Newborn biometrical data Number of participants (n=9) Gestational age at delivery 39 +1 (38 +6 – 40 +2 ) weeks Birth weight 3405 (3187 – 3660) g Birth cranial circumference 34.5 (34 – 34.5) cm Birth length 51 ( 49 – 53.8) cm Apgar 1 minute 6 1 (11.1%) 8 3 (33.3%) 9 4 (44.4%) 10 1 (11.1%) Apgar 5 minutes 8 1 (11.1%) 9 6 (66.7%) 10 2 (22.2%) Arterial pH 7.25 (7.18 – 7.27) Fetal sex Female 6 (66.7%) Male 3 (33.3%) Mode of delivery Spontaneous Vaginal 3 (33.3%) Assisted Vaginal 1 (11.1%) Cesarian 4 (44.4%) Table 2: Fetus and delivery descriptive statistics. Continuous variables are presented with medians and interquartile ranges (IQR). Data was missing for one fetus. c. Artery visualization On ultrasound, vessels in the cerebral hemisphere closer to the probe were better visualized than those on the contralateral side. The MCA was visualized in all patients. Other proximal arteries could be visualized on Doppler ultrasound, particularly using slow flow techniques, though this was not quantified as this was not the goal of the study. On MRI, the arteries of the CW were well visualized. Representative TOF sequence images of the fetal CW are shown in Fig. 3 . Table 3 displays the frequency of visualisation of the arteries surrounding the CW. Eight of the ten patients yielded TOF images that allowed for adequate visualization of the vessels. One patient was unable to complete the MRI due to discomfort preventing the acquisition of the TOF sequence; in the other patient excessive motion artifacts prevented clear visualization of the fetal arteries, with no repeat acquisition attempted. Frequency of artery visualisation was calculated using the eight remaining images. The ICA, as well as the M1 and proximal M2 segments of the MCA were visible in all patients ( Fig. 4 ). The A1 and proximal A2 segments of the ACA were identifiable in more than 75% of the cases and the PCA in 87.5%. The P1 segments of the PCA were visualized together with their corresponding proximal P2 segments, except in two cases where P1 was not visible. In these instances, the posterior communicating artery (Pcom) and P2 were both visible on the same side, because of a fetal origin of the PCA ( Fig. 5 ). Notably, no Pcom was visualized in the absence of a fetal origin of PCA morphology and the anterior communicating arteries (Acom) could not be visualized. The venous sinuses such as the superior sagittal sinus, straight sinus, and sigmoid sinuses were visible in all subjects. The transverse sinuses, however, were inconsistently visualized, which may be attributed to their orientation relative to the TOF sequencing plane and/or to transverse sinus hypoplasia, an anatomical variant. An example 3D reconstruction of the arterial vessels from one fetus is shown in Fig. 4 . Frequency of visualization of CW arteries Left Artery Right Artery Internal carotid artery 100% (8/8) 100% (8/8) Basilar artery 100% (8/8) 100% (8/8) Anterior cerebral artery 87.5% (7/8) 75% (6/8) Middle cerebral artery 100% (8/8) 100% (8/8) Posterior cerebral artery 87.5% (7/8) 87.5% (7/8) Anterior communicating artery 0% (0/8) 0% (0/8) Posterior communicating artery 12.5% (1/8) 12.5% (1/8) Table 3: Depiction of the frequency of visualization of each artery surrounding the fetal CW 2 on TOF sequences. d. MCA diameter Lumen diameters are shown in Table 4 . The average MCA diameter measured using grayscale ultrasound (on the side closer to the probe, n=9) was 2.44 mm (SD=0.34) while Doppler measurements yielded an average diameter of 2.67 mm (SD=0.43; n=9). For MRI measurements (n=8), the average MCA diameter was 1.56 mm (SD=0.20) on the left and 1.58 mm (SD=0.22) on the right. To allow direct comparison between modalities, an analysis was performed including only patients who had measurements from both modalities (n=7) and considering only the side that was measured by ultrasound. The average diameter was 2.36 mm (SD=0.30) for grayscale, 2.53 mm (SD=0.33) for Doppler ultrasound, and 1.56 mm (SD=0.22) for MRA. While the difference between Doppler and grayscale ultrasound was not statistically significant ( p =0.11), MRA measurements were significantly smaller than both grayscale and Doppler ultrasound ( p =0.016 for both comparisons). Inter-rater reliability for MRA measurements was 0.84. No significant increase in MCA diameter with fetal age was observed. ( Fig. 6 ). Similarly, no significant relationship was found between vessel diameter and estimated fetal weight ( p =0.752 for grayscale; 0.780 for Doppler; 0.372 for MRI). Ultrasound and MRA 1 MCA 2 measurements Ultrasound MRA Patient Side of measure Grayscale diameter (mm) Doppler diameter (mm) Left MCA diameter (mm) Right MCA diameter (mm) 1 Right 2.87 2.93 Evaluator 1: 1.9 Evaluator 2: 1.9 Evaluator 1: 1.8 Evaluator 2: 1.9 2 Right 2.15 2.30 Evaluator 1: 1.4 Evaluator 2: 1.5 Evaluator 1: 1.4 Evaluator 2: 1.3 3 Left 2.30 2.00 Evaluator 1: 1.5 Evaluator 2: 1.6 Evaluator 1: 1.7 Evaluator 2:1.7 4 Right 2.43 2.90 No TOF due to premature exam termination. No TOF due to premature exam termination. 5 Right 2.57 2.57 Evaluator 1: 1.5 Evaluator 2: 1.2 Evaluator 1: 1.5 Evaluator 2: 1.4 6 Evaluator 1: 1.6 Evaluator 2: 1.6 Evaluator 1: 1.4 Evaluator 2: 1.4 7 Right 2.45 2.45 Evaluator 1: 1.4 Evaluator 2: 1.2 Evaluator 1: 1.4 Evaluator 2: 1.2 8 Right 1.93 2.93 Evaluator 1: 1.7 Evaluator 2: 1.7 Evaluator 1: 1.9 Evaluator 2: 1.8 9 Left 3.00 3.47 Too much movement artefacts Too much movement artefacts 10 Left 2.25 2.50 Evaluator 1: 1.6 Evaluator 2: 1.6 Evaluator 1: 1.6 Evaluator 2: 1.7 Average of total 2.44 2.67 Evaluator 1: 1.58 (SD=0.167) Evaluator 2: 1.54 (SD=0.239) Both evaluators: 1.56 (SD=0.221) Evaluator 1: 1.59 (SD=0.196) Evaluator 2: 1.56 (SD=0.256) Both evaluators: 1.57 (SD=0.200) Table 4: Lumen diameters of fetal MCA arteries. Ultrasound values are given as average of 3 different measures. MRA values are given as average of single measures from two different readers. The MRA MCA measurements ipsilateral to ultrasound are in bold. SD: standard deviation. e. Anxiety scores The median STAI anxiety score prior to MRI was 24.5 (interquartile range: 20.8 - 29.0) while the median score prior to ultrasound was 21.0 (interquartile range: 20.0 - 22.0). This difference was statistically significant ( p =0.042). Table 5 illustrates the median score and interquartile ranges for perceived discomfort across different side effects and imaging modalities, as well as the result of the Wilcoxon Signed Rank Test. All participants stated they would accept to undergo ultrasound again, both for research as well as medical purposes. Regarding MRI, all participants would undergo the exam again for medical reasons; however, one participant expressed unwillingness to participate in MRI again for research purpose. MRI (n = 10) Median (IQR) Ultrasound (n = 10) Median (IQR) Wilcoxon Signed Rank Test p value General discomfort 52.0 (12.0 – 65.0) 15.0 (0 – 23.3) 0.011 General positioning 50.0 (6.5 – 64.8) 0 (0.0 – 2.5) 0.012 Lying down for a prolonged period 51.5 (9.5 – 63.3) 9 (0 – 50) 0.028 Ambient temperature 1.0 (0 – 19.3) 0.5 (0 – 22.3) 0.917 Noise level 37.5 (13.8 – 66.3) 0 (0 – 4.0) 0.015 Narrowness of the device 10.5 (0 – 52.3) N/A N/A Movement 2.5 (0 – 33.8) N/A N/A Heat 32.5 (0 – 69.3) N/A N/A Having little contact with others during the exam 0 (0 – 17.0) N/A N/A Vertigo 14.0 Experienced by 3 participants N/A N/A Metallic taste Experienced by none of the participants N/A N/A Global acceptability (n = 9) 88.0 (76.5 – 100) 100 (93.5 - 100) 0.68 Table 5: Side effects experienced by patients based on imaging modality. Scale is from 0-100 percent discomfort, with 0 = no discomfort whatsoever and 100 = unbearable. Discussion a. Vessel visualisation To our knowledge, only one study has evaluated fetal intracranial vessel visibility with MRI[10], successfully visualizing the vertebral, basilar, and middle cerebral arteries on a 1.5T MR scanner. In our study, we used a 3T scanner, which improved visualization of the brain arteries forming the fetal CW and the proximal segments of major intracranial arteries. In contrast, ultrasound imaging offered a more restricted view of the CW and its main vessels, particularly in the hemisphere farther from the probe. b. Diameter measurement In this study, MCA diameter was measured using MRI, grayscale ultrasound and Doppler ultrasound. Doppler ultrasound yielded slightly larger MCA lumen diameter measurements compared to grayscale ultrasound (2.5 mm vs 2.4 mm), though this difference was not statistically significant. This could be caused by blooming artefacts, which could artificially increase apparent vessel size. This notion is illustrated on Fig. 1 . In contrast, TOF MRI measurements (~1.6 mm) showed an MCA diameter almost 1 mm smaller than ultrasound techniques. Our ultrasound-based MCA diameter measurements were smaller than those reported in previous studies. Konje et al.[18] used Doppler ultrasound to measure the diameter of the MCA in fetuses, reporting a mean diameter of 4.5 (±1) mm at 36 weeks GA and 4.6 (±1) mm at 38 weeks GA. Veille et al.[19] reported an inner MCA diameter of 3.4 (±0.2) mm for fetuses at 37 weeks GA. We hypothesize that Doppler-based MCA diameter measurements in the literature overestimate the true size of the fetal MCA, as a multimodal meta-analysis reported a mean adult MCA diameter of 2.55 ± 0.42 mm[20]. Given this, it would be surprising for the fetal MCA to be larger than in adults. Two anatomopathological studies have measured the diameter of fetal CW arteries. Gielecki et al.[21] examined fetuses fixed in formalin using intravascular injection of suspended latex. For fetuses between 37 and 40 weeks of GA, the mean M1 MCA outer diameter was 1.22 (±0.21) mm, which is closer to our MRI measures (~1.6mm) than those obtained by ultrasound (~2.4mm). This difference, however, could be due to vascular shrinkage caused by formalin fixation, or the lack of vessel distension by endoluminal pressure that would occur in a living fetus. Indeed, formalin fixation can shrink tissue samples by up to 40% [22]. If we apply this correction factor, the estimated in vivo MCA diameter would be 1.7mm, which is very similar to our TOF MRI values. In another related study, Seydel et al. analysed the ratio of MCA to ICA diameters in 98 post-mortem human fetuses[23], reporting an average MCA/ICA ratio of 0.75 (SD=0.11). Using a similar approach for our TOF MRI measurements, we observed an average ratio of 0.797 (SD=0.124), thus indicating a high degree of similarity between MRI measurements and postmortem findings. Several factors might explain the differences in MCA diameter values between the two modalities. The smaller vessel size observed with TOF MRI may be due to its high sensitivity to intraluminal flow, which excludes vessel wall thickness from the measurement. In contrast, on grayscale ultrasound, the vessel wall may be difficult to visualize, and it may be included in the measurement when using digital calipers ( Fig. 1a ). Given that normal MCA wall thickness is 0.2-0.3mm[24], this could result in an overestimation of vessel diameter of 0.4-0.6mm when using ultrasound. Additionally, there is some evidence that ultrasound may overestimate arterial wall thickness[25]. Other technical factors could also impact ultrasound image quality, such as patient body habitus, use of image zoom, and gain modifications. c. Anxiety and tolerability To our knowledge, this is the first study to assess patients’ perspective on their MRI imaging experience and directly compare it to ultrasound examination. Although anxiety levels preceding the MRI exam were higher than those reported before the ultrasound, this difference is unlikely to have significant clinical impact and overall, the levels of stress preceding both exams were low. The most important MRI-related factors contributing to general discomfort were noise, positioning, and the need to lie down for an extended period, which is expected, as it is well known that the decubitus position can be quite uncomfortable late in pregnancy. Limited contact with the examiner, the narrowness of the MRI machine, ambient temperature, and device movement were perceived as less significant sources of discomfort. A few participants experienced mild heat or dizziness/vertigo. Over 90% of participants indicated they would be willing to undergo both imaging modalities again for medical and research purposes. d. Applications The in-vivo visualization of the fetal CW arteries could have numerous clinical applications. It could enable the detailed description of the normal development and morphology of the fetal intracranial vasculature in relation to the developing brain, as well as aid in diagnosing fetal brain pathology. For example, antenatal diagnosis and characterization of vascular malformations and antenatal strokes. Additionally, this approach could open avenues for research into the effects of various antenatal exposures, such as medications, drugs, or toxins ingested by the mother on fetal cerebral vasculature, with a particular focus on investigating vasoconstrictive effects on the fetus. e. Limitations The primary limitation of this study is its small sample size, as this is a pilot study. Additionally, the patient population was exclusively Caucasian (reflecting the local population), limiting generalizability. Participation in the study was voluntary, potentially excluding participants who might be significantly more anxious or uncomfortable during obstetrical examinations, thereby introducing a sampling bias. Conclusion Non-contrast MRA using TOF sequence allows visualization of the main fetal brain arteries, providing a comprehensive view of the fetal CW and proximal cerebral arteries. While MCA lumen diameters measured by MRI are significantly smaller than those measured by ultrasound, the difference is less than 1 mm. Additionally, MRI appears to be a generally well-tolerated and acceptable imaging modality for most pregnant women, even in advanced stages of pregnancy, with no significant differences in acceptability compared to ultrasound. This data supports the exploration of MRI sequences in pregnancy to improve our understanding of fetal intracerebral vasculature and brain development without placing undue burden on patients. Declarations Ethical approval The study received both ethical and scientific approval from the university hospital’s ethical review board. Table 5 Side effects experienced by patients based on imaging modality. Scale is from 0-100 percent discomfort, with 0 = no discomfort whatsoever and 100 = unbearable. Conclusion Non-contrast MRA using TOF sequence allows visualization of the main fetal brain arteries, providing a comprehensive view of the fetal CW and proximal cerebral arteries. While MCA lumen diameters measured by MRI are significantly smaller than those measured by ultrasound, the difference is less than 1 mm. Additionally, MRI appears to be a generally well-tolerated and acceptable imaging modality for most pregnant women, even in advanced stages of pregnancy, with no significant differences in acceptability compared to ultrasound. This data supports the exploration of MRI sequences in pregnancy to improve our understanding of fetal intracerebral vasculature and brain development without placing undue burden on patients. Author Contribution DV wrote the main manuscript, participated in the data gathering for the MRI part , and did some of the statistical analysis and data interpretation.KS gathered and preprocessed most of the MRI data, and participated in writing the manuscript.MP was involved in data gathering for the MRI part, computed some statistics, and participated in writing the paper.CW wrote the initial protocol of the study and gathered and analyzed data notably concerning the questionnaires. AO supervised the clinical aspects of the project notably patient recrutment, questionaire administration, data gathering, and ultrasound image acquisition.KW supervised the imaging aspect of the project, notably the MRI image acquisition and analysis.DV and KS co-first authors (equal contribution)AO and KW co-senior authors (equal contribution) References Hagberg H, Mallard C (2000) Antenatal brain injury: aetiology and possibilities of prevention. Seminars in Neonatology 5:41–51. https://doi.org/10.1053/SINY.1999.0114 Govaert P (2009) Prenatal stroke. Semin Fetal Neonatal Med 14:250–266. https://doi.org/10.1016/J.SINY.2009.07.008 Raybaud C (2010) Normal and Abnormal Embryology and Development of the Intracranial Vascular System. Neurosurg Clin N Am 21:399–426. https://doi.org/10.1016/J.NEC.2010.03.011 Özduman K, Pober BR, Barnes P, Copel JA, Ogle EA, Duncan CC, Ment LR (2004) Fetal stroke. 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Stroke: Vascular and Interventional Neurology 4:. https://doi.org/10.1161/SVIN.123.001177 Gielecki J, Zurada A, Kozlłowska H, Nowak D, Loukas M (2009) Morphometric and volumetric analysis of the middle cerebral artery in human fetuses. Acta Neurobiol Exp (Wars) 69:129–137. https://doi.org/10.55782/ANE-2009-1735 Kerns MJJ, Darst MA, Olsen TG, Fenster M, Hall P, Grevey S (2008) Shrinkage of cutaneous specimens: formalin or other factors involved? J Cutan Pathol 35:1093–1096. https://doi.org/10.1111/J.1600-0560.2007.00943.X Seydel HG (1964) The diameters of the cerebral arteries of the human fetus. Anat Rec 150:79–88. https://doi.org/10.1002/AR.1091500108 Mandell DM, Mossa-Basha M, Qiao Y, Hess CP, Hui F, Matouk C, Johnson MH, Daemen MJAP, Vossough A, Edjlali M, Saloner D, Ansari SA, Wasserman BA, Mikulis DJ (2017) Intracranial Vessel Wall MRI: Principles and Expert Consensus Recommendations of the American Society of Neuroradiology. AJNR Am J Neuroradiol 38:218. https://doi.org/10.3174/AJNR.A4893 Mallery JA, Tobis JM, Griffith J, Gessert J, McRae M, Moussabeck O, Bessen M, Moriuchi M, Henry WL (1990) Assessment of normal and atherosclerotic arterial wall thickness with an intravascular ultrasound imaging catheter. Am Heart J 119:1392–1400. https://doi.org/10.1016/S0002-8703(05)80190-5 Footnotes BMI: Body Mass index. CW: Circle of Willis. MRA: Magnetic Resonance Imaging MCA: Middle Cerebral Artery. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7715526","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":528155145,"identity":"77c25bff-6bde-4faf-8dd5-f79faf60e918","order_by":0,"name":"Davy 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09:12:56","extension":"html","order_by":16,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":115898,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7715526/v1/cc645fee151c5ded656064fb.html"},{"id":93573775,"identity":"b01e9164-285b-4509-a35e-fb00e58c6222","added_by":"auto","created_at":"2025-10-15 09:12:55","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1308908,"visible":true,"origin":"","legend":"\u003cp\u003eFetal middle cerebral artery measurements in a) using grayscale ultrasound and b) in Doppler mode for the same patient, transabdominal axial view.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7715526/v1/7e0b6b3851a40b164ee2901e.png"},{"id":93574952,"identity":"9bf54395-27d0-4a69-823d-71f117cac6f8","added_by":"auto","created_at":"2025-10-15 09:20:56","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":583531,"visible":true,"origin":"","legend":"\u003cp\u003ea) Example of an unprocessed TOF image of a fetal brain in oblique axial view showing hypersignal in the fetal cerebral vessels as well as in surrounding maternal uterine vessels. b) T2-weighted sequence of mother’s pelvis displaying axial view of fetal brain. c) Axial T2-weighted image (left) and Axial TOF image (right) in slight Maximum Intensity Projection (MIP) view after brain extraction.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7715526/v1/6a5e141613cb46b3eb4f8723.png"},{"id":93573777,"identity":"1c981fe8-6ea1-44a1-97cd-3b1d4f44654e","added_by":"auto","created_at":"2025-10-15 09:12:55","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":2093444,"visible":true,"origin":"","legend":"\u003cp\u003eExamples of four axial TOF sequences centered on the circle of Willis with a slight MIP component. Arrowheads: anterior cerebral arteries; open arrows: middle cerebral arteries, closed arrows: posterior cerebral arteries.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7715526/v1/b9d854d57092bdd842439e5b.png"},{"id":93574950,"identity":"659abc88-157c-46ad-8d79-768bf3d271be","added_by":"auto","created_at":"2025-10-15 09:20:55","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":918081,"visible":true,"origin":"","legend":"\u003cp\u003eExample of 3D reconstruction of the arterial vessels from one fetus. a) Axial MIP and b) posterior left oblique MIP views of arteries around the circle of Willis. c) axial, d) sagittal, and e) posterior left oblique MIP views of the same arteries with outline of fetal head. Internal carotid arteries are depicted in blue, middle cerebral arteries in beige, A1 segment of anterior cerebral arteries in yellow, A2 segment of anterior cerebral artery in red, basilar artery in pink, and P1 segment of posterior cerebral arteries in purple.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7715526/v1/77d657cd616788696a88bacb.png"},{"id":93573779,"identity":"a9f36435-1c8b-47f1-a341-252864d2f892","added_by":"auto","created_at":"2025-10-15 09:12:55","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1196742,"visible":true,"origin":"","legend":"\u003cp\u003eAxial TOF sequence slightly caudal to the circle of Willis with a visible left posterior communicating artery (curved arrow). Closed arrows: posterior cerebral arteries (PCA); open arrows: middle cerebral arteries; arrowhead: basilar artery. No P1 segment of PCA was visible on the left, thus indicative of a fetal origin of the left PCA.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-7715526/v1/b40fc9c0b64e8b06d9cac89c.png"},{"id":93574955,"identity":"00a8bbeb-38b0-44f8-975c-45ce698d58e2","added_by":"auto","created_at":"2025-10-15 09:20:56","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":287890,"visible":true,"origin":"","legend":"\u003cp\u003eScatter plot of MCA diameter according to gestational age measured by MRI as well as grayscale and doppler ultrasound. There is no trend toward increasing size of vessels with gestational age. Doppler measurements tended to be slightly larger than grayscale ultrasound. MRI measurements were constantly smaller than those made on ultrasound. MCA: Middle Cerebral Artery.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-7715526/v1/abbc4ba295c03337712b66d4.png"},{"id":95228948,"identity":"79cb2390-87bf-4dc0-b9cc-b08830cb5df5","added_by":"auto","created_at":"2025-11-05 16:34:18","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7756611,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7715526/v1/d1d5ca29-7122-479a-a2ea-74f768e2e01b.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Cerebral Time-of-Flight MRI in Third Trimester Fetuses: Visibility of the Circle of Willis, Diameter of the Middle Cerebral Artery, and Tolerability of the Technique Compared with Ultrasound","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe fetal brain is a rapidly developing organ throughout gestation. Because of this longitudinal development and important metabolic needs, which are supported by a constantly adaptative vasculature, the developing brain is highly susceptible to ischemic insults that can lead to long term consequences[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe milestones of fetal intracranial vasculature development are generally well understood[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], but their intrauterine evaluation is limited due to the small size of the vessels and their location within the abdominal cavity. Yet, intrauterine imaging of the intracerebral vessels could provide useful early information to clinicians, especially in cases of fetal brain anatomic malformations or fetal stroke[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. While Doppler ultrasound can visualize fetal intracranial arteries[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], its effectiveness is user dependent and limited by factors such as maternal obesity, abnormal fetus position, and ossified structures[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. MRI can address some of these limitations[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], but MRI-based intrauterine diagnosis of cerebral pathology is typically based on sequences depicting brain parenchyma rather than vessel-focussed Magnetic Resonance Angiography (MRA). This is due to challenges including the small size of blood vessels, the distance between fetal arteries and the MRI\u0026rsquo;s radiofrequency coils, fetal movements, and the relative contraindication of gadolinium injection during pregnancy. One promising way to visualize intracranial arteries is using a non-contrast-enhanced, flow-sensitive sequence such as Time-of-Flight (TOF). This method has previously been used to image the main fetal vessels such as the aorta, the carotid and vertebral arteries, and the basilar artery and middle cerebral arteries. However, it has shown limited effectiveness in the evaluation of the entire circle of Willis (CW) and intracranial arteries[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe primary objective of this study was to assess the feasibility of using non-contrast enhanced TOF MRI to visualize not only the major intracranial vessels making up the fetal CW but also to compare lumen diameter measurements obtained with TOF MRI to those acquired through more conventional ultrasound-based methods. A secondary objective was to evaluate the tolerability and acceptability of MR imaging of the fetal CW compared to Doppler Ultrasound.\u003c/p\u003e"},{"header":"Methods","content":"\u003ch3\u003ea) Study design\u003c/h3\u003e\n\u003cp\u003eThis was a prospective cross-sectional unicentric observational study.\u003c/p\u003e\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eb) Participants\u003c/h2\u003e\u003cp\u003eEligible participants included pregnant women between the ages of 18 and 40 years old with a monofetal pregnancy between the week 36 and 40 of gestational age (GA). Exclusion criteria included contra-indications to MRI, obstetrical complications (such as preterm labour, preterm premature rupture of membranes, etc.), and known fetal malformations. Participants were initially approached during routine obstetrical ultrasound (US) appointments and formally recruited via telephone calls for the participants who accepted to be contacted with further information. Written informed consent was obtained from all participants prior to their involvement.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003ec) Procedure\u003c/h3\u003e\n\u003cp\u003eAll participants were scheduled for two imaging sessions on the same day. One session was a fetal MRI with TOF sequences, while the other was a Doppler ultrasound. Both exams aimed to assess the fetal cerebral vasculature and evaluate patient acceptability and tolerability of the examinations. Participants were free to discontinue the imaging session at any time.\u003c/p\u003e\u003cp\u003eParticipants were asked to complete several questionnaires throughout their participation in the study. Sociodemographic data was collected at first contact, as well as postnatally. Before each imaging session, participants completed the State-Trait Anxiety Inventory, Form Y-1[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The comfort and tolerability questionnaires were completed immediately following each exam.\u003c/p\u003e\n\u003ch3\u003ed) Ultrasound exam\u003c/h3\u003e\n\u003cp\u003ePatients underwent a routine third trimester fetal ultrasound exam (GE Voluson E10) with an additional 2D and color Doppler assessment of the main fetal intracranial arteries. Four different ultrasonographers participated in the project and were instructed to perform an axial view of the fetal brain at the level of the CW with an optimal 75% screen zoom and the lowest gain and power doppler levels needed to adequately visualize the vascular walls of the middle cerebral artery (MCA) in its first originating segment (M1). Three different measures of the inner diameter of the M1 segment of the MCA that was closest to the probe at 1 cm from its origin on the CW were collected, both with and without doppler imaging (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The final diameter value for each technique was determined by averaging these three measurements (in mm). The mean duration of the ultrasound exam (including both routine US and intracranial artery evaluation) was 29.9 minutes.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\n\u003ch3\u003ee) MR Imaging\u003c/h3\u003e\n\u003cp\u003eFetal MRI was performed on a 3T Ingenia Phillips scanner. Participants were accompanied by a member of the research team throughout the process. They were placed in a left lateral decubitus position to avoid compression of the inferior vena cava by the gravid uterus. Their positioning was adjusted using various wedge pillows to maximise comfort. A body coil was placed over the gravid abdomen, and auditory protection was provided.\u003c/p\u003e\u003cp\u003eRoutine fetal brain anatomical scans using an axial 2D T2-weighted sequence was followed by an axial 2D MRA sequence for imaging the fetal intracranial vessels. For the TOF-MRA acquisition, the following imaging parameters were used: repetition time/echo time 20/7.6 ms, flip angle 50 degrees, slice thickness 2 mm, number of slices 46, flow direction feet to head, field of view 180 x 180 x 101 and voxel size 0.46 x 0.46 x 2.2 mm. The total scan time for the TOF sequence was under 4 minutes. A fetal functional MRI sequence was also performed for other research purposes not discussed here.\u003c/p\u003e\n\u003ch3\u003ef) MRI image processing and measurements\u003c/h3\u003e\n\u003cp\u003eAn example of an unprocessed TOF image is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea. To improve visibility of the fetal CW, we manually segmented the fetal brain from the T2-weighted image (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb) using FSLeyes[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] and used it as a mask to suppress maternal vessels on the unprocessed TOF (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). Next, intracranial arteries in the CW were visually inspected using 3D Slicer[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]: internal carotid artery (ICA), A1 segment of anterior cerebral artery (A1-ACA), M1 segment of middle cerebral artery (M1-MCA), P1 segment of posterior cerebral artery (P1-PCA), and basilar artery (BA).\u003c/p\u003e\u003cp\u003eM1-MCA diameters were measured by digital calipers on 3D Slicer[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] at 1cm from the CW by two authors (DV and MP). The average of the two measurements was considered the true diameter and inter-observer agreement was computed.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eg) Questionnaires\u003c/h2\u003e\u003cp\u003eParticipant\u0026rsquo;s anxiety prior to each imaging modality was assessed using the State-Trait Anxiety Inventory (STAI), Form Y-1. The STAI is one of the most commonly used questionnaires to measure anxiety in pregnant women[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], with the Y-1 form being specific to current levels of anxiety.\u003c/p\u003e\u003cp\u003eTo evaluate tolerability and comfort, participants completed a questionnaire which contained various visual analogue scales of perceived discomfort immediately after each imaging session. The questionnaire was adapted from the one developed by Heilmaier et al.[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] for evaluating the perception of discomfort in adults, modified to include additional MRI side effects that have been reported in the literature. A slightly modified version was administered after the ultrasound exam, as not all MRI-related side effects are applicable to ultrasound. The discomfort scale ranged from 0 to 100, with 0\u0026thinsp;=\u0026thinsp;no discomfort and 100\u0026thinsp;=\u0026thinsp;unbearable discomfort. If the exam was discontinued, the specific reason was detailed. Any other sources of discomfort not included in the scale were also documented. The questionnaire further assessed the overall perceived acceptability of the exam and whether participants would be willing to undergo the exam again. Recall bias was minimized by administering questionnaires immediately before and after each examination.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003eh) Statistical Analysis\u003c/h2\u003e\u003cp\u003eAnalysis was performed using MATLAB and Excel. Socio-demographic and clinical variables are presented with frequencies and percentages for nominal variables. Continuous variables are presented as medians and interquartile ranges considering the small sample size. Two-sided tests and a 5% significance level were used. The Wilcoxon Signed Rank test for paired data was performed to compare vessel diameters and STAI scores obtained before each exam, to determine if anxiety levels differed between modalities, as well as to compare the scores for each of the potential side effects, when applicable. Spearman correlation coefficients were used to calculate significance of correlation between continuous variables. Inter-rater reliability was assessed in accordance with Shrout and Fleiss[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], using a one-way intraclass correlation coefficient[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Data sharing is available upon request to the corresponding author.\u003c/p\u003e\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003ei) Ethical approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study received both ethical and scientific approval from the university hospital\u0026rsquo;s ethical review board.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003ea. \u0026nbsp; Demographical data\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBetween December 2020 and October 2021, approximately 100 potential participants were approached, of which 42 accepted to be contacted for further information. Ultimately, 10 participants met inclusion/exclusion criteria and desired to participate in the study. Sociodemographic characteristics of the participants are presented in \u003cstrong\u003eTable 1\u003c/strong\u003e. Median maternal age at imaging was 30 years old. Median gestational age was 37\u003csup\u003e+1\u003c/sup\u003e weeks at both ultrasound and MRI examination. Medical conditions and tobacco and drug use are also displayed.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2\u003c/strong\u003e illustrates demographical information about the fetuses and their mode of delivery. Head biometrics and fetal weight were within normal range and all newborns were delivered free of complications.\u003c/p\u003e\n\u003cp\u003eb. \u003cstrong\u003eImaging sessions\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe average duration of MRI examination was 50.8 minutes (standard deviation (SD)=15.7), including the TOF as well as structural and functional MRI sequences (acquired for research purposes, not discussed here). In comparison the entire ultrasound examination had an average duration of 29.9 minutes (SD=6.7). MRI and ultrasound were done on the same day for all but two patients, who needed to reschedule one of the exams for personal reasons; one patient underwent MRI the day after their ultrasound, while the other had MRI five days prior.\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 304px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePatient characteristics\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eParticipants (n = 10) \u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 304px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eGestational age at MRI\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e37\u003csup\u003e+1\u003c/sup\u003e (36\u003csup\u003e+5\u003c/sup\u003e \u0026ndash; 37\u003csup\u003e+5\u003c/sup\u003e) weeks\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 304px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eGestational age at ultrasound\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e37\u003csup\u003e+1\u003c/sup\u003e (36\u003csup\u003e+5\u003c/sup\u003e \u0026ndash; 38) weeks\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 304px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMaternal age\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e30 (26.5 \u0026ndash; 33.25) years\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"4\" valign=\"top\" style=\"width: 154px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eNumber of prior deliveries\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e2 (20%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e4 (40%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e2 (20%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e2 (20%)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 154px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eEthnicity\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCaucasian\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e10 (100%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" valign=\"top\" style=\"width: 154px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCountry of birth\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCanada\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e9 (90%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFrance\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e1 (10%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" valign=\"top\" style=\"width: 154px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMother tongue\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFrench\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e9 (90%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 150px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eEnglish\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e1 (10%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 304px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePre-pregnancy BMI\u003cstrong\u003e\u003csup\u003e1\u003c/sup\u003e\u003c/strong\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e24.5 (20.1 \u0026ndash; 27.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 304px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eDiabetes (pre-existing or gestational)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e3 (30%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 304px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eHypertension (chronic or gestational)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e1 (10%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 304px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eHypothyroidism (pre-existing or gestational)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e1 (10%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 304px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAnemia\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e1 (10%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 304px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMedication use in pregnancy\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e2 (20%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 304px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTobacco use\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e1 (10%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 304px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCannabis use\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e1 (10%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 304px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAlcohol use\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 304px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eDrugs (other)\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 297px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1:\u003c/strong\u003e demographic data for study participants. Continuous variables are presented with medians and interquartile ranges (IQR).\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"623\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eNewborn biometrical data\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eNumber of participants (n=9)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eGestational age at delivery \u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e39\u003csup\u003e+1\u003c/sup\u003e\u0026nbsp;\u003c/strong\u003e(38\u003csup\u003e+6\u003c/sup\u003e \u0026ndash; 40\u003csup\u003e+2\u003c/sup\u003e) weeks\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eBirth weight\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e3405\u003c/strong\u003e (3187 \u0026ndash; 3660) g\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eBirth cranial circumference \u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e34.5\u003c/strong\u003e (34 \u0026ndash; 34.5) cm\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eBirth length\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e51 (\u003c/strong\u003e49 \u0026ndash; 53.8) cm\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"4\" valign=\"top\" style=\"width: 156px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eApgar 1 minute\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 156px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e6\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e1 (11.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 156px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e8\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e3 (33.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 156px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e9\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e4 (44.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 156px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e10\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e1 (11.1%)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 156px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eApgar 5 minutes\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 156px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e8\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e1 (11.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 156px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 156px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e9\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e6 (66.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 156px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 156px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e10\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e2 (22.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eArterial pH\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e7.25 (7.18 \u0026ndash; 7.27)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" valign=\"top\" style=\"width: 156px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFetal sex\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 156px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFemale\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e6 (66.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 156px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMale\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e3 (33.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" valign=\"top\" style=\"width: 156px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMode of delivery \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 156px;\"\u003e\n \u003cp\u003eSpontaneous Vaginal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e3 (33.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 156px;\"\u003e\n \u003cp\u003eAssisted Vaginal\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e1 (11.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 156px;\"\u003e\n \u003cp\u003eCesarian\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 312px;\"\u003e\n \u003cp\u003e4 (44.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2:\u003c/strong\u003e Fetus and delivery descriptive statistics. Continuous variables are presented with medians and interquartile ranges (IQR). Data was missing for one fetus.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ec. \u0026nbsp; Artery visualization\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOn ultrasound, vessels in the cerebral hemisphere closer to the probe were better visualized than those on the contralateral side. The MCA was visualized in all patients. Other proximal arteries could be visualized on Doppler ultrasound, particularly using slow flow techniques, though this was not quantified as this was not the goal of the study.\u003c/p\u003e\n\u003cp\u003eOn MRI, the arteries of the CW were well visualized. Representative TOF sequence images of the fetal CW are shown in \u003cstrong\u003eFig. 3\u003c/strong\u003e. \u003cstrong\u003eTable 3\u003c/strong\u003e displays the frequency of visualisation of the arteries surrounding the CW. Eight of the ten patients yielded TOF images that allowed for adequate visualization of the vessels. One patient was unable to complete the MRI due to discomfort preventing the acquisition of the TOF sequence; in the other patient excessive motion artifacts prevented clear visualization of the fetal arteries, with no repeat acquisition attempted. Frequency of artery visualisation was calculated using the eight remaining images. The ICA, as well as the M1 and proximal M2 segments of the MCA were visible in all patients (\u003cstrong\u003eFig. 4\u003c/strong\u003e). The A1 and proximal A2 segments of the ACA were identifiable in more than 75% of the cases and the PCA in 87.5%. The P1 segments of the PCA were visualized together with their corresponding proximal P2 segments, except in two cases where P1 was not visible. In these instances, the posterior communicating artery (Pcom) and P2 were both visible on the same side, because of a fetal origin of the PCA (\u003cstrong\u003eFig. 5\u003c/strong\u003e). Notably, no Pcom was visualized in the absence of a fetal origin of PCA morphology and the anterior communicating arteries (Acom) could not be visualized. The venous sinuses such as the superior sagittal sinus, straight sinus, and sigmoid sinuses were visible in all subjects. The transverse sinuses, however, were inconsistently visualized, which may be attributed to their orientation relative to the TOF sequencing plane and/or to transverse sinus hypoplasia, an anatomical variant. An example 3D reconstruction of the arterial vessels from one fetus is shown in \u003cstrong\u003eFig. 4\u003c/strong\u003e.\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"3\" valign=\"top\" style=\"width: 595px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFrequency of visualization of CW arteries\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 284px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 161px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eLeft Artery\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 151px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eRight Artery\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 284px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eInternal carotid artery\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e100% (8/8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 151px;\"\u003e\n \u003cp\u003e100% (8/8)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 284px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eBasilar artery\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e100% (8/8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e100% (8/8)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 284px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAnterior cerebral artery\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e87.5% (7/8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 151px;\"\u003e\n \u003cp\u003e75% (6/8)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 284px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMiddle cerebral artery\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e100% (8/8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 151px;\"\u003e\n \u003cp\u003e100% (8/8)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 284px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePosterior cerebral artery\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e\u0026nbsp;87.5% (7/8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 151px;\"\u003e\n \u003cp\u003e87.5% (7/8)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 284px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAnterior communicating artery\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e0% (0/8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e0% (0/8)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 284px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePosterior communicating artery\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e12.5% (1/8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 151px;\"\u003e\n \u003cp\u003e12.5% (1/8)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3:\u0026nbsp;\u003c/strong\u003eDepiction of the frequency of visualization of each artery surrounding the fetal CW\u003csup\u003e2\u003c/sup\u003e on TOF sequences.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ed. \u0026nbsp; MCA diameter\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eLumen diameters are shown in \u003cstrong\u003eTable 4\u003c/strong\u003e. \u0026nbsp;The average MCA diameter measured using grayscale ultrasound (on the side closer to the probe, n=9) was 2.44 mm (SD=0.34) while Doppler measurements yielded an average diameter of 2.67 mm (SD=0.43; n=9). For MRI measurements (n=8), the average MCA diameter was 1.56 mm (SD=0.20) on the left and 1.58 mm (SD=0.22) on the right. To allow direct comparison between modalities, an analysis was performed including only patients who had measurements from both modalities (n=7) and considering only the side that was measured by ultrasound. The average diameter was 2.36 mm (SD=0.30) for grayscale, 2.53 mm (SD=0.33) for Doppler ultrasound, and 1.56 mm (SD=0.22) for MRA. While the difference between Doppler and grayscale ultrasound was not statistically significant (\u003cem\u003ep\u003c/em\u003e=0.11), MRA measurements were significantly smaller than both grayscale and Doppler ultrasound (\u003cem\u003ep\u003c/em\u003e=0.016 for both comparisons). Inter-rater reliability for MRA measurements was 0.84. No significant increase in MCA diameter with fetal age was observed. (\u003cstrong\u003eFig. 6\u003c/strong\u003e). Similarly, no significant relationship was found between vessel diameter and estimated fetal weight (\u003cem\u003ep\u003c/em\u003e=0.752 for grayscale; 0.780 for Doppler; 0.372 for MRI).\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"605\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"5\" valign=\"top\" style=\"width: 535px;\"\u003e\n \u003cp\u003eUltrasound and MRA\u003csup\u003e1\u003c/sup\u003e MCA\u003csup\u003e2\u003c/sup\u003e measurements\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 3px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" valign=\"top\" style=\"width: 274px;\"\u003e\n \u003cp\u003eUltrasound\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 262px;\"\u003e\n \u003cp\u003eMRA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 3px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003ePatient\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 75px;\"\u003e\n \u003cp\u003eSide of measure\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eGrayscale diameter (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003eDoppler diameter (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eLeft MCA diameter (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eRight MCA diameter (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 75px;\"\u003e\n \u003cp\u003eRight\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003e2.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003e2.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eEvaluator 1: 1.9\u003c/p\u003e\n \u003cp\u003eEvaluator 2: 1.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eEvaluator 1: \u003cstrong\u003e1.8\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eEvaluator 2: \u003cstrong\u003e1.9\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 75px;\"\u003e\n \u003cp\u003eRight\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003e2.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003e2.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eEvaluator 1: 1.4\u003c/p\u003e\n \u003cp\u003eEvaluator 2: 1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eEvaluator 1: \u003cstrong\u003e1.4\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eEvaluator 2: \u003cstrong\u003e1.3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 75px;\"\u003e\n \u003cp\u003eLeft\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003e2.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003e2.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eEvaluator 1: \u003cstrong\u003e1.5\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eEvaluator 2: \u003cstrong\u003e1.6\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eEvaluator 1: 1.7\u003c/p\u003e\n \u003cp\u003eEvaluator 2:1.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 75px;\"\u003e\n \u003cp\u003eRight\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003e2.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003e2.90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eNo TOF due to premature exam termination.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eNo TOF due to premature exam termination.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 75px;\"\u003e\n \u003cp\u003eRight\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003e2.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003e2.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eEvaluator 1: 1.5\u003c/p\u003e\n \u003cp\u003eEvaluator 2: 1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eEvaluator 1: \u003cstrong\u003e1.5\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eEvaluator 2: \u003cstrong\u003e1.4\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 75px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eEvaluator 1: 1.6\u003c/p\u003e\n \u003cp\u003eEvaluator 2: 1.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eEvaluator 1: 1.4\u003c/p\u003e\n \u003cp\u003eEvaluator 2: 1.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 75px;\"\u003e\n \u003cp\u003eRight\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003e2.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003e2.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eEvaluator 1: 1.4\u003c/p\u003e\n \u003cp\u003eEvaluator 2: 1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eEvaluator 1: \u003cstrong\u003e1.4\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eEvaluator 2: \u003cstrong\u003e1.2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 75px;\"\u003e\n \u003cp\u003eRight\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003e1.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003e2.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eEvaluator 1: 1.7\u003c/p\u003e\n \u003cp\u003eEvaluator 2: 1.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eEvaluator 1:\u003cstrong\u003e1.9\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003eEvaluator 2: \u003cstrong\u003e1.8\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 75px;\"\u003e\n \u003cp\u003eLeft\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003e3.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003e3.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eToo much movement artefacts\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eToo much movement artefacts\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 75px;\"\u003e\n \u003cp\u003eLeft\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003e2.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003e2.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eEvaluator 1: \u003cstrong\u003e1.6\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eEvaluator 2: \u003cstrong\u003e1.6\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eEvaluator 1: 1.6\u003c/p\u003e\n \u003cp\u003eEvaluator 2: 1.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003eAverage of total\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 75px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003e2.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 104px;\"\u003e\n \u003cp\u003e2.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eEvaluator 1: 1.58 (SD=0.167)\u003c/p\u003e\n \u003cp\u003eEvaluator 2: 1.54 (SD=0.239)\u003c/p\u003e\n \u003cp\u003eBoth evaluators: 1.56 (SD=0.221)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eEvaluator 1: 1.59 (SD=0.196)\u003c/p\u003e\n \u003cp\u003eEvaluator 2: 1.56 (SD=0.256)\u003c/p\u003e\n \u003cp\u003eBoth evaluators: 1.57 (SD=0.200)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 68px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 129px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 3px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eTable 4:\u0026nbsp;\u003c/strong\u003eLumen\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ediameters of fetal MCA arteries. Ultrasound values are given as average of 3 different measures. MRA values are given as average of single measures from two different readers. The MRA MCA measurements ipsilateral to ultrasound are in bold. SD: standard deviation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ee. \u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eAnxiety scores\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe median STAI anxiety score prior to MRI was 24.5 (interquartile range: 20.8 - 29.0) while the median score prior to ultrasound was 21.0 (interquartile range: 20.0 - 22.0). This difference was statistically significant (\u003cem\u003ep\u003c/em\u003e=0.042).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 5\u003c/strong\u003e illustrates the median score and interquartile ranges for perceived discomfort across different side effects and imaging modalities, as well as the result of the Wilcoxon Signed Rank Test.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAll participants stated they would accept to undergo ultrasound again, both for research as well as medical purposes. Regarding MRI, all participants would undergo the exam again for medical reasons; however, one participant expressed unwillingness to participate in MRI again for research purpose.\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 166px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMRI\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e(n = 10)\u003c/p\u003e\n \u003cp\u003eMedian (IQR)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 157px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eUltrasound\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e(n = 10)\u003c/p\u003e\n \u003cp\u003eMedian (IQR)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 133px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eWilcoxon Signed Rank Test\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cem\u003e\u0026nbsp;p\u0026nbsp;\u003c/em\u003evalue\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 166px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eGeneral discomfort\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e52.0\u0026nbsp;\u003c/strong\u003e(12.0 \u0026ndash; 65.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 157px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e15.0\u0026nbsp;\u003c/strong\u003e(0 \u0026ndash; 23.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 133px;\"\u003e\n \u003cp\u003e0.011\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 166px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eGeneral positioning\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e50.0\u003c/strong\u003e (6.5 \u0026ndash; 64.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 157px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0\u0026nbsp;\u003c/strong\u003e(0.0 \u0026ndash; 2.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 133px;\"\u003e\n \u003cp\u003e0.012\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 166px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eLying down for a prolonged period\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e51.5\u0026nbsp;\u003c/strong\u003e(9.5 \u0026ndash; 63.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 157px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e9\u0026nbsp;\u003c/strong\u003e(0 \u0026ndash; 50)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 133px;\"\u003e\n \u003cp\u003e0.028\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 166px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAmbient temperature\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e1.0\u003c/strong\u003e (0 \u0026ndash; 19.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 157px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.5\u003c/strong\u003e (0 \u0026ndash; 22.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 133px;\"\u003e\n \u003cp\u003e0.917\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 166px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eNoise level\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e37.5\u0026nbsp;\u003c/strong\u003e(13.8 \u0026ndash; 66.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 157px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0\u0026nbsp;\u003c/strong\u003e(0 \u0026ndash; 4.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 133px;\"\u003e\n \u003cp\u003e0.015\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 166px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eNarrowness of the device\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e10.5\u003c/strong\u003e (0 \u0026ndash; 52.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 157px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 133px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 166px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMovement\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e2.5\u003c/strong\u003e (0 \u0026ndash; 33.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 157px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 133px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 166px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eHeat\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e32.5\u0026nbsp;\u003c/strong\u003e(0 \u0026ndash; 69.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 157px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 133px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 166px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eHaving little contact with others during the exam\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0\u0026nbsp;\u003c/strong\u003e(0 \u0026ndash; 17.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 157px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 133px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 166px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eVertigo\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e14.0\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eExperienced by 3 participants\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 157px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 133px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 166px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMetallic taste\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 146px;\"\u003e\n \u003cp\u003eExperienced by none of the participants\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 157px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 133px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 166px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eGlobal acceptability\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e(n = 9)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 146px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e88.0\u0026nbsp;\u003c/strong\u003e(76.5 \u0026ndash; 100)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 157px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e100\u0026nbsp;\u003c/strong\u003e(93.5 - 100)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 133px;\"\u003e\n \u003cp\u003e0.68\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eTable 5:\u003c/strong\u003e Side effects experienced by patients based on imaging modality. Scale is from 0-100 percent discomfort, with 0 = no discomfort whatsoever and 100 = unbearable.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003e\u003cstrong\u003ea.\u0026nbsp; \u0026nbsp;Vessel visualisation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo our knowledge, only one study has evaluated fetal intracranial vessel visibility with MRI[10], successfully visualizing the vertebral, basilar, and middle cerebral arteries on a 1.5T MR scanner. In our study, we used a 3T scanner, which improved visualization of the brain arteries forming the fetal CW and the proximal segments of major intracranial arteries. In contrast, ultrasound imaging offered a more restricted view of the CW and its main vessels, particularly in the hemisphere farther from the probe.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eb. \u003cstrong\u003eDiameter measurement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn this study, MCA diameter was measured using MRI, grayscale ultrasound and Doppler ultrasound. Doppler ultrasound yielded slightly larger MCA lumen diameter measurements compared to grayscale ultrasound (2.5 mm vs 2.4 mm), though this difference was not statistically significant. This could be caused by blooming artefacts, which could artificially increase apparent vessel size. This notion is illustrated on \u003cstrong\u003eFig. 1\u003c/strong\u003e. In contrast, TOF MRI measurements (~1.6 mm) showed an MCA diameter almost 1 mm smaller than ultrasound techniques.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOur ultrasound-based MCA diameter measurements were smaller than those reported in previous studies. Konje et al.[18] used Doppler ultrasound to measure the diameter of the MCA in fetuses, reporting a mean diameter of 4.5 (±1) mm at 36 weeks GA and 4.6 (±1) mm at 38 weeks GA. Veille et al.[19] reported an inner MCA diameter of 3.4 (±0.2) mm for fetuses at 37 weeks GA. We hypothesize that Doppler-based MCA diameter measurements in the literature overestimate the true size of the fetal MCA, as a multimodal meta-analysis reported a mean adult MCA diameter of 2.55\u0026nbsp;±\u0026nbsp;0.42 mm[20]. Given this, it would be surprising for the fetal MCA to be larger than in adults.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTwo anatomopathological studies have measured the diameter of fetal CW arteries. Gielecki et al.[21] examined fetuses fixed in formalin using intravascular injection of suspended latex. For fetuses between 37 and 40 weeks of GA, the mean M1 MCA outer diameter was 1.22 (±0.21) mm, which is closer to our MRI measures (~1.6mm) than those obtained by ultrasound (~2.4mm). This difference, however, could be due to vascular shrinkage caused by formalin fixation, or the lack of vessel distension by endoluminal pressure that would occur in a living fetus. Indeed, formalin fixation can shrink tissue samples by up to 40% [22]. If we apply this correction factor, the estimated in vivo MCA diameter would be 1.7mm, which is very similar to our TOF MRI values. In another related study, Seydel et al. analysed the ratio of MCA to ICA diameters in 98 post-mortem human fetuses[23], reporting an average MCA/ICA ratio of 0.75 (SD=0.11). Using a similar approach for our TOF MRI measurements, we observed an average ratio of 0.797 (SD=0.124), thus indicating a high degree of similarity between MRI measurements and postmortem findings.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSeveral factors might explain the differences in MCA diameter values between the two modalities. \u0026nbsp;The smaller vessel size observed with TOF MRI may be due to its high sensitivity to intraluminal flow, which excludes vessel wall thickness from the measurement. In contrast, on grayscale ultrasound, the vessel wall may be difficult to visualize, and it may be included in the measurement when using digital calipers (\u003cstrong\u003eFig. 1a\u003c/strong\u003e). Given that normal MCA wall thickness is 0.2-0.3mm[24], this could result in an overestimation of vessel diameter of 0.4-0.6mm when using ultrasound. Additionally, there is some evidence that ultrasound may overestimate arterial wall thickness[25]. Other technical factors could also impact ultrasound image quality, such as patient body habitus, use of image zoom, and gain modifications.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ec.\u0026nbsp; \u0026nbsp;Anxiety and tolerability\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo our knowledge, this is the first study to assess patients’ perspective on their MRI imaging experience and directly compare it to ultrasound examination. Although anxiety levels preceding the MRI exam were higher than those reported before the ultrasound, this difference is unlikely to have significant clinical impact and overall, the levels of stress preceding both exams were low.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe most important MRI-related factors contributing to general discomfort were noise, positioning, and the need to lie down for an extended period, which is expected, as it is well known that the decubitus position can be quite uncomfortable late in pregnancy. Limited contact with the examiner, the narrowness of the MRI machine, ambient temperature, and device movement were perceived as less significant sources of discomfort. A few participants experienced mild heat or dizziness/vertigo. Over 90% of participants indicated they would be willing to undergo both imaging modalities again for medical and research purposes.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ed.\u0026nbsp; \u0026nbsp;Applications\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe in-vivo visualization of the fetal CW arteries could have numerous clinical applications. It could enable the detailed description of the normal development and morphology of the fetal intracranial vasculature in relation to the developing brain, as well as aid in diagnosing fetal brain pathology. For example, antenatal diagnosis and characterization of vascular malformations and antenatal strokes. Additionally, this approach could open avenues for research into the effects of various antenatal exposures, such as medications, drugs, or toxins ingested by the mother on fetal cerebral vasculature, with a particular focus on investigating vasoconstrictive effects on the fetus.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ee.\u0026nbsp; \u0026nbsp;Limitations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe primary limitation of this study is its small sample size, as this is a pilot study. Additionally, the patient population was exclusively Caucasian (reflecting the local population), limiting generalizability. Participation in the study was voluntary, potentially excluding participants who might be significantly more anxious or uncomfortable during obstetrical examinations, thereby introducing a sampling bias.\u0026nbsp;\u003c/p\u003e"},{"header":"Conclusion ","content":"\u003cp\u003eNon-contrast MRA using TOF sequence allows visualization of the main fetal brain arteries, providing a comprehensive view of the fetal CW and proximal cerebral arteries. While MCA lumen diameters measured by MRI are significantly smaller than those measured by ultrasound, the difference is less than 1 mm.\u003c/p\u003e\n\u003cp\u003eAdditionally, MRI appears to be a generally well-tolerated and acceptable imaging modality for most pregnant women, even in advanced stages of pregnancy, with no significant differences in acceptability compared to ultrasound. This data supports the exploration of MRI sequences in pregnancy to improve our understanding of fetal intracerebral vasculature and brain development without placing undue burden on patients.\u0026nbsp;\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eEthical approval\u003c/h2\u003e\u003cp\u003e The study received both ethical and scientific approval from the university hospital\u0026rsquo;s ethical review board.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003ch2\u003eTable\u0026nbsp;5\u003c/h2\u003e\u003cp\u003eSide effects experienced by patients based on imaging modality. Scale is from 0-100 percent discomfort, with 0\u0026thinsp;=\u0026thinsp;no discomfort whatsoever and 100\u0026thinsp;=\u0026thinsp;unbearable.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003ch2\u003eConclusion\u003c/h2\u003e\u003cp\u003eNon-contrast MRA using TOF sequence allows visualization of the main fetal brain arteries, providing a comprehensive view of the fetal CW and proximal cerebral arteries. While MCA lumen diameters measured by MRI are significantly smaller than those measured by ultrasound, the difference is less than 1 mm.\u003c/p\u003e\u003cp\u003eAdditionally, MRI appears to be a generally well-tolerated and acceptable imaging modality for most pregnant women, even in advanced stages of pregnancy, with no significant differences in acceptability compared to ultrasound. This data supports the exploration of MRI sequences in pregnancy to improve our understanding of fetal intracerebral vasculature and brain development without placing undue burden on patients.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eDV wrote the main manuscript, participated in the data gathering for the MRI part , and did some of the statistical analysis and data interpretation.KS gathered and preprocessed most of the MRI data, and participated in writing the manuscript.MP was involved in data gathering for the MRI part, computed some statistics, and participated in writing the paper.CW wrote the initial protocol of the study and gathered and analyzed data notably concerning the questionnaires. AO supervised the clinical aspects of the project notably patient recrutment, questionaire administration, data gathering, and ultrasound image acquisition.KW supervised the imaging aspect of the project, notably the MRI image acquisition and analysis.DV and KS co-first authors (equal contribution)AO and KW co-senior authors (equal contribution)\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eHagberg H, Mallard C (2000) Antenatal brain injury: aetiology and possibilities of prevention. Seminars in Neonatology 5:41\u0026ndash;51. https://doi.org/10.1053/SINY.1999.0114\u003c/li\u003e\n\u003cli\u003eGovaert P (2009) Prenatal stroke. Semin Fetal Neonatal Med 14:250\u0026ndash;266. https://doi.org/10.1016/J.SINY.2009.07.008\u003c/li\u003e\n\u003cli\u003eRaybaud C (2010) Normal and Abnormal Embryology and Development of the Intracranial Vascular System. Neurosurg Clin N Am 21:399\u0026ndash;426. https://doi.org/10.1016/J.NEC.2010.03.011\u003c/li\u003e\n\u003cli\u003e\u0026Ouml;zduman K, Pober BR, Barnes P, Copel JA, Ogle EA, Duncan CC, Ment LR (2004) Fetal stroke. Pediatr Neurol 30:151\u0026ndash;162. https://doi.org/10.1016/J.PEDIATRNEUROL.2003.08.004\u003c/li\u003e\n\u003cli\u003eArbeille PH, Tranquart F, Berson M, Roncin A, Saliba E, Pourcelot L (1989) Visualization of the fetal circle of Willis and intra-cerebral arteries by color-coded Doppler. Eur J Obstet Gynecol Reprod Biol 32:195\u0026ndash;198. https://doi.org/10.1016/0028-2243(89)90035-X\u003c/li\u003e\n\u003cli\u003eDanon E, Weisz B, Achiron R, Pretorius DH, Weissmann-Brenner A, Gindes L (2016) Three-dimensional ultrasonographic depiction of fetal brain blood vessels. Prenat Diagn 36:407\u0026ndash;417. https://doi.org/10.1002/PD.4791\u003c/li\u003e\n\u003cli\u003eHendler I, Blackwell SC, Bujold E, Treadwell MC, Mittal P, Sokol RJ, Sorokin Y (2005) Suboptimal second-trimester ultrasonographic visualization of the fetal heart in obese women: should we repeat the examination? J Ultrasound Med 24:1205\u0026ndash;1210. https://doi.org/10.7863/JUM.2005.24.9.1205\u003c/li\u003e\n\u003cli\u003eBlondiaux E, Garel C (2013) Fetal cerebral imaging - Ultrasound vs. MRI: An update. Acta radiol 54:1046\u0026ndash;1054. https://doi.org/10.1258/AR.2012.120428\u003c/li\u003e\n\u003cli\u003eNeelavalli J, Krishnamurthy U, Jella PK, Mody SS, Yadav BK, Hendershot K, Hernandez-Andrade E, Yeo L, Cabrera MD, Haacke EM, Hassan SS, Romero R (2016) Magnetic resonance angiography of fetal vasculature at 3.0 T. Eur Radiol 26:4570\u0026ndash;4576. https://doi.org/10.1007/S00330-016-4243-4\u003c/li\u003e\n\u003cli\u003eSampaio L, Morana G, Gon\u0026ccedil;alves H, Rossi A, Ramalho C (2024) Fetal brain MR angiography at 1.5 T: a feasible study. Neuroradiology 66:271\u0026ndash;278. https://doi.org/10.1007/S00234-023-03243-5\u003c/li\u003e\n\u003cli\u003eEvans K, Spiby H, Morrell CJ (2015) A psychometric systematic review of self-report instruments to identify anxiety in pregnancy. J Adv Nurs 71:1986\u0026ndash;2001. https://doi.org/10.1111/JAN.12649\u003c/li\u003e\n\u003cli\u003eMcCarthy P (2024) FSLeyes\u003c/li\u003e\n\u003cli\u003eD Slicer image computing platform | 3D Slicer. https://www.slicer.org/. Accessed 3 Nov 2024\u003c/li\u003e\n\u003cli\u003eFedorov A, Beichel R, Kalpathy-Cramer J, Finet J, Fillion-Robin JC, Pujol S, Bauer C, Jennings D, Fennessy F, Sonka M, Buatti J, Aylward S, Miller J V., Pieper S, Kikinis R (2012) 3D Slicer as an image computing platform for the Quantitative Imaging Network. Magn Reson Imaging 30:1323\u0026ndash;1341. https://doi.org/10.1016/J.MRI.2012.05.001\u003c/li\u003e\n\u003cli\u003eHeilmaier C, Theysohn JM, Maderwald S, Kraff O, Ladd ME, Ladd SC (2011) A large-scale study on subjective perception of discomfort during 7 and 1.5 T MRI examinations. Bioelectromagnetics 32:610\u0026ndash;619. https://doi.org/10.1002/BEM.20680\u003c/li\u003e\n\u003cli\u003eShrout PE, Fleiss JL (1979) Intraclass correlations: uses in assessing rater reliability. Psychol Bull 86:420\u0026ndash;428. https://doi.org/10.1037//0033-2909.86.2.420\u003c/li\u003e\n\u003cli\u003eBrownhill K Intraclass correlation coefficients - File Exchange - MATLAB Central. https://www.mathworks.com/matlabcentral/fileexchange/21501-intraclass-correlation-coefficients. Accessed 7 Nov 2024\u003c/li\u003e\n\u003cli\u003eKonje JC, Abrams K, Bell SC, De Chazal RC, Taylor DJ (2000) The application of color power angiography to the longitudinal quantification of blood flow volume in the fetal middle cerebral arteries, ascending aorta, descending aorta, and renal arteries during gestation. Am J Obstet Gynecol 182:393\u0026ndash;400. https://doi.org/10.1016/S0002-9378(00)70230-4\u003c/li\u003e\n\u003cli\u003eVeille JC, Hanson R, Tatum K (1993) Longitudinal quantitation of middle cerebral artery blood flow in normal human fetuses. Am J Obstet Gynecol 169:1393\u0026ndash;1398. https://doi.org/10.1016/0002-9378(93)90406-9\u003c/li\u003e\n\u003cli\u003eMirza M, Kummer K, Touchette J, McCarthy R, Rai A, Brouwer P, Gilvarry M (2024) Variability in Intracranial Vessel Diameters and Considerations for Neurovascular Models: A Systematic Review and Meta‐Analysis. Stroke: Vascular and Interventional Neurology 4:. https://doi.org/10.1161/SVIN.123.001177\u003c/li\u003e\n\u003cli\u003eGielecki J, Zurada A, Kozlłowska H, Nowak D, Loukas M (2009) Morphometric and volumetric analysis of the middle cerebral artery in human fetuses. Acta Neurobiol Exp (Wars) 69:129\u0026ndash;137. https://doi.org/10.55782/ANE-2009-1735\u003c/li\u003e\n\u003cli\u003eKerns MJJ, Darst MA, Olsen TG, Fenster M, Hall P, Grevey S (2008) Shrinkage of cutaneous specimens: formalin or other factors involved? J Cutan Pathol 35:1093\u0026ndash;1096. https://doi.org/10.1111/J.1600-0560.2007.00943.X\u003c/li\u003e\n\u003cli\u003eSeydel HG (1964) The diameters of the cerebral arteries of the human fetus. Anat Rec 150:79\u0026ndash;88. https://doi.org/10.1002/AR.1091500108\u003c/li\u003e\n\u003cli\u003eMandell DM, Mossa-Basha M, Qiao Y, Hess CP, Hui F, Matouk C, Johnson MH, Daemen MJAP, Vossough A, Edjlali M, Saloner D, Ansari SA, Wasserman BA, Mikulis DJ (2017) Intracranial Vessel Wall MRI: Principles and Expert Consensus Recommendations of the American Society of Neuroradiology. AJNR Am J Neuroradiol 38:218. https://doi.org/10.3174/AJNR.A4893\u003c/li\u003e\n\u003cli\u003eMallery JA, Tobis JM, Griffith J, Gessert J, McRae M, Moussabeck O, Bessen M, Moriuchi M, Henry WL (1990) Assessment of normal and atherosclerotic arterial wall thickness with an intravascular ultrasound imaging catheter. Am Heart J 119:1392\u0026ndash;1400. https://doi.org/10.1016/S0002-8703(05)80190-5\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Footnotes","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003e BMI: Body Mass index.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003e CW: Circle of Willis.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003e MRA: Magnetic Resonance Imaging\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003e MCA: Middle Cerebral Artery.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-7715526/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7715526/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe evaluation of the fetal intracranial arteries remains a challenge. A potential solution could be non-contrast enhanced MRI.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eObjectives:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEvaluating the visibility and size of major intracranial arteries by time-of-flight (TOF) MRI in third trimester pregnancies and evaluate the acceptability and tolerability of MRI in third trimester pregnancies.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMaterials and methods:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCross-sectional observational study with ten healthy monofetal pregnancies. Participants underwent 3T fetal MRI and Doppler ultrasound to visualize the fetal cerebral vasculature and completed comfort and tolerability questionnaires.\u003c/p\u003e\n\u003cp\u003eThe visibility of the arteries forming the fetal circle of Willis (CoW) was evaluated on TOF MRI. Diameters of the middle cerebral arteries (MCA) were compared between MRI and ultrasound.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMedian maternal age was 30 years, and median gestational age was 37\u003csup\u003e+1\u003c/sup\u003e weeks. The internal carotid arteries and the MCA were visible in all patients. The anterior cerebral arteries were visible in more than 75% of the cases and the posterior cerebral artery in 87.5%. Average MCA diameter was 2.36 mm (± 0.30) for grayscale ultrasound, 2.53 mm (± 0.33) for Doppler, and 1.56 mm (± 0.22) on TOF. Participants expressed high satisfaction levels regarding both examinations.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEven if ultrasound is the most used fetal imaging modality, TOF MRI could become an additional tool to visualize and measure the fetal intracranial vasculature and to evaluate vascular anomalies in-utero. Vessel diameter measurements by TOF MRI were on average 1 mm smaller than their ultrasound counterparts.\u003c/p\u003e","manuscriptTitle":"Cerebral Time-of-Flight MRI in Third Trimester Fetuses: Visibility of the Circle of Willis, Diameter of the Middle Cerebral Artery, and Tolerability of the Technique Compared with Ultrasound","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-15 09:12:51","doi":"10.21203/rs.3.rs-7715526/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"d2d1ee58-ca79-4a68-8ef0-0de581f357f8","owner":[],"postedDate":"October 15th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-11-05T15:53:49+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-15 09:12:51","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7715526","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7715526","identity":"rs-7715526","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}