Comparison of cone beam CT and low-field MRI of the distal limb of 85 standing sedated horses

Comparison of cone beam CT and low-field MRI of the distal limb of 85 standing sedated horses | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL Equine Veterinary Education This is a preprint and has not been peer reviewed. Data may be preliminary. 19 May 2025 V1 Latest version Share on Comparison of cone beam CT and low-field MRI of the distal limb of 85 standing sedated horses Authors : Sarah Taylor 0000-0002-9714-8495 [email protected] , Padraig Kelly , Carola Daniel 0000-0002-4801-5151 , Oliver James 0000-0002-7399-9690 , Mattie McMaster , and Tobias Schwarz Authors Info & Affiliations https://doi.org/10.22541/au.174767603.34807364/v1 549 views 254 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Background Cone beam computed tomography (CBCT) and magnetic resonance imaging (MRI) of the equine foot under standing sedation are increasingly available yet there is little published information to guide veterinarians on how both modalities compare to optimise horse management. Objective To describe dual modality CBCT and MRI findings in the equine foot of images acquired in the standing sedated horse on the same day for clinical purposes. Study design Retrospective descriptive study Methods Clinical records, CBCT and MRI DICOM images of patients that underwent advanced imaging with both modalities on the same day (April 2024-April 2025) were reviewed. Key imaging findings were categorised to allow comparison of CBCT and MRI findings. Results Imaging studies of 85 horses met the inclusion criteria resulting in imaging of 120 foot and 38 pastern regions. Twenty-four of 85 horses had a primary soft tissue injury that was detected on MRI but not visible on CBCT. Forty-four horses had increased STIR signal on MRI within the phalanges or navicular bone. CBCT identified small sequestration of the distal phalanx that was identified on MRI retrospectively subsequent to CBCT evaluation. CBCT allowed clearer evaluation of cortical bone specifically at the margins of the flexor cortex of the navicular bone and the articular surfaces of the phalanges. Main limitations Imaging findings were not verified by a gold standard and are subjective and descriptive. Categorical representation of primary diagnosis was difficult for some horses. The horses evaluated are limited to a mixed referral population of horses in Scotland. Conclusions The primary diagnosis was provided by MRI in more horses than CBCT due to the ability of MRI to identify soft tissue injury. Combined MRI and CBCT imaging of the foot can provide additional information in horses of solar penetration or where careful evaluation of cortical bone is needed. Comparison of cone beam CT and low-field MRI of the distal limb of 85 standing sedated horses Sarah E. Taylor, Padraig Kelly, Carola Daniel, Oliver James, Mattie McMaster, and Tobias Schwarz The University of Edinburgh, Royal (Dick) School of Veterinary Studies and Roslin Institute, Roslin, Midlothian, UK, EH25 9RG Keywords: MRI; CT; computed tomography; dual modality advanced imaging; equine foot Background Cone beam computed tomography (CBCT) and magnetic resonance imaging (MRI) of the equine foot carried out under standing sedation are increasingly available yet there is little published information to guide veterinarians on how both modalities compare to optimise horse management. Objective To describe dual modality CBCT and MRI findings in the equine foot of images acquired in the standing sedated horse on the same day for clinical purposes. Study design Retrospective descriptive study Methods Clinical records, CBCT and MRI DICOM images of patients that underwent advanced imaging with both modalities on the same day (April 2024-April 2025) were reviewed. Key imaging findings were categorised to allow comparison of CBCT and MRI findings. Results Imaging studies of 85 horses met the inclusion criteria resulting in imaging of 120 foot and 38 pastern regions. Twenty-four of 85 horses had a primary soft tissue injury that was detected on MRI but not visible on CBCT. Forty-four horses had increased STIR signal on MRI within the phalanges or navicular bone. CBCT identified small sequestration of the distal phalanx that was identified on MRI retrospectively subsequent to CBCT evaluation. CBCT allowed clearer evaluation of cortical bone specifically at the margins of the flexor cortex of the navicular bone and the articular surfaces of the phalanges. Main limitations Imaging findings were not verified by a gold standard and are subjective and descriptive. Categorical representation of primary diagnosis was difficult for some horses. The horses evaluated are limited to a mixed referral population of horses in Scotland. Conclusions The primary diagnosis was provided by MRI in more horses than CBCT due to the ability of MRI to identify soft tissue injury. Combined MRI and CBCT imaging of the foot can provide additional information in horses of solar penetration or where careful evaluation of cortical bone is needed. Clinical relevance • Primary diagnoses were yielded by MRI in more horses than CBCT • CBCT provided additional information in horses where there was a fracture of the distal phalanx or osteolysis at a joint surface • Dual-modality CBCT and MRI imaging is complimentary in horses of osteoarthropathy of the distal interphalangeal joint INTRODUCTION Low-field magnetic resonance imaging (MRI) in the standing seated horse was first available in 2002 in the United Kingdon and since this date has become widely accessible worldwide. Standing cone beam computed tomography (CBCT) has recently been developed and is becoming more widely available. Whilst there are many studies that describe the prevalence of lesions detected on low-field MRI (Cillan-Garcia et al. 2013; Gutierrez-Nibeyro et al. 2020) and a study of fan beam CT of the distal limb (Pauwels et al. 2021), there is a paucity of scientific literature describing the findings of CBCT of the equine foot (Stewart et al. 2021) despite published comparisons for the equine metacarpophalangeal joint (Lin et al. 2025). Both MRI and CBCT are able to provide multi-plane and multi-slice, cross-sectional images of tissues which provide detailed information of the area imaged. Structural imaging is a detailed representation of the tissue of interest and is dependent on several factors. Spatial resolution, which determines the detail of an image, is dependent on voxel size. Voxel size is partially dependent on slice thickness. Computed tomography images often have thinner slice thickness and excel at spatial resolution. They also provide better detail of the edges of structures (Abdulkareem et al. 2023) such as the bone at a joint surface. Functional imaging is the detection of parameters related to physiology or pathology of tissues. Magnetic resonance imaging is dependent on the movement of protons within a tissue and is able to detect the water content of tissues. Short tau inversion recovery (STIR) sequences suppress the fat signal so that water content of cancellous bone can be identified hence providing information about bruising or haemorrhage in that tissue that would not be evident on CBCT. Conversely, tissue that have very tightly bound protons, such as cortical bone typically, have very low signal on MRI and appear hypointense on MR images. CT on the other hand is able to provide detailed information on cortical bone. Combining high resolution structural imaging and functional imaging has the potential to optimise clinical cross-sectional imaging to provide the most information for the patient. For example, CT can provide better structural information of cortical and subchondral bone but is not able to identify bruising or ‘bone oedema’ that would be detectable by MRI and indicate an active injury. The aim of this study was to document and compare changes identified with both low-field MRI and CBCT of the equine foot and pastern of studies acquired in the standing sedated horse on the same day. It was hypothesized that the primary diagnosis for the horse would be given by low-filed MRI in more cases that by CBCT and that all osseous features detectable on CBCT would be evident on low-field MRI. MATERIALS AND METHODS Materials A retrospective review of clinical records, MRI and CT DICOM images of the foot/feet and pastern regions from horses imaged at Royal (Dick) School of Veterinary Studies, The University of Edinburgh, for clinical reasons was conducted. Inclusion criteria for the study were images from horses with pain localised to the front foot/feet undergoing both standing low-field (0.27 Tesla) MRI (Hallmarq sMRI, Hallmarq Veterinary Imaging Ltd) and standing CBCT (Hallmarq Vision CT, Hallmarq Veterinary Imaging Ltd) imaging on the same day between April 2024 and April 2025 for clinical reasons. The decision to undertake both MRI and CT was made due to a policy change at The University of Edinburgh whereby the clench check formerly performed with radiographs was replaced with CBCT. Ethical approval for the study was granted by The University of Edinburgh Veterinary Ethical Research Committee (VERC 189.23) and informed, written client consent was obtained for all horses. Localisation of pain to the foot was performed with diagnostic analgesia if a positive response was found following a palmar digital nerve block, abaxial sesamoid nerve block or intra-articular analgesia of the distal interphalangeal joint. The decision to image one foot, both feet or foot and pastern regions was at the discretion of the clinician reading the live images with knowledge of the lameness history and blocking pattern. Clinical findings of a recent solar penetration or draining tract of the foot or lameness following medication of the distal interphalangeal joint were also considered as localising pain to the foot. MR images acquired included T1W HR gradient echo (GRE), T2*W GRE, T2W fast spin echo (FSE) and STIR FSE sequences in dorsal, sagittal and transverse planes. CBCT image acquisition variables were 75 kV and 0.7 mA, 20 cm × 20 cm field of view and matrix size of 800 × 800 × 800 voxels with 0.25 mm thickness after reconstruction. Methods Image analyses CBCT and MRI images were retrospectively reviewed by an experienced interpreter (S.E.T). Imaging findings were recorded by describing the presence, location and characteristics of the CT attenuation/MRI signal intensity of lesions. Imaging findings were compared retrospectively, to clinical findings in the patient clinical notes (O.J, M.M. and P.K.) and the clinical imaging reports written (by T.S., S.E.T. and C.D.) at the time of image acquisition. Categorisation of CBCT and MRI findings Lesions observed on CBCT and MRI were categorised into one of the following categories: Soft tissue abnormalities 1. Increased T1, T2*, T2 FSE and STIR signal within the deep digital flexor tendon consistent with tendinopathy (seen on MRI only). 2. Increased T2 FSE or STIR signal indicative of desmopathy of collateral ligaments of the distal interphalangeal joint (seen on MRI only). 3. Increased T2 FSE or STIR signal indicative of desmopathy of one of the ligaments of the foot and pastern (seen on MRI only). Osseous abnormalities 1. Increased STIR signal consistent with bone bruising of distal, middle or proximal phalanges (seen on MRI only). 2. Navicular bone abnormalities; bone oedema (increased STIR signal on MRI), distal border fragment, elongation of flexor cortex, increased number/size of synovial invaginations, sclerosis or lysis of the spongiosa bone. 3. Regions of suspected bone sclerosis of the proximal, middle and distal phalanges or ungual cartilages (reduced T1, T2* and T2 FSE signal on MRI and/or hyperattenuation on CBCT) 4. Regions of suspected bone lysis of the proximal, middle and distal phalanges (reduced T1, T2* and T2 FSE signal on MRI and/or hypoattenuation on CBCT) 5. Distal phalanx fracture or ungual cartilage fracture. Hoof wall abnormalities Hoof wall abnormalities: Solar penetration; presence of a tract visible as a susceptibility artefact on MRI or hypoattenuation due to gas or fluid seen on CBCT. Laminar tearing, keratoma, quittor, hoof wall abnormalities seen on CBCT and/or MRI. Osteoarthropathy Osteoarthropathy of the distal or proximal interphalangeal joints or metacarpophalangeal joint; osteophytes, joint space narrowing, signal alteration of cartilage, subchondral bone oedema, condylar sclerosis, subchondral bone thickening. Data analysis Descriptive analysis was used to compare CBCT and MRI data for each category. RESULTS Study Population Eighty-five horses met the inclusion criteria (48 geldings, 36 mares and one stallion). Median age of horses was 12 years (range 4-21 years). The breeds were typical of the mixed referral population at The Dick Vet Equine Hospital; there were two Arabians, 10 Cobs, seven Connemaras, one Fresian, three Highland ponies, one Hunter, five Irish Draughts, fourteen Irish sports horses, two Quarter horses, four Sports Horses, one Shetland pony, eight Thoroughbreds, 15 Warmbloods, three Welsh Section B-D and nine horses where breed was not reported. Lameness and blocking findings Seventeen horses were presented as bilaterally lame, 33 horses were lame on the left forelimb, 25 horses were lame on the right forelimb, 3 were lame on the left hind limb and 2 were lame on the right hind limb. The lameness was abolished by a palmar digital nerve block in 18 horses, in 15 horses a palmar digital nerve block switched the lameness to the contralateral limb and in 11 horses the lameness was improved by a palmar digital nerve block and then further improved following an abaxial sesamoid nerve block. The lameness of three horses improved following intra-articular anaesthesia of the distal interphalangeal joint. The lameness was abolished by an abaxial sesamoid nerve block in 19 horses and in 4 horses an abaxial sesamoid nerve block switched the lameness to the contralateral limb. Nine horses did not undergo diagnostic analgesia but lameness was localised to the foot due to the presence of a draining tract, recent solar penetration or lameness following medication of the distal interphalangeal joint. Regions imaged The regions imaged using MRI were as follows: Twenty-eight horses had a single foot imaged (23 front and 5 hind), 25 horses had both front feet imaged, 22 horses had a single front foot and pastern region imaged, 4 horses had bilateral front feet and a unilateral pastern region imaged, 6 horses had bilateral front feet and bilateral pastern regions imaged. In total 120 foot and 38 pastern regions were imaged using MRI. Thirty-five horses had bilateral CT of the foot and pastern region and 50 horses had unilateral CT of the foot and pastern. In total 120 foot and pastern regions were imaged. The regions imaged for each specific horse with the blocking history can be found in Table S1. Categorisation of imaging findings by primary diagnosis Twenty four of 85 horses had a primary soft tissue injury that was detected on MRI but not visible on CBCT. The primary diagnosis and the categorised CBCT and MRI findings are listed in Supplementary Table S2. The reported CBCT and MRI findings of ALL horses are reported in Supplementary Table S1. Sixteen horses were categorised as 1 – deep digital flexor tendinopathy, six horses as 2– collateral ligament injury, two horses as category 3-desmopathy of the small ligaments of the foot or pastern, seventeen horses were placed in category 4– increased STIR signal of the phalanges, eleven horses were categorised as 5- navicular bone changes, one horse as category 6 - MRI and CT changes consistent with sclerosis or increased bone mineral density as the primary diagnosis, four horses were placed as category 7 - MRI and CT changes consistent with lysis or reduced bone mineral density, and five horses as category 8 - fracture of the distal phalanx or ungual cartilages, ten horses as category 9 – hoof wall abnormalities; laminar tearing, keratoma, quittor, hoof wall defects, solar penetration tracts and there were thirteen horses where category 10 - osteoarthropathy of the distal interphalangeal joint, proximal interphalangeal joint or metacarpophalangeal joint was classed as the primary diagnosis. The primary diagnosis considered most clinically relevant to the lameness and prognosis differed between CBCT and MRI in 43 of the 85 horses (Table S2). When the primary diagnosis of CBCT was considered alone 22 horses were placed in category 5 – navicular bone changes, 12 in category 6 – sclerosis, 8 in category 7 – osteolysis, 5 in category 8 - fracture, 14 in category 9 with hoof wall abnormalities and 24 in category 10 – osteoarthropathy. Soft tissue abnormalities Category 1 – deep digital flexor tendinopathy Twenty-two horses had deep digital flexor tendinopathy reported but only 16 of 85 horses in the current study were categorised as having a deep digital flexor tendinopathy as the primary cause of lameness. Of these 16 horses, 12 had concurrent navicular bone changes that were evident on CBCT and MRI. One of these horses (horse 1) had an insertional injury of the deep digital flexor tendon and concurrent lysis of the flexor cortex of the distal phalanx that was evident on CBCT. The concurrent injuries thought to be more significant than the deep digital flexor tendinopathy of the remaining 6 horses as follows: Two horses had concurrent navicular bone changes that were considered more significant than the deep digital flexor tendon changes (horses 14 and 33). One horse had a concurrent injury of the medial glenoid of the proximal phalanx (horse that was considered the most clinically important finding (horse 63). One horse had an active (increased STIR signal on MRI and fracture line visible on CT) fracture at the base of the lateral collateral cartilage (horse 51). One horse had increased STIR signal at the dorsodistal aspect of the middle phalanx (horse 11) and another horse had marked increase in STIR signal within the distal phalanx with concurrent focal increase in radiopharmaceutical uptake on nuclear scintigraphy in the lame limb and a deep digital flexor tendon injury in the contralateral limb (horse 18). Category 2 – collateral ligament injury Six horses were considered to have injury to the collateral ligaments of the distal interphalangeal joint and one horse had injury to the short medial collateral ligament of the metacarpophalangeal joint (horse 83) as the primary finding on MRI. Of the injured distal interphalangeal joint collateral ligaments, 3 horses (13, 29 and 31) had medial collateral ligament desmopathy, one had mild lateral collateral ligament (horse 72) desmopathy and one had chronic biaxial collateral ligament desmopathy (horse 53). CBCT evaluation identified marked modelling of the collateral fossae of the distal phalanx in two horses (29 and 53) and marked ossification of the collateral cartilages in three horses (13, 31, 53) that was also evident on MR evaluation. Catergory 3 – desmopathy of the small ligaments of the foot or pastern Category 3 was identified as the primary diagnosis in just two horses. One horse had desmopathy of the palmar ligaments of the pastern (horse 68) and another had thickening of the digital flexor tendon sheath (horse 60). Osseous abnormalities Category 4 – increased STIR signal of the phalanges Seventeen horses were categorised with a primary diagnosis of increased STIR signal within the phalanges or navicular bone. Five horses had increase in STIR signal in the distal phalanx, two (horses 58 and 61) of these five horses were considered a bone bruise of the distal phalanx discrete from the articular surface, two horses had enthesopathy of the flexor cortex of the distal phalanx (horse 5 and 37) and one horse had laminar change (horse 75). Horses 11 and 58 had a bone bruise of the middle phalanx. Two horses (horses 54 and 63) had bone bruising of the medial glenoid cavity of the proximal phalanx. Three horses had increased STIR signal of the distal phalanx and ossified ungual cartilage (horses 8, 35 and 47). Three horses had increased STIR signal of the distal phalanx associated with the subchondral bone of the distal phalanx (horses 2, 43 and 61). One horse had mild increase in signal of the middle and distal phalanges and the navicular bone post arthroscopic lavage of the distal interphalangeal joint (horse 12). A further 27 horses had increased STIR signal described in the MRI report but the primary diagnosis was not increased STIR signal of the phalanges. Sixteen of these had increased STIR signal within the navicular bone, one horse had increased STIR signal of the distal phalanx adjacent to a keratoma (horse 57), horse 68 had increased STIR signal of the proximal phalanx consistent with enthesopathy of the palmar ligaments of the pastern, one horse had an avulsion fragment at the base of the proximal sesamoid bone (horse 64) and one horse had quittor (horse 32). Category 5 - navicular bone changes Forty-three horses had navicular bone abnormalities identified on CBCT and 43 horses had navicular bone changes identified on MRI. The navicular bone changes were considered the primary diagnosis in 11 of the horses for both CBCT and MRI. Twelve of the 43 horses had a concurrent deep digital flexor tendon injury considered as the primary diagnosis on MRI. Four horses had a primary desmopathy of the collateral ligaments of the distal interphalangeal joint with concurrent navicular bone changes. Distal border fragmentation was easier to visualise on the CBCT and multiple distal border fragments were identified on CBCT where a single fragment had been reported on MRI of horses 69 and 77 (Figure 1) and 77. Evaluation of the integrity of the flexor cortex surrounding a cyst of the navicular bone was also easier with CBCT compared to MRI for horse 80 (Figure 2). Category 6 – MRI and CBCT changes consistent with sclerosis or increased bone mineral density Thirty-five horses had sclerosis mentioned in the MRI report and 35 horses had sclerosis measured in the CBCT report. Concurrent sclerosis and STIR signal in the phalanges were identified in 8 horses that was considered the primary cause of lameness. Thirty-one of these horses had concurrent features consistent with osteoarthopathy. Seven of these horses had a concurrent injury to the deep digital flexor tendon. Four horses had sclerosis associated with fracture of the distal phalanx or ossified ungual cartilage. Category 7 - MRI and CT changes consistent with lysis or reduced bone mineral density Two horses (horses 42 and 48) had evidence of reduced mineral density or osteolysis on CT with concurrent features of osteoarthropathy of the proximal interphalangeal joint (Figure 3). One horse had evidence of marked osteolysis at the site of an involucrum associated with a sequestrum of the distal phalanx subsequent to a solar penetration that was more clearly evident on CBCT than MRI (horse 85). Two horses (horses 22 and 28) showed indentation of the articular surface of the distal phalanx that was evident on both MRI and CBCT, however MRI underestimated the osteolysis in the subchondral bone when compared to CBCT. horses (4, 79 and 84) had a fracture of the distal phalanx and 2 further horses (15 and 51) had a fracture of the ungualar cartilages. Multiplanar reconstructions of the CBCT allowed more accurate determination of the course of the fracture lines and more accurate assessment of the degree of comminution. Three-dimensional volume rendering was useful to ascertain if fractures of the palmar processes (horse 84) had an articular component (Figure 4) and supplementary video info S2. Hoof wall abnormalities Category 9 - Laminar tearing, keratoma, quittor, hoof wall abnormalities and solar penetrations There were 10 horses where category 9 was considered the primary diagnosis 11 horses where features from category 9 were mentioned in the imaging reports but not considered the primary cause of lameness. Of the 10 horses where category 9 was considered the primary diagnosis, 4 of these horses had solar penetration (horses 50, 66,78 and 85), 1 horse was defined as quittor with a draining tract (horse 32), 2 horses had keratomas and 3 horses showed evidence of laminitis (horses 10, 39 and 74). A small circular ring of T1, T2 and STIR hyperintensity was identified on MRI of the flexor cortex of the distal phalanx of horse 85, a solar penetration horse consistent with a small osseous fragment or sequestrum. CBCT images clearly delineated this sequestrum within a region of osteolysis or involucrum. The penetrating tract could not be seen on CBCT of this horse but the tract could be seen on MRI where fluid signal was evident within the digital cushion (horse 85) (Figure 5). The tract of the solar penetration was visible in 1 of 4 horses on CBCT and 4 of 4 horses on MRI. The draining tract of the quittor horse was visible on MRI but not CBCT. Osteoarthropathy Category 10 - Osteoarthropathy of the distal interphalangeal joint, proximal interphalangeal joint or metacarpophalangeal joint Osteoarthropathy of the distal interphalangeal joint, proximal interphalangeal joint or metacarpophalangeal joints was considered the primary diagnosis in 13 horses (8 distal interphalangeal joint, 3 proximal interphalangeal joint and 2 proximal interphalangeal joint). Four of the horses of distal interphalangeal joint osteoarthropathy had minimal MRI changes and the remaining four had concurrent navicular bone changes. Just 9 of the 85 horses did not show MRI or CT changes that were considered consistent with osteoarthropathy, the remaining 76 horses had evidence of osteoarthropathy but this was not believed to be the primary cause of lameness. More severe horses of osteoarthropathy were placed in category 4 as the significant increase in STIR signal identified in the subchondral and subjacent bone of the distal or proximal phalanges was considered relevant to the clinical lameness. One horse (horse 43) with persistent severe lameness returned for re-evaluation 5 months following presentation, in this horse contrast CBCT arthrography of the distal interphalangeal joint was useful providing further information on the degree of cartilage damage at the articular surface of the distal phalanx and also the suspected joint space collapse (Figure 6). Furthermore, the two horses with osteolysis of the condyles of the middle phalanx were placed in category 7 as the primary cause of lameness. DISCUSSION This descriptive study compared the primary diagnoses found when MRI and CBCT were performed on 85 standing sedated horses on the same day. It identified that the primary diagnosis was produced more times from the MRI images than the CBCT images in agreement with our first hypothesis. This was unsurprising due to the ability of MRI to detect additional changes within the soft tissues and fluid within bone. Interestingly the frequency of deep digital flexor tendon injury in the current study as a primary diagnosis was less than 20% (16 out of 85 horses) which is lower than a larger previously reported MRI study that saw 47% abnormalities in the deep digital flexor tendon (Gutierrez-Nibeyro et al. 2020). The differences between the two studies may reflect differing study populations or differing opinions on the significance of MR change within the deep digital flexor tendon. Dorsal border fibrillation within the proximal recess of the navicular bursa, presence of axial soft tissue within the proximal recess of the navicular bursa and irregularity of the margins of the dorsal border of the deep digital flexor tendon at the level of the distal sesamoidean impar ligament were not classed as primary causes of lameness in the current study. Fine linear increase in signal intensity on gradient echo sequences was only classed as an abnormality if there was concurrent increase in signal on T2 FSE and STIR sequences. In a multi-detector CT study under general anaesthesia evaluating the distal limb with the use of contrast material (arteriography, bursography and arthrography) the rate of injury to the deep digital flexor tendon was reported at 43% (Pauwels et al. 2021). The use of multiple contrast techniques in the standing horse was considered unnecessary give the simultaneous use of MRI in the current study. Cone beam CT identified fragmentation of distal border fragments more clearly than MRI even when high resolution (3mm slice thickness) MRI scans were compared to CBCT (0.25mm slice thickness) in the current study. A previous comparison of low-field MRI and a contrast CT using a helical CT machine with a slice thickness of 3mm (where MRI slices were 5mm) demonstrated low-field MRI failed to identify soft tissue mineralisation (Vallance et al. 2012), however, this study did not specifically focus on distal border fragmentation. Assessment of distal phalanx fractures can be enhanced through the use of advanced imaging (Mizobe et al. 2019), MRI has the ability to detect abnormal tissue fluid and therefore is able to provide information on the presence of bone oedema, bruising or haemorrhage that is not detectable on CBCT currently. Cone beam CT on the other hand is able to provide detailed information on cortical bone and its edges (Abdulkareem et al. 2023) and both the multiplanar reconstruction and the three-dimensional reconstruction possible with CBCT were useful to more precisely document fracture configuration and evaluate articular involvement. One case in the current series had biaxial subchondral bone changes in the condyles of the proximal phalanx on CBCT but only uniaxial changes were recorded on MRI disproving the second hypothesis. Assessment of subchondral bone at the articular surface was enhanced on CBCT in comparison to MRI for horses such as indentation of the distal phalanx or horses where there was osteolysis of the distal condyle of the proximal phalanx or proximal glenoid cavity of the middle phalanx. Osteolysis at the joint surface appears as hypoattenuation on CBCT and hyperintensity on MRI due to the accumulation of synovial fluid or cyst contents within the area of bone resorption. The signal change on MRI indicated less bone lysis than the degree of bone lysis identified on CBCT in several horses in the current study however there was no post mortem comparison possible due to the use of clinical horses that were not subjected to euthanasia. Reduced signal on T1W and T2W gradient echo and fast spin echo sequences in bone indicates the presence of increased bone mineral density consistent with bone sclerosis but there is no direct relationship on MRI as the signal change is dependent on the exact tissue and its fluid content that is replacing the normal bone tissue. Detection of naturally occurring cartilage injury using MRI in the standing horse can be unreliable (van Zadelhoff et al. 2019) even with the use of specialised sequences (Baker et al. 2023) as changes can be underestimated due to weight bearing (Evrard et al. 2019). One technique used in the current study that may assist in the detection of focal cartilage injury was the use of contrast enhanced CBCT arthrography however, further work is needed to validate how weight bearing influences this technique. In conclusion, this study has highlighted that MRI and CBCT are complimentary techniques. CBCT can provide additional information in horses where careful evaluation of cortical or subchondral bone is needed, whilst MRI provides information on soft tissue injuries that are currently not detectable on standing CBCT without the use of contrast media. The use of a limited MRI protocol including STIR sequences for functional imaging and CT scanning for structural imaging may be a possibility in the future to reduce scan times and optimise the acquisition of imaging information. AUTHOR CONTRIBUTIONS ST, PK, TS conceived study, all authors were responsible for data collection, analysis and interpretation, ST drafted the initial manuscript, all authors critically reviewed and approved the final version submitted for publication. ACKNOWLEDGEMENTS We acknowledge the clients whose horses partook in this study, the referring veterinary surgeons and the nurses and grooms involved in image acquisition . FUNDING INFORMATION A clinical research agreement between the University of Edinburgh and Hallmarq allowed CBCT acquisitions to be performed free of charge to the client. CONFLICT OF INTEREST STATEMENT No conflicts of interest are reported. ETHICS STATEMENT Ethical approval for the study was granted by The University of Edinburgh Veterinary Ethical Research Committee (VERC 189.23) and informed, written client consent was obtained for all horses. REFERENCES Abdulkareem NK, Hajee SI, Hassan FF et al. (2023) Investigating the slice thickness effect on noise and diagnostic content of single-source multi-slice computerized axial tomography. J Med Life 16 , 862-867. Baker ME, Kershaw LE, Carstens A et al. (2023) T2 mapping of cartilage in the equine distal interphalangeal joint with corresponding histology using 0.27 T and 3.0 T magnetic resonance imaging. Equine Vet J 55 , 843-852. Cillan-Garcia E, Milner PI, Talbot A et al. (2013) Deep digital flexor tendon injury within the hoof capsule; does lesion type or location predict prognosis? Vet Rec 173 , 70. Evrard L, Audigie F, Bertoni L et al. (2019) Low-field magnetic resonance imaging of the equine distal interphalangeal joint: Comparison between weight-bearing and non-weight-bearing conditions. PLoS One 14 , e0211101. Gutierrez-Nibeyro SD, Werpy NM, Gold SJ et al. (2020) Standing MRI lesions of the distal interphalangeal joint and podotrochlear apparatus occur with a high frequency in warmblood horses. 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(2012) Comparisons of computed tomography, contrast-enhanced computed tomography and standing low-field magnetic resonance imaging in horses with lameness localised to the foot. Part 2: Lesion identification. Equine Vet J 44 , 149-156. van Zadelhoff C, Schwarz T, Smith S et al. (2019) Identification of Naturally Occurring Cartilage Damage in the Equine Distal Interphalangeal Joint Using Low-Field Magnetic Resonance Imaging and Magnetic Resonance Arthrography. Front Vet Sci 6 , 508. TABLE LEGENDS Supplemetary Table S1: Cone beam computed tomography and magnetic resonance imaging findings in 85 foot +/- pastern studies. Abbreviation: DIPJ (distal interphalangeal joint), PIPJ (proximal interphalangeal joint), MCPJ (metacarpophalangeal joint), RF (right forelimb), LF (left forelimb), RH (right hind limb), LH (left hind limb), PDNB (palmar digital nerve block), ASNB (abaxial sesamoid nerve block), ISH (Irish Sports Horse, SH (Sports Horse), TB (Thoroughbred), WB (Warmblood), ID (Irish Draught). Category: (1) deep digital flexor tendon injury, (2) collateral ligament injury, (3) other ligamentous injury of the foot or pastern (4) bone bruising of the phalanges or ungual cartilages, (5) navicular bone abnormalities, (6) sclerosis of the phalanges or ungual cartilages, (7) lysis of the phalanges, (8) fracture of the phalanges or ungual cartilages (9) hoof wall abnormalities; laminar injury, keratoma, solar penetration, quittor (10) Osteoarthropathy of the DIPJ/PIPJ/MCPJ. Number in bold considered the primary diagnosis. Supplementary Table S2: Categorisation of CBCT and MRI findings and primary diagnoses. Primary diagnosis numbers are entered in bold for *CBCT and **MRI. Category 1 – deep digital flexor tendinopathy, category 2 – collateral ligament injury, category 3 - desmopathy of the small ligaments of the foot or pastern, category 4 – increased STIR signal of the phalanges, category 5- navicular bone changes, category 6 - MRI and CT changes consistent with sclerosis or increased bone mineral density as the primary diagnosis, category 7 - MRI and CT changes consistent with lysis or reduced bone mineral density, category 8 - fracture of the distal phalanx or ungual cartilages, category 9 – hoof wall abnormalities; laminar tearing, keratoma, quittor, hoof wall defects, solar penetration tracts and category 10 - osteoarthropathy of the distal interphalangeal joint, proximal interphalangeal joint or metacarpophalangeal joint. FIGURE LEGENDS Figure 1: Top panel of images from left to right, T2* sagittal, T1 transverse and T1 dorsal MR sequences of horse 69, show a focal area of low signal (arrows) at the junction of the distal and medial sloping border of the navicular bone consistent with a large distal border fragment. There is a further linear hyperintensity axial to the distal border fragment (arrowheads). Bottom panel of images; sagittal, transverse and dorsal multiplanar CBCT reconstruction images show two discrete distal border fragments (arrows). Figure 2: Top panel; MR images from left to right, T2*W sagittal, T1W transverse and T1W dorsal MR sequences of horse 80 show a circular ring of T1 hyperintensity (arrows) consistent with a large cystic structure within the proximopalmar spongiosa bone of the navicular bone. The margins of the dorsal border of the deep digital flexor tendon and the flexor cortex of the navicular bone are difficult to completely differentiate. Bottom panel; CBCT images from left to right, sagittal, transverse and dorsal multiplanar reconstructions show an oval area of hypoattenuation within proximopalmar spongiosa bone of the navicular bone with a clear rim of compact bone palmar to the cystic region. CBCT allow better visualisation of the palmar margin of the navicular bone than low-field MRI. Figure 3: Top panel; MR images, from left to right, T1W sagittal, T2*W transverse and T2*W dorsal images of the pastern region of horse 48, there is focal, triangular reduction in T1 signal surrounding increase in T2* signal within the medial condyle of the proximal phalanx (arrows). Bottom panel; CBCT images, from left to right, sagittal, transverse and dorsal multiplanar reconstructions show a focal region of hypoattenuation consistent with osteolysis of EACH condyle of the proximal phalanx and both glenoid cavities of the middle phalanx. CBCT provided additional information that was not evident on MRI in horse 48. Figure 4: Top panel of images; sagittal, transverse and dorsal multiplanar CBCT reconstruction images of horse 84, a broad curvilinear region of osteolysis is evident within the lateral palmar process of the distal phalanx that is surrounded by diffuse hyperattenuation consistent with a fracture within a sclerotic lateral palmar process. Middle panel of images; from left to right, T1W sagittal, T1W transverse and T1W dorsal MR sequences of horse 84, a focal linear T1 hyperintensity is evident within the lateral palmar process of the distal phalanx that is surrounded by diffuse reduction in T1 signal. Bottom panel of images from left to right, STIR sagittal, STIR transverse and STIR dorsal MR sequences of horse 84 show diffuse increase in STIR signal within the lateral palmar process of the distal phalanx consistent with bruising and/or bone oedema indicative of ongoing inflammation. Figure 5: Top panel of images; sagittal, transverse and dorsal multiplanar CBCT reconstruction images show a discrete osseous fragment of the flexor cortex of the distal phalanx within a region of osteolysis consistent with a sequestrum within an involucrum. No penetrating tract was evident on CBCT images acquired 14 days after the solar penetration of horse 85 occurred. Middle panel of images; from left to right, T1W sagittal, T2*W transverse and T1W dorsal MR sequences of horse 85, a ring of T1 hyperintensity within the flexor cortex of the distal phalanx (pink arrows) consistent with a sequestrum. Additionally, there is reduced T1 signal within the extensor process of the distal phalanx. Bottom panel of images; from left to right, T1W sagittal, T2* transverse and T1 dorsal MR sequences one slice (3mm) palmar to the middle panel, focal hyperintensity is evident within the axial portion of the insertion of the deep digital flexor tendon (green arrows). Figure 6: Top panel of CBCT images; sagittal, transverse and dorsal multiplanar reconstruction images of Horse 43 post-injection of iohexol into the distal interphalangeal joint show contrast medium within the space where cartilage should be overlying the medial and lateral glenoid of the distal phalanx (pink arrowheads). There is hyperattenuation and thickening of the subchondral bone of the medial glenoid cavity (pink arrows). There is marked loss of the joint space of the distal interphalangeal joint medially (blue arrow). Bottom panel; T2*W sagittal, T1W transverse and T1W dorsal MRI scans of the same horse show loss of T1 signal within the articular cartilage of the medial glenoid in the same place as the CBCT shows uptake of contrast media consistent with focal cartilage injury of the medial glenoid cavity of the distal phalanx. Information & Authors Information Version history V1 Version 1 19 May 2025 Copyright This work is licensed under a Non Exclusive No Reuse License. Collection Equine Veterinary Education Keywords cbct dual modality advanced imaging equine foot mri Authors Affiliations Sarah Taylor 0000-0002-9714-8495 [email protected] The University of Edinburgh View all articles by this author Padraig Kelly The University of Edinburgh View all articles by this author Carola Daniel 0000-0002-4801-5151 The University of Edinburgh View all articles by this author Oliver James 0000-0002-7399-9690 The University of Edinburgh View all articles by this author Mattie McMaster The University of Edinburgh View all articles by this author Tobias Schwarz The University of Edinburgh View all articles by this author Metrics & Citations Metrics Article Usage 549 views 254 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Sarah Taylor, Padraig Kelly, Carola Daniel, et al. Comparison of cone beam CT and low-field MRI of the distal limb of 85 standing sedated horses. Authorea . 19 May 2025. 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