Ultrasound-guided percutaneous microwave ablation assisted by a three-dimensional visualization treatment platform (3DVOPS) for large uterine fibroids.

This single-center, retrospective study protocol was approved by the Ethics Committee of the Fifth Medical Center of the Chinese PLA General Hospital (Beijing, China) and was conducted in accordance with the principles of the Declaration of Helsinki. From October 2020 to December 2023, a cohort of 30 patients who underwent ultrasound-guided percutaneous microwave ablation (US-PMWA) with the aid of a 3D visualization operative planning system were enrolled in the study. A separate cohort of 60 patients who underwent US-PMWA using conventional 2D image operative planning methods served as controls. Data from the patients were extracted from our maintained registry database (ratification no. 20100930-004, registration no. ChiCTR-TRC-10001119). These patients were matched for lesion volume and lesion location. The inclusion criteria for US-PMWA were as follows: (1) a single uterine fibroid (≥ 5 cm) diagnosed by MRI and ultrasound with a clinical syndrome such as menorrhagia and dysmenorrhea; (2) patients with no plans for future pregnancy; (3) US-PMWA not combined with other treatments such as ethanol injection; and (4) patients with MRI examinations within 7 days before and after US-PMWA. The exclusion criteria included the coexistence of other pelvic or uterine diseases (e.g., pelvic inflammatory diseases, ovarian endometriomas, or uterine adenomyosis) or previous treatment such as uterine artery embolization, radiofrequency ablation (RFA), or high-intensity focused ultrasound. All patients with uterine fibroids underwent MRI to delineate the target lesion within 3 days before ablation. A desktop computer (Lenovo) with an Intel Core i5 processor was used for an empirical study in our department to perform 3D visualization preoperative planning. A series of MRI data (0.625 mm- or 2.5 mm-thick slices) of the lesion before ablation were converted to DICOM format and then imported into the 3D visualization treatment platform (Hokai Company, Zhuhai, China). The 3D visualization platform used in this study was a research prototype developed by Ping Liang (Hokai Company, Zhuhai, China) during the trial period (2020–2023). It has since undergone CE certification and commercialization as part of ongoing technology transfer efforts. The current commercial version retains the core functionalities described herein. Our group (PingLiang) originally developed the 3D visualization platform software, which has novel functions as follows: (1) rapid segmentation of the target (within 2 min); (2) volume calculation of the target; (3) simulation of the thermal field; (4) interactive pre-ablative planned strategy by manual operation; and (5) assessment of ablative effect by tumor mapping (Fig.  1 ). The graphical user interface displayed the real-time simulation 2D ultrasound-guided planning and the 3D visualization planning, as well as the planning path from the transverse, coronal, and sagittal planes. The application of 3D visualization technology enables a radiologist to perform various operations on the 3D image, such as free movement, rotation, and scaling, to develop a puncture plan by seeing more intuitively. The myoma with a 5-mm margin, endometrium, and surrounding vital structures were segmented and reconstructed, which can be demonstrated via stereo display in the 3D visualization (Fig.  1 ). Fig. 1 A MRI was performed before microwave ablation for each patient (slice thickness less than 0.5 mm); B The MRI with DICOM format data of 3D group patients was transformed into a 3D visualisation preoperative planning system for processing and analysis.(Yellow: uterus;green:lesion;red:uterine endometrium white:bladder black:intestinal tract); C 3D visualization operative planning system showed the location and relationship with the lesion and the surrounding organs and the quantitative distance between the lesion and surrounding vital structures were acquired (Dark pink silhouette:uterus; dark yellow and bright yellow:lesions; red:uterine endometrium blue:bladder;Dark gray:rectum;light gray:spine); D , E The volume of the lesion and uterus was quantized by the operative planning system and microwave ablation power and action time were calculated according to the dose–effect relationship of microwave ablation. Then 3D visualization operative planning system projected the number and the pathway of the ablation antenna implantation, the ablation time and energy, simulated the thermal field, and provided the location of the aspiration. The 3D planning system simulated 13 overlapping ablation zones in this case ( D represented one ablation zone) to ensure complete fibroid coverage. Two percutaneous punctures were made, and the antenna were repositioned 11 times along predefined intralesional trajectories ( E ) to replicate the simulated thermal fields. F In the MRI image 3 m after ablation, the lesion residual nuclear and ablation zones were clearly demonstrated and the NPV ratio was calculated. A MRI was performed before microwave ablation for each patient (slice thickness less than 0.5 mm); B The MRI with DICOM format data of 3D group patients was transformed into a 3D visualisation preoperative planning system for processing and analysis.(Yellow: uterus;green:lesion;red:uterine endometrium white:bladder black:intestinal tract); C 3D visualization operative planning system showed the location and relationship with the lesion and the surrounding organs and the quantitative distance between the lesion and surrounding vital structures were acquired (Dark pink silhouette:uterus; dark yellow and bright yellow:lesions; red:uterine endometrium blue:bladder;Dark gray:rectum;light gray:spine); D , E The volume of the lesion and uterus was quantized by the operative planning system and microwave ablation power and action time were calculated according to the dose–effect relationship of microwave ablation. Then 3D visualization operative planning system projected the number and the pathway of the ablation antenna implantation, the ablation time and energy, simulated the thermal field, and provided the location of the aspiration. The 3D planning system simulated 13 overlapping ablation zones in this case ( D represented one ablation zone) to ensure complete fibroid coverage. Two percutaneous punctures were made, and the antenna were repositioned 11 times along predefined intralesional trajectories ( E ) to replicate the simulated thermal fields. F In the MRI image 3 m after ablation, the lesion residual nuclear and ablation zones were clearly demonstrated and the NPV ratio was calculated. The 3D operation planning system of US-PMWA should adhere to the following principles: (1) avoid ablation of the bladder, ovary, and intestinal tract, particularly the endometrium; (2) minimize the number of antenna insertions and ablation points; and (3) minimize the distance of antenna insertion trajectories while avoiding puncture pathways through critical structures. The planning system was designed to iterate these goals until a reasonable and feasible plan was achieved [ 14 ] (Fig.  1 ). A cooled-shaft MW tumor coagulator (KY-2000; Kangyou Medical, Nanjing, China) consisting of a 15-gauge needle antenna with a 1.1 cm exposed tip was used. This microwave ablation tumor coagulator can produce 100W of power at 2450 MHz. A power output between 40 and 60W was used during ablation. The antenna was percutaneously inserted into the lesion under the guidance of transabdominal ultrasound. The entire ablation procedure was performed under real-time US guidance [ 1 ]. Proper microwave ablation power and ablation time were chosen according to the preoperative plan of the 3DVOPS. The antennae were inserted into the location of the lesion according to the 3DVOPS. The hyperechoic area of ablation was monitored by real-time greyscale ultrasound, and the end of ablation was determined when the hyperechoic coverage of the proposed ablation area. The effectiveness of ablation was then immediately assessed using contrast-enhanced ultrasonography (CEUS, SonoVue, Bracco SinePharm, Milan, Italy). Nonenhanced regions on CEUS indicated necrotic areas. For the technical efficacy evaluation, the ablation time, ablation energy, non-perfused volume (NPV), and NPV ratio were assessed. The ablation energy was calculated as ablation power × ablation time. The extent of the NPV was evaluated by enhanced MRI performed within 3 days after the ablation. The NPV and lesion volume were calculated as 0.5233 × superoinferior diameter × anteroposterior diameter × transverse diameter. The NPV ratio was calculated by the following equation: NPV ratio = (Necrotic tissue volume/lesion volume) × 100%. For the evaluation of safety, MRI was performed within 3 days after the ablation to evaluate the injury to the surrounding organs. The complications were classified according to the unified standardized Society of Interventional Radiology (SIR) grading system. Data were analyzed using SPSS 21.0 for Windows (SPSS Inc., Chicago, IL, USA). The paired t-test or x 2 test was used to compare values between the groups. The comparison of continuous variables between two groups was performed via Student’s t-test or the Mann–Whitney U -test. Pearson chi-squared analysis or Fisher exact tests were performed to compare the categorical variables. P values < 0.05 were considered statistically significant.

The baseline information of the patients is shown in Table  1 . No significant difference was found between the two groups (P > 0.05). The median time for preoperative planning was longer in the 3D group (25 ± 6 min) compared to the 2D group (10 ± 3 min, P < 0.01), but this was offset by reduced intraprocedural adjustments. The non-perfused volume (NPV) ratio (a marker of ablation completeness) was similar between groups (3D: 92.1 ± 5.3% vs. 2D: 90.7 ± 6.1%, P = 0.28). (Table  1 ).The ablation time and ablation energy in the 3D group were significantly less than 2D group (Table  1 ). The comparison between 3D and 2D planning group Location of uterine fibroid: A anterior, P posterior, D fundus Follow-up ultrasound at 6 months post-ablation (available for 19/30 patients in the 3D group and 36/60 in the 2D group) showed no significant difference in fibroid volume reduction (3D: 65.2 ± 12.1% vs. 2D: 62.8 ± 14.3%, P = 0.42). Long-term data collection is ongoing. No haematuria was observed in the 3D group after the procedure. In contrast, 3 cases developed transient gross haematuria without any symptoms in the 2D group immediately after the ablation. This phenomenon disappeared in 24 h after alkalinization of urine and hydration with 5% sodium bicarbonate and sterile normal saline and 5% glucose intravenous infusion. All three patients had the ablation zone on the anterior uterine wall.Vaginal discharge lasting for more than 7 days was noticed in 8 patients in the 2D group while two patients in the 3D group,the difference was statistically significant. All adverse events were grade A or B according to the unified standardised SIR grading system.Except haematuria and vaginal discharge,no statistically significant differences were found between the two groups (Table  2 ). Table 2 Complications after procedure Complications SIR class 3D group 2D group P values Major complications 0 0 Minor complications   Haematuria A 0 3 < 0.05  Vaginal discharge A 2 8 0.05  Fever A 5 12 > 0.05 Complications after procedure

Preoperative treatment planning is beneficial for optimizing the ablation strategy. 3D images, with their stereoscopic characteristics, have been widely used in interventional therapy and surgeries [ 16 ]. Our team began utilizing a 3DVOPS for US-PMWA of liver and renal cancer in 2012 [ 13 – 15 ], which improved the rate of complete ablation and reduced the ablation time and energy. In this comparative study, the 3D system reduced ablation time/energy without compromising NPV. This suggested that the use of the 3D planning system reduced the instances of repeated and excessive ablation for uterine fibroids. Ablation of large uterine fibroids is challenging due to the complex anatomy involved. Additionally, the spatial relationships between the uterus and surrounding pelvic organs are difficult to discern on 2D ultrasound guidance, making them subject to the operator's perception. Hyo et al. reported a case of rectouterine fistula after laparoscopic ultrasound-guided RFA of an intramural uterine fibroid [ 17 ]. The incidence of hematuria after ablation in the 3D group was much lower than that in the 2D group. These results indicated that the 3D visualization preoperative planning system provided valuable anatomical information regarding the lesion and surrounding pelvic organs, displayed in a stereoscopic manner. Considering the endometrium, it can sometimes be discerned under ultrasound guidance, although microbubbles may interfere with the vision during ablation. Thermal injuries to the endometrium can lead to vaginal discharge post-ablation [ 10 ]. In the present study, the incidence of vaginal discharge after ablation in the 3D group was significantly lower than that in the 2D group. This suggests that 3D visualization preoperative planning is useful for the operator in calculating the antenna insertion sites and sessions, as well as the distance between the lesion and endometrium, which may help in avoiding thermal damage to the endometrium. In this study, a 3D visualization software system was used to process the MRI image data of patients and reconstruct the visual 3D structural model of the lesion tissue and adjacent organs. Accurate measurement and calculation of the length of each diameter line, distance between structures, and volume of the uterine fibroid have altered the conventional mode of judging the spatial structure of the target region based on two-dimensional image data and the surgeon's experience.While preoperative 3D planning optimizes antenna trajectories, real-time ultrasound guidance during ablation accounts for dynamic changes (e.g., bowel movement). Future iterations could integrate intraoperative 3D-US/MRI fusion for live updates, though this was beyond the scope of our current system. There was no significant difference in the treatment effect between the two groups. This suggests that the 3DVOPS may not provide a superior clinical effect. However, the true value of the comparison between the two groups might be affected by selection bias, as all procedures were completed by the same operator, Zhang Jing, who had extensive experience with US-PMWA for uterine adenomyosis. The NPV ratio was comparable between the two groups, and the clinical effectiveness was highly related to the NPV ratio [ 18 ]. This study presents several inherent limitations. First, we could not evaluate the true value of the 3D visualization operative planning system in ultrasound-guided percutaneous microwave ablation for uterine fibroids, as we could not perform a prospective randomized controlled study. Second, the value of the comparison between the two groups might be affected by selection bias, as the operator (Zhang Jing) had extensive experience with US-PMWA for uterine fibroids; thus, the 3D visualization treatment platform may be more valuable for less experienced operators. 3DVOPS-assisted US-PMWA for large uterine fibroids reduces ablation time and energy while maintaining high NPV ratios. Its stereoscopic visualization may enhance safety by minimizing collateral damage, though long-term outcomes warrant further study. This approach is particularly valuable for complex anatomies but requires additional planning time preoperatively.

Ultrasound-guided thermal ablation has been proven to not only alleviate the symptoms of patients with uterine fibroids but may also offer a safe and effective alternative to existing treatments for women who wish to preserve their fertility [ 1 – 6 ]. For large uterine fibroids, 2D ultrasound imaging presents challenges in visualizing the relationships of these fibroids with surrounding structures, such as the endometrium, bladder, ovary, and intestinal tract, in a three-dimensional perspective [ 7 , 8 ]. Traditionally, 2D ultrasound can provide valuable information about the anatomical structure, but it is challenging to precisely provide the spatial positioning information of volumetric data that clinicians require for thermal ablation. The results of human error, such as imperfect hand–eye coordination or a weakness in spatial sense, often lead to imprecise needle positioning or thermal energy localization. Especially for women who wish to preserve fertility, how to avoid damaging the endometrium and surrounding pelvic organs (bladder, ovary, and intestinal tract) simultaneously remains a challenge for surgeons [ 7 – 10 ]. A three-dimensional (3D) visualization operation planning system not only displays the location and spatial relationship of the lesion with surrounding structures, quantifies the size and volume of the lesion, predicts the time–temperature profile, and improves the safety and effectiveness of ablation but also enables planning of the implantation route and accurate positioning of the ablation antenna [ 11 – 13 ]. In our preliminary study, 3D-visualisation operative treatment planning system was used in US-PMWA for liver and renal cancer, and it promoted precise therapy [ 14 , 15 ]. Therefore, this novel technique might provide more information and valuable assistance in US-PMWA treatment for uterine fibroids.The purpose of this study was to explore the clinical value of a 3D visualization operative planning system in US-PMWA for large uterine fibroids.