Factors influencing thermal injury to skin and abdominal wall structures in HIFU ablation of uterine fibroids

Objective: To investigate the factors which may cause thermal injury of abdominal wall structures in ultrasound-guided high-intensity focussed ultrasound (USgHIFU) ablation of uterine fibroids.

Method: A total of 892 patients with uterine fibroids diagnosed on contrast-enhanced magnetic resonance imaging (MRI) scans received HIFU ablation and follow-up MRI scanning. After therapy, thermal injury to the skin was assessed via measurement of skin redness, blisters, subcutaneous nodules and to the abdominal wall structures via measurement of signal intensity on T2-weighted MRI images. A total of 151 patients were assigned to the injury group, 741 patients were assigned to the non-injury group. The relationship between patient and treatment parameters and injury were analysed using univariate and multiple logistic regression analyses.

Results: Univariate logistic regression revealed that sonication time, sonication time per hour, total energy deposited, distance from uterine fibroid ventral side to skin, volume of uterine fibroids, abdominal wall scar, abdominal wall thickness and body mass index (BMI) all affected whether thermal injury occurred (p?p?=?0.000, OR?=?2.228, 95% CI 1.831–2.712), abdominal wall scar (p?=?0.019, OR?=?1.639, 95% CI 1.085–2.477) and abdominal wall thickness (p?=?0.000, OR?=?1.562, 95% CI 1.313–1.857) were significantly correlated with thermal injury.

Conclusion: Multiple logistic regression analysis revealed that abdominal wall thickness, total energy and abdominal wall scar were the most significant influencing factors that influenced minimal thermal injury of abdominal wall structures in USgHIFU ablation of uterine fibroids.     

Nonresective treatments for uterine fibroids: a systematic review of uterine and fibroid volume reductions

Patients are increasingly seeking uterus-preserving, minimally invasive treatments for symptomatic uterine fibroids. This has led to a greater use of nonresective treatments such as uterine artery embolization (UAE), focused ultrasound (FUS) and more recently, radiofrequency ablation (RFA) of fibroids. This systematic review, following PRISMA guidelines, examines the change in uterine and fibroid volumes associated with UAE, FUS, and RFA. Pubmed and MedlinePlus databases were searched from 1956 to 2016. The keywords used were ‘radiofrequency ablation,’ ‘magnetic resonance guided focused ultrasound,’ ‘ultrasound guided focused ultrasound’, ‘uterine artery embolization,’ ‘uterine fibroid embolization,’ and ‘leiomyoma’ or ‘fibroid’. Publications with at least 20 patients were included. Data were collected and analyzed using Microsoft Excel^® (Microsoft Corporation, Redmond, WA) software. Eighty-one relevant papers were identified: 52 related to UAE, 11 to RFA, 17 to FUS, 1 compared UAE and FUS. We report the published uterine volume and fibroid volume changes seen in these studies at 1 to 36?months. The pooled fibroid volume reductions at six months seen with RFA were 70%, UAE 54% and FUS 32%. All three types of nonresective treatment result in fibroid volume reduction. However, fibroid volume reduction is most marked with RFA, with UAE resulting in the next most volume reduction. Additional larger cohort studies, including those that are randomized and/or comparative, would enable definitive conclusions. This is the first systematic review comparing uterine and fibroid volume reduction after RFA, UAE and MRgFUS.     

Establishment of a scoring system for predicting the difficulty level of high-intensity focussed ultrasound ablation of uterine fibroids

Purpose: To establish a scoring system that predicts the difficulty level of high-intensity focussed ultrasound (HIFU) ablation of uterine fibroids.

Materials and methods: Four hundred and twenty-two patients with fibroids were enrolled. The energy efficiency factor (EEF) and sonication time were set as dependent variables, with factors possibly affecting EEF and sonication time including age, body mass index (BMI), the volume of fibroids, the location of the uterus, the type of fibroids, the signal intensity on the T2-weighted imaging (T2WI), the enhancement type, the thickness of the rectus abdominis and the subcutaneous fat layer, the distance from the anterior/posterior surface of the fibroid to the skin, and the abdominal wall scars were set as predictors for building optimal scaling regression models.

Results: The volume of the fibroids, the location of the uterus, the signal intensity on T2WI, enhancement type, rectus abdominis thickness, subcutaneous fat thickness, and distance from the anterior surface of fibroid to the skin were related to EEF. Signal intensity on T2WI, the volume of fibroids, distance from the posterior surface of fibroid to the skin, and enhancement type were related to sonication time. Models that can predict the difficulty level of HIFU for fibroids have been established: for EEF, y?′?=?0.338X?′₁???0.231X?′₂+0.156X?′₃+0.167X?′₄?; for sonication time, y?=?0.227X₁+0.321X₂+0.157X₃+0.194X₄.

Conclusions: A scoring system for predicting the difficulty level of HIFU treatment for uterine fibroids has been established and it can be used to help select patients and to predict the sonication time for a given fibroid.     

Effects of a microbubble ultrasound contrast agent on high-intensity focused ultrasound for uterine fibroids: a randomised controlled trial

Objective: To investigate the effects of a microbubble ultrasound contrast agent on high-intensity focused ultrasound (HIFU) treatment of uterine fibroids.

Methods: A total of 120 patients with solitary uterine fibroid were randomly assigned into Groups A, B, C and D. Patients in Groups A and B received 1.5?ml of SonoVue, Groups C and D received 1.5?ml of saline before HIFU ablation. HIFU sonication started at 6?min after administration of SonoVue or saline in Groups A and C, whereas it started at 10?min in Groups B and D. On day 1 after HIFU, magnetic resonance imaging was performed. Patients were followed up via phone or clinic visit during the first week after HIFU.

Results: No significant difference was observed in terms of age, fibroid location, diameter of fibroids, signal intensity on T2-weighted imaging, or tumour volume among the four groups (p?>?0.05). The use of SonoVue significantly shortened the treatment time and sonication time. The sonication start time of 6?min, relative to 10?min, had significant effects on the treatment time and sonication time. The use of intravenous SonoVue followed by HIFU ablation 6?min later significantly increased the rate of significant grey-scale changes (55.9%) and the non-perfused volume ratio (94.2%?±?10.6%). No significant differences were observed in the incidence of intra-procedure and post-HIFU adverse effects among the four groups (p?>?0.05).

Conclusions: SonoVue could be safely used to enhance the ablation effects of HIFU treatment of uterine fibroids.     

A comparison of ultrasound-guided high intensity focused ultrasound for the treatment of uterine fibroids in patients with an anteverted uterus and a retroverted uterus

Objective: The aim of this study was to compare the treatment outcomes of ultrasound-guided high-intensity focused ultrasound (USgHIFU) for uterine fibroids in patients with an anteverted uterus versus a retroverted uterus.

Materials and methods: Based on the principles of statistics we enrolled 221patients with an anteverted uterus and 221 with a retroverted uterus. All patients had a solitary uterine fibroid and every fibroid was identified as hypointense on the T2 weighted images (T2WI) on magnetic resonance. The baseline characteristics of the patients, treatment results and adverse events were compared between the two groups.

Results: There were no significant differences in baseline characteristics between the two groups. The average non-perfused volume ratio of fibroids was 85.2?±?18.7% in the group of patients with a retroverted uterus, while it was 87.7?±?11.8% in patients with an anteverted uterus (P?Conclusion: The results of this study indicated that uterine fibroids with hypointensity on T2WI in a retroverted uterus can be safely and effectively treated with USgHIFU. However, the fibroids in an anteverted uterus are easier to treat with USgHIFU.     

A retrospective study of ultrasound-guided high intensity focussed ultrasound ablation for multiple uterine fibroids in South Africa

Objective: To evaluate the shrinkage rate, symptom relief and improvement of the quality of life following ultrasound-guided high intensity focussed ultrasound (USgHIFU) for multiple uterine fibroids.

Methods: From October 2015 to November 2016, 81 black women with multiple symptomatic fibroids underwent USgHIFU. The number of the fibroids ranged from 3 to 9. The shrinkage rate of fibroids, symptom severity score and quality of life were evaluated following USgHIFU. Magnetic resonance imaging (MRI), the uterine fibroid symptom and quality of life (UFS-QOL) questionnaire were used for evaluation.

Results: The mean age of patients was 35.3?±?5.9 years. The average weight of these patients was 68.4?±?11.4?kg, with the median abdominal subcutaneous fat thickness of 38.0?±?11.4?mm. The median fibroid volume was 36.0 (range: 1.8–1220.1) cm³. During HIFU, 60.5% of the patients reported lower abdominal pain, 43.2% sciatic/buttock pain, 60.5% skin “burning” sensation, 6.2% abnormal vaginal discharge and 13.6% transient leg pain. No severe complications were observed. The average volume reduction rate of fibroids in 21 patients who completed the follow-up was 32.5?±?24.0, 42.3?±?32.2 and 52.5?±?36.3% 1, 3 and 6 months after HIFU, respectively. The UFS score decreased and the QOL values significantly increased during the follow-up period. Re-intervention treatment occurred in two of the 21 patients 6 months after HIFU. One patient conceived 3 months after HIFU, and she had a term vaginal delivery without any obstetrical complications.

Conclusions: Based on our results, USgHIFU is safe and effective in treating patients with multiple uterine fibroids.     

Effectiveness of ultrasound-guided percutaneous microwave ablation for symptomatic uterine fibroids: a multicentre study in China

Purpose: To evaluate the clinical efficacy of ultrasound-guided percutaneous microwave ablation (PMWA) therapy for symptomatic uterine fibroids in a multicentre study.

Materials and methods: Patients with symptomatic uterine fibroids who underwent PMWA at multiple treatment centres in China between January 2013 and August 2015 were prospectively studied to compare the reduction rate of uterine fibroids, haemoglobin level and uterine fibroid symptom and health-related quality of life questionnaire (UFS-QOL) scores before and at 3, 6 and 12 months after ablation.

Results: A total of 311 patients (405 leiomyomas) from eight treatment centres underwent the treatment (age, 29–55 years; mean?±?SD, 41?±?5.11 years). The mean diameter of the myomas ranged from 2.03 to 12.50?cm (mean, 5.10?±?1.28?cm) and the volume ranged from 4.40 to 1022.14?cm³ (mean, 95.01?±?70.29?cm³). Forty-eight myomas were identified as FIGO type 1/2 fibroids, 256 as type 3/4 fibroids and 101 as type 5/6 fibroids. The mean ablation rate was 86.6% (54.0–100%). The mean reduction rate was 63.5%, 78.5% and 86.7% at 3, 6 and 12 months posttreatment, respectively. The haemoglobin level increased significantly from 88.84?±?9.31?g/L before treatment to 107.14?±?13.32, 116.05?±?7.66 and 117.79?±?6.51?g/L at 3, 6 and 12 months posttreatment, respectively (p?=?.000). The symptom severity score (SSS) and health-related quality of life (HRQL) scores were also significantly improved posttreatment compared with before treatment (p?=?.000).

Conclusion: PMWA is an effective, minimally invasive treatment for symptomatic leiomyomas that can significantly improve the quality of life of patients.     

Factors influencing MR changes associated with sacral injury after high-intensity focused ultrasound ablation of uterine fibroids

Purpose: We investigated the risk factors influencing MR changes associated with sacral injury from ultrasound-guided high-intensity focused ultrasound (USgHIFU) ablation for uterine fibroids.

Methods: We retrospectively analyzed a total of 346 patients with symptomatic uterine fibroids who received USgHIFU ablation. All of the patients underwent contrast-enhanced magnetic resonance imaging (CE-MRI) before and after treatment. Injury to the sacrum was set as the dependent variable, while fibroid features and the treatment parameters were set as independent variables. These variables were used to assess respectively their correlation with sacral injury by using univariate and multivariate analyses.

Results: The results of univariate analysis revealed that the volume, distance from the fibroid to the skin, maximal diameter, distance from the fibroid to the sacrum, fibroid types, degree of enhancement, therapeutic dosimetry (TD), energy efficiency factor (EEF) and non-perfused volume (NPV) ratio manifested significant correlations with the sacral injury (p?<?.05). Multivariate analysis showed that the degree of enhancement, TD and EEF were independent risk factors for sacral injury (p?<?.05), while the distance from fibroid to sacrum and intramural or subserosal types were protective factors (p?<?.05). The incidence of sacral tail pain and leg pain showed a significant positive correlation with sacral injury (p?<?.05).

Conclusion: As important affecting factors, the degree of enhancement, distance from fibroid to sacrum and fibroid types all possess significant correlations with MR changes associated with sacral injury.     

Uterine myomas treated with microwave ablation: The agreement between ablation volumes obtained from contrast-enhanced sonography and enhanced MRI

Purpose: This study explores the agreement between ablated uterine myoma volumes obtained from contrast-enhanced sonography and enhanced magnetic resonance imaging (MRI) after microwave ablation therapy. Materials and methods: Twenty uterine myomas in 18 patients (average size: 5.56?±?1.26?cm) were successfully treated by microwave ablation. Contrast-enhanced sonography and enhanced MRI were performed within 7 days after the treatment. The ablation range of uterine myomas was observed and the ablation volume was calculated. By using the intraclass correlation coefficient (ICC) and Bland-Altman regression analysis, the agreement between ablated uterine myoma volumes obtained from contrast-enhanced sonography and enhanced MRI after microwave ablation therapy was analysed. Results: The ablated volume ranged from 13.66 to 135.27?cm³ after ablation, and the mean volume was 66.59?±?35.71?cm³ by using contrast-enhanced sonography. Respectively, the ablated volume ranged from 10.88 to 137.83?cm³, and the mean volume was 66.81?±?35.45?cm³ by using enhanced MRI. The limits of agreement between the two methods were (?10.83?cm³, 8.39?cm³), ICC was 0.991 (F?=?209.61, P?Conclusions: Contrast-enhanced sonography and enhanced MRI can be used interchangeably in observing the ablation range of uterine myomas treated with microwave ablation. Contrast-enhanced sonography can be used as a preferred non-invasive examination and for follow-up. Meanwhile, enhanced MRI can be used to comprehensively determine the relationships among uterine myomas, the entire uterus, and surrounding tissues.     

Ultrasound-guided percutaneous microwave ablation for symptomatic uterine fibroid treatment – A clinical study

Objective: The aim of this study was to assess the feasibility, safety and therapeutic effects of ultrasound (US)-guided percutaneous microwave thermal ablation (PMTA) in situ for the treatment of symptomatic uterine fibroid.

Materials and methods: The microwave (MW) antenna was percutaneously inserted into the fibroid under US guidance to perform the ablation. The ultrasound images, any complications and side effects were assessed during and after ablation. The shrinkage rate of the fibroid was calculated after the treatment.

Results: Forty patients underwent the treatment. The baseline fibroid volume was 14.6 to 341.1 cm³ (mean 140.1?±?87.4 cm³). When the MW therapy started, a heightened echo around the MW emission aperture of the antenna was observed and gradually propagated throughout the fibroid while the ablation continued. The mean ablation time was 490 s. Contrast enhanced MRI showed no enhancement in the fibroid post-ablation. The shrinkage rate of the fibroid was 61.8%, 78.7%, 73.2% and 93.1% at 3, 6, 9, and 12 months after ablation, respectively. Six patients felt pain in their lower abdomens or waists within 12 hours post-ablation, and the discomfort rapidly disappeared. Seven patients had a small amount of vaginal bloody secretions within one to two weeks after treatment, and six of these patients recovered from the bleeding without any therapy after one week. No patient developed complications and fever during or after the ablation.

Conclusions: PMTA for fibroid is feasible and safe, and it is an easy and fast procedure that is minimally invasive.     

Magnetic resonance texture parameters are associated with ablation efficiency in MR-guided high-intensity focussed ultrasound treatment of uterine fibroids

Objectives: The objective of this study is to assess the association between texture parameter analysis derived from T2-weighted images and efficiency of magnetic resonance-guided focussed ultrasound (MRgFUS) ablation for the treatment of uterine fibroids.

Materials and methods: Fifty-five women treated by MRgFUS were included in this retrospective analysis. Texture parameters were calculated using three 2D regions of interest placed on three consecutive slices on the same sagittal 3D T2-weighted images obtained at the beginning of MRgFUS ablation. Using uni- and multi-variate linear regression, texture parameters, fibroids/muscular T2W ratio (T2Wr), Funaki type, and fibroid depth were correlated with ablation efficiency, defined as the ratio of non-perfused volume (NPV) on post-treatment contrast-enhanced MRI by total volume of treatment-cell sizes used. Inter-rater reproducibility for texture analysis was assessed using variation coefficients.

Results: The mean total treatment cell volume was 49.5 (±30) ml, corresponding to a mean NPV of 57.2 (±57) ml (28%). The mean ablation efficiency was 1.14 (±0.7), with a range of 0.03–3.6. In addition to fibroid/muscular T2Wr, seven of the 14 texture parameters were significantly correlated with ablation efficiency: mean signal intensity (p?=?.047); Skewness (p?=?.03); Kurtosis (p?=?.015); mean uniformity (p?=?.052); mean sum of square (p?=?.045); mean sum entropy (p?=?.021) and mean entropy (p?=?.051). In multivariate linear regression, fibroid/muscular T2Wr and sum of entropy were associated with ablation efficiency. The inter-rater coefficient of variation for sum entropy was 2.6%.

Conclusions: Uterine fibroid texture parameters provide complementary information to T2Wr, and are associated with MRgFUS efficiency.

• Key points

• Mean sum entropy is negatively correlated with MRgFUS efficiency (ρ?=??0.307, p?=?.021).

• Fibroids/muscular T2-weighted ratio and entropy are associated with MRgFUS efficiency.

• Texture parameters are better predictors of MRgFUS efficiency than Funaki type.

• Fibroid MR texture analysis can improve patient selection for MRgFUS.

     

High intensity focused ultrasound ablation for submucosal fibroids: A comparison between type I and type II

Abstract

Objective: The aim of this study was to compare high-intensity focused ultrasound (HIFU) treatment for type I and type II submucosal fibroids. Materials and methods: From October 2011 to October 2013, 55 patients with submucosal fibroids were enrolled in this study. Based on submucosal fibroid classification, 27 patients were grouped as type I submucosal fibroids, and 28 patients were classified as type II submucosal fibroids. All patients received HIFU treatment and completed 1-, 6-, and 12-month follow-ups. Adverse effects were recorded. Results: There were no significant differences in the baseline characteristics between the two groups (p?>?0.05). Using similar sonication power, sonication time, and acoustic energy, the non-perfused volume (NPV) ratio was 83.0?±?17.3% in the type I group, and 92.0?±?9.5% in the type II group. All the patients tolerated the procedure well, and no serious adverse events occurred. During the follow-up intervals, the treated fibroids shrank and fibroid-related symptoms were relieved. No other reinterventional procedures were performed during the follow-up period. Conclusion: Based on our results with a small number of subjects, HIFU is suitable for both type I and type II submucosal fibroids. It seems that type II submucosal fibroids are more sensitive to HIFU ablation. Future studies with larger sample sizes and longer follow-up times to investigate the long-term results, including long-term symptom relief, pregnancy outcomes, and the recurrence rate as well as the reintervention rate are needed.     

子宫肌瘤栓塞治疗后闭经的临床分析

背景与目的:子宫肌瘤的栓塞治疗是子宫肌瘤的治疗方法之一,但存在治疗后闭经的问题.本研究探讨子宫肌瘤栓塞治疗后发生闭经的原因.方法:对在中山大学附属第一医院行子宫肌瘤栓塞治疗的487例患者追踪随访1年观察闭经的发生情况.所有病例均采用双侧子宫动脉插管经导管注入栓塞剂方法,其中104例以超液化碘油加平阳霉素作为栓塞剂,栓塞剂用量超液化碘油8～15 mL(平均10 mL)、平阳霉素6～16 mg(平均8 mg);158例以聚乙烯醇作为栓塞剂,用量80～150 ms(平均100 mg);225例以明胶海绵作为栓塞剂,用量1-2 g(平均1.5g).结果:栓塞后临床有效率为98.97%(482/487):栓塞失败率1.03%(5/487).栓塞后共有6(1.23%)例出现闭经,其中碘油组3例.碘油在卵巢区沉积;聚乙烯醇组1例;明胶海绵组2例.除明胶海绵组1例外.其余5例均出现雌二醇下降,促卵泡生成素上升.另外1例经多次超声检查发现子宫内膜仅3 mm,而雌二醇和促卵泡生成素正常,宫腔镜证实为内膜萎缩.结论:常用的栓塞材料均有可能导致子宫肌瘤柃塞后闭经,子宫肌瘤栓塞后闭经发生率为1.23%,其原凶与卵巢受损和子宫内膜受损萎缩有关.     

Clinical 24 month experience of the first MRgFUS Unit for treatment of uterine fibroids in Australia

Aim: To describe and evaluate treatment of uterine fibroids using Magnetic Resonance Guided Focused Ultrasound (MRgFUS) during its first 24 months of use at The Royal Women's Hospital Melbourne. Methods: One hundred Victorian women were treated with MRgFUS using the ExAblate 2000 system. Treatment outcomes based on fibroid volume shrinkage measured at 4 and 12 months post‐treatment and symptom severity score assessment (Symptom Severity Score Quality of Life – SSS‐QOL) pre‐ and post‐ (4–6 weeks, 4, 6 and 12 months) treatment. Results: Mean non‐perfused volume of the treated fibroids were 67% ± 25% (n = 100) immediately post‐treatment. At 4 months post‐treatment, the treated fibroids demonstrated an average volume reduction of 29% ± 32% (n = 74) and at 12 months 38% ± 45% (n = 32). Mean symptom severity scores (SSS‐QOL) improved by 51% from 59 ± 21 (n = 97) at baseline to 29 ± 17 (n = 36) by 12 months. Conclusion: From our experience, we believe there is a role for MRgFUS in the treatment of uterine fibroids in selected women.     

Radiofrequency ablation lesion detection using MR-based electrical conductivity imaging: A feasibility study of ex vivo liver experiments

Abstract

Purpose: The aim of this study was to show the potential of magnetic resonance electrical impedance tomography (MREIT) conductivity imaging in terms of its capability to detect ablated lesions and differentiate tissue conditions in liver radiofrequency (RF) ablation. Materials and methods: RF ablation procedures were performed in bovine livers using a LeVeen RF needle electrode. Ablation lesions were created using a power-controlled mode at 30, 50, and 70?W for 1, 3, and 5?min of exposure time, respectively. After the ablation, the liver was cut into several blocks including the ablated lesion, and positioned inside a phantom filled with agarose gel. Electrodes were attached on the side of the phantom and it was placed inside the MRI bore. For MREIT imaging, multi-spin-echo pulse sequence was used to obtain the magnetic flux density data according to the injection currents. Results: The conductivity of ablation lesions was significantly changed with the increase of exposure time (pKW?<?0.01, Kruskal-Wallis test). With RF powers of 30 and 50?W, significant differences between the coagulation necrosis and hyperaemic rim were observed for more than 5?min and 3?min, respectively (pMW?<?0.01, Mann-Whitney test). At 70?W, all cases showed significant differences except 3?min (pMW?<?0.01). The positive correlation between the exposure time and tissue conductivity was observed in both two ablation areas (pSC?<?0.01, Spearman correlation). Conclusions: This ex vivo feasibility study demonstrates that current MREIT conductivity imaging can detect liver RF ablation lesions without using any contrast media or additional MR scan.     

次全子宫切除两种手术方式的临床研究

目的:比较腹式次全子宫切除术和腹腔镜次全子宫切除术两种手术方式的术式选择及临床效果。方法:回顾性分析九江市妇幼保健院2009年1月-2012年12月收治的100例子宫良性病变（子宫肌瘤35例、子宫腺肌症42例、子宫内膜复杂性增生17例、功能失调性子宫出血6例）行手术治疗患者的临床资料,其中36例行腹式次全子宫切除术,64例行腹腔镜下次全子宫切除术,比较两组手术时间、术中出血量、术后肛门排气时间,评价术后性生活满意程度。结果:两组术后肛门排气时间、术中出血量、术后性生活满意程度比较差异有统计学意义（P<0.05）,手术时间比较两组无明显差异（P>0.05）。结论:腹腔镜下次全子宫切除术能减少术中出血量、术后恢复快,适用于宫颈无恶性病变的患者。     

Feasible temperature of percutaneous microwave ablation of dog liver abutting the bowel

Purpose: This study used a dog model to determine the optimal temperature of percutaneous microwave ablation that causes complete necrosis of liver but not the adjacent bowel, supporting the use of this method to specifically and effectively treat liver tumour abutting the bowel.

Materials and methods: Ultrasound-guided percutaneous microwave ablation of liver abutting the bowel was performed on healthy adult dogs. Temperature of the ablation margin was monitored and controlled through inserted thermal monitoring needles. Dogs were divided into three groups and received microwave ablation at 75–95°C, 65–75°C, or 55–65°C. Imaging and histological examination were used to evaluate the damage of the bowel adjacent to the ablated liver.

Results: Within one hour of treatment, the bowel adjacent to the ablated liver was seriously burned in the group receiving 75–95°C microwave ablation. Inflammation and congestion were found in the submucosa of the bowel in the group receiving 65–75°C microwave ablation. Minor inflammation was found in the mucosa of the bowel in the group receiving 55–65°C microwave ablation. Moreover, in the group receiving 55–65°C microwave ablation, ablated liver areas were covered with omenta, and histological examination revealed inflammatory reaction of the omenta 28 days after ablation.

Conclusions: Microwave ablation at 55–65°C for 6?min is preferred for ablation of liver tissue abutting the bowel in dogs. These findings may provide some valuable reference for percutaneous microwave ablation of human liver tumour adjacent to the bowel.     

Radiofrequency versus microwave ablation for intraoperative treatment of colorectal liver metastases

IntroductionIntraoperative radiofrequency ablation (RFA) and the newer technique of microwave ablation (MWA) can both be of additional value in parenchyma preserving surgical treatment of colorectal liver metastases (CRLM). MWA is less influenced by the heat-sink effect of surrounding vessels and can generate more heat in less time but RFA is still widely used. True comparing studies are scarce.MethodsThis single centre retrospective cohort study analyzed patients who underwent ultrasound guided intraoperative ablation as a part of the surgical treatment of CRLM between 2013 and 2018. In September 2015, MWA was substituted for RFA. Outcomes included unsuccessful ablation rates at 1-year postoperative, 30-days major complication rates, progression free survival (PFS) and overall survival (OS). Logistic regression models were used for univariable and multivariable analyses to identify predictors of unsuccessful ablation.ResultsForty-one patients underwent RFA of 98 lesions (median 2) and 79 patients underwent MWA of 193 lesions (median 2). The median diameter of the ablated lesions was 9 mm for both RFA and MWA. Unsuccessful ablation was observed in 7 metastases (7.1%) after RFA and 14 metastases (7.3%) after MWA (p = 1.000). Complications requiring re-intervention were observed after 8 procedures, 2 complications in the RFA group (4.9%) versus 6 complications in the MWA group (7.6%, p = 0.714), of which 6 were liver-related. Ninety-day mortality did not occur. Ablation technique was not associated with unsuccessful ablations. CRLM size was associated with unsuccessful ablation in the per lesion analysis (p < 0.001).ConclusionIntraoperative RFA and MWA were equally effective for treatment of small CRLM.     

Study of the relationship between the target tissue necrosis volume and the target tissue size in liver tumours using two-compartment finite element RFA modelling

Purpose: The aim of this study was to investigate the relationship between the target tissue necrosis volume and the target tissue size during the radiofrequency ablation (RFA) procedure.

Materials and methods: The target tissues with four different sizes (d_xy?=?20, 25, 30 and 35?mm) were modelled using a two-compartment radiofrequency ablation model. Different voltages were applied to seek the maximum target tissue necrosis volume for each target tissue size. The first roll-off occurrence or the standard ablation time (12?min) was taken as the sign for the termination of the RFA procedure.

Results: Four different maximum voltages without the roll-off occurrence were found for the four different sizes of target tissues (d_xy?=?20, 25, 30 and 35?mm), and they were 36.6, 35.4, 33.9 and 32.5?V, respectively. The target tissues with diameters of 20, 25?mm can be cleanly ablated at their own maximum voltages applied (MVA) but the same finding was not found for the 35-mm target tissue. For the target tissue with diameter of 30?mm, the 50?°C isothermal contour (IT50) result showed that the target tissue can be cleanly ablated, but the same result did not show in the Arrhenius damage model result. Furthermore, two optimal RFA protocols with a minimal thermal damage to the healthy tissues were found for the target tissues with diameters of 20 and 25?mm, respectively.

Conclusions: The study suggests that target tissues of different sizes should be treated with different RFA protocols. The maximum target tissue volume was achieved with the MVA without the roll-off occurrence for each target tissue size when a constant RF power supply was used.     

Reasons for different therapeutic effects of high-intensity focused ultrasound ablation on excised uterine fibroids with different signal intensities on T2-weighted MRI: a study of histopathological characteristics

Objective: The objective of this study was to explore the correlations between the therapeutic effect of high intensity focused ultrasound (HIFU) and histopathological characteristics of excised uterine fibroids with different signal intensities as visualized on T2-weighted magnetic resonance imaging (MRI).

Methods: We collected 47 specimens of uterine fibroids after surgical resection and classified them into four groups according to preoperative T2-weighted MRI hypo-intense, isointense, heterogeneous intense and homogeneous hyper-intense. Then, specimens in each group were irradiated by HIFU with the same parameters and the necrotic tissue volume was calculated. The smooth muscle cell (SMC) count and collagen fiber content were quantitatively measured and compared between different groups. We analyzed the correlation between the necrotic tissue volume and SMC count and the collagen fiber content.

Results: Necrotic tissue volume gradually decreased from the hypo-intense group to the homogeneous hyper-intense group (p?=?.008). The SMC count from the hypo-intense group to the homogeneous hyper-intense group was 215.6?±?59.3, 237.0(89.5), 232.3?±?72.5 and 330.5?±?30.9, respectively; collagen fiber content was 0.65?±?0.07, 0.64?±?0.10, 0.53?±?0.11 and 0.41?±?0.06, respectively. Comparison among the four groups showed that SMC count progressively increased (p?=?.001) but collagen fiber content progressively decreased (p?=?.000) from the hypo-intense group to the homogeneous hyper-intense group. Correlation analysis showed that necrotic tissue volume was negatively correlated with SMC count (R?=??0.488, p=.013) but positively correlated with collagen fiber content (R?=?0.534, p?=?.005).

Conclusions: Differences in histopathological characteristics may be one of the reasons for different therapeutic effects of HIFU ablation on uterine fibroids with different signal intensities on T2-weighted MRI.