MRI-guided focused ultrasound surgery of uterine leiomyomas

Model based deep learning method for focused ultrasound pathway scanning

The primary purpose of high-intensity focused ultrasound (HIFU), a non-invasive medical therapy, is to precisely target and ablate tumors by focusing high-frequency ultrasound from an external power source. A series of ablations must be performed in order to treat a big volume of tumors, as a single ablation can only remove a small amount of tissue. To maximize therapeutic efficacy while minimizing adverse side effects such as skin burns, preoperative treatment planning is essential in determining the focal site and sonication duration for each ablation. Here, we introduce a machine learning-based approach for designing HIFU treatment plans, which makes use of a map of the material characteristics unique to a patient alongside an accurate thermal simulation. A numerical model was employed to solve the governing equations of HIFU process and to simulate the HIFU absorption mechanism, including ensuing heat transfer process and the temperature rise during the sonication period. To validate the accuracy of this numerical model, a series of tests was conducted using ex vivo bovine liver. The findings indicate that the developed models properly represent the considerable variances observed in tumor geometrical shapes and proficiently generate well-defined closed treated regions based on imaging data. The proposed strategy facilitated the formulation of high-quality treatment plans, with an average tissue over- or under-treatment rate of less than 0.06%. The efficacy of the numerical model in accurately predicting the heating process of HIFU, when combined with machine learning techniques, was validated through quantitative comparison with experimental data. The proposed approach in cooperation with HIFU simulation holds the potential to enhance presurgical HIFU plan.

Numerical studies on shortening the duration of HIFU ablation therapy and their experimental validation

High Intensity Focused Ultrasound (HIFU) is used in clinical practice for thermal ablation of malignant and benign solid tumors located in various organs. One of the reason limiting the wider use of this technology is the long treatment time resulting from i.a. the large difference between the size of the focal volume of the heating beam and the size of the tumor. Therefore, the treatment of large tumors requires scanning their volume with a sequence of single heating beams, the focus of which is moved in the focal plane along a specific trajectory with specific time and distance interval between sonications. To avoid an undesirable increase in the temperature of healthy tissues surrounding the tumor during scanning, the acoustic power and exposure time of each HIFU beam as well as the time intervals between sonications should be selected in such a way as to cover the entire volume of the tumor with necrosis as quickly as possible. This would reduce the costs of treatment. The aim of this study was to quantitatively evaluate the hypothesis that selecting the average acoustic power and exposure time for each individual heating beam, as well as the temporal intervals between sonications, can significantly shorten treatment time. Using 3D numerical simulations, the dependence of the duration of treatment of a tumor with a diameter of 5 mm or 9 mm (requiring multiple exposure to the HIFU beam) on the sonication parameters (acoustic power, exposure time) of each single beam capable of delivering the threshold thermal dose (CEM43 = 240 min) to the treated tissue volume was examined. The treatment duration was determined as the sum of exposure times to individual beams and time intervals between sonications. The tumor was located inside the ex vivo tissue sample at a depth of 12.6 mm. The thickness of the water layer between the HIFU transducer and the tissue was 50 mm. The sonication and scanning parameters selected using the developed algorithm shortened the duration of the ablation procedure by almost 14 times for a 5-mm tumor and 20 times for a 9-mm tumor compared to the duration of the same ablation plan when a HIFU beam was used of a constant acoustic power, constant exposure time (3 s) and constant long time intervals (120 s) between sonications. Results of calculations of the location and size of the necrotic lesion formed were experimentally verified on ex vivo pork loin samples, showing good agreement between them. In this way, it was proven that the proper selection of sonication and scanning parameters for each HIFU beam allows to significantly shorten the time of HIFU therapy.

MRgFUS ablation of a recurrent tenosynovial giant cell tumor in the foot using ExAblate 2100 system in combination with patient immobilization device

INTRODUCTION

Magnetic Resonance-guided Focused Ultrasound (MRgFUS) treatment for certain anatomy locations can be extremely challenging due to patient positioning and potential motion. This present study describes the treatment of a recurrent tenosynovial giant cell tumor of the plantar forefoot using the ExAblate 2100 system in combination with patient immobilization device.

METHODS

Prior to the treatment, several patient immobilization devices were investigated. Vacuum cushions were selected and tested for safety and compatibility with the treatment task and the MR environment.

RESULTS

During the treatment, one vacuum cushion immobilized the patient's right leg in knee flexion and allowed the bottom of the foot to be securely positioned on the treatment window. Another vacuum cushion supported the patient upper body extended outside the scanner bore. 19 sonications were successfully executed. The treatment was judged to be successful. No immediate complications were observed.

CONCLUSIONS

MRgFUS treatment of a recurrent tenosynovial giant cell tumor of the right plantar forefoot was successful with the use of patient immobilization vacuum cushions.

IMPLICATIONS FOR PRACTICE

The immobilization system could be utilized to aid future MRgFUS treatment of lesions in challenging anatomic locations. Various sizes of the vacuum cushions are available to potentially better accommodate other body parts and treatment configurations.

Abnormal uterine bleeding successfully treated via ultrasound-guided microwave ablation of uterine myoma lesions: Three case reports

BACKGROUND

Microwave endometrial ablation (MEA) is a minimally invasive treatment method for heavy menstrual bleeding. However, additional treatment is often required after recurrence of uterine myomas treated with MEA. Additionally, because this treatment ablates the endometrium, it is not indicated for patients planning to become pregnant. To overcome these issues, we devised a method for ultrasound-guided microwave ablation of uterine myoma feeder vessels. We report three patients successfully treated for heavy menstrual bleeding, secondary to uterine myoma, using our novel method.

CASE SUMMARY

All patients had a favorable postoperative course, were discharged within 4 h, and experienced no complications. Further, no postoperative recurrence of heavy menstrual bleeding was noted. Our method also reduced the myoma's maximum diameter.

CONCLUSION

This method does not ablate the endometrium, suggesting its potential application in patients planning to become pregnant.

Application value of contrast-enhanced ultrasonography in the treatment of uterine fibroids by high-intensity focused ultrasound ablation: A retrospective study

PURPOSE

To determine efficacy and safety of contrast-enhanced ultrasonography (CEUS) in high-intensity focused ultrasound (HIFU) ablation of uterine fibroids (UFs).

METHODS

We retrospectively reviewed women undergoing HIFU ablation for UFs between June 2018 and January 2020. Before and after HIFU, patients underwent CEUS and magnetic resonance imaging (MRI) examinations. The relationship between CEUS features and ablation rate was analyzed. The time-intensity curves on CEUS were measured before and after HIFU ablation, and compared with those obtained using MRI. Adverse reactions were recorded.

RESULTS

A total of 64 patients were included. The immediate HIFU ablation rate significantly differed between low-, iso-, and high-enhancement UFs (87.2% ± 1.6%, 83.3% ± 2.1%, and 72.9% ± 3.1%, respectively; p < 0.05). On CEUS, the peak time of the time-intensity curve was significantly longer after treatment than before treatment (32.2 ± 9.7 and 26.7 ± 9.4 s, respectively; p < 0.05). Peak intensity was significantly lower after treatment than before treatment (13.7 ± 7.5 and 30.9 ± 11.2 dB, respectively; p < 0.05). All measurements were comparable between CEUS and MRI. The most common peri- and post-procedure adverse reaction was pain, which was temporary.

CONCLUSION

CEUS could dynamically and safely evaluate the immediate effects of the HIFU ablation of UFs.

Experimental evaluation of the near-field and far-field heating of focused ultrasound using the thermal dose concept

BACKGROUND

Conventional motion algorithms utilized during High Intensity Focused Ultrasound (HIFU) procedures usually sonicate successive tissue cells, thereby inducing excess deposition of thermal dose in the pre-focal region. Long delays (~60 s) are used to reduce the heating around the focal region. In the present study the experimental evaluation of six motion algorithms so as to examine the required delay and algorithm for which the pre-focal (near-field) and post-focal (far-field) heating can be reduced using thermal dose estimations is presented.

MATERIALS AND METHODS

A single element spherically focused transducer operating at 1.1 MHz and focusing beam at 9 cm, was utilized for sonication on a 400 mm2 area of an agar-based phantom. Movement of the transducer was performed with each algorithm, using 0-60 s (10 s step) delays between sonications. Temperatures were recorded at both near and far-field regions and thermal dose calculations were implemented.

RESULTS

With the algorithms used in the present study, a delay of 50-60 s was required to reduce heating in the near-field region. A 30 s delay induced a safe thermal dose in the far-field region using all algorithms except sequential which still required 60 s delay.

CONCLUSIONS

The study verified the conservative need for 60 s delay for the sequential plan treatment. Nevertheless, present findings suggest that prolonged treatment times can be significantly reduced in homogeneous tissues by selection of the optimized nonlinear algorithm and delay.

Can magnetic resonance image-guided focused ultrasound surgery replace local oncology treatments? A review

Magnetic resonance image-guided focused ultrasound surgery (MRgFUS) is an innovative technology in the new panorama of treatment using ultrasound. It combines two well-known and distinct methodologies: high-intensity focused ultrasound (HIFU) and a magnetic resonance imaging system (MRI). This review on MRgFUS is focused on the technical aspects and the current clinical applications in oncology. More precisely, the advantages/disadvantages of MRgFUS compared to other local approaches such as surgery and radiotherapy are discussed in detail.

Minimally invasive procedures in the management of uterine fibroids

Uterine fibroids are benign uterine tumors. In women during the reproductive period, uterine fibroids occur in about 25%, whereas after this time, they are observed in more than 40% of women. In the majority of women (about 20-50%), such tumors do not cause discomfort and do not require treatment. Asymptomatic uterine fibroids usually undergo only regular medical control, whereas symptomatic fibroids are an indication for treatment. Current treatment methods include surgical, pharmacological and minimally invasive treatment. Among the current commonly used methods, there are minimally invasive treatment options, which include Uterine Artery Embolization (UAE), Magnetic Resonance Guided Ultrasound Surgery (MRgFUS), MR-guided High Intensity Focused Ultrasound (MR-HIFU) and Laparoscopic Uterine Artery Occlusion (LUAO). The minimally invasive Ultrasound-guided High Intensity Focused Ultrasound method (US-HIFU) is new, but still experimental. The use of MRgFUS/MR-HIFU for the thermoablative treatment of fibroids was approved by the FDA (Food and Drug Administration) in 2004. As a minimally invasive method, it enables preservation of the uterus and eliminates the need for general anesthesia. LUAO is based on the use of the vascular clip, which is placed on the uterine artery at the level of the internal iliac artery. This procedure is performed bilaterally.

The use of UAE in obstetrics and gynecology was first described in 1987 as an effective method in the treatment of hemorrhage, which allows avoiding surgical intervention and enables the uterus to be preserved. An appropriate qualification of patients is crucial for high clinical efficacy and prevention of complications after UAE. The candidates should be women with symptomatic uterine fibroids, without other pathologies within the pelvis, who do not plan to get pregnant in the future.

The variety of uterine fibroids as for the location, size, and symptoms they can evoke, has enforced a very individual approach to each patient, to begin with observation and regular gynecological control, through a number of pharmacological and minimally invasive treatment methods, and ending with the removal of the uterus. It gives the doctors the tools, which, if used properly, can manage uterine fibroids and fulfil the expectations of the patient.

Safety issues and updates under MR environments

Magnetic resonance (MR) imaging is a useful imaging tool with superior soft tissue contrast for diagnostic evaluation. The MR environments poses unique risks to patients and employees differently from ionizing radiation exposure originated from computed tomography and plain x-ray films. The technology associated with MR system has evolved continuously since its introduction in the late 1970s. MR systems have advanced with static magnetic fields, faster and stronger gradient magnetic fields and more powerful radiofrequency transmission coils. Higher field strengths of MR offers greater signal to noise capability and better spatial resolution, resulting in better visualization of anatomic detail, with a reduction in scan time. With the rapid evolution of technology associated with MR, we encounter new MR-related circumstances and unexpected dangerous conditions. A comprehensive update of our knowledge about MR safety is necessary to prevent MR-related accidents and to ensure safety for patients and staff associated with MR. This review presents an overview about MR-related safety issues and updates.

Preclinical MRI-Guided Focused Ultrasound: A Review of Systems and Current Practices

Effective preclinical research is a vital component in the development of MRI-guided focused ultrasound (MRgFUS) and its translation to clinic. In this review, we seek to outline the challenges at hand for effective preclinical research, survey different solutions, and underline best practices. Furthermore, we summarize efforts to build and characterize dedicated preclinical MRgFUS equipment, including lab prototypes and available commercial products. Finally, we discuss constraints and considerations specific to using clinical MRgFUS equipment in preclinical research. Specifically, we examine additional hardware that has been used to adapt clinical MRgFUS equipment to better position, constrain, and image preclinical subjects, as well as software solutions that have been used to extend the potential and capabilities of clinical devices.

High-Intensity Focused Ultrasound Ablation of Uterine Fibroids - Potential Impact on Fertility and Pregnancy Outcome

Laparoscopic myomectomy is regarded as the gold standard for women with symptomatic fibroids who wish to become pregnant. High-intensity focused ultrasound (HIFU or MRgFUS) ablation of uterine fibroids is also being discussed as a non-surgical, minimally invasive, therapeutic option. This review examines the available data on the impact of HIFU/MRgFUS on fertility and pregnancy, focusing particularly on potential direct side-effects of this type of intervention on ovaries, fallopian tubes and uterus and potential late effects on pregnancy and birth, based on the current literature. All pregnancies after HIFU/MRgFUS published to date (around 100 cases) were evaluated. The published case series suggest that HIFU/MRgFUS ablation has no impact on the rate of miscarriages or other obstetrical outcome parameters. Because no prospective studies exist which permit firm conclusions to be drawn on the impact of HIFU/MRgFUS on fertility and pregnancy outcome in women with symptomatic fibroids, this approach is currently only recommended for women with suspected fertility problems due to uterine fibroids who either decline surgery or who have an unacceptably high surgical risk.

Application status of high intensity focused ultrasound in treatment of colorectal cancer liver metastases

The liver is the most common and important site of metastases for colorectal cancer, and liver metastasis is one of the important factors leading to treatment failure in colorectal cancer. The traditional methods for treating liver metastases of colorectal cancer (CRLM) are not satisfactory and are often associated with a poor prognosis. High intensity focused ultrasound (HIFU) as a new technique for local ablation of solid tumors not only has advantages of less trauma, fewer complications, faster recovery and definite tumor necrosis, but also can preserve and enhance the host anti-tumor immunity. In recent years, HIFU ablation has been increasingly used for the therapy of tumors in clinical settings. This paper gives an overview of mechanisms of action and application status of HIFU in the treatment of colorectal cancer liver metastases, and explores current challenges and future perspectives.

MR-guided focused ultrasound for the novel and innovative management of osteoarthritic knee pain

Background

Severe knee pain associated with osteoarthritis (OA) is one of the most common and troublesome symptoms in the elderly. Recently, local bone denervation by MR-guided focused ultrasound (MRgFUS) has been demonstrated as a promising tool for pain palliation of bone metastases. The purpose of this study was to develop a novel treatment for knee OA using MRgFUS, and to validate its safety and efficacy.

Methods

Eight patients with medial knee pain and eligible for total knee arthroplasty were included. MR-guided focused sonication treatments were applied to bone surface just below the rim osteophyte of medial tibia plateau with real-time monitoring of the temperature in the target sites. The pain intensity during walking was assessed on a 100 mm visual analog scale (VAS) before and after treatment. Pressure pain thresholds (PPTs) were also evaluated over several test sites adjacent to the sonication area and control sites one month after treatment.

Results

Six patients (75%) showed immediate pain alleviation after treatment, and four of them demonstrated long-lasting effect at 6-month follow up (mean VAS reduction; 72.6%). In responders, PPTs in medial knee were significantly increased after treatment (Median; pre- 358 kpa vs post- 534 kpa, p?<?0.0001). There were no adverse side effects or complications during and after treatment.

Conclusions

These initial results illustrate the safety and efficacy of the newly developing MRgFUS treatment. Significant increase of PPTs on treated area showed successful denervation effect on the nociceptive nerve terminals. MRgFUS is a promising and innovative procedure for noninvasive pain management of knee OA.

Trial registration

Trial Registration: UMIN000010193

Mid-term clinical efficacy of a volumetric magnetic resonance-guided high-intensity focused ultrasound technique for treatment of symptomatic uterine fibroids

OBJECTIVE

To assess the mid-term efficacy of magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) using a volumetric ablation technique for treating uterine fibroids.

METHODS

Forty-six premenopausal women with 58 symptomatic uterine fibroids were prospectively included for MR-HIFU. After treatment, CE-MRI allowed measurement of the non-perfused volume (NPV) ratio, defined as the non-enhancing part of the fibroid divided by fibroid volume. Clinical symptoms and fibroid size on T2W-MRI were quantified at 3 and 6 months' follow-up. The primary endpoint was a clinically relevant improvement in the transformed Symptom Severity Score (tSSS) of the Uterine Fibroid Symptom and Quality of Life questionnaire, defined as a 10-point reduction.

RESULTS

Volumetric ablation resulted in a mean NPV ratio of 0.40 ± 0.22, with a mean NPV of 141 ± 135 cm(3). Mean fibroid volume was 353 ± 269 cm(3) at baseline, which decreased to 271 ± 225 cm(3) at 6 months (P < 0.001), corresponding to a mean volume reduction of 29 % ± 20 %. Clinical follow-up showed that 54 % (25/46) of the patients reported a more than 10-point reduction in the tSSS. Mean tSSS improved from 50.9 ± 18.4 at baseline to 34.7 ± 20.2 after 6 months (P < 0.001).

CONCLUSION

Volumetric MR-HIFU is effective for patients with symptomatic uterine fibroids. At 6 months, significant symptom improvement was observed in 54 % of patients.

KEY POINTS

• Volumetric MR-guided high-intensity focused ultrasound is a novel ablation technique for leiomyomatosis. • We prospectively evaluated the outcome of volumetric MR-HIFU ablation for symptomatic fibroids. • This study showed that volumetric MR-HIFU results in an effective treatment. • A randomised controlled trial would set this technique in an appropriate context.

MR imaging-controlled transurethral ultrasound therapy for conformal treatment of prostate tissue: initial feasibility in humans

PURPOSE

To evaluate the feasibility and safety of magnetic resonance (MR) imaging-controlled transurethral ultrasound therapy for prostate cancer in humans.

MATERIALS AND METHODS

This pilot study was approved by the institutional review board and was performed in eight men (mean age, 60 years; range, 49-70 years) with localized prostate cancer (Gleason score≤7, prostate-specific antigen level #15 μg/L) immediately before radical prostatectomy. All patients provided written informed consent. This phase 0 feasibility and safety study is the first evaluation in humans. Transurethral ultrasound therapy was performed with the patient under spinal anesthesia by using a clinical 1.5-T MR unit. Patients then underwent radical prostatectomy, and the resected gland was sliced in the plane of treatment to compare the MR imaging measurements with the pattern of thermal damage. The overall procedure time and coagulation rate were measured. In addition, the spatial targeting accuracy was evaluated, as was the thermal history along the thermal damage boundaries in the gland.

RESULTS

The average procedure time was 3 hours, with 2 or fewer hours spent in the MR unit. The treatment was well tolerated by all patients, and a temperature uncertainty of less than 2°C was observed in the treatments. The mean temperature and thermal dose measured along the boundary of thermal coagulation were 52.3°C±2.1 and 3457 (cumulative equivalent minutes at 43°C)±5580, respectively. The mean treatment rate was 0.5 mL/min, and a spatial targeting accuracy of -1.0 mm±2.6 was achieved.

CONCLUSION

MR imaging-controlled transurethral ultrasound therapy is feasible, safe, and well tolerated. This technology could be an attractive approach for whole-gland or focal therapy.

Focused ultrasound surgery in oncology: overview and principles

Focused ultrasound surgery (FUS) is a noninvasive image-guided therapy and an alternative to surgical interventions. It presents an opportunity to revolutionize cancer therapy and to affect or change drug delivery of therapeutic agents in new focally targeted ways. In this article the background, principles, technical devices, and clinical cancer applications of image-guided FUS are reviewed.

Quality-of-life assessment of fibroid treatment options and outcomes

PURPOSE

To obtain utilities (a unit of measure of a person's relative preferences for different health states compared with death or worst possible outcome) for uterine fibroids before and after treatment and to measure short-term utilities for the following uterine fibroid treatments: abdominal hysterectomy, magnetic resonance (MR) imaging-guided focused ultrasound surgery, and uterine artery embolization (UAE).

MATERIALS AND METHODS

This retrospective study was approved by the institutional review board and was HIPAA compliant. The waiting trade-off (WTO) method, a variation on the time trade-off (TTO) method, is used to obtain utilities for diagnostic procedures on the basis of the fact that people wait longer to avoid noxious tests and/or procedures. The WTO method provides short-term quality of life tolls in terms of quality-adjusted life-weeks by scaling wait times with pre- and posttreatment utilities. Utilities for uterine fibroids before and after treatment were obtained with the TTO method and a visual analog scale (VAS) by using a questionnaire administered by means of a phone interview. WTO wait times were adjusted for quality of life with VAS and TTO utilities and a transformation of VAS. Wait times were compared by using nonparametric tests. The study participants included 62 patients who had undergone abdominal hysterectomy, 74 who had undergone UAE, and 61 who had undergone MR imaging-guided focused ultrasound surgery.

RESULTS

Quality of life increased with all treatments. The median WTO wait time was higher for hysterectomy (21.6 weeks) than for UAE or MR imaging-guided focused ultrasound surgery (14.1 weeks for both) (P < .05). Quality-adjusted life-week tolls were smaller when scaled according to TTO than when scaled according to VAS or transformation of VAS.

CONCLUSION

Quality of life increased after all fibroid treatments. WTO is feasible for assessing the quality-adjusted morbidity of treatment procedures.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11100704/-/DC1.

A unified approach to combine temperature estimation and elastography for thermal lesion determination in focused ultrasound thermal therapy

Sonogram-based temperature estimation and elastography have both shown promise as methods of monitoring focused ultrasound (FUS) treatments to induce thermal ablation in tissue. However, each method has important limitations. Temperature estimates based on echo delays become invalid when the relationship between sound speed and temperature is nonlinear, and are further complicated by thermal expansion and other changes in tissue. Elastography can track thermal lesion formation over a wider range of elasticity, but with low specificity and high noise. Furthermore, this method is poor at small lesion detection. This study proposes integrating the two estimates to improve the quality of monitoring FUS-induced thermal lesions. Our unified computational kernel is tested on three types of phantoms. Experiments with type I and type II phantoms were conducted to calibrate the thermal mapping and elastography methods, respectively. The optimal settings were then used in experiments with the type III phantom, which contains ex vivo swine liver tissue. Three different spatial-peak temporal-average intensities (I(spta); 35, 133 and 240 W cm(-2)) were delivered with a sonication time of 60 s. The new procedure can closely monitor heating while identifying the dimensions of the thermal lesion, and is significantly better at the latter task than either approach alone. This work may help improve the current clinical practice, which employs sonograms to guide the FUS-induced thermal ablation procedure.

High-intensity focused ultrasound ablation of uterine localized adenomyosis

PURPOSE OF REVIEW

To introduce recent developments in a noninvasive treatment of using high-intensity focused ultrasound (HIFU) for ablating uterine localized adenomyosis, and to discuss their potential in this application.

RECENT FINDINGS

This literature roughly reviewed conservative therapy for uterine localized adenomyosis and emphasized using HIFU for ablating it. The main histological change of HIFU treatment was the coagulative necrosis of adenomyosis cells, with damage on small blood vessels of adenomyoma. MR-guided focused ultrasound surgery (MRgFUS) and ultrasound-guided HIFU ablation of focal adenomyosis were with satisfactory results. MRgFUS was less invasive and safely ablated adenomyosis tissue close to the endometrium or to serosal surface. HIFU might be safe and effective for treating patients with adenomyosis, and the acoustic intensity was a key factor for therapeutic efficacy as the severity of symptoms might correlate with lesion extent in some patients. At a given therapeutic dose, the influence of acoustic intensity on focal temperature rise was greater than that of exposure time. Some other experiments showed that the size of adenomyoma was increased 3-4 months after HIFU treatment. The reasons were related to the size of tumor, treatment parameters, operation procedure, and the blood supply of the targeted tissue. Although recent results have been very encouraging, further trials are essential to evaluate the long-term efficacy, and cost-effectiveness of HIFU ablation in localized adenomyosis.

SUMMARY

Compared with current conservative treatments, HIFU may be a noninvasive approach and may offer complete ablation of adenomyoma, with less trauma, less complication, and low cost and short hospital stay for treating patients with uterine localized adenomyosis.

Leiomyoma shrinkage after MRI-guided focused ultrasound treatment: report of 80 patients

OBJECTIVE

The purpose of this study was to assess the degree of leiomyoma ablation and shrinkage after MRI-guided focused ultrasound treatment performed according to U.S. Food and Drug Administration protocols for commercial trials.

MATERIALS AND METHODS

A total of 147 symptomatic leiomyomas in 80 women (average age, 46 years; range, 34-55 years) were managed with MRI-guided focused ultrasound. The average volume of treated fibroids was 175+/-201 (SD) cm3. Before treatment, T2-weighted MR images in three planes were obtained to measure leiomyoma volume. Immediately after treatment, T1-weighted contrast-enhanced fat-suppressed MR images in three planes were used to measure nonperfused volume ratio. Similar images obtained 6 months after treatment were used to determine leiomyoma shrinkage. Qualitative and quantitative relations between fibroid volume, nonperfused volume ratio at treatment, and 6-month shrinkage were measured.

RESULTS

The average nonperfused volume ratio was 55%+/-25% immediately after treatment. Six months after treatment, the average volume of treated fibroids had decreased to 112+/-141 cm3 (n=81) (p<0.0001) with an average volume reduction of 31%+/-28%. A linear regression model showed highly significant correlation between posttreatment nonperfused volume ratio and shrinkage at 6 months (p<0.0001).

CONCLUSION

MRI-guided focused ultrasound therapy for leiomyoma can result in nonperfused volume ratio and shrinkage that exceed those in previous clinical trials because the treatment guidelines have been relaxed to allow a greater amount of tissue ablation. The results suggest that a larger nonperfused volume ratio can be achieved, resulting in greater shrinkage and improved relief of symptoms.

Non-invasive magnetic resonance-guided focused ultrasound treatment of uterine fibroids in a large Japanese population: impact of the learning curve on patient outcome

OBJECTIVES

To describe the learning curve effect of magnetic resonance-guided focused ultrasound surgery (MRgFUS) on the outcomes of patients treated for uterine fibroids in four centers in Japan.

METHODS

The extent of fibroid ablation (often used to measure treatment success) was evaluated using the non-perfused volume (NPV) ratio in 287 Japanese patients. The patients were divided into two equal groups according to the chronological treatment time and results were compared between these groups to estimate the learning curve effect. Results were also compared with published data from clinical trials.

RESULTS

The NPV ratio increased chronologically, from 39.3% to 54.0% (P < 0.001), indicating increasing effectiveness of the treatment with experience. The mean NPV ratios for the entire patient population were over double that of previous clinical trials (46.6% vs. 21.9%; P < 0.001). No serious complications were reported.

CONCLUSION

The learning process and accumulation of data on MRgFUS enable the optimization of treatments in order to safely achieve large NPV ratios and sustained clinical benefit.

Safety and efficacy of high intensity focused ultrasound ablation therapy for adenomyosis

RATIONALE AND OBJECTIVES

In patients with adenomyosis, the severity of symptoms correlates roughly with the extent of adenomyosis. Thus, it was hypothesized that the ablation of enough volume of adenomyosis might alleviate symptoms. The aim of this study was to investigate the safety and efficacy of high-intensity focused ultrasound (HIFU) ablation for the treatment of adenomyosis.

MATERIALS AND METHODS

Phase I HIFU ablation of adenomyosis was performed on 12 patients. Three patients each were treated using four different acoustic intensities (290, 340, 380, and 420 W) step by step. Contrast-enhanced ultrasound was used to evaluate the necrotic region of treated adenomyosis. The efficacy of therapy was evaluated after 3 months of follow-up.

RESULTS

All patients in the four groups tolerated the therapy well, and no severe complications were found during follow-up. After treatment, nonenhanced necrotic regions were shown on contrast-enhanced ultrasound in all treated adenomyosis. The mean volumes of the nonenhanced regions were 72, 75, 68, and 124 cm(3) in the 290-W, 340-W, 380-W, and 420-W groups, respectively. At 3 months after therapy, the mean pain relief in the four groups was 25%, 58.3%, 66.7%, and 83.3%, respectively.

CONCLUSIONS

HIFU may be a safe and effective method to treat adenomyosis, and an acoustic intensity of 420 W may be able to produce larger volumes of necrosis and better pain relief.

An MRI-compatible system for focused ultrasound experiments in small animal models

The development of novel MRI-guided therapeutic ultrasound methods including potentiated drug delivery and targeted thermal ablation requires extensive testing in small animals such as rats and mice due to the widespread use of these species as models of disease. An MRI-compatible, computer-controlled three-axis positioning system was constructed to deliver focused ultrasound exposures precisely to a target anatomy in small animals for high-throughput preclinical drug delivery studies. Each axis was constructed from custom-made nonmagnetic linear ball stages driven by piezoelectric actuators and optical encoders. A range of motion of 5 x 5 x 2.5 cm3 was achieved, and initial bench top characterization demonstrated the ability to deliver ultrasound to the brain with a spatial accuracy of 0.3 mm. Operation of the positioning system within the bore of a clinical 3 T MR imager was feasible, and simultaneous motion and MR imaging did not result in any mutual interference. The system was evaluated in its ability to deliver precise sonications within the mouse brain, linear scanned exposures in a rat brain for blood barrier disruption, and circular scans for controlled heating under MR temperature feedback. Initial results suggest that this is a robust and precise apparatus for use in the investigation of novel ultrasound-based therapeutic strategies in small animal preclinical models.

Prevention of post-focal thermal damage by formation of bubbles at the focus during high intensity focused ultrasound therapy

Safety concerns exist for potential thermal damage at tissue-air or tissue-bone interfaces located in the post-focal region during high intensity focused ultrasound (HIFU) treatments. We tested the feasibility of reducing thermal energy deposited at the post-focal tissue-air interfaces by producing bubbles (due to acoustic cavitation and/or boiling) at the HIFU focus. HIFU (in-situ intensities of 460-3500 W/cm2, frequencies of 3.2-5.5 MHz) was applied for 30 s to produce lesions (in turkey breast in-vitro (n = 37), and rabbit liver (n = 4) and thigh muscle in-vivo (n = 11)). Tissue temperature was measured at the tissue-air interface using a thermal (infrared) camera. Ultrasound imaging was used to detect bubbles at the HIFU focus, appearing as a hyperechoic region. In-vitro results showed that when no bubbles were present at the focus (at lower intensities of 460-850 W/cm2), the temperature at the interface increased continuously, up to 7.3 +/- 4.0 degrees C above the baseline by the end of treatment. When bubbles formed immediately after the start of HIFU treatment (at the high intensity of 3360 W/cm2), the temperature increased briefly for 3.5 s to 7.4 +/- 3.6 degrees C above the baseline temperature and then decreased to 4.0 +/- 1.4 degrees C above the baseline by the end of treatment. Similar results were obtained in in-vivo experiments with the temperature increases (above the baseline temperature) at the muscle-air and liver-air interfaces at the end of the high intensity treatment lower by 7.1 degrees C and 6.0 degrees C, respectively, as compared to the low intensity treatment. Thermal effects of HIFU at post-focal tissue-air interfaces, such as in bowels, could result in clinically significant increases in temperature. Bubble formation at the HIFU focus may provide a method for shielding the post-focal region from potential thermal damage.

Rabbit VX2 tumors as an animal model of uterine fibroids and for uterine artery embolization

PURPOSE

To determine the suitability of the rabbit VX2 tumor animal model for uterine fibroids and uterine artery embolization (UAE).

MATERIALS AND METHODS

The authors implanted and grew one uterine VX2 tumor per rabbit in six rabbits. UAE was performed by using 100-300 microm embolic particles and confirmed with x-ray digital subtraction angiography, magnetic resonance (MR) imaging, and necropsy. Unenhanced and contrast medium-enhanced MR images of VX2 tumors were obtained before and after UAE. Relative MR signal-to noise-ratio (SNR) was measured in the uterine VX2 tumor and in normal uterine tissue before and after UAE and compared by using a paired t-test (P = .05).

RESULTS

VX2 uterine tumors were successfully grown, and both VX2 tumor presence in the uterus and UAE were seen angiographically and confirmed with necropsy in all six rabbits. Statistically significant reductions in relative SNRs were measured in tumors (SNR before UAE, 15.3 +/- 5.15; SNR after UAE, 3.84 +/- 3.94; P < .0001). No statistically significant decrease in SNR was measured in normal uterine tissue before and after UAE (P = .63 for the right uterine horn and P = .93 for the left uterine horn).

CONCLUSION

Rabbit VX2 uterine tumors may be a suitable animal model of uterine fibroids and UAE.

Short-duration-focused ultrasound stimulation of Hsp70 expression in vivo

The development of transgenic reporter mice and advances in in vivo optical imaging have created unique opportunities to assess and analyze biological responses to thermal therapy directly in living tissues. Reporter mice incorporating the regulatory regions from the genes encoding the 70 kDa heat-shock proteins (Hsp70) and firefly luciferase (luc) as reporter genes can be used to non-invasively reveal gene activation in living tissues in response to thermal stress. High-intensity-focused ultrasound (HIFU) can deliver measured doses of acoustic energy to highly localized regions of tissue at intensities that are sufficient to stimulate Hsp70 expression. We report activation of Hsp70-luc expression using 1 s duration HIFU heating to stimulate gene expression in the skin of the transgenic reporter mouse. Hsp70 expression was tracked for 96 h following the application of 1.5 MHz continuous-wave ultrasound with spatial peak intensities ranging from 53 W cm(-2) up to 352 W cm(-2). The results indicated that peak Hsp70 expression is observed 6-48 h post-heating, with significant activity remaining at 96 h. Exposure durations were simulated using a finite-element model, and the predicted temperatures were found to be consistent with the observed Hsp70 expression patterns. Histological evaluation revealed that the thermal damage starts at the stratum corneum and extends deeper with increasing intensity. These results indicated that short-duration HIFU may be useful for inducing heat-shock expression, and that the period between treatments needs to be greater than 96 h due to the protective properties of Hsp70.

Magnetic resonance-guided focused ultrasound surgery

Uterine leiomyomas pose a significant health issue to reproductive-age women. Many women desire uterine conservation, and previously safe and efficacious therapies have been limited. Magnetic resonance-guided focused ultrasound surgery is a new noninvasive therapy that has been proven to be both safe and efficacious in the treatment of fibroids.

Magnetic resonance-guided high-intensity ultrasound ablation of the prostate

OBJECTIVES

This paper describes our work in developing techniques and devices for magnetic resonance (MR)-guided high-intensity ultrasound ablation of the prostate and includes review of relevant literature.

METHODS

Catheter-based high-intensity ultrasound applicators, in interstitial and transurethral configurations, were developed to be used under MR guidance. Magnetic resonance thermometry and the relevant characteristics and artifacts were evaluated during in vivo thermal ablation of the prostate in 10 animals. Contrast-enhanced MR imaging (MRI) and diffusion-weighted MRI were used to assess tissue damage and compared with histology.

RESULTS

During evaluation of these applicators, MR thermometry was used to monitor the temperature distributions in the prostate in real time. Magnetic resonance-derived maximum temperature thresholds of 52 degrees C and thermal dose thresholds of 240 minutes were used to control the extent of treatment and qualitatively correlated well with posttreatment imaging studies and histology. The directional transurethral devices are selective in their ability to target well-defined regions of the prostate gland and can be rotated in discrete steps to conform treatment to prescribed boundaries. The curvilinear applicator is the most precise of these directional techniques. Multisectored transurethral applicators, with dynamic angular control of heating and no rotation requirements, offer a fast and less complex means of treatment with less selective contouring.

CONCLUSIONS

The catheter-based ultrasound devices can produce spatially selective regions of thermal destruction in prostate. The MR thermal imaging and thermal dose maps, obtained in multiple slices through the target volume, are useful for controlling therapy delivery (rotation, power levels, duration). Contrast-enhanced T1-weighted MRI and diffusion-weighted imaging are useful tools for assessing treatment.

Magnetic resonance imaging of benign uterine pathology

Magnetic resonance imaging is commonly used for the identification and characterization of many pelvic abnormalities. Magnetic resonance provides the most comprehensive and detailed view of the uterus of any imaging modality. This article focuses on the magnetic resonance imaging features used to recognize and describe congenital uterine anomalies and benign conditions of the uterus.

Thermal ablation of uterine fibroids using MR-guided focused ultrasound-a truly non-invasive treatment modality

Uterine fibroids are a significant source of morbidity for women of reproductive age. Definitive treatment has traditionally been a hysterectomy, but increasingly women are not prepared to undergo such an invasive procedure for a benign and usually self-limiting condition. Although a number of minimally invasive techniques are now available, focused ultrasound has a considerable advantage over them as it is completely non-invasive and does not require an anaesthetic. Improvements in imaging techniques, particularly magnetic resonance imaging (MRI), have enabled the accurate planning, targeting and monitoring of treatments. We review the early experience of focused ultrasound surgery for the treatment of fibroids, and, in particular, the results of the recent phase I, II and III multi-centre clinical trials. These trials and other studies which demonstrate that MR-guided focused ultrasound ablation is feasible, safe and appears to have an efficacy that is comparable with other treatment modalities are described. This technique has the advantages of being non-invasive and being deliverable as an out-patient procedure.

MAGNETIC RESONANCE IMAGING-GUIDED FOCUSED ULTRASOUND FOR THERMAL ABLATION IN THE BRAIN

INTRODUCTION

Magnetic resonance imaging (MRI)-guided focused ultrasound is a novel technique that was developed to enable precise, image-guided targeting and destruction of tumors by thermocoagulation. The system, ExAblate2000, is a focused ultrasound delivery system embedded within the MRI bed of a conventional diagnostic MRI scanner. The device delivers small volumetric sonications from an ultrasound phased array transmitter that converge energy to selectively destroy the target. Temperature maps generated by the MRI scanner verify the location and thermal rise as feedback, as well as thermal destruction. To assess the safety, feasibility, and precision of this technology in the brain, we have used the ExAblate system to create predefined thermal lesions in the brains of pigs.

METHODS

Ten pigs underwent bilateral craniectomy to provide a bone window for the ultrasound beams. Seven to 10 days later, the animals were anesthetized and positioned in the ExAblate system. A predefined, 1-cm frontal para ventricular region was delineated as the target and treated with multiple sonications. MRI was performed immediately and 1 week after treatment. The animals were then sacrificed and the brains removed for pathological study. The size of individual sonication points and the location of the lesion were compared between the planned dose maps, posttreatment MRI scans, and pathological specimen.

RESULTS

High-energy sonications led to precise coagulation necrosis of the specified targets as shown by subsequent MRI, macroscopic, and histological analysis. The thermal lesions were sharply demarcated from the surrounding brain with no anatomic or histological abnormalities outside the target.

CONCLUSION

MRI-guided focused ultrasound proved a precise and an effective means to destroy anatomically predefined brain targets by thermocoagulation with minimal associated edema or damage to adjacent structures. Contrast-enhanced T1-, T2-, and diffusion-weighted MRI scans may be used for real-time assessment of tissue destruction.

Successful term pregnancy following MR-guided focused ultrasound treatment of uterine leiomyoma

OBJECTIVE

Term vaginal delivery after magnetic resonance-guided focused ultrasound therapy (MRgFU) for symptomatic uterine leiomyoma.

STUDY DESIGN

A 38-year-old nulligravida underwent MRgFU treatment per study protocol for a solitary 9 x 10 x 10 cm uterine myoma and conceived 18 months following the procedure. She was counseled on the unknown implications of MRgFU during subsequent pregnancy. Myoma size increased significantly during gestation. At 39 weeks, she underwent indicated labor induction with vacuum-assisted vaginal delivery of a healthy male infant.

CONCLUSION

In one pregnancy following MRgFU, there were no associated antepartum or intrapartum obstetrical complications.

The role of magnetic resonance imaging in minimal access surgery

PURPOSE OF REVIEW

Magnetic resonance imaging is commonly used for gynaecological malignancies, but also is increasingly used for the investigation of benign gynaecological complaints. This review summarizes the current evidence regarding its use as an adjunct to minimal access surgery for endometriosis, adenomyosis, adhesions and fibroids.

RECENT FINDINGS

Magnetic resonance imaging appears to be equal in efficacy to ultrasound for the diagnosis of both fibroids and endometriosis, and perhaps superior for the diagnosis of adenomyosis. It is extremely useful for the preoperative investigation of severe endometriosis, especially recto-vaginal disease. Milder endometriosis is, however, still difficult to diagnose by either ultrasound or magnetic resonance imaging. Magnetic resonance imaging can also be helpful for the detection of adhesions, pelvic collections, congenital defects and fibroids. It is also useful following fibroid embolization.

SUMMARY

Currently, it is not cost-effective to use magnetic resonance imaging as the modality of first choice when investigating pelvic pain and or menstrual disorders. If preoperative patients are carefully selected, however, it can substantially reduce surgical morbidity by using it to diagnose severe endometriosis and adhesions which may lead to cost savings overall.