MR imaging-guided focused ultrasound surgery of uterine leiomyomas: a feasibility study

Enhancing ablation effects of a microbubble-enhancing contrast agent ("SonoVue") in the treatment of uterine fibroids with high-intensity focused ultrasound: a randomized controlled trial

PURPOSE

To evaluate the role of the ultrasound contrast agent SonoVue in enhancing the ablation effects of ultrasound-guided high-intensity focused ultrasound (HIFU) on uterine fibroids.

METHODS

Eighty patients with solitary uterine fibroids at a single center were randomly assigned to a control or SonoVue group. Of these, 40 were treated using HIFU alone; 40 who were pretreated with SonoVue received a bolus before the HIFU procedure. All patients underwent magnetic resonance imaging (MRI) scan before and after HIFU treatment.

RESULTS

The post-HIFU MRI showed the nonperfused volume (NPV) in all of the treated uterine fibroids; the mean fractional ablation (NPV ratio) was 90.4 ± 8.3 % (range 66.4-100 %) in the SonoVue group and 82.8 ± 13.3 % (range 53.4-100 %) in the control group. The frequency of massive gray-scale changes that occurred during HIFU was greater in the group that received SonoVue than the group that did not. The average sonication time to reach massive gray-scale changes was significantly shorter in the group receiving SonoVue than the group without SonoVue. The acoustic energy for treating 1 mm(3) of uterine fibroid was less in the SonoVue group than the control group. No any major complication occurred in this study.

CONCLUSION

Based on the results of this randomized controlled trial, SonoVue could be safely used to enhance the effects of HIFU treatment for uterine fibroids.

Endoluminal MR-guided ultrasonic applicator embedding cylindrical phased-array transducers and opposed-solenoid detection coil

PURPOSE

MR-guided high-intensity contact ultrasound (HICU) was suggested as an alternative therapy for esophageal and rectal cancer. To offer high-quality MR guidance, two prototypes of receive-only opposed-solenoid coil were integrated with 64-element cylindrical phased-array ultrasound transducers (rectal/esophageal).

METHODS

The design of integrated coils took into account the transducer geometry (360° acoustic window within endoluminal space). The rectal coil was sealed on a plastic support and placed reversibly on the transducer head. The esophageal coil was fully embedded within the transducer head, resulting in one indivisible device. Comparison of integrated versus external coils was performed on a clinical 1.5T scanner.

RESULTS

The integrated coils showed higher sensitivity compared with the standard extracorporeal coil with factors of up to 7.5 (rectal applicator) and 3.3 (esophageal applicator). High-resolution MR images for both anatomy (voxel 0.4 × 0.4 × 5 mm(3)) and thermometry (voxel 0.75 × 0.75 × 8 mm(3), 2 s/image) were acquired in vivo with the rectal endoscopic device. The temperature feedback loop accurately controlled multiple control points over the region of interest.

CONCLUSION

This study showed significant improvement of MR data quality using endoluminal integrated coils versus standard external coil. Inframillimeter spatial resolution and accurate feedback control of MR-guided HICU thermotherapy were achieved.

Uterine fibroids: current perspectives

Uterine fibroids are a major cause of morbidity in women of a reproductive age (and sometimes even after menopause). There are several factors that are attributed to underlie the development and incidence of these common tumors, but this further corroborates their relatively unknown etiology. The most likely presentation of fibroids is by their effect on the woman's menstrual cycle or pelvic pressure symptoms. Leiomyosarcoma is a very rare entity that should be suspected in postmenopausal women with fibroid growth (and no concurrent hormone replacement therapy). The gold standard diagnostic modality for uterine fibroids appears to be gray-scale ultrasonography, with magnetic resonance imaging being a close second option in complex clinical circumstances. The management of uterine fibroids can be approached medically, surgically, and even by minimal access techniques. The recent introduction of selective progesterone receptor modulators (SPRMs) and aromatase inhibitors has added more armamentarium to the medical options of treatment. Uterine artery embolization (UAE) has now been well-recognized as a uterine-sparing (fertility-preserving) method of treating fibroids. More recently, the introduction of ultrasound waves (MRgFUS) or radiofrequency (VizAblate™ and Acessa™) for uterine fibroid ablation has added to the options of minimal access treatment. More definite surgery in the form of myomectomy or hysterectomy can be performed via the minimal access or open route methods. Our article seeks to review the already established information on uterine fibroids with added emphasis on contemporary knowledge.

MR-guided focused ultrasound

The joining of high-intensity focused ultrasound with high-resolution MR guidance has created a system that can produce tissue destruction deep within solid organs without any invasion. Accurate targeting and thermal mapping are provided by MRI and allow very accurate deposition of energy in tissues that can be altered in response to near real-time thermal imaging produced by MR so that the variation in tissue response that is otherwise observed can be overcome. Current areas of successful application of MR-guided focused ultrasound are described in the treatment of uterine fibroids and other areas of emerging applications in additional solid organs are also discussed.

Proceedings from the Third National Institutes of Health International Congress on Advances in Uterine Leiomyoma Research: comprehensive review, conference summary and future recommendations

BACKGROUND Uterine fibroids are the most common gynecologic tumors in women of reproductive age yet the etiology and pathogenesis of these lesions remain poorly understood. Age, African ancestry, nulliparity and obesity have been identified as predisposing factors for uterine fibroids. Symptomatic tumors can cause excessive uterine bleeding, bladder dysfunction and pelvic pain, as well as associated reproductive disorders such as infertility, miscarriage and other adverse pregnancy outcomes. Currently, there are limited noninvasive therapies for fibroids and no early intervention or prevention strategies are readily available. This review summarizes the advances in basic, applied and translational uterine fibroid research, in addition to current and proposed approaches to clinical management as presented at the 'Advances in Uterine Leiomyoma Research: 3rd NIH International Congress'. Congress recommendations and a review of the fibroid literature are also reported. METHODS This review is a report of meeting proceedings, the resulting recommendations and a literature review of the subject. RESULTS The research data presented highlights the complexity of uterine fibroids and the convergence of ethnicity, race, genetics, epigenetics and environmental factors, including lifestyle and possible socioeconomic parameters on disease manifestation. The data presented suggest it is likely that the majority of women with uterine fibroids will have normal pregnancy outcomes; however, additional research is warranted. As an alternative to surgery, an effective long-term medical treatment for uterine fibroids should reduce heavy uterine bleeding and fibroid/uterine volume without excessive side effects. This goal has not been achieved and current treatments reduce symptoms only temporarily; however, a multi-disciplined approach to understanding the molecular origins and pathogenesis of uterine fibroids, as presented in this report, makes our quest for identifying novel targets for noninvasive, possibly nonsystemic and effective long-term treatment very promising. CONCLUSIONS The Congress facilitated the exchange of scientific information among members of the uterine leiomyoma research and health-care communities. While advances in research have deepened our knowledge of the pathobiology of fibroids, their etiology still remains incompletely understood. Further needs exist for determination of risk factors and initiation of preventive measures for fibroids, in addition to continued development of new medical and minimally invasive options for treatment.

Magnetic resonance imaging-guided focused ultrasound treatment of symptomatic uterine fibroids: impact of technology advancement on ablation volumes in 115 patients

OBJECTIVES

The aim of this study was to assess the impact of the advanced technology of the new ExAblate 2100 system (Insightec Ltd, Haifa, Israel) for magnetic resonance imaging (MRI)-guided focused ultrasound surgery on treatment outcomes in patients with symptomatic uterine fibroids, as measured by the nonperfused volume ratio.

MATERIALS AND METHODS

This is a retrospective analysis of 115 women (mean age, 42 years; range, 27-54 years) with symptomatic fibroids who consecutively underwent MRI-guided focused ultrasound treatment in a single center with the new generation ExAblate 2100 system from November 2010 to June 2011. Mean ± SD total volume and number of treated fibroids (per patient) were 89 ± 94 cm and 2.2 ± 1.7, respectively. Patient baseline characteristics were analyzed regarding their impact on the resulting nonperfused volume ratio.

RESULTS

Magnetic resonance imaging-guided focused ultrasound treatment was technically successful in 115 of 123 patients (93.5%). In 8 patients, treatment was not possible because of bowel loops in the beam pathway that could not be mitigated (n = 6), patient movement (n = 1), and system malfunction (n = 1). Mean nonperfused volume ratio was 88% ± 15% (range, 38%-100%). Mean applied energy level was 5400 ± 1200 J, and mean number of sonications was 74 ± 27. No major complications occurred. Two cases of first-degree skin burn resolved within 1 week after the intervention. Of the baseline characteristics analyzed, only the planned treatment volume had a statistically significant impact on nonperfused volume ratio.

CONCLUSIONS

With technological advancement, the outcome of MRI-guided focused ultrasound treatment in terms of the nonperfused volume ratio can be enhanced with a high safety profile, markedly exceeding results reported in previous clinical trials.

Clinical and Technical Aspects of MR-Guided High Intensity Focused Ultrasound for Treatment of Symptomatic Uterine Fibroids

Although many women undergo hysterectomy for treatment of uterine fibroids, there are more options than ever before for fibroid treatment. A combination of objective criteria, including clinical parameters, anatomic factors, fibroid characteristics, and patient desires influence the choice of optimal therapeutic modality for a woman with symptomatic uterine fibroids. Magnetic resonance imaging-guided high intensity focused ultrasound (MR-HIFU) is the only noninvasive treatment option for women with symptomatic uterine fibroids unresponsive to medical treatment. The procedure has been shown to be safe and effective. MR-HIFU couples the three-dimensional multiplanar anatomic imaging and thermal monitoring capability of MR imaging with the therapeutic thermal-based coagulative necrosis mechanism of HIFU to safely and effectively ablate limited volume classical fibroids. In the author's experience, a multidisciplinary fibroid clinic facilitates a unified approach between gynecologists, radiologists, and others to individualize the most appropriate fibroid treatment options for each woman. This article describes the MR-HIFU technique and outcomes, as well as patient selection and treatment assessment.

Biomechanical properties of bone treated by magnetic resonance-guided focused ultrasound - an in vivo porcine model study

The magnetic resonance-guided focused ultrasound (MRgFUS) system uses MR imaging for real-time aiming of thermal ablation of bone and soft tissue tumors. Past clinical studies showed no increase in fracture rate after MRgFUS treatment. The purpose of this study was to determine the effect of MRgFUS treatment on mechanical properties of bone and correlate the effect to histological findings of treated bone. Four fully grown mini-pigs were treated by MRgFUS. Six consecutive right normal ribs were treated in each animal, and the left corresponding ribs served as controls. The animals were sacrificed at pre-set intervals (0, 2, 6 and 12weeks after treatment), and the treated and control bones were extracted. Mechanical properties of each bone were examined using three points bending studies for comparing treated bones to the corresponding controls. Histologic properties using Masson and hematoxylin-eosin stains were also compared. The ratio between treated and control biomechanical properties showed reduction in bone biomechanical properties at 6weeks post-MRgFUS treatment. The mean±SD yield load ratio and maximum ratios were 0.69±0.11 and 0.71±0.13, respectively (both p=0.031). These findings showed some recovery trend at 12weeks after treatment. Histological analysis showed a reduction in mean osteon size at 2weeks after treatment (0.58×10(-3)±0.1×10(-3)mm and 0.16×10(-3)±0.017×10(-3)mm) in control vs. treated bones, respectively (p=0.005). Treatment with the MRgFUS system resulted in a ~30% reduction in mechanical strength at 6weeks post-treatment. The reduction showed a reversible trend, with a 25%-20% decrease in strength at 12weeks post-treatment.

Temperature feedback based heating strategy for ultrasound thermal surgery

Phased array transducer has the ability to generate multiple-focus pattern by adjusting the driving signal of individual element of the array. For the treatment of large target volume, several multiple-focus pattern could be used by using temporal switching technique among these power patterns. Typically, to obtain a uniform thermal dose, properly adjust the power level within the target volume is important. In this study, we proposed a temperature feedback based heating strategy without the need of power level adjustment. Several parameters, such as the setting temperature, sonication time, power level and blood perfusion, may affect the final thermal dose. Simulation results show that setting temperature is the key parameter to determine the final thermal dose while the effects of blood perfusion could be neglected and the sonication time should be as short as possible. Small power level is not suggested because the resulting thermal dose would extended owing to the thermal conduction.

Noninvasive lipoma size reduction using high-intensity focused ultrasound

BACKGROUND

Lipomas are common benign mesenchymal tumors commonly removed using excision, but in certain cases, surgery is undesirable or ineffective. High-intensity focused ultrasound (HIFU) offers a noninvasive tumor ablation tool increasingly used in the clinic.

OBJECTIVE

To evaluate the efficacy and safety of a noninvasive lipoma size reduction technology using HIFU.

MATERIALS & METHODS

Twelve lipomas in nine patients were treated. Patients underwent four treatment sessions with a 3-week interval between treatments. Blood and urine tests and tolerability based on a standard visual analogue scale (VAS) were used to monitor patients for adverse effects. Lipoma volume was determined by measuring width and length (manually) and depth (ultrasonically).

RESULTS

The range of lipoma size was 2.7-169.4 cm3 before treatment and 0.2-119.8 cm3 after treatment. Mean volume reduction was 58.1 ± 22.8%. When palpated, the lipomas felt much softer than before treatment. The average VAS score was 4.1 ± 2.4. No significant adverse effects were noted.

CONCLUSION

The treatment was shown to be effective in noninvasively reducing lipoma size. The average volume reduction was substantial and statistically significant. The treatment was safe and well-tolerated. HIFU may be an alternative treatment modality in cases of lipoma.

Ultrasonic enhancement of drug penetration in solid tumors

Increasing the penetration of drugs within solid tumors can be accomplished through multiple ultrasound-mediated mechanisms. The application of ultrasound can directly change the structure or physiology of tissues or can induce changes in a drug or vehicle in order to enhance delivery and efficacy. With each ultrasonic pulse, a fraction of the energy in the propagating wave is absorbed by tissue and results in local heating. When ultrasound is applied to achieve mild hyperthermia, the thermal effects are associated with an increase in perfusion or the release of a drug from a temperature-sensitive vehicle. Higher ultrasound intensities locally ablate tissue and result in increased drug accumulation surrounding the ablated region of interest. Further, the mechanical displacement induced by the ultrasound pulse can result in the nucleation, growth and collapse of gas bubbles. As a result of such cavitation, the permeability of a vessel wall or cell membrane can be increased. Finally, the radiation pressure of the propagating pulse can translate particles or tissues. In this perspective, we will review recent progress in ultrasound-mediated tumor delivery and the opportunities for clinical translation.

Sonographically guided high-intensity focused ultrasound for the management of uterine fibroids

High-intensity focused ultrasound therapy has received increasing interest in the management of solid malignancies and benign tumors. Magnetic resonance imaging has always been used to define the target for controlling and monitoring the ablation. Recently, sonographically guided high-intensity focused ultrasound has been introduced to monitor the ablation process. This article provides an overview of the background, clinical use, and treatment outcomes of sonographically guided high-intensity focused ultrasound in the treatment of uterine fibroids.

Ultrasound thermal mapping based on a hybrid method combining cross-correlation and zero-crossing tracking

A hybrid method for estimating temperature with spatial mapping using diagnostic ultrasound, based on detection of echo shifts from tissue undergoing thermal treatment, is proposed. Cross-correlation and zero-crossing tracking are two conventional algorithms used for detecting echo shifts, but their practical applications are limited. The proposed hybrid method combines the advantages of both algorithms with improved accuracy in temperature estimation. In vitro experiments were performed on porcine muscle for preliminary validation and temperature calibration. In addition, thermal mapping of rabbit thigh muscle in vivo during high-intensity focused ultrasound heating was conducted. Results from the in vitro experiments indicated that the difference between the estimated temperature change by the proposed hybrid method and the actual temperature change measured by the thermocouple was generally less than 1 °C when the increase in temperature due to heating was less than 10 °C. For the in vivo study, the area predicted to experience the highest temperature coincided well with the focal point of the high-intensity focused ultrasound transducer. The computational efficiency of the hybrid algorithm was similar to that of the fast cross-correlation algorithm, but with an improved accuracy. The proposed hybrid method could provide an alternative means for non-invasive monitoring of limited temperature changes during hyperthermia therapy.

Transcostal high-intensity focused ultrasound treatment using phased array with geometric correction

In the high-intensity focused ultrasound treatment of liver tumors, ultrasound propagation is affected by the rib cage. Because of the diffraction and absorption of the bone, the sound distribution at the focal plane is altered, and more importantly, overheating on the rib surface might occur. To overcome these problems, a geometric correction method is applied to turn off the elements blocked by the ribs. The potential of steering the focus of the phased-array along the propagation direction to improve the transcostal treatment was investigated by simulations and experiments using different rib models and transducers. The ultrasound propagation through the ribs was computed by a hybrid method including the Rayleigh-Sommerfeld integral, k-space method, and angular spectrum method. A modified correction method was proposed to adjust the output of elements based on their relative area in the projected "shadow" of the ribs. The simulation results showed that an increase in the specific absorption rate gain up to 300% was obtained by varying the focal length although the optimal value varied in each situation. Therefore, acoustic simulation is required for each clinical case to determine a satisfactory treatment plan.

Assessment of high-intensity focused ultrasound treatment of rodent mammary tumors using ultrasound backscatter coefficients

Fischer 344 rats with subcutaneous mammary adenocarcinoma tumors were exposed to therapeutic ultrasound at one of three exposure levels (335, 360, and 502 W/cm(2) spatial-peak temporal-average intensity). Quantitative ultrasound estimates were generated from ultrasound radio frequency (RF) data from tumors before and after high-intensity focused ultrasound treatment. Treatment outcome was independently assessed by triphenyl tetrazolium chloride (TTC) staining, histological analysis by a pathologist, and thermocouple data. The average backscatter coefficient (BSC) and integrated backscatter coefficient (IBSC) were estimated before and after therapeutic ultrasound exposure for each tumor from RF data collected using clinical (Ultrasonix Sonix RP) and small-animal (Visualsonics Vevo 2100) array systems. Changes in the BSC with treatment were comparable to inter-sample variation of untreated tumors, but statistically significant differences in the change in the IBSCs were observed when comparing the exposures collectively (p < 0.10 for Sonix RP, p < 0.05 for Vevo 2100). Several exposure levels produced statistically significant differences in the change in IBSC when examined pair-wise, including two exposures having similar intensities (p < 0.05, Vevo 2100). A comparison of the IBSC results with temperature data, histology, and TTC staining revealed that the BSC was not always sensitive to thermal insult and that peak exposure pressure appeared to correlate with observed BSC increases.

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.

Targeted manipulation of apoptotic pathways by using High Intensity Focused Ultrasound in cancer treatment

Apoptosis, or programmed cell death, is a mechanism of cell death, which has been exploited for the treatment of cancers over the past few years. The understanding of apoptosis pathways (intrinsic and extrinsic) has led to discovery of treatment strategies which selectively target the cancer cells and spare the normal ones. This article reviews the current understanding of the apoptotic pathways which are utilized for targeting cancer cells using High Intensity Focused Ultrasound (HIFU).

Is fibroid heterogeneity a significant issue for clinicians and researchers?

The clinical and scientific literature overwhelmingly deals with fibroids as a single entity or disease. This convenient assumption of homogeneity may be an important oversight given that substantial evidence exists for heterogeneity between fibroids at many levels. Failure to recognize and accommodate fibroid heterogeneity can have significant ramifications for both clinical treatment decisions and research protocol design. The aim of this article is to review the current knowledge of fibroid heterogeneity and to identify key areas where fibroid heterogeneity should be taken into consideration both clinically and when designing research protocols. Uterine leiomyomata display significant and well-documented heterogeneity in symptoms, diagnostic imaging appearance, pathology, genetic background and therapeutic requirements. Additional research is needed to better understand fibroid heterogeneity as it relates to pathogenesis, molecular targets for potential new therapies, patient symptoms and, ultimately, treatment. To this list should also be added heterogeneity of genetics, lifestyle and individual clinical characteristics of the fibroid. Increasingly, an understanding of uterine leiomyoma heterogeneity will be of importance for clinicians who see patients with this common and costly disease.

Evaluation of dose distribution of molecular delivery after blood-brain barrier disruption by focused ultrasound with treatment planning

The permeability of the blood-brain barrier (BBB) can be enhanced by focused ultrasound (FUS) in localized regions with applications of ultrasound contrast agent (UCA). The purpose of this study was to evaluate the dose distribution of Evans blue (EB) in the targeted brain by sonication with treatment strategy. FUS exposure was applied with an ultrasound frequency of 1 MHz, a 5% duty cycle and a repetition frequency of 1 Hz. Single sonication with two doses of UCA and two sonications at the same location or an interval of 3 mm to induce BBB disruption for assessing dose distribution. The permeability of the BBB was measured quantitatively based on EB extravasation. Gadolinium deposition was monitored by contrast enhanced MR imaging for dose distribution of the focal plane. Hematoxylin and eosin staining was performed for histologic observation. No significant difference was found for EB in the focal regions between the single sonication with UCA at a dose of 300 μL/kg and repeated sonication with UCA at a lower dose of 150 μL/kg. There was a sharper dose distribution in the brain with repeated sonication at the same location, compared with the brain receiving two sonications at an interval of 3 mm. Compared with a single sonication with UCA at a dose of 150 μL/kg, the histologic evaluation of the sonicated regions indicated that more erythrocytes were seen in the brain treated with single sonication at a higher dose of 300 μL/kg or repeated sonication at a dose of 150 μL/kg. This study demonstrated that the dose distribution of molecular delivery could be regulated by sonication with treatment planning.

Magnetic resonance-guided focused ultrasound surgery: Part 2: A review of current and future applications

Magnetic resonance-guided focused ultrasound surgery (MRgFUS) is a novel combination of technologies that is actively being realized as a noninvasive therapeutic tool for a myriad of conditions. These applications are reviewed with a focus on neurological use. A combined search of PubMed and MEDLINE was performed to identify the key events and current status of MRgFUS, with a focus on neurological applications. MRgFUS signifies a potentially ideal device for the treatment of neurological diseases. As it is nearly real time, it allows monitored provision of treatment location and energy deposition; is noninvasive, thereby limiting or eliminating disruption of normal tissue; provides focal delivery of therapeutic agents; enhances radiation delivery; and permits modulation of neural function. Multiple clinical applications are currently in clinical use and many more are under active preclinical investigation. The therapeutic potential of MRgFUS is expanding rapidly. Although clinically in its infancy, preclinical and early-phase I clinical trials in neurosurgery suggest a promising future for MRgFUS. Further investigation is necessary to define its true potential and impact.

MR-guided focused ultrasound (MRgFUS) is effective for the distinct pattern of uterine fibroids seen in African-American women: data from phase III/IV, non-randomized, multicenter clinical trials

Background

Uterine fibroids are common among women at the reproductive age. Magnetic resonance-guided focused ultrasound surgery (MRgFUS) is a novel and a conservative treatment for symptomatic cases. The aim of the study was to evaluate the efficacy of MRgFUS in African-American (AA) women compared with that in non-African-Americans (non-AA).

Methods

A single-armed phase IV study was conducted to establish the efficacy of treatment in AA women. Comparison of patient, fibroid, and treatment characteristics from this trial was compared with that of the previously published phase III trial. Both studies were approved by the IRB of each medical center.

Results

Sixty-three AA and 59 non-AA women were treated with MRgFUS. Although AA women had a different pattern of disease, outcomes were similar in both groups. AA patients had a significant higher total number of fibroids compared with non-AA (median 6.0, interquartile range (IQR) 3.0–10.0 vs. 2.0, IQR 1.0–4.0, respectively, p < 0.001), although their total fibroid volume was significantly smaller (median 196.9 cm³, IQR 112.8–415.3 cm³ vs. 394.8 cm³, IQR 189.8–674.4 cm³, respectively, p < 0.001). AA women were younger compared with non-AA (mean ± SD 43.4 ± 5.1 vs. 46.3 ± 4.1 years of age, respectively, p = 0.001) when they presented for treatment. The rate of alternative treatments as well as fibroid-associated symptoms at follow-up time points (3, 6, 12, 24, and 36 months, period following MRgFUS treatment) did not differ according to race (p ≥ 0.62).

Conclusion

Despite differences in the pattern of fibroid disease, MRgFUS for uterine fibroids has a similar efficacy for AA women compared with non-AA women.

Reduction in the vascular bed volume of uterine fibroids after hormonal treatment: evaluation with dynamic double-echo R₂* imaging

PURPOSE

To demonstrate the reduction in vascular bed volume (VBV) of uterine fibroids after administration of gonadotropin-releasing hormone analogue (GnRHa) using magnetic resonance (MR) imaging including dynamic double-echo R₂* imaging (DDE-R₂*I) and to assess the value of DDE-R₂*I as a predictor of such reduction.

METHODS

Twenty-one women with uterine intramural fibroids underwent MR imaging including DDE-R₂*I before GnRHa treatment. DDE-R₂*I was acquired using a single-section, double-echo, fast spoiled gradient recalled acquisition in the steady state (SPGR) sequence. We calculated the area under the curve (AUC) of the signal intensity on R₂*I within a 3×3-cm²region of interest that served to represent the VBV. We repeated MR imaging after 2 administrations of GnRHa and repeated image analyses. We statistically analyzed correlations between (A) pre-treatment AUC (AUC(pre)) and AUC reduction and (B) AUC(pre) and volume reduction.

RESULTS

The interval between the 2 MR studies ranged from 56 to 119 days (mean: 80.4 days). The average volume of the fibroids before GnRHa treatment was 647.8 mL compared with 463.4 mL after the therapy (decreased by an average of 28.5%; P<0.0001). Meanwhile, measured AUC was reduced by 55.3% (483.4 vs. 206.5; P<0.0001). AUC(pre) correlated with volume reduction (r=0.68), but not AUC reduction.

CONCLUSIONS

We confirmed reduction in the VBV of fibroids using DDE-R₂*I. The measurement of AUC(pre) on DDE-R₂*I aids prediction of fibroid volume reduction but correlates poorly with the percentage of AUC reduction.

Targeted delivery of GDNF through the blood-brain barrier by MRI-guided focused ultrasound

Neurotrophic factors, such as glial cell line-derived neurotrophic factor (GDNF), are promising therapeutic agents for neurodegenerative diseases. However, the application of GDNF to treat these diseases effectively is limited because the blood–brain barrier (BBB) prevents the local delivery of macromolecular therapeutic agents from entering the central nervous system (CNS). Focused ultrasound combined with microbubbles (MBs) using appropriate parameters has been previously demonstrated to be able to open the BBB locally and noninvasively. This study investigated the targeted delivery of GDNF MBs through the BBB by magnetic resonance imaging (MRI)-guided focused ultrasound. Evans Blue extravasation and histological examination were used to determine the optimum focused ultrasound parameters. Enzyme-linked immunosorbent assay was performed to verify the effects of GDNF bound on MBs using a biotin–avidin bridging chemistry method to promote GDNF delivery into the brain. The results showed that GDNF can be delivered locally and noninvasively into the CNS through the BBB using MRI-guided focused ultrasound combined with MBs under optimum parameters. MBs that bind GDNF combined with MRI-guided focused ultrasound may be an effective way of delivering neurotrophic factors directly into the CNS. The method described herein provides a potential means of treating patients with CNS diseases.

MRIgHIFU: a tool for image-guided therapeutics

High-intensity focused ultrasound (HIFU) provides focal delivery of mechanical energy deep into the body. This energy can be used to elevate the tissue temperature to such a degree that ablation is achieved. The elevated temperature can also be used to release drugs from temperature-sensitive carriers or activate therapeutic molecules using mechanical or thermal energy. Lower dose exposures modify the vasculature to allow large molecules to diffuse from blood in the surrounding tissue for local drug delivery. The energy delivery can be targeted and monitored using magnetic resonance imaging (MRI). The online image guidance and monitoring provides treatment delivery that is customized to each patient such that optimal, effective treatment can be achieved. This ability to localize and customize treatment delivery may further enhance the future potential of targeted drugs that are personalized for each patient. This review examines the rapid development of MRI-guided HIFU (MRIgHIFU) methods over the past few years and discuss their future potential.

Low-pressure pulsed focused ultrasound with microbubbles promotes an anticancer immunological response

Background

High-intensity focused-ultrasound (HIFU) has been successfully employed for thermal ablation of tumors in clinical settings. Continuous- or pulsed-mode HIFU may also induce a host antitumor immune response, mainly through expansion of antigen-presenting cells in response to increased cellular debris and through increased macrophage activation/infiltration. Here we demonstrated that another form of focused ultrasound delivery, using low-pressure, pulsed-mode exposure in the presence of microbubbles (MBs), may also trigger an antitumor immunological response and inhibit tumor growth.

Methods

A total of 280 tumor-bearing animals were subjected to sonographically-guided FUS. Implanted tumors were exposed to low-pressure FUS (0.6 to 1.4 MPa) with MBs to increase the permeability of tumor microvasculature.

Results

Tumor progression was suppressed by both 0.6 and 1.4-MPa MB-enhanced FUS exposures. We observed a transient increase in infiltration of non-T regulatory (non-Treg) tumor infiltrating lymphocytes (TILs) and continual infiltration of CD8+ cytotoxic T-lymphocytes (CTL). The ratio of CD8+/Treg increased significantly and tumor growth was inhibited.

Conclusions

Our findings suggest that low-pressure FUS exposure with MBs may constitute a useful tool for triggering an anticancer immune response, for potential cancer immunotherapy.

Volumetric MR-guided high-intensity focused ultrasound ablation of uterine fibroids: treatment speed and factors influencing speed

OBJECTIVES

To assess the treatment speed of volumetric magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) ablation of symptomatic uterine fibroids, with a focus on factors affecting treatment speed.

METHODS

We received Institutional Review Board approval, and informed consent was obtained from all participants. Among 109 patients referred, 43 women (39.4 %) (mean age, 43.7 years), with 112 fibroids passed the screening. We treated 53 symptomatic uterine fibroids (47.3 %, 53/112) (volume, 341.2 ± 256.5 ml) using volumetric MR-HIFU ablation. We assessed procedure times, non-perfused volume (NPV) and treatment speed (NPV/treatment time). We statistically analysed the factors affecting treatment speed using multiple logistic regression tests.

RESULTS

Technical success was achieved in 42 of 43 cases. MR room time (from entrance to exit) and treatment time (from first to last sonication) were 216.0 ± 40.6 min and 131.5 ± 55.9 min, respectively. Immediate NPV was 178.9 ± 147.3 ml, which was 57.4 ± 25.5 % of the fibroid volume. Treatment speed was 81.8 ± 48.0 ml/h. Multivariate analysis showed that a large fibroid volume (P < 0.001), a low signal intensity ratio of fibroid to skeletal muscle on T2-weighted images (P = 0.009) and timing after completion of the learning curve (P < 0.001) significantly increased treatment speed.

CONCLUSION

Volumetric MR-HIFU ablation can effectively treat symptomatic uterine fibroids. The treatment speed appeared to improve when treating large and/or dark fibroids as well as upon completion of the learning curve.

Effects of different parameters in the fast scanning method for HIFU treatment

PURPOSE

High-intensity focused ultrasound is a promising method for the noninvasive treatment of benign and malignant tumors. This study analyzes the effects of scanning path, applied power, and geometric characteristics of the transducer on ablation using fast scanning method, a new scanning method that uses high-intensity focused ultrasound at different blood perfusion levels.

METHODS

Two transducers, six scanning paths, and three focal patterns were used to examine the ablation results of the fast scanning method using power densities from 1.35 × 10(7) W∕m(3) to 4.5 × 10(7) W∕m(3) and blood perfusion rates from 2 × 10(-3) ml∕ml∕s to 16 × 10(-3) ml∕ml∕s. The Pennes equation was solved using the finite-difference time-domain method to simulate the heating procedure.

RESULTS

Based on the results of the fast-scanning method, the different scanning paths exhibited small effect on the total treatment time supported by both simulation and least-square fit. Similar-sized lesions can result from the five different repeated paths, whereas a random path may lead to relative large fluctuations in ablation volume because of asymmetry of the lesions. Higher power levels increase the lesion volume and decrease the treatment time required for ablating a target area using the fast scanning method, whereas increased blood perfusion has the opposite effect on ablation volume and treatment time. A symmetric lesion can be produced through fast scanning method using a 65-element and a 90-element transducer. However, lesion production using the same operation scheme differs between the two transducers.

CONCLUSIONS

Unlike traditional scanning methods, fast scanning method produces a planned lesion regardless of scanning path, as long as the path consists of repeated subsequences. This attribute makes fast scanning method an easy-operation scheme that produces relatively large symmetric lesions in homogeneous tissues. Applied power is the most important factor; however, high blood perfusion levels can limit or even hinder the full ablation of the target area. Therefore, tissue perfusion and transducer type should be given special attention to ensure the success and safety of ablation treatment.

Application of Zernike polynomials towards accelerated adaptive focusing of transcranial high intensity focused ultrasound

PURPOSE

To study the phase aberrations produced by human skulls during transcranial magnetic resonance imaging guided focused ultrasound surgery (MRgFUS), to demonstrate the potential of Zernike polynomials (ZPs) to accelerate the adaptive focusing process, and to investigate the benefits of using phase corrections obtained in previous studies to provide the initial guess for correction of a new data set.

METHODS

The five phase aberration data sets, analyzed here, were calculated based on preoperative computerized tomography (CT) images of the head obtained during previous transcranial MRgFUS treatments performed using a clinical prototype hemispherical transducer. The noniterative adaptive focusing algorithm [Larrat et al., "MR-guided adaptive focusing of ultrasound," IEEE Trans. Ultrason. Ferroelectr. Freq. Control 57(8), 1734-1747 (2010)] was modified by replacing Hadamard encoding with Zernike encoding. The algorithm was tested in simulations to correct the patients' phase aberrations. MR acoustic radiation force imaging (MR-ARFI) was used to visualize the effect of the phase aberration correction on the focusing of a hemispherical transducer. In addition, two methods for constructing initial phase correction estimate based on previous patient's data were investigated. The benefits of the initial estimates in the Zernike-based algorithm were analyzed by measuring their effect on the ultrasound intensity at the focus and on the number of ZP modes necessary to achieve 90% of the intensity of the nonaberrated case.

RESULTS

Covariance of the pairs of the phase aberrations data sets showed high correlation between aberration data of several patients and suggested that subgroups can be based on level of correlation. Simulation of the Zernike-based algorithm demonstrated the overall greater correction effectiveness of the low modes of ZPs. The focal intensity achieves 90% of nonaberrated intensity using fewer than 170 modes of ZPs. The initial estimates based on using the average of the phase aberration data from the individual subgroups of subjects was shown to increase the intensity at the focal spot for the five subjects.

CONCLUSIONS

The application of ZPs to phase aberration correction was shown to be beneficial for adaptive focusing of transcranial ultrasound. The skull-based phase aberrations were found to be well approximated by the number of ZP modes representing only a fraction of the number of elements in the hemispherical transducer. Implementing the initial phase aberration estimate together with Zernike-based algorithm can be used to improve the robustness and can potentially greatly increase the viability of MR-ARFI-based focusing for a clinical transcranial MRgFUS therapy.

Coagulation of human prostate volumes with MRI-controlled transurethral ultrasound therapy: results in gel phantoms

PURPOSE

The feasibility and safety of magnetic resonance imaging (MRI)-controlled transurethral ultrasound therapy were demonstrated recently in a preliminary human study in which a small subvolume of prostate tissue was treated prior to radical prostatectomy. Translation of this technology to full clinical use, however, requires the capability to generate thermal coagulation in a volume up to that of the prostate gland itself. The aim of this study was to investigate the parameters required to treat a full 3D human prostate accurately with a multi-element transurethral applicator and multiplanar MR temperature control.

METHODS

The approach was a combination of simulations (to select appropriate parameters) followed by experimental confirmation in tissue-mimicking phantoms. A ten-channel, MRI-compatible transurethral ultrasound therapy system was evaluated using six human prostate models (average volume: 36 cm(3)) obtained from the preliminary human feasibility study. Real-time multiplanar MR thermometry at 3 T was used to control the spatial heating pattern in up to nine planes simultaneously. Treatment strategies incorporated both single (4.6 or 8.1 MHz) and dual (4.6 and 14.4 MHz) frequencies, as well as maximum acoustic surface powers of 10 or 20 W cm(-2).

RESULTS

Treatments at 4.6 MHz were capable of coagulating a volume equivalent to 97% of the prostate. Increasing power from 10 to 20 W cm(-2) reduced treatment times by approximately 50% with full treatments taking 26 ± 3 min at a coagulation rate of 1.8 ± 0.4 cm(3) min(-1). A dual-frequency 4.6∕14.4 MHz treatment strategy was shown to be the most effective configuration for achieving full human prostate treatment while maintaining good treatment accuracy for small treatment radii. The dual-frequency approach reduced overtreatment close to the prostate base and apex, confirming the simulations.

CONCLUSIONS

This study reinforces the capability of MRI-controlled transurethral ultrasound therapy to treat full prostate volumes in a short treatment time with good spatial targeting accuracy and provides key parameters necessary for the next clinical trial.

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.

Safety and efficacy of US-guided high-intensity focused ultrasound for treatment of submucosal fibroids

OBJECTIVES

To evaluate the safety and efficacy of US-guided high-intensity focused ultrasound (HIFU) ablation for the treatment of submucosal fibroids

METHODS

A total of 76 women with 78 submucosal uterine fibroids (68 type II fibroids, 10 type I fibroids) underwent US-guided HIFU ablation. The pretreatment fibroid diameter ranged from 2.4 to 13.5 cm (mean 5.7 ± 2.3 cm). The fibroids were ablated using a power output of 420-520 W. During follow-up, the volume shrinkage of the ablated fibroids was continuously observed on contrast-enhanced MR and/or contrast-enhanced ultrasound (CEUS). The change of symptoms was evaluated by using the symptom severity score questionnaire.

RESULTS

HIFU ablation was well tolerated in all patients. No major complications occurred. The mean nonperfused ablation ratio was 80 ± 12 % on CEUS. During follow-up, the ablated fibroids shrank significantly over time. The symptoms were alleviated significantly. No patients had amenorrhoea after treatment. Vaginal expulsion of necrotic tissue was seen in 58 % (44/76) of patients after HIFU ablation which disappeared after 2-4 menstrual cycles. Four patients received repeated HIFU ablation for enlarged residual fibroids.

CONCLUSIONS

US-guided HIFU ablation may be a safe and effective treatment for submucosal fibroids. Further studies are warranted to observe its influence on fertility.

KEY POINTS

• High-intensity focused ultrasound (HIFU) is a new minimally invasive therapeutic technique. • HIFU ablation may be safe and effective for treatment of submucosal fibroids • Treatment is minimally invasive and repeatable. • Vaginal expulsion of necrotic tissue is common after treatment.

Magnetic resonance imaging-guided volumetric ablation of symptomatic leiomyomata: correlation of imaging with histology

PURPOSE

To describe the preliminary safety and accuracy of a magnetic resonance (MR) imaging-guided high-intensity-focused ultrasound (HIFU) system employing new technical developments, including ablation control via volumetric thermal feedback, for the treatment of uterine leiomyomata with histopathologic correlation.

MATERIALS AND METHODS

In this phase I clinical trial, 11 women underwent MR-guided HIFU ablation (Sonalleve 1.5T; Philips Medical Systems, Vantaa, Finland), followed by hysterectomy within 30 days. Adverse events, imaging findings, and pathologic confirmation of ablation were assessed. The relationship between MR imaging findings, thermal dose estimates, and pathology and HIFU spatial accuracy were assessed using Bland-Altman analyses and intraclass correlations.

RESULTS

There were 12 leiomyomata treated. No serious adverse events were observed. Two subjects decided against having hysterectomy and withdrew from the study before surgery. Of 11 women, 9 underwent hysterectomy; all leiomyomata demonstrated treatment in the expected location. A mean ablation volume of 6.92 cm(3) ± 10.7 was observed at histopathologic examination. No significant differences between MR imaging nonperfused volumes, thermal dose estimates, and histopathology ablation volumes were observed (P > .05). Mean misregistration values perpendicular to the ultrasound beam axis were 0.8 mm ± 1.2 in feet-head direction and 0.1 mm ± 1.0 in and left-right direction and -0.7 mm ± 3.1 along the axis.

CONCLUSIONS

Safe, accurate ablation of uterine leiomyomata was achieved with an MR-guided HIFU system with novel treatment monitoring capabilities, including ablation control via volumetric thermal feedback.

Investigation of power and frequency for 3D conformal MRI-controlled transurethral ultrasound therapy with a dual frequency multi-element transducer

Transurethral ultrasound therapy uses real-time magnetic resonance (MR) temperature feedback to enable the 3D control of thermal therapy accurately in a region within the prostate. Previous canine studies showed the feasibility of this method in vivo. The aim of this study was to reduce the procedure time, while maintaining targeting accuracy, by investigating new combinations of treatment parameters. Simulations and validation experiments in gel phantoms were used, with a collection of nine 3D realistic target prostate boundaries obtained from previous preclinical studies, where multi-slice MR images were acquired with the transurethral device in place. Acoustic power and rotation rate were varied based on temperature feedback at the prostate boundary. Maximum acoustic power and rotation rate were optimised interdependently, as a function of prostate radius and transducer operating frequency. The concept of dual frequency transducers was studied, using the fundamental frequency or the third harmonic component depending on the prostate radius. Numerical modelling enabled assessment of the effects of several acoustic parameters on treatment outcomes. The range of treatable prostate radii extended with increasing power, and tended to narrow with decreasing frequency. Reducing the frequency from 8 MHz to 4 MHz or increasing the surface acoustic power from 10 to 20 W/cm(2) led to treatment times shorter by up to 50% under appropriate conditions. A dual frequency configuration of 4/12 MHz with 20 W/cm(2) ultrasound intensity exposure can treat entire prostates up to 40 cm(3) in volume within 30 min. The interdependence between power and frequency may, however, require integrating multi-parametric functions in the controller for future optimisations.

Hyperthermia-triggered drug delivery from temperature-sensitive liposomes using MRI-guided high intensity focused ultrasound

In the continuous search for cancer therapies with a higher therapeutic window, localized temperature-induced drug delivery may offer a minimal invasive treatment option. Here, a chemotherapeutic drug is encapsulated into a temperature-sensitive liposome (TSL) that is released at elevated temperatures, for example, when passing through a locally heated tumor. Consequently, high drug levels in the tumor tissue can be achieved, while reducing drug exposure to healthy tissue. Although the concept of temperature-triggered drug delivery was suggested more than thirty years ago, several chemical and technological challenges had to be addressed to advance this approach towards clinical translation. In particular, non-invasive focal heating of tissue in a controlled fashion remained a challenge. For the latter, high intensity focused ultrasound (HIFU) allows non-invasive heating to establish hyperthermia (40-45 °C) of tumor tissue over time. Magnetic resonance imaging (MRI) plays a pivotal role in this procedure thanks to its superb spatial resolution for soft tissue as well as the possibility to acquire 3D temperature information. Consequently, MRI systems emerged with an HIFU ultrasound transducer embedded in the patient bed (MR-HIFU), where the MRI is utilized for treatment planning, and to provide spatial and temperature feedback to the HIFU. For tumor treatment, the lesion is heated to 42 °C using HIFU. At this temperature, the drug-loaded TSLs release their payload in a quantitative fashion. The concept of temperature-triggered drug delivery has been extended to MR image-guided drug delivery by the co-encapsulation of a paramagnetic MRI contrast agent in the lumen of TSLs. This review will give an overview of recent developments in temperature-induced drug delivery using HIFU under MRI guidance.

Adapting MRI acoustic radiation force imaging for in vivo human brain focused ultrasound applications

A variety of magnetic resonance imaging acoustic radiation force imaging (MR-ARFI) pulse sequences as the means for image guidance of focused ultrasound therapy have been recently developed and tested ex vivo and in animal models. To successfully translate MR-ARFI guidance into human applications, ensuring that MR-ARFI provides satisfactory image quality in the presence of patient motion and deposits safe amount of ultrasound energy during image acquisition is necessary. The first aim of this work was to study the effect of motion on in vivo displacement images of the brain obtained with 2D Fourier transform spin echo MR-ARFI. Repeated bipolar displacement encoding configuration was shown less sensitive to organ motion. The optimal signal-to-noise ratio of displacement images was found for the duration of encoding gradients of 12 ms. The second aim was to further optimize the displacement signal-to-noise ratio for a particular tissue type by setting the time offset between the ultrasound emission and encoding based on the tissue response to acoustic radiation force. A method for measuring tissue response noninvasively was demonstrated. Finally, a new method for simultaneous monitoring of tissue heating during MR-ARFI acquisition was presented to enable timely adjustment of the ultrasound energy aimed at ensuring the safety of the MR-ARFI acquisition.

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.

Overview of therapeutic ultrasound applications and safety considerations

Applications of ultrasound in medicine for therapeutic purposes have been accepted and beneficial uses of ultrasonic biological effects for many years. Low-power ultrasound of about 1 MHz has been widely applied since the 1950s for physical therapy in conditions such as tendinitis and bursitis. In the 1980s, high-pressure-amplitude shock waves came into use for mechanically resolving kidney stones, and "lithotripsy" rapidly replaced surgery as the most frequent treatment choice. The use of ultrasonic energy for therapy continues to expand, and approved applications now include uterine fibroid ablation, cataract removal (phacoemulsification), surgical tissue cutting and hemostasis, transdermal drug delivery, and bone fracture healing, among others. Undesirable bioeffects can occur, including burns from thermal-based therapies and severe hemorrhage from mechanical-based therapies (eg, lithotripsy). In all of these therapeutic applications of ultrasound bioeffects, standardization, ultrasound dosimetry, benefits assurance, and side-effect risk minimization must be carefully considered to ensure an optimal benefit to risk ratio for the patient. Therapeutic ultrasound typically has well-defined benefits and risks and therefore presents a manageable safety problem to the clinician. However, safety information can be scattered, confusing, or subject to commercial conflicts of interest. Of paramount importance for managing this problem is the communication of practical safety information by authoritative groups, such as the American Institute of Ultrasound in Medicine, to the medical ultrasound community. In this overview, the Bioeffects Committee of the American Institute of Ultrasound in Medicine outlines the wide range of therapeutic ultrasound methods, which are in clinical use or under study, and provides general guidance for ensuring therapeutic ultrasound safety.

Feasibility study of ultrasonic computed tomography-guided high-intensity focused ultrasound

The aim of this study was to establish a proof of concept for an ultrasonic image-guided high-intensity focused ultrasound (HIFU) breast treatment system. An ultrasonic computed tomography (UCT) scanner served as a platform for image acquisition and thermal mapping. With this system, images depicting the speed of sound (SOS) can be obtained. After HIFU activation, the resulting changes in SOS can be mapped. For the temperature range T ≤ 45°C, the temperature elevation is obtained directly from the change in SOS. For thermal ablation, monitoring is obtained by studying the temporal derivative of the SOS while continuous HIFU heating is applied. The method was implemented to in vitro tissue specimens and the ability for thermal monitoring was demonstrated. The results indicate that the suggested concept is indeed feasible.

MR-guided focused ultrasound for the treatment of uterine fibroids

Magnetic resonance imaging-guided focused ultrasound (MRgFUS) ablation of uterine fibroids provides a minimally invasive outpatient technique for targeting and treating symptomatic uterine fibroids. Magnetic resonance imaging provides a guidance platform that has high temporal and spatial resolution for guiding, as well as thermal monitoring of the procedure. The high-intensity focused ultrasound provides a mechanism for delivering large amounts of energy directly into the fibroid without causing detrimental effects to the nontarget tissues. Early and intermediate follow-up of patients treated with MRgFUS provided promising results on the efficacy of the technique for providing symptom relief to patients. As more long-term follow-up data are published, the efficacy of this technique can be compared to more invasive surgical and minimally invasive catheter treatments.