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

Volumetric MR-guided high-intensity focused ultrasound ablation with a one-layer strategy to treat large uterine fibroids: initial clinical outcomes

PURPOSE

To evaluate initial clinical outcomes of volumetric magnetic resonance (MR)-guided high-intensity focused ultrasound (HIFU) ablation by using a one-layer strategy to treat large (>10 cm in diameter) uterine fibroids, with investigation of the correlation between effectiveness of the one-layer strategy and dynamic contrast material-enhanced (DCE) MR parameters.

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained. Twenty-seven women (mean age, 44.5 years) with 27 large uterine fibroids (mean diameter, 11.3 cm ± 1.4 [standard deviation] [range, 10.1-16.0 cm]; fibroid volume, 502.5 mL ± 214.3 [range, 253.8-1184.0 mL]) underwent volumetric MR-guided HIFU ablation with a one-layer strategy. (All treatment cells were placed in one coronal plane at a depth of half to anterior two-thirds of the anteroposterior dimension of fibroids.) Treatment time, immediate nonperfused volume (NPV), and effectiveness of a one-layer strategy (ratio of immediate NPV to total volume of treatment cells planned) correlating with baseline DCE MR parameters (volume transfer constant [K(trans)], fractional extravascular extracellular space, and fractional blood plasma volume [Pearson correlation test]), complications, 3-month follow-up volumes, and symptom severity score (SSS) changes (paired t test) were assessed retrospectively.

RESULTS

All treatments showed technical success in one session (mean treatment time, 166.2 minutes ± 38.9). NPV was 301.3 mL ± 119.1, which was 64.2% ± 19.9 (<50%, n = 4; ≥ 50%, n = 23) of fibroid volume. Ratio of immediate NPV to total volume of treatment cells (1.79 ± 0.61) negatively correlated with DCE MR imaging K(trans) values (r = -0.426, P = .017). Minor complications occurred in five patients (18.5% [thermal injury of abdominal wall, n = 3; 30-day leg numbness, n = 1; cystitis, n = 1]). At 3-month follow-up (n = 18), mean SSS had decreased from 37.4 at baseline to 24.0 (P < .001), and volume reduction ratio was 0.64 ± 0.15 (P < .001).

CONCLUSION

Volumetric MR-guided HIFU ablation with a one-layer strategy is safe and effective for treatment of large uterine fibroids. Effectiveness of this strategy showed a significant negative correlation with K(trans) values at baseline DCE MR imaging.

Intermediate-term effects of intracardiac communications created noninvasively by therapeutic ultrasound (histotripsy) in a porcine model

The authors have demonstrated that histotripsy (pulsed cavitational ultrasound) can create atrial septal defects and ventricular septal defects (VSDs) in an open-chest canine model transcutaneously through the intact chest of neonatal pigs. To assess the potential untoward effects of these applications, the clinical, systemic, and pathologic effects of histotripsy-induced intracardiac communications were analyzed. Six neonatal pigs received noninvasive ultrasound therapy to their ventricular septa, then were allowed to survive 1 month for evaluation of intermediate-term effects. The results were compared with those of six previous animals killed immediately and three others killed 2-3 days after the procedure. Brain magnetic resonance imaging (MRI) and an assessment of cardiac function were performed with long-term survivors, and pathologic specimens were obtained when the animals were killed. In all 15 animals, VSDs 2-6.5 mm wide were successfully created. No fatalities occurred, and all the animals thrived, achieving normal weight gain by the time they were killed. Brain MRI and lung pathology exhibited no evidence of thromboembolic events. No damage to intervening tissue was observed. Pathologic analysis showed demarcated damage to the ventricular septa. Flanking injury and hemorrhage observed acutely were resolved by 1 month, with tissue remodeling present. Transcutaneous histotripsy is a safe and effective technique for creating intracardiac communications noninvasively without intermediate-term untoward effects. With further refinement and development, histotripsy has the potential to become an effective tool for palliation of congenital heart disease.

Targeted vessel ablation for more efficient magnetic resonance-guided high-intensity focused ultrasound ablation of uterine fibroids

Purpose

To report the first clinical experience with targeted vessel ablation during magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) treatment of symptomatic uterine fibroids.

Methods

Pretreatment T1-weighted contrast-enhanced magnetic resonance angiography was used to create a detailed map of the uterine arteries and feeding branches to the fibroids. A three-dimensional overlay of the magnetic resonance angiography images was registered on 3D T2-weighted pretreatment imaging data. Treatment was focused primarily on locations where supplying vessels entered the fibroid. Patients were followed 6 months after treatment with a questionnaire to assess symptoms and quality of life (Uterine Fibroid Symptom and Quality of Life) and magnetic resonance imaging to quantify shrinkage of fibroid volumes.

Results

In two patients, three fibroids were treated with targeted vessel ablation during MR-HIFU. The treatments resulted in almost total fibroid devascularization with nonperfused volume to total fibroid volume ratios of 84, 68, and 86%, respectively, of treated fibroids. The predicted ablated volumes during MR-HIFU in patients 1 and 2 were 45, 40, and 82 ml, respectively, while the nonperfused volumes determined immediately after treatment were 195, 92, and 190 ml respectively, which is 4.3 (patient 1) and 2.3 (patient 2) times higher than expected based on the thermal dose distribution. Fibroid-related symptoms reduced after treatment, and quality of life improved. Fibroid volume reduction ranged 31–59% at 6 months after treatment.

Conclusion

Targeted vessel ablation during MR-HIFU allowed nearly complete fibroid ablation in both patients. This technique may enhance the use of MR-HIFU for fibroid treatment in clinical practice.

Alternatives to hysterectomy: focus on global endometrial ablation, uterine fibroid embolization, and magnetic resonance-guided focused ultrasound

The aim of this study was to inform the clinician of alternatives to hysterectomy through a critical evaluation of three treatment options: global endometrial ablation, uterine fibroid embolization, and magnetic resonance-guided focused ultrasound. Studies published in English-language, peer-reviewed journals were systematically searched using Cochrane and Medline. Keywords used included "alternatives to hysterectomy," "endometrial ablation," "uterine fibroid embolization," "uterine artery embolization," and "focused ultrasound." Articles meeting the inclusion criteria were reviewed and analyzed for themes and similarities. All three alternative methods of treatment reviewed are currently approved for use in the United States and abroad. In fact, five different global endometrial ablation devices are approved by the Food and Drug Administration for treatment of menorrhagia. Patient satisfaction scores after endometrial ablation are high (90%-95%), but amenorrhea rates are much lower (15%-60%). Data from randomized trials demonstrate that uterine fibroid embolization results in a shorter hospital stay and quicker return to work as compared with abdominal hysterectomy for leiomyomas, but after embolization, up to 20% of women need a second procedure. Ex-ablative therapy of leiomyomas with focused ultrasound is the newest of the three methods. It has a special set of patient selection criteria and is only available at less than 20 medical centers in the United States. Leiomyoma symptom relief after focused ultrasound therapy at 1 year post-procedure is high (85%-95%). There are many effective alternatives to hysterectomy in women with menorrhagia and/or symptomatic leiomyomas. However, because these procedures are performed by individuals from different subspecialists, primarily gynecologists and interventional radiologists, clinicians must consider using a multidisciplinary approach to find the best procedure for a given patient. There are no randomized trials comparing uterine fibroid embolization to vaginal hysterectomy, laparoscopic hysterectomy, or laparoscopic myomectomy.

Volumetric MR-HIFU ablation of uterine fibroids: role of treatment cell size in the improvement of energy efficiency

PURPOSE

To evaluate the energy efficiency of differently sized volumetric ablations in MR-guided high-intensity focused ultrasound (MR-HIFU) treatment of uterine fibroids.

MATERIALS AND METHODS

This study was approved by the institutional review board and informed consent was obtained from all participants. Ten symptomatic uterine fibroids (mean diameter 8.9 cm) in 10 women (mean age 42.2) were treated by volumetric MR-HIFU ablation under binary feedback control. The energy efficiency (mm3/J) of each sonication was calculated as the volume of lethal thermal dose (240 equivalent minutes at 43 °C) per unit acoustic energy applied. Operator-controllable parameters and signal intensity ratio of uterine fibroid to skeletal muscle on T2-weighted MR images were tested with univariate and multivariate analyses to discern which parameters significantly correlated with the ablation energy efficiency.

RESULTS

We analyzed a total of 236 sonications. The energy efficiency of the ablations was 0.42±0.25 mm3/J (range 0.004-1.18) with energy efficiency improving with the treatment cell size (4 mm, 0.06±0.06 mm3/J; 8 mm, 0.29±0.12 mm3/J; 12 mm, 0.58±0.18 mm3/J; 16 mm, 0.91±0.17 mm3/J). Treatment cell size (r=0.814, p<0.001), distance of ultrasound propagation (r=-0.151, p=0.020), sonication frequency (1.2 or 1.45 MHz; p<0.001), and signal intensity ratio (r=-0.205, p=0.002) proved to be significant by univariate analysis, while multivariate analysis revealed treatment cell size (B=0.075, p<0.001), US propagation distance (B=-6.928, p<0.001), and signal intensity ratio (B=-0.024, p=0.001) to be independently significant.

CONCLUSION

Energy efficiency in volumetric MR-HIFU ablation of uterine fibroids improves with increased treatment cell size, independent of other significant contributors such as distance of ultrasound propagation or signal intensity of the tumor on T2-weighted MR imaging.

Volumetric feedback ablation of uterine fibroids using magnetic resonance-guided high intensity focused ultrasound therapy

Objective

The purpose of this prospective multicenter study was to assess the safety and technical feasibility of volumetric Magnetic Resonance-guided High Intensity Focused Ultrasound (MR-HIFU) ablation for treatment of patients with symptomatic uterine fibroids.

Methods

Thirty-three patients with 36 fibroids were treated with volumetric MR-HIFU ablation. Treatment capability and technical feasibility were assessed by comparison of the Non-Perfused Volumes (NPVs) with MR thermal dose predicted treatment volumes. Safety was determined by evaluation of complications or adverse events and unintended lesions. Secondary endpoints were pain and discomfort scores, recovery time and length of hospital stay.

Results

The mean NPV calculated as a percentage of the total fibroid volume was 21.7%. Correlation between the predicted treatment volumes and NPVs was found to be very strong, with a correlation coefficient r of 0.87. All patients tolerated the treatment well and were treated on an outpatient basis. No serious adverse events were reported and recovery time to normal activities was 2.3 ± 1.8 days.

Conclusion

This prospective multicenter study proved that volumetric MR-HIFU is safe and technically feasible for the treatment of symptomatic uterine fibroids.

Key Points

• Magnetic-resonance-guided high intensity focused ultrasound allows non-invasive treatment of uterine fibroids.

• Volumetric feedback ablation is a novel technology that allows larger treatment volumes

• MR-guided ultrasound ablation of uterine fibroids appears safe using volumetric feedback

Treatment of small hepatocellular carcinomas with US-guided high-intensity focused ultrasound

High-intensity focused ultrasound (HIFU) is a noninvasive method that can cause complete coagulation necrosis without requiring the insertion of any instruments. The purpose of this study was to evaluate the safety and efficacy of HIFU treatment for small liver cancers without performing transcatheter arterial chemoembolization (TACE) or rib resection. HIFU ablation was performed without rib resection or the aid of TACE or percutaneous ethanol injection (PEI) in 12 patients with hepatocelullar carcinoma. The HIFU system (Chongqing Haifu Tech, Chongqing, China) was used under ultrasound guidance. All 12 patients completed the treatment without experiencing any adverse events. Complete coagulation was achieved by applying the sonications from the intercostal space when the tumor was located in the right lobe. After treatment, serum alanine aminotransferase (ALT) and serum aspartate aminotransferase (AST) levels were significantly higher than the baseline values; these levels recovered within 1 week. C-reactive protein (CRP) levels increased 1 week after treatment but decreased within 1 month. An epidural anesthetic provided sufficient pain suppression during the procedure. Edema of the subcutaneous tissue was detected in five cases, but the edema disappeared within 1 month. None of the patients developed acute hepatic failure, liver abscess or renal dysfunction. In conclusion, HIFU is effective for the treatment of patients with small liver cancer.

Epidural anesthesia with intravenous dexmedetomidine sedation in the successful anesthetic management of MRI-guided focused ultrasound ablation of early prostatic cancer

We report on five patients who underwent MRI-guided focused ultrasound ablation of prostatic cancer under epidural anesthesia with intravenous dexmedetomidine sedation. This pioneering procedure requires an immobile therapeutic field with adequate sedation and analgesia provided to the patients. Duration of the procedure is longer compared to diagnostic MRI scans. In combination with epidural anesthesia, dexmedetomidine was used to provide moderate levels of sedation without causing respiratory depression or hemodynamic instability, and was useful in preventing shivering. The pharmacological properties of dexmedetomidine contribute to make this technique safe and effective.

Reconstruction of fully three-dimensional high spatial and temporal resolution MR temperature maps for retrospective applications

Many areas of MR-guided thermal therapy research would benefit from temperature maps with high spatial and temporal resolution that cover a large three-dimensional volume. This article describes an approach to achieve these goals, which is suitable for research applications where retrospective reconstruction of the temperature maps is acceptable. The method acquires undersampled data from a modified three-dimensional segmented echo-planar imaging sequence and creates images using a temporally constrained reconstruction algorithm. The three-dimensional images can be zero-filled to arbitrarily small voxel spacing in all directions and then converted into temperature maps using the standard proton resonance frequency shift technique. During high intensity focused ultrasound heating experiments, the proposed method was used to obtain temperature maps with 1.5 mm × 1.5 mm × 3.0 mm resolution, 288 mm × 162 mm × 78 mm field of view, and 1.7 s temporal resolution. The approach is validated to demonstrate that it can accurately capture the spatial characteristics and time dynamics of rapidly changing high intensity focused ultrasound-induced temperature distributions. Example applications from MR-guided high intensity focused ultrasound research are shown to demonstrate the benefits of the large coverage fully three-dimensional temperature maps, including characterization of volumetric heating trajectories and near- and far-field heating.

Evaluation of a vessel-tracking-based technique for dynamic targeting in human liver

The purpose of this study was to evaluate a novel vessel-tracking-based technique for tracking of human liver. The novelty of the proposed technique is that it measures the translation and deformation of a local tissue region based on the displacements of a set of vessels of interest instead of the entire organ. The position of the target point was estimated from the relative positions of the center-of-masses of the vessels, assuming that the topological relationship between the target point and center-of-masses is unchanged during breathing. To reduce inaccuracy due to the delay between vessel image acquisition and sonication, the near-future target position was predicted based on the vessel displacements in the images extracted from an image library acquired before the tracking stage. Experiments on healthy volunteers demonstrated that regardless of the respiratory condition, appropriate combinations of three center-of-masses from the vessels situated around the target-tissue position yielded an estimation error of less than 2 mm, which was significantly smaller than that obtained when using a single center-of-mass trio. The effect of the tracking delay was successfully compensated, with a prediction error of less than 3 mm, by using over four images selected from the image library.

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.

Thermal ablation and high-temperature thermal therapy: Overview of technology and clinical implementation

High-temperature hyperthermia or thermal therapy is being applied for destruction of cancerous tissue, eradication or reduction of benign tumours and targeted tissue modification and remodelling. Many of these high-temperature technologies provide a minimally-invasive alternative with lower morbidities compared to the traditional surgical procedures. The effects of high-temperature thermal exposure on tissues, examples of heating technology and procedures of clinical practice related to high-temperature thermal therapy are reviewed. This brief review encompasses interstitial, endocavity, intraluminal and external applications of RF, microwave, ultrasound, laser and thermal conduction energy sources. The technology is prevalent and in various levels of advancement, with the move toward more spatially-accurate and controllable heating systems combined with image-guidance and treatment verification warranted, especially for the treatment of cancer.

Magnetic resonance-guided focused ultrasound of uterine leiomyomas: review of a 12-month outcome of 130 clinical patients

PURPOSE

To assess 12-month outcomes and safety of clinical magnetic resonance (MR)-guided focused ultrasound (US) treatments of uterine leiomyomas.

MATERIALS AND METHODS

Between March 2005 and December 2009, 150 women with symptomatic uterine leiomyomas were clinically treated with MR-guided focused US at a single institution; 130 patients completed treatment and agreed to have their data used for research purposes. Patients were followed through retrospective review of medical records and phone interviews conducted at 3-, 6-, and 12-month intervals after treatment to assess additional procedures and symptom relief. Outcome measures and treatment complications were analyzed for possible correlations with the appearance of the tumors on T2-weighted imaging.

RESULTS

The cumulative incidence of additional tumor-related treatments 12 months after MR-guided focused US was 7.4% by the Kaplan-Meier method. At 3-, 6-, and 12-month follow-up, 86% (90 of 105), 93% (92 of 99), and 88% (78 of 89) of patients reported relief of symptoms, respectively. No statistically significant correlation between tumor appearance on T2-weighted imaging and 12-month outcome was found. Treatment-related complications were observed in 17 patients (13.1%): 16 patients had minor complications and one had a major complication (deep vein thrombosis). All complications were resolved within the 12-month follow-up period.

CONCLUSIONS

MR-guided focused US is a noninvasive treatment option that can be used to effectively and safely treat uterine leiomyomas and delivers significant and lasting symptom relief for at least 12 months. The incidence of additional treatment during this time period is comparable with those in previous reports of uterine artery embolization.

Multipathway sequences for MR thermometry

MR-based thermometry is a valuable adjunct to thermal ablation therapies as it helps to determine when lethal doses are reached at the target and whether surrounding tissues are safe from damage. When the targeted lesion is mobile, MR data can further be used for motion-tracking purposes. The present work introduces pulse sequence modifications that enable significant improvements in terms of both temperature-to-noise-ratio properties and target-tracking abilities. Instead of sampling a single magnetization pathway as in typical MR thermometry sequences, the pulse-sequence design introduced here involves sampling at least one additional pathway. Image reconstruction changes associated with the proposed sampling scheme are also described. The method was implemented on two commonly used MR thermometry sequences: the gradient-echo and the interleaved echo-planar imaging sequences. Data from the extra pathway enabled temperature-to-noise-ratio improvements by up to 35%, without increasing scan time. Potentially of greater significance is that the sampled pathways featured very different contrast for blood vessels, facilitating their detection and use as internal landmarks for tracking purposes. Through improved temperature-to-noise-ratio and lesion-tracking abilities, the proposed pulse-sequence design may facilitate the use of MR-monitored thermal ablations as an effective treatment option even in mobile organs such as the liver and kidneys.

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.

Rapid MR-ARFI method for focal spot localization during focused ultrasound therapy

MR-guided focused ultrasound (FUS) is a noninvasive therapy for treating various pathologies. MR-based acoustic radiation force imaging (MR-ARFI) measures tissue displacement in the focal spot due to acoustic radiation force. MR-ARFI also provides feedback for adaptive focusing algorithms that could correct for phase aberrations caused by the skull during brain treatments. This work developed a single-shot echo-planar imaging-based MR-ARFI method that reduces scan time and ultrasound energy deposition. The new method was implemented and tested in a phantom and ex vivo brain tissue. The effect of the phase aberrations on the ultrasound focusing was studied using displacement maps obtained with echo-planar imaging and two-dimensional spin-warp MR-ARFI. The results show that displacement in the focal spot can be rapidly imaged using echo-planar imaging-based MR-ARFI with high signal-to-noise ratio efficiency and without any measurable tissue heating. Echo-planar imaging-based displacement images also demonstrate sufficient sensitivity to phase aberrations and can serve as rapid feedback for adaptive focusing in brain treatments and other applications.

High-intensity focused ultrasound (HIFU) in patients with solid malignancies: evaluation of feasibility, local tumour response and clinical results

PURPOSE

The purpose of this study was to evaluate the safety and efficacy of ultrasound-guided high-intensity focused ultrasound (USgHIFU) for ablation of solid tumours without damaging the surrounding structures.

MATERIALS AND METHODS

A specific written informed consent was obtained from every patient before treatment. From September 2008 to April 2009, 22 patients with 29 lesions were treated: nine patients with liver and/or soft-tissue metastases from colorectal carcinoma (CRC), six with pancreatic solid lesions, three with liver and/or bone metastases from breast cancer, one with osteosarcoma, one with muscle metastasis from lung cancer, one with iliac metastasis from multiple myeloma and one with abdominal liposarcoma. The mean diameter of tumours was 4.2 cm. All patients were evaluated 1 day, 1 month and 3 months after HIFU treatment by multidetector computed tomography (MDCT), positron-emission tomography (PET)-CT and clinical evaluation. The treatment time and adverse events were recorded.

RESULTS

All patients had one treatment. Average treatment and sonication times were, respectively, 162.7 and 37.4 min. PET-CT or/and MDCT showed complete response in 11/13 liver metastases; all bone, soft-tissue and pancreatic lesions were palliated in symptoms, with complete response to PET-CT, MDCT or magnetic resonance imaging (MRI); the liposarcoma was almost completely ablated at MRI. Local oedema was observed in three patients. No other side effects were observed. All patients were discharged 1-3 days after treatment.

CONCLUSIONS

According to our preliminary experience in a small number of patients, we conclude that HIFU ablation is a safe and feasible technique for locoregional treatment and is effective in pain control.

Real-time monitoring of high-intensity focused ultrasound lesion formation using acousto-optic sensing

High-intensity focused ultrasound (HIFU) is a promising modality that is used to noninvasively ablate soft tissue tumors. Nevertheless, real-time treatment monitoring with diagnostic ultrasound still poses a significant challenge since tissue necrosis, in the absence of cavitation or boiling, provides little acoustic contrast with normal tissue. In comparison, the optical properties of tissue are significantly altered accompanying lesion formation. A photorefractive crystal-based acousto-optic (AO) sensing system that uses a single HIFU transducer to simultaneously generate tissue necrosis and pump the AO interaction is used to monitor the real-time optical changes associated with thermal lesions induced in chicken breast ex vivo. It is found that the normalized change in AO response increases proportionally with the volume of necrosis. This study demonstrates AO sensing can identify the onset and growth of lesion formation in real time and, when used as feedback to guide exposures, results in more predictable lesion formation.

High frame rate ultrasound monitoring of high intensity focused ultrasound-induced temperature changes: a novel asynchronous approach

PURPOSE

When applying diagnostic ultrasound to guide focused ultrasound (FUS) thermal therapy, high frame rate ultrasonic temperature monitoring is valuable in better treatment control and dose monitoring. However, one of the potential problems encountered when performing ultrasonic temperature monitoring of a FUS procedure is interference between the FUS and imaging systems. Potential means of overcoming this problem include the switch between the FUS system and the imaging system (limited by a reduced frame rate of thermal imaging) or the development of complex synchronization protocols between the FUS therapeutic system and the ultrasonic imaging apparatus (limited by implementation efforts both for software and hardware designs, and low potential for widespread diffusion). In this paper, we apply an asynchronous idea to retrieving high frame rate and FUS-interference-free thermal imaging during FUS thermal therapy.

METHODS

Tone-burst delivery mode of the FUS energy is employed in our method, and the imaging and FUS systems are purposely operated in an asynchronous manner. Such asynchronous operation causes FUS interference to saturate sequential image frames at different A-lines; thus clean A-lines from several image frames can be extracted by a total energy-thresholding technique and then combined to reconstruct interference-free B-mode images at a high frame rate for temperature estimation. The performance of the proposed method is demonstrated by phantom experiments. Relationships of the FUS duty-cycle with the maximum reconstructed frame rate of thermal imaging and the corresponding maximum temperature increase are also studied. Its performance was also evaluated and compared with the existing manually synchronous and synchronous approaches.

RESULTS

By proper selection of the FUS duty-cycle, using our method, the frame rate of thermal imaging can be increased up to tenfold compared with that provided by the manually synchronous approach. Our method is capable of pushing the frame rate of thermal images to the same order as that of the synchronous approach while avoiding sacrificing the observable field of view (FOV) of temperature mapping.

CONCLUSIONS

The asynchronous method can be easily implemented and allows thermal imaging at an improved frame rate, without the need for complex synchronization protocols between the FUS therapeutic system and the ultrasonic imaging apparatus and without sacrifice of observable FOV. This technology may provide an effective alternative for real-time temperature measuring during thermal ablation procedures and can be easily integrated into current high intensity focused ultrasound systems.

Inhibition of glioma growth by microbubble activation in a subcutaneous model using low duty cycle ultrasound without significant heating

OBJECT

In this study, the authors sought determine whether microbubble (MB) destruction with pulsed low duty cycle ultrasound can be used to reduce brain tumor perfusion and growth through nonthermal microvascular ablation.

METHODS

Studies using C57BLJ6/Rag-1 mice inoculated subcutaneously with C6 glioma cells were approved by the institutional animal care and use committee. Microbubbles were injected intravenously, and 1 MHz ultrasound was applied with varying duty cycles to the tumor every 5 seconds for 60 minutes. During treatment, tumor heating was quantified. Following treatment, tumor growth, hemodynamics, necrosis, and apoptosis were measured.

RESULTS

Tumor blood flow was significantly reduced immediately after treatment, with posttreatment flow ranging from 36% (0.00002 duty cycle) to 4% (0.01 duty cycle) of pretreatment flow. Seven days after treatment, tumor necrosis and apoptosis were significantly increased in all treatment groups, while treatment with ultrasound duty cycles of 0.005 and 0.01 inhibited tumor growth by 63% and 75%, respectively, compared with untreated tumors. While a modest duty cycle-dependent increase in intratumor temperature was observed, it is unlikely that thermal tissue ablation occurred.

CONCLUSIONS

In a subcutaneous C6 glioma model, MB destruction with low-duty cycle 1-MHz ultrasound can be used to markedly inhibit growth, without substantial tumor tissue heating. These results may have a bearing on the development of transcranial high-intensity focused ultrasound treatments for brain tumors that are not amenable to thermal ablation.

Localised drug release using MRI-controlled focused ultrasound hyperthermia

PURPOSE

Thermosensitive liposomes provide a mechanism for triggering the local release of anticancer drugs, but this technology requires precise temperature control in targeted regions with minimal heating of surrounding tissue. The objective of this study was to evaluate the feasibility of using MRI-controlled focused ultrasound (FUS) and thermosensitive liposomes to achieve thermally mediated localised drug delivery in vivo.

MATERIALS AND METHODS

Results are reported from ten rabbits, where a FUS beam was scanned in a circular trajectory to heat 10-15 mm diameter regions in normal thigh to 43°C for 20-30 min. MRI thermometry was used for closed-loop feedback control to achieve temporally and spatially uniform heating. Lyso-thermosensitive liposomal doxorubicin was infused intravenously during hyperthermia. Unabsorbed liposomes were flushed from the vasculature by saline perfusion 2 h later, and tissue samples were harvested from heated and unheated thigh regions. The fluorescence intensity of the homogenised samples was used to calculate the concentration of doxorubicin in tissue.

RESULTS

Closed-loop control of FUS heating using MRI thermometry achieved temperature distributions with mean, T90 and T10 of 42.9°C, 41.0°C and 44.8°C, respectively, over a period of 20 min. Doxorubicin concentrations were significantly higher in tissues sampled from heated than unheated regions of normal thigh muscle (8.3 versus 0.5 ng/mg, mean per-animal difference = 7.8 ng/mg, P < 0.05, Wilcoxon matched pairs signed rank test).

CONCLUSIONS

The results show the potential of MRI-controlled focused ultrasound hyperthermia for enhanced local drug delivery with temperature-sensitive drug carriers.

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.

Future potential of MRI-guided focused ultrasound brain surgery

Magnetic resonance image-guided focused ultrasound surgery (MRgFUS) has surfaced as a viable noninvasive image-guided therapeutic method that integrates focused ultrasound (FUS), the therapeutic component, with magnetic resonance imaging (MRI), the image guidance module, into a real-time therapy delivery system with closed-loop control of energy delivery. The main applications for MRgFUS of the brain are thermal ablations for brain tumors and functional neurosurgery, and nonthermal, nonablative uses for disruption of the blood brain barrier (BBB) or blood clot and hematoma dissolution by liquification. The disruption of the BBB by FUS can be used for targeted delivery of chemotherapy and other therapeutic agents. MRI is used preoperatively for target definition and treatment planning, intraoperatively for procedure monitoring and control, and postoperatively for validating treatment success. Although challenges still remain, this integrated noninvasive therapy delivery system is anticipated to change current treatment paradigms in neurosurgery and the clinical neurosciences.

Comparison between diffusion-weighted imaging, T2-weighted, and postcontrast T1-weighted imaging after MR-guided, high intensity, focused ultrasound treatment of uterine leiomyomata: preliminary results

PURPOSE

To investigate the comparison between diffusion-weighted imaging (DWI), T2-weighted imaging, (T2WI) and contrast T1-weighted imaging (cT1WI) in uterine leiomyoma following treatment by magnetic resonance imaging-guided, high intensity focused ultrasound surgery (MRg-HIFUS).

METHODS

Twenty one patients (45 +/- 5 yrs) with clinical symptoms of uterine leiomyoma (fibroids) were treated by MRg-HIFUS using an integrated 1.5T MRI-HIFUS system. MRI parameters consisted of DWI, T2WI, and T1-weighted fast spoiled gradient echo before and after contrast. The post-MRg-HIFUS treatment volume in the fibroid was assessed by cT1WI and DWI. Trace apparent diffusion coefficient maps were constructed for quantitative analysis. The regions of the treated uterine tissue were defined by a semisupervised segmentation method called the "eigenimage filter," using both cT1WI and DWI. Signal-to-noise ratios were determined for the T2WI pretreatment images. Segmented regions were tested by a similarity index for congruence. Descriptive, regression, and Bland-Altman statistics were calculated.

RESULTS

All the patients exhibited heterogeneously increased DWI signal intensity localized in the treated fibroid regions and were colocalized with the cT1WI defined area. The mean pretreatment T2WI signal intensity ratios were T2WI/muscle = 1.8 +/- 0.7 and T2WI/myometrium = 0.7 +/- 0.4. The congruence between the regions was significant, with a similarity of 84% and a difference of 8% between the regions. Regression analyses of the cT1WI and DWI segmented treatment volume were found to be significantly correlated (r2 = 0.94, p < 0.05) with the linear equation, (cT1WI) = 1.1 (DWI)-0.66. There is good agreement between the regions defined by cT1WI and DWI in most of the cases as shown from the Bland-Altman plots.

CONCLUSIONS

Diffusion-weighted imaging exhibited excellent agreement, congruence, and correlation with the cT1WI-defined region of treatment in uterine fibroid. Therefore, DWI could be useful as an adjunct for assessing treatment of uterine fibroids by MRg-HIFUS.

Eligibility and accessibility of magnetic resonance-guided focused ultrasound (MRgFUS) for the treatment of uterine leiomyomas

OBJECTIVE

To evaluate patient eligibility and accessibility of magnetic resonance-guided focused ultrasound (MRgFUS) for women with symptomatic uterine leiomyomas who desire conservative therapy.

DESIGN

Retrospective analysis of 169 patients referred for minimally invasive treatment of leiomyomas between November 2007 and February 2009. Clinical eligibility for MRgFUS was determined by Food and Drug Administration-based treatment guidelines. All patients underwent pretreatment pelvic imaging to determine candidacy for the procedure.

PATIENT(S)

Premenopausal women with symptomatic uterine leiomyomas.

SETTING

Academic medical center.

MAIN OUTCOME MEASURE(S)

Eligibility for MRgFUS based on clinical and anatomic patient criteria.

RESULT(S)

Forty-seven percent of patients (80/169) were determined clinically eligible for the procedure. Of these, 16% of patients (27/169) were found to be eligible for MRgFUS based on imaging results. Overall, the main reasons for ineligibility were very large leiomyomas (8%; 14/169), cost (12%; 21/169), and desired fertility (14%; 23/169). An additional 48% of patients declined MRgFUS for unstated reasons, often after obtaining financial and insurance coverage information.

CONCLUSION(S)

Currently, many women with leiomyomas are unable to obtain MRgFUS treatment for multiple reasons, including uterine size, desire for fertility, and, most commonly, financial limitations. With increasing clinical experience, further research, and broadened insurance coverage, it may be possible to increase accessibility and expand eligibility criteria for this minimally invasive therapy.

Therapeutic ultrasound to noninvasively create intracardiac communications in an intact animal model

OBJECTIVE

To determine if pulsed cavitational ultrasound therapy (histotripsy) can accurately and safely generate ventricular septal defects (VSDs) through the intact chest of a neonatal animal, with the eventual goal of developing a noninvasive technique of creating intra-cardiac communications in patients with congenital heart disease.

BACKGROUND

Histotripsy is an innovative ultrasonic technique that generates demarcated, mechanical tissue fractionation utilizing high intensity ultrasound pulses. Previous work has shown that histotripsy can create atrial septal defects in a beating heart in an open-chest canine model.

METHODS

Nine neonatal pigs were treated with transcutaneous histotripsy targeting the ventricular septum. Ultrasound pulses of 5-μsec duration at a peak negative pressure of 13 MPa and a pulse repetition frequency of 1 kHz were generated by a 1 MHz focused transducer. The procedure was guided by real-time ultrasound imaging.

RESULTS

VSDs were created in all pigs with diameters ranging from 2 to 6.5 mm. Six pigs were euthanized within 2 hrs of treatment, while three were recovered and maintained for 2-3 days to evaluate lesion maturation and clinical side effects. There were only transient clinical effects and pathology revealed mild collateral damage around the VSD with no significant damage to other cardiac or extra-cardiac structures.

CONCLUSIONS

Histotripsy can accurately and safely generate VSDs through the intact chest in a neonatal animal model. These results suggest that with further advances, histotripsy can be a useful, noninvasive technique to create intracardiac communications, which currently require invasive catheter-based or surgical procedures, to clinically stabilize newborn infants with complex congenital heart disease.

Ultrasound-induced activation of Wnt signaling in human MG-63 osteoblastic cells

The benefit from an ultrasound (US) exposure for fracture healing has been clearly shown. However, the molecular mechanisms behind this effect are not fully known. Recently, the canonical Wnt signaling pathway has been recognized as one of the essential regulators of osteoblastogenesis and bone mass, and thereby considered crucial for bone health. Mechanical loading and fluid shear stress have been reported to activate the canonical Wnt signaling pathway in bone cells, but previous reports on the effects of therapeutic US on Wnt signaling in general or in bone, in particular, have not been published yet. Therefore, activation of Wnt signaling pathway was assayed in human osteoblastic cells, and indeed, this pathway was found to be activated in MG-63 cells through the phosphoinositol 3-kinase/Akt (PI3K/Akt) and mTOR cascades following a single 10 min US exposure (2 W, 1.035 MHz). In addition to the reporter assay results, the Wnt pathway activation was also observed as nuclear localization of beta-catenin. Wnt activation showed also temperature dependence at elevated temperatures, and the expression of canonical Wnt ligands was induced under the thermal exposures. However, existence of a specific, non-thermal US component was evident as well, perhaps evidence of a potential dual action of therapeutic US on bone. Neither US nor heat exposures affected cell viability in our experiments. In summary, this is the first study to report that Wnt signaling cascade, important for osteoblast function and bone health, is one of the pathways activated by therapeutic US as well as by hyperthermia in human osteoblastic cells. Our results provide evidence for the potential molecular mechanisms behind the beneficial effects of US on fracture healing. Combinations of US, heat, and possible pharmacological treatment could provide useful flexibility for clinical cases in treating various bone disorders.

Focused ultrasound as a local therapy for liver cancer

Conventional surgical treatments of liver cancer are invasive (including minimally invasive) with a high incidence of new metastasis and poor success, even after multiple resections or ablations. These limitations motivated research into new, less invasive solutions for liver cancer treatment.Focused ultrasound surgery (FUS), or high-intensity focused ultrasound, has been recognized as a noninvasive technology for benign and malignant tumor treatment. Previously, FUS was guided with ultrasound that has limited target definition and monitoring capability of the ablation process. Combining magnetic resonance imaging (MRI) with multiple-element phased-array transducers to create MRI-guided focused ultrasound thermal therapy provides more accurate targeting and real-time temperature monitoring. This treatment is hindered by the ribcage that limits the acoustic windows to the liver and the respiratory motion of the liver. New advances in MRI and transducer design will likely resolve these limitations and make MRI-guided FUS a powerful tool in local liver cancer therapy. This article reviews this technology and advances that can expand its use for cancer treatment in general and liver cancer in particular.

Hysterectomy-current methods and alternatives for benign indications

Hysterectomy is the commonest gynecologic operation performed not only for malignant disease but also for many benign conditions such as fibroids, endometrial hyperplasia, adenomyosis, uterine prolapse, dysfunctional uterine bleeding, and cervical intraepithelial neoplasia. There are many approaches to hysterectomy for benign disease: abdominal hysterectomy, vaginal hysterectomy, laparoscopic assisted vaginal hysterectomy (LAVH) where a vaginal hysterectomy is assisted by laparoscopic procedures that do not include uterine artery ligation, total laparoscopic hysterectomy (TLH) where the laparoscopic procedures include uterine artery ligation, and subtotal laparoscopic hysterectomy (STLH) where there is no vaginal component and the uterine body is removed using a morcelator. In the last decades, many new techniques, alternative to hysterectomy with conservation of the uterus have been developed. They use modern technologies and their results are promising and in many cases comparable with hysterectomy. This paper is a review of all the existing hysterectomy techniques and the alternative methods for benign indications.

A long arm for ultrasound: a combined robotic focused ultrasound setup for magnetic resonance-guided focused ultrasound surgery

PURPOSE

Focused ultrasound surgery (FUS) is a highly precise noninvasive procedure to ablate pathogenic tissue. FUS therapy is often combined with magnetic resonance (MR) imaging as MR imaging offers excellent target identification and allows for continuous monitoring of FUS induced temperature changes. As the dimensions of the ultrasound (US) focus are typically much smaller than the targeted volume, multiple sonications and focus repositioning are interleaved to scan the focus over the target volume. Focal scanning can be achieved electronically by using phased-array US transducers or mechanically by using dedicated mechanical actuators. In this study, the authors propose and evaluate the precision of a combined robotic FUS setup to overcome some of the limitations of the existing MRgFUS systems. Such systems are typically integrated into the patient table of the MR scanner and thus only provide an application of the US wave within a limited spatial range from below the patient.

METHODS

The fully MR-compatible robotic assistance system InnoMotion (InnoMedic GmbH, Herxheim, Germany) was originally designed for MR-guided interventions with needles. It offers five pneumatically driven degrees of freedom and can be moved over a wide range within the bore of the magnet. In this work, the robotic system was combined with a fixed-focus US transducer (frequency: 1.7 MHz; focal length: 68 mm, and numerical aperture: 0.44) that was integrated into a dedicated, in-house developed treatment unit for FUS application. A series of MR-guided focal scanning procedures was performed in a polyacrylamide-egg white gel phantom to assess the positioning accuracy of the combined FUS setup. In animal experiments with a 3-month-old domestic pig, the system's potential and suitability for MRgFUS was tested.

RESULTS

In phantom experiments, a total targeting precision of about 3 mm was found, which is comparable to that of the existing MRgFUS systems. Focus positioning could be performed within a few seconds. During in vivo experiments, a defined pattern of single thermal lesions and a therapeutically relevant confluent thermal lesion could be created. The creation of local tissue necrosis by coagulation was confirmed by post-FUS MR imaging and histological examinations on the treated tissue sample. During all sonications in phantom and in vivo, reliable MR imaging and online MR thermometry could be performed without compromises due to operation of the combined robotic FUS setup.

CONCLUSIONS

Compared to the existing MRgFUS systems, the combined robotic FUS approach offers a wide range of spatial flexibility so that highly flexible application of the US wave would be possible, for example, to avoid risk structures within the US field. The setup might help to realize new ways of patient access in MRgFUS therapy. The setup is compatible with any closed-bore MR system and does not require an especially designed patient table.

Automatic temperature control for MR-guided interstitial ultrasound ablation in liver using a percutaneous applicator: ex vivo and in vivo initial studies

Image-guided thermal ablation offers minimally invasive options for treating hepatocellular carcinoma and colorectal metastases in liver. Here, the feasibility and the potential benefit of active temperature control for MR-guided percutaneous ultrasound ablation was investigated in pig liver. An MR-compatible interstitial ultrasound applicator (flat transducer), a positioning system with rotation-translation guiding frame, and an orbital ring holder were developed. Step-by-step rotated elementary lesions were produced, each being formed by directive heating of a flame-shaped volume of tissue. In vivo feasibility of automatic temperature control was investigated on two pigs. Proton Resonance Frequency Shift (PRFS)-based MR thermometry was performed on a 1.5-T clinical scanner, using SENSE acceleration and respiratory gating. MR follow-up of animals and macroscopic analysis were performed at 3 and, respectively, 4 days postprocedure. No sonication-related radiofrequency artifacts were detected on MR images. The temperature controller converged to the target elevation within +/-2 degrees C unless the requested power level exceeded the authorized limit. Large variability of the controller's applied powers from one sonication to another was found both ex vivo and in vivo, indicating highly anisotropic acoustic coupling and/or tissue response to identical beam pattern along different radial directions. The automatic control of the temperature enabled reproducible shape of lesions (15 +/- 2 mm radial depth).