Feasibility of magnetic resonance imaging-guided focused ultrasound surgery as an adjunct to tamoxifen therapy in high-risk surgical patients with breast carcinoma

MR Imaging-Guided Focused Ultrasound for Breast Tumors

Breast tumors remain a complex and prevalent health burden impacting millions of individuals worldwide. Challenges in treatment arise from the invasive nature of traditional surgery and, in malignancies, the complexity of treating metastatic disease. The development of noninvasive treatment alternatives is critical for improving patient outcomes and quality of life. This review aims to explore the advancements and applications of focused ultrasound (FUS) technology over the past 2 decades. FUS offers a promising noninvasive, nonionizing intervention strategy in breast tumors including primary breast cancer, fibroadenomas, and metastatic breast cancer.

Non-Surgical Definitive Treatment for Operable Breast Cancer: Current Status and Future Prospects

This article reviews the results of various non-surgical curative treatments for operable breast cancer. Radiotherapy is considered the most important among such treatments, but conventional radiotherapy alone and concurrent chemoradiotherapy do not achieve high cure rates. As a radiosensitization strategy, intratumoral injection of hydrogen peroxide before radiation has been investigated, and high local control rates (75-97%) were reported. The authors treated 45 patients with whole-breast radiotherapy, followed by stereotactic or intensity-modulated radiotherapy boost, with or without a radiosensitization strategy employing either hydrogen peroxide injection or hyperthermia plus oral tegafur-gimeracil-oteracil potassium. Stages were 0-I in 23 patients, II in 19, and III in 3. Clinical and cosmetic outcomes were good, with 5-year overall, progression-free, and local recurrence-free survival rates of 97, 86, and 88%, respectively. Trials of carbon ion radiotherapy are ongoing, with promising interim results. Radiofrequency ablation, focused ultrasound, and other image-guided ablation treatments yielded complete ablation rates of 20-100% (mostly ≥70%), but long-term cure rates remain unclear. In these treatments, combination with radiotherapy seems necessary to treat the extensive intraductal components. Non-surgical treatment of breast cancer is evolving steadily, with radiotherapy playing a major role. In the future, proton therapy with the ultra-high-dose-rate FLASH mode is expected to further improve outcomes.

Ablative Therapies for Breast Cancer: State of Art

Breast cancer (BC) is the most frequently diagnosed malignancy among women. In the past two decades, new technologies and BC screening have led to the diagnosis of smaller and earlier-stage BC (ESBC). Therefore, percutaneous minimally invasive techniques (PMIT) were adopted to treat patients unfit for surgery, women who refuse it, or elderly patients with comorbidities that could make surgery a difficult and life-threatening treatment. The target of PMIT is small-size ESBC with the scope of obtaining similar efficacy as surgery. Minimally invasive treatments are convenient alternatives with promising effectiveness, lower morbidity, less cost, less scarring and pain, and more satisfying cosmetic results. Ablative techniques used in BC are cryoablation, radiofrequency ablation, microwave ablation, high-intensity focused ultrasound (US), and laser ablation. The aim of our study is to discuss the current status of percutaneous management of BC, evaluate the clinical outcomes of PMIT in BC, and analyze future perspectives regarding ablation therapy in BC.

Percutaneous Management of Breast Cancer: a Systematic Review

PURPOSE OF REVIEW

Surgical treatment of breast cancer is becoming increasingly more minimally invasive. We review the development status of percutaneous management for primary breast cancer and the evidence relating to tumor size as a fundamental determinant of treatment clinical outcome.

RECENT FINDINGS

It is safe and feasible for percutaneous management to treat breast cancer. For tumor size ≤ 2 cm, percutaneous management is a promising alternative modality. For tumor size ≤ 3 cm, it is controversial whether percutaneous management can achieve similar effects to surgery, especially its long-term effects. For tumor size > 3 cm, it is still in the initial exploration stage and showed the potential in the treatment of unresectable cancer by benefitting the local control of primary cancer. Percutaneous management of breast cancer is a valuable method for breast cancer treatment in selected patients. However, it will be necessary to provide the high level of evidence for widespread clinical application.

Magnetic Nanoparticle-Mediated Heating for Biomedical Applications

Magnetic nanoparticles, especially superparamagnetic nanoparticles (SPIONs), have attracted tremendous attention for various biomedical applications. Facile synthesis and functionalization together with easy control of the size and shape of SPIONS to customize their unique properties, have made it possible to develop different types of SPIONs tailored for diverse functions/applications. More recently, considerable attention has been paid to the thermal effect of SPIONs for the treatment of diseases like cancer and for nanowarming of cryopreserved/banked cells, tissues, and organs. In this mini-review, recent advances on the magnetic heating effect of SPIONs for magnetothermal therapy and enhancement of cryopreservation of cells, tissues, and organs, are discussed, together with the non-magnetic heating effect (i.e., high Intensity focused ultrasound or HIFU-activated heating) of SPIONs for cancer therapy. Furthermore, challenges facing the use of magnetic nanoparticles in these biomedical applications are presented.

Image-guided Microinvasive Percutaneous Treatment of Breast Lesions: Where Do We Stand?

Treatment of breast lesions has evolved toward the use of less-invasive or minimally invasive techniques. Minimally invasive treatments destroy focal groups of cells without surgery; hence, less anesthesia is required, better cosmetic outcomes are achieved because of minimal (if any) scarring, and recovery times are shorter. These techniques include cryoablation, radiofrequency ablation, microwave ablation, high-intensity focused US, laser therapy, vacuum-assisted excision, and irreversible electroporation. Each modality involves the use of different mechanisms and requires specific considerations for application. To date, only cryoablation and vacuum-assisted excision have received U.S. Food and Drug Administration approval for treatment of fibroadenomas and have been implemented as part of the treatment algorithm by the American Society of Breast Surgeons. Several clinical studies on this topic have been performed on outcomes in patients with breast cancer who were treated with these techniques. The results are promising, with more data for radiofrequency ablation and cryoablation available than for other minimally invasive methods for treatment of early-stage breast cancer. Clinical decisions should be made on a case-by-case basis, according to the availability of the technique. MRI is the most effective imaging modality for postprocedural follow-up, with the pattern of enhancement differentiating residual or recurrent disease from postprocedural changes. ^©RSNA, 2021.

A Breast-Specific MR Guided Focused Ultrasound Platform and Treatment Protocol: First-in-Human Technical Evaluation

OBJECTIVE

This paper presents and evaluates a breast-specific magnetic resonance guided focused ultrasound (MRgFUS) system. A first-in-human evaluation demonstrates the novel hardware, a sophisticated tumor targeting algorithm and a volumetric magnetic resonance imaging (MRI) protocol.

METHODS

At the time of submission, N = 10 patients with non-palpable T0 stage breast cancer have been treated with the breast MRgFUS system. The described tumor targeting algorithm is evaluated both with a phantom test and in vivo during the breast MRgFUS treatments. Treatments were planned and monitored using volumetric MR-acoustic radiation force imaging (MR-ARFI) and temperature imaging (MRTI).

RESULTS

Successful technical treatments were achieved in 80 % of the patients. All patients underwent the treatment with no sedation and 60 % of participants had analgesic support. The total MR treatment time ranged from 73 to 114 minutes. Mean error between desired and achieved targeting in a phantom was 2.9 ±1.8 mm while 6.2 ±1.9 mm was achieved in patient studies, assessed either with MRTI or MR-ARFI measurements. MRTI and MR-ARFI were successful in 60 % and 70 % of patients, respectively.

CONCLUSION

The targeting accuracy allows the accurate placement of the focal spot using electronic steering capabilities of the transducer. The use of both volumetric MRTI and MR-ARFI provides complementary treatment planning and monitoring information during the treatment, allowing the treatment of all breast anatomies, including homogeneously fatty breasts.

Design and evaluation of an open-source, conformable skin-cooling system for body magnetic resonance guided focused ultrasound treatments

PURPOSE

Magnetic resonance guided focused ultrasound (MRgFUS) treatment of tumors uses inter-sonication delays to allow heat to dissipate from the skin and other near-field tissues. Despite inter-sonication delays, treatment of tumors close to the skin risks skin burns. This work has designed and evaluated an open-source, conformable, skin-cooling system for body MRgFUS treatments to reduce skin burns and enable ablation closer to the skin.

METHODS

A MR-compatible skin cooling system is described that features a conformable skin-cooling pad assembly with feedback control allowing continuous flow and pressure maintenance during the procedure. System performance was evaluated with hydrophone, phantom and in vivo porcine studies. Sonications were performed 10 and 5 mm from the skin surface under both control and forced convective skin-cooling conditions. 3D MR temperature imaging was acquired in real time and the accumulated thermal dose volume was measured. Gross analysis of the skin post-sonication was further performed. Device conformability was demonstrated at several body locations.

RESULTS

Hydrophone studies demonstrated no beam aberration, but a 5-12% reduction of the peak pressure due to the presence of the skin-cooling pad assembly in the acoustic near field. Phantom evaluation demonstrated there is no MR temperature imaging precision reduction or any other artifacts present due to the coolant flow during MRgFUS sonication. The porcine studies demonstrated skin burns were reduced in size or eliminated when compared to the control condition.

CONCLUSION

An open-source design of an MRgFUS active skin cooling system demonstrates device conformability with a reduction of skin burns while ablating superficial tissues.

An MRI-Guided Ring High-Intensity Focused Ultrasound System for Noninvasive Breast Ablation

High-intensity focused ultrasound (HIFU) has been used for noninvasive treatment of breast tumors, but the present magnetic resonance imaging (MRI)-guided HIFU (MRI-HIFU) systems encounter skin burn. In this study, a novel MRI-HIFU breast ablation system was developed to improve the above problem. The system consisted of the ring HIFU phased-array transducer, a commercial power amplifier, the mechanical positioner, and the graphical user interface control software. MRI thermometry was also established to monitor the temperature in the HIFU-treated tissue. Ablation of pork and the in vivo rabbit leg were carried out to validate the developed system. Results of fat-surrounding pork ablation showed that the ring HIFU system reached a safe margin of 3 mm without fat burn. Moreover, precision of the positioner moving the HIFU focal zone was within 6% error under MRI circumstances. The representative MRI temperature images show that the peak temperatures among the five ablations ranged between 66 °C and 91 °C, and their thermal doses were over 10000. The system could also ablate the biceps femoris of a rabbit without skin burn to form a lesion of 2.5 mm beneath the skin. With the HIFU dose of 315 W/10 s, the MRI temperature map revealed that the maximum temperature and the thermal dose were 60 °C and 3380, respectively. The MRI-guided ring HIFU system can ablate the target tissue near subcutaneous fat without fat burn. The system prototype is a promising tool for clinical implementation.

Repeat magnetic resonance imaging-guided focused ultrasound thalamotomy for recurrent essential tremor: case report and review of MRI findings

An 86-year-old right-handed man with medically refractory essential tremor was treated using left-sided MRI-guided focused ultrasound (MRgFUS) thalamotomy targeting the dentatorubrothalamic tract (DRTT) at its intersection with the ventral intermediate nucleus of the thalamus, with immediate symptomatic improvement and immediate postprocedure imaging demonstrating disruption of the DRTT. The patient experienced a partial return of symptoms 9 weeks following the procedure, and MRI demonstrated retraction of the left thalamic ablation site. The patient underwent repeat left-sided MRgFUS thalamotomy 4 months after initial treatment, resulting in reduced tremor. MR thermometry temperature measurements during the second MRgFUS procedure were unreliable with large fluctuations and false readings, likely due to susceptibility effects from the initial MRgFUS procedure. Final sonications were therefore monitored using the amount of energy delivered. The patient fared well after the second procedure and had sustained improvement in tremor control at the 12-month follow-up. This is the first report to describe the technical challenges of repeat MRgFUS with serial imaging.

Real-Time Photoacoustic Thermometry Combined With Clinical Ultrasound Imaging and High-Intensity Focused Ultrasound

High-intensity focused ultrasound (HIFU) treatment is a promising non-invasive method for killing or destroying the diseased tissues by locally delivering thermal and mechanical energy without damaging surrounding normal tissues. In HIFU, measuring the temperature at the site of delivery is important for improving therapeutic efficacy, controlling safety, and appropriately planning a treatment. Several researchers have proposed photoacoustic thermometry for monitoring HIFU treatment, but they had many limitations, including the inability to image while the HIFU is on, inability to provide two-dimensional monitoring, and the inability to be used clinically. In this paper, we propose a novel integrated real-time photoacoustic thermometry system for HIFU treatment monitoring. The system provides ultrasound B-mode imaging, photoacoustic structural imaging, and photoacoustic thermometry during HIFU treatment in real-time for both in vitro and in vivo environments, without any interference from the strong therapeutic HIFU waves. We have successfully tested the real-time photoacoustic thermometry by investigating the relationship between the photoacoustic amplitude and the measured temperature with in vitro phantoms and in vivo tumor-bearing mice. The results show the feasibility of a real-time photoacoustic thermometry system for safe and effective monitoring of HIFU treatment.

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

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

High-intensity focused ultrasound in the treatment of breast tumours

High-intensity focused ultrasound (HIFU) is a minimally invasive technique that has been used for the treatment of both benign and malignant tumours. With HIFU, an ultrasound (US) beam propagates through soft tissue as a high-frequency pressure wave. The US beam is focused at a small target volume, and due to the energy building up at this site, the temperature rises, causing coagulative necrosis and protein denaturation within a few seconds. HIFU is capable of providing a completely non-invasive treatment without causing damage to the directly adjacent tissues. HIFU can be either guided by US or magnetic resonance imaging (MRI). Guided imaging is used to plan the treatment, detect any movement during the treatment and monitor response in real-time. This review describes the history of HIFU, the HIFU technique, available devices and gives an overview of the published literature in the treatment of benign and malignant breast tumours with HIFU.

Magnetic Resonance-guided High Intensity Focused Ultrasound in the presence of biopsy markers

Background

Magnetic Resonance guided High Intensity Focused ultrasound (MR-HIFU) offers precise non-invasive thermotherapy for clinical applications such as the treatment of breast lesions. However, patients with a biopsy marker are usually not eligible for MR-HIFU treatment. This study investigates the interaction of some MR-compatible markers with MR-HIFU thermotherapy.

Methods

The MR-HIFU compatibility of 14 markers (6 Gold Anchor and 4 Visicoil markers in gold, 1 Visicoil marker in brass, 3 BiomarC markers in carbon coated) were tested using the Sonalleve breast MR-HIFU platform at 1.5 T. The impact of these markers was assessed by counting the number of voxels with low signal intensity on MR thermal maps and by comparing temperature increases induced by the HIFU beam.

Results

Most markers were visible on thermal maps with an apparent size 4.2 ± 3.1 and 2 ± 1.8 times larger than their respective actual width and length. The volume of masked voxels was for most of the markers much larger than the actual volume of the marker (up to a factor 65.1). However, it represents only a small fraction of the 12 mm diameter targeted region (up to 8.8 voxels which represents 19% of this targeted region). Some differences in the maximal temperature increase were observed especially for BiomarC 1 × 3 and BiomarC 2 × 4 markers enhancing the heating. These differences were less pronounced at the edge of the targeted region.

Conclusion

All markers had a minimal impact on the volume above the thermal dose threshold of 240 EM since the differences measured were smaller than the in-plane image resolution of 1.56 mm.

Delayed intestinal perforation and vertebral osteomyelitis after high-intensity focused ultrasound treatment for uterine leiomyoma

High-intensity focused ultrasound (HIFU) is a non-invasive uterine fibroid treatment option for patients who want to preserve fertility. However, according to several reports regarding ablation of solid tumors by HIFU, there are rare complications in patients with uterine leiomyomas, and overall data are still insufficient. Here, we report rare and major complications of HIFU, such as delayed intestinal perforation, uterine perforation with recto-uterine fistula, and osteomyelitis 29 days after the HIFU procedure to treat multiple myomas. Thus, we present a very serious case resulting from HIFU treatment of uterine fibroids and a review of the literature.

Early health technology assessment of magnetic resonance-guided high intensity focused ultrasound ablation for the treatment of early-stage breast cancer

BACKGROUND

Magnetic resonance-guided high intensity focused ultrasound (MR-HIFU) ablation is in development for minimally invasive treatment of breast cancer. Cost-effectiveness has not been assessed yet. An early health technology assessment was performed to estimate costs of MR-HIFU ablation, compared to breast conserving treatment (BCT).

METHODS

An MR-HIFU treatment model using the dedicated MR-HIFU breast system (Sonalleve, Philips Healthcare) was developed. Input parameters (treatment steps and duration) were based on the analysis of questionnaire data from an expert panel. MR-HIFU experts assessed face validity of the model. Data collected by questionnaires were compared to published data of an MR-HIFU breast feasibility study. Treatment costs for tumours of 1 to 3 cm were calculated.

RESULTS

The model structure was considered of acceptable face validity by consulted experts, and questionnaire data and published data were comparable. Costs of MR-HIFU ablation were higher than BCT costs. MR-HIFU best-case scenario costs exceeded BCT costs with approximately €1000. Cooling times and breathing correction contributed most to treatment costs.

CONCLUSIONS

MR-HIFU ablation is currently not a cost-effective alternative for BCT. MR-HIFU experience is limited, increasing uncertainty of estimations. The potential for cost-effectiveness increases if future research reduces treatment durations and might substantiate equal or improved results.

Ablative techniques for the treatment of benign and malignant breast tumours

Minimally invasive techniques like high intensity focused ultrasound, radiofrequency ablation, cryo-ablation, laser ablation and microwave ablation have been used to treat both breast fibroadenomata and breast cancer as an alternative to surgical excision, potentially reducing the complications, improving cosmesis and reducing hospital stay. This review describes the most common minimally invasive techniques available, their history and some of the studies performed with these techniques in both benign and malignant lesions. In addition we described some of the difficulties of using these minimally invasive techniques such as optimization of anaesthesia, imaging and immobilisation in order to increase the complete histopathological ablation rates.

Technical success, technique efficacy and complications of minimally-invasive imaging-guided percutaneous ablation procedures of breast cancer: A systematic review and meta-analysis

OBJECTIVES

To systematically review studies concerning imaging-guided minimally-invasive breast cancer treatments.

METHODS

An online database search was performed for English-language articles evaluating percutaneous breast cancer ablation. Pooled data and 95% confidence intervals (CIs) were calculated. Technical success, technique efficacy, minor and major complications were analysed, including ablation technique subgroup analysis and effect of tumour size on outcome.

RESULTS

Forty-five studies were analysed, including 1,156 patients and 1,168 lesions. Radiofrequency (n=577; 50%), microwaves (n=78; 7%), laser (n=227; 19%), cryoablation (n=156; 13%) and high-intensity focused ultrasound (HIFU, n=129; 11%) were used. Pooled technical success was 96% (95%CI 94-97%) [laser=98% (95-99%); HIFU=96% (90-98%); radiofrequency=96% (93-97%); cryoablation=95% (90-98%); microwave=93% (81-98%)]. Pooled technique efficacy was 75% (67-81%) [radiofrequency=82% (74-88); cryoablation=75% (51-90); laser=59% (35-79); HIFU=49% (26-74)]. Major complications pooled rate was 6% (4-8). Minor complications pooled rate was 8% (5-13%). Differences between techniques were not significant for technical success (p=0.449), major complications (p=0.181) or minor complications (p=0.762), but significant for technique efficacy (p=0.009). Tumour size did not impact on variables (p>0.142).

CONCLUSIONS

Imaging-guided percutaneous ablation techniques of breast cancer have a high rate of technical success, while technique efficacy remains suboptimal. Complication rates are relatively low.

KEY POINTS

• Imaging-guided ablation techniques for breast cancer are 96% technically successful. • Overall technique efficacy rate is 75% but largely inhomogeneous among studies. • Overall major and minor complication rates are low (6-8%).

Alternate update of shifted extended keyholes (AUSEK): A new accelerating strategy for interventional MRI

Real-time or near-real-time acquisition plays a key role in providing immediate image guidance for interventional magnetic resonance imaging (iMRI). However, the requirement of accurate needle tip localization has made several accelerating techniques, like Keyhole imaging or sliding window reconstruction, difficult to be applied to iMRI. The purpose of this work was to further explore the possible ways of applying view sharing techniques to iMRI. Inspired by Keyhole imaging, we present an easy-to-implement accelerating strategy called "Alternate update of shifted extended keyholes (AUSEK)". In this method, the keyhole views are not only extended but also shifted towards either high-frequency edge to form two divisions in k-space. The divisions which are mirrored to each other along the center are alternately updated following a reference scan. By using simulations and experiments, we demonstrate that AUSEK could effectively preserve the spatial resolution of the image, especially of the needle, at a temporal acceleration rate of about 2.5. AUSEK was implemented online in an open-configuration low-field MR imaging system.

Minimally invasive ablative techniques in the treatment of breast cancer: a systematic review and meta-analysis

PURPOSE

Breast-conserving surgery is effective for breast cancer treatment but is associated with morbidity in particular high re-excision rates. We performed a systematic review and meta-analysis to assess the current evidence for clinical outcomes with minimally invasive ablative techniques in the non-surgical treatment of breast cancer.

METHODS

A systematic search of the literature was performed using PubMed and Medline library databases to identify all studies published between 1994 and May 2016. Studies were considered eligible for inclusion if they evaluated the role of ablative techniques in the treatment of breast cancer and included ten patients or more. Studies that failed to fulfil the inclusion criteria were excluded.

RESULTS

We identified 63 studies including 1608 patients whose breast tumours were treated with radiofrequency (RFA), high intensity focussed ultrasound (HIFU), cryo-, laser or microwave ablation. Fifty studies reported on the number of patients with complete ablation as found on histopathology and the highest rate of complete ablation was achieved with RFA (87.1%, 491/564) and microwave ablation (83.2%, 89/107). Short-term complications were most often reported with microwave ablation (14.6%, 21/144). Recurrence was reported in 24 patients (4.2%, 24/570) and most often with laser ablation (10.7%, 11/103). The shortest treatment times were observed with RFA (15.6 ± 5.6 min) and the longest with HIFU (101.5 ± 46.6 min).

CONCLUSION

Minimally invasive ablative techniques are able to successfully induce coagulative necrosis in breast cancer with a low side effect profile. Adequately powered and prospectively conducted cohort trials are required to confirm complete pathological ablation in all patients.

Damage effect of high-intensity focused ultrasound on breast cancer tissues and their vascularities

BACKGROUND

High-intensity focused ultrasound (HIFU) is a noninvasive therapy that makes entire coagulative necrosis of a tumor in deep tissue through the intact skin. There are many reports about the HIFU's efficacy in the treatment of patients with breast cancer, but randomized clinical trials are rare which emphasize on the systematic assessment of histological changes in the ablated tumor vascularities, while clinical trials utilizing bevacizumab and other anti-angiogenic drugs in breast cancer have not demonstrated overall survival benefit. The purpose of this study is to evaluate the damage effect of HIFU on breast cancer tissues and their vascularities.

METHODS

Randomized clinical trials and the modality of treat-and-resect protocols were adopted. The treated outcome of all patients was followed up in this study. The target lesions of 25 breast cancer patients treated by HIFU were observed after autopsy. One slide was used for hematoxylin-eosin (HE) staining, one slide was used for elastic fiber staining by Victoria blue and Ponceau's histochemical staining, and one slide was used for vascular endothelial cell immunohistochemical staining with biotinylated-ulex europaeus agglutinin I (UEAI); all three slides were observed under an optical microscopic. One additional slide was systematically observed by electron microscopy.

RESULTS

The average follow-up time was 12 months; no local recurrence or a distant metastatic lesion was detected among treated patients. Histological examination of the HE slides indicated that HIFU caused coagulative necrosis in the tumor tissues and their vascularities: all feeder vessels less than 2 mm in diameter in the insonated tumor were occluded, the vascular elasticity provided by fibrin was lost, the cells were disordered and delaminated, and UEAI staining of the target lesions was negative. Immediately after HIFU irradiation, the tumor capillary ultrastructure was destroyed, the capillary endothelium was disintegrated, the peritubular cells were cavitated, and the plasma membrane was incomplete.

CONCLUSIONS

HIFU ablation can destroy all proliferating tumor cells and their growing vascularities simultaneously; this may break interdependent vicious cycle of tumor angiogenesis and neoplastic cell growth that results in infinite proliferation. While it cannot cause tumor resistance to HIFU ablation, it may be a new anti-angiogenic strategy that needs further clinical observation and exploration. Furthermore, the treatment indications of HIFU ablation were reviewed and discussed in this manuscript.

Phase aberration simulation study of MRgFUS breast treatments

PURPOSE

This simulation study evaluates the effects of phase aberration in breast MR-guided focused ultrasound (MRgFUS) ablation treatments performed with a phased-array transducer positioned laterally to the breast. A quantification of these effects in terms of thermal dose delivery and the potential benefits of phase correction is demonstrated in four heterogeneous breast numerical models.

METHODS

To evaluate the effects of varying breast tissue properties on the quality of the focus, four female volunteers with confirmed benign fibroadenomas were imaged using 3T MRI. These images were segmented into numerical models with six tissue types, with each tissue type assigned standard acoustic properties from the literature. Simulations for a single-plane 16-point raster-scan treatment trajectory centered in a fibroadenoma in each modeled breast were performed for a breast-specific MRgFUS system. At each of the 16 points, pressure patterns both with and without applying a phase correction technique were determined with the hybrid-angular spectrum method. Corrected phase patterns were obtained using a simulation-based phase aberration correction technique to adjust each element's transmit phase to obtain maximized constructive interference at the desired focus. Thermal simulations were performed for both the corrected and uncorrected pressure patterns using a finite-difference implementation of the Pennes bioheat equation. The effect of phase correction was evaluated through comparison of thermal dose accumulation both within and outside a defined treatment volume. Treatment results using corrected and uncorrected phase aberration simulations were compared by evaluating the power required to achieve a 20 °C temperature rise at the first treatment location. The extent of the volumes that received a minimum thermal dose of 240 CEM at 43 °C inside the intended treatment volume as well as the volume in the remaining breast tissues was also evaluated in the form of a dose volume ratio (DVR), a DVR percent change between corrected and uncorrected phases, and an additional metric that measured phase spread.

RESULTS

With phase aberration correction applied, there was an improvement in the focus for all breast anatomies as quantified by a reduction in power required (13%-102%) to reach 20 °C when compared to uncorrected simulations. Also, the DVR percent change increased by 5%-77% in seven out of eight cases, indicating an improvement to the treatment as measured by a reduction in thermal dose deposited to the nontreatment tissues. Breast compositions with a higher degree of heterogeneity along the ultrasound beam path showed greater reductions in thermal dose delivered outside of the treatment volume with correction applied than beam trajectories that propagated through more homogeneous breast compositions. An increasing linear trend was observed between the DVR percent change and the phase-spread metric (R(2) = 0.68).

CONCLUSIONS

These results indicate that performing phase aberration correction for breast MRgFUS treatments is beneficial for the small-aperture transducer (14.4 × 9.8 cm) evaluated in this work. While all breast anatomies could benefit from phase aberration correction, greater benefits are observed in more heterogeneous anatomies.

Magnetic Resonance-Guided High Intensity Focused Ultrasound Ablation of Breast Cancer

This chapter describes several aspects of MR-HIFU treatment for breast cancer. The current and future applications, technical developments and clinical results are discussed. MR-HIFU ablation is under investigation for the treatment of breast cancer, but is not yet ready for clinical implementation. Firstly, the efficacy of MR-HIFU ablation should be investigated in large trials. The existing literature shows that results of initial, small studies are moderate, but opportunities for improvement are available. Careful patient selection, taking treatment margins into account and using a dedicated breast system might improve treatment outcomes. MRI-guidance has proven to be beneficial for the accuracy and safety of HIFU treatments because of its usefulness before, during and after treatments. In conclusion, MR-HIFU is promising for the treatment of breast cancer and might lead to a change in breast cancer care in the future.

Systematic review of high-intensity focused ultrasound ablation in the treatment of breast cancer

BACKGROUND

A systematic review was undertaken to assess the clinical efficacy of non-invasive high-intensity focused ultrasound (HIFU) ablation in the treatment of breast cancer.

METHODS

MEDLINE/PubMed library databases were used to identify all studies published up to December 2013 that evaluated the role of HIFU ablation in the treatment of breast cancer. Studies were eligible if they were performed on patients with breast cancer and objectively recorded at least one clinical outcome measure of response (imaging, histopathological or cosmetic) to HIFU treatment.

RESULTS

Nine studies fulfilled the inclusion criteria. The absence of tumour or residual tumour after treatment was reported for 95·8 per cent of patients (160 of 167). No residual tumour was found in 46·2 per cent (55 of 119; range 17-100 per cent), less than 10 per cent residual tumour in 29·4 per cent (35 of 119; range 0-53 per cent), and between 10 and 90 per cent residual tumour in 22·7 per cent (27 of 119; range 0-60 per cent). The most common complication associated with HIFU ablation was pain (40·1 per cent) and less frequently oedema (16·8 per cent), skin burn (4·2 per cent) and pectoralis major injury (3·6 per cent). MRI showed an absence of contrast enhancement after treatment in 82 per cent of patients (31 of 38; range 50-100 per cent), indicative of coagulative necrosis. Correlation of contrast enhancement on pretreatment and post-treatment MRI successfully predicted the presence of residual disease.

CONCLUSION

HIFU treatment can induce coagulative necrosis in breast cancers. Complete ablation has not been reported consistently on histopathology and no imaging modality has been able confidently to predict the percentage of complete ablation. Consistent tumour and margin necrosis with reliable follow-up imaging are required before HIFU ablation can be evaluated within large, prospective clinical trials.

Magnetic Resonance Imaging-Guided Breast Interventions: Role in Biopsy Targeting and Lumpectomies

Contrast-enhanced breast MR imaging is increasingly being used to diagnose breast cancer and to perform biopsy procedures. The American Cancer Society has advised women at high risk for breast cancer to have breast MR imaging screening as an adjunct to screening mammography. This article places special emphasis on biopsy and operative planning involving MR imaging and reviews use of breast MR imaging in monitoring response to neoadjuvant chemotherapy. Described are peer-reviewed data on currently accepted MR imaging-guided procedures for addressing benign and malignant breast diseases, including intraoperative imaging.

Update on Clinical Magnetic Resonance-Guided Focused Ultrasound Applications

In this review, several clinical applications of magnetic resonance (MR)-guided focused ultrasound (FUS) are updated. MR-guided FUS is used clinically for thermal ablation of uterine fibroids and bone metastases. Thousands of patients have successfully been treated. Transcranial MR-guided FUS has received CE certification for ablation of deep, central locations in the brain. Thermal ablation of specific parts of the thalamus can result in relief of the symptoms in a number of neurological disorders. Several approaches have been proposed for ablation of prostate and breast cancer and clinical trials should show the potential of MR-guided FUS for these and other applications.

Hollow iron-silica nanoshells for enhanced high intensity focused ultrasound

BACKGROUND

High intensity-focused ultrasound (HIFU) is an alterative ablative technique currently being investigated for local treatment of breast cancer and fibroadenomas. Current HIFU therapies require concurrent magnetic resonance imaging monitoring. Biodegradable 500 nm perfluoropentane-filled iron-silica nanoshells have been synthesized as a sensitizing agent for HIFU therapies, which aid both mechanical and thermal ablation of tissues. In low duty cycle high-intensity applications, rapid tissue damage occurs from mechanical rather than thermal effects, which can be monitored closely by ultrasound obviating the need for concurrent magnetic resonance imaging.

MATERIALS AND METHODS

Iron-silica nanoshells were synthesized by a sol-gel method on polystyrene templates and calcined to yield hollow nanoshells. The nanoshells were filled with perfluoropentane and injected directly into excised human breast tumor, and intravenously (IV) into healthy rabbits and Py8119 tumor-bearing athymic nude mice. HIFU was applied at 1.1 MHz and 3.5 MPa at a 2% duty cycle to achieve mechanical ablation.

RESULTS

Ex vivo in excised rabbit livers, the time to visually observable damage with HIFU was 20 s without nanoshells and only 2 s with nanoshells administered IV before sacrifice. Nanoshells administered IV into nude mice with xenograft tumors were activated in vivo by HIFU 24 h after administration. In this xenograft model, applied HIFU resulted in a 13.6 ± 6.1 mm(3) bubble cloud with the IV injected particles and no bubble cloud without particles.

CONCLUSIONS

Iron-silica nanoshells can reduce the power and time to perform HIFU ablative therapy and can be monitored by ultrasound during low duty cycle operation.

Review of MRI positioning devices for guiding focused ultrasound systems

BACKGROUND

This article contains a review of positioning devices that are currently used in the area of magnetic resonance imaging (MRI) guided focused ultrasound surgery (MRgFUS).

METHODS

The paper includes an extensive review of literature published since the first prototype system was invented in 1991.

RESULTS

The technology has grown into a fast developing area with application to any organ accessible to ultrasound. The initial design operated using hydraulic principles, while the latest technology incorporates piezoelectric motors. Although, in the beginning there were fears regarding MRI safety, during recent years, the deployment of MR-safe positioning devices in FUS has become routine. Many of these positioning devices are now undergoing testing in clinical trials.

CONCLUSION

Existing MRgFUS systems have been utilized mostly in oncology (fibroids, brain, liver, kidney, bone, pancreas, eye, thyroid, and prostate). It is anticipated that, in the near future, there will be a positioning device for every organ that is accessible by focused ultrasound.

Nonsurgical ablation of breast cancer: future options for small breast tumors

The surgical management of breast cancer has evolved significantly, facilitated by advancements in technology and imaging and improvements in adjuvant therapy. The changes in surgical management have been characterized by equal or improved outcomes with significantly less morbidity. The next step in this evolution is the minimally invasive or noninvasive ablation of breast cancers as an alternative to lumpectomy. In this article, the various modalities for nonsurgical breast cancer ablation and the clinical experience are reviewed, and some of the next steps necessary for their clinical implementation are outlined.

A novel high intensity focused ultrasound robotic system for breast cancer treatment

High intensity focused ultrasound (HIFU) is a promising technique for cancer treatment owing to its minimal invasiveness and safety. However, skin burn, long treatment time and incomplete ablation are main shortcomings of this method. This paper presents a novel HIFU robotic system for breast cancer treatment. The robot has 4 rotational degrees of freedom with the workspace located in a water tank for HIFU beam imaging and ablation treatment. The HIFU transducer combined with a diagnostic 2D linear ultrasound probe is mounted on the robot end-effector, which is rotated around the HIFU focus when ablating the tumor. HIFU beams are visualized by the 2D probe using beam imaging. Skin burn can be prevented or alleviated by avoiding long time insonification towards the same skin area. The time cost could be significantly reduced, as there is no need to interrupt the ablation procedure for cooling the skin. In addition, our proposed robot control strategies can avoid incomplete ablation. Experiments were carried out and the results showed the effectiveness of our proposed system.

In vivo evaluation of a breast-specific magnetic resonance guided focused ultrasound system in a goat udder model

PURPOSE

This work further evaluates the functionality, efficacy, and safety of a new breast-specific magnetic resonance guided high intensity focused ultrasound (MRgFUS) system in an in vivo goat udder model.

METHODS

Eight female goats underwent an MRgFUS ablation procedure using the breast-specific MRgFUS system. Tissue classification was achieved through the 3D magnetic resonance imaging (MRI) acquisition of several contrasts (T1w, T2w, PDw, 3-point Dixon). The MRgFUS treatment was performed with a grid trajectory executed in one or two planes within the glandular tissue of the goat udder. Temperature was monitored using a 3D proton resonance frequency (PRF) MRI technique. Delayed contrast enhanced-MR images were acquired immediately and 14 days post MRgFUS treatment. A localized tissue excision was performed in one animal and histological analysis was performed. Animals were available for adoption at the conclusion of the study.

RESULTS

The breast-specific MRgFUS system was able to ablate regions ranging in size from 0.4 to 3.6 cm(3) in the goat udder model. Tissue damage was confirmed through the correlation of thermal dose measurements obtained with realtime 3D MR thermometry to delayed contrast enhanced-MR images immediately after the treatment and 14 days postablation. In general, lesions were longer in the ultrasound propagation direction, which is consistent with the dimensions of the ultrasound focal spot. Thermal dose volumes had better agreement with nonenhancing areas of the DCE-MRI images obtained 14 days after the MRgFUS treatment.

CONCLUSIONS

The system was able to successfully ablate lesions up to 3.6 cm(3). The thermal dose volume was found to correlate better with the 14-day postablation nonenhancing delayed contrast enhanced-MR image volumes. While the goat udder is not an ideal model for the human breast, this study has proven the feasibility of using this system on a wide variety of udder shapes and sizes, demonstrating the flexibility that would be required in order to treat human subjects.

An experimental model to investigate the targeting accuracy of MR-guided focused ultrasound ablation in liver

Background

Magnetic Resonance-guided High Intensity Focused Ultrasound (MRgHIFU) is a hybrid technology that aims to offer non-invasive thermal ablation of targeted tumors or other pathological tissues. Acoustic aberrations and non-linear wave propagating effects may shift the focal point significantly away from the prescribed (or, theoretical) position. It is therefore mandatory to evaluate the spatial accuracy of ablation for a given HIFU protocol and/or device. We describe here a method for producing a user-defined ballistic target as an absolute reference marker for MRgHIFU ablations.

Methods

The investigated method is based on trapping a mixture of MR contrast agent and histology stain using radiofrequency (RF) ablation causing cell death and coagulation. A dedicated RF-electrode was used for the marker fixation as follows: a RF coagulation (4 W, 15 seconds) and injection of the mixture followed by a second RF coagulation. As a result, the contrast agent/stain is encapsulated in the intercellular space. Ultrasonography imaging was performed during the procedure, while high resolution T1w 3D VIBE MR acquisition was used right after to identify the position of the ballistic marker and hence the target tissue. For some cases, after the marker fixation procedure, HIFU volumetric ablations were produced by a phased-array HIFU platform. First ex vivo experiments were followed by in vivo investigation on four rabbits in thigh muscle and six pigs in liver, with follow-up at Day 7.

Results

At the end of the procedure, no ultrasound indication of the marker’s presence could be observed, while it was clearly visible under MR and could be conveniently used to prescribe the HIFU ablation, centered on the so-created target. The marker was identified at Day 7 after treatment, immediately after animal sacrifice, after 3 weeks of post-mortem formalin fixation and during histology analysis. Its size ranged between 2.5 and 4 mm.

Conclusions

Experimental validation of this new ballistic marker method was performed for liver MRgHIFU ablation, free of any side effects (e.g. no edema around the marker, no infection, no bleeding). The study suggests that the absolute reference marker had ultrasound conspicuity below the detection threshold, was irreversible, MR-compatible and MR-detectable, while also being a well-established histology staining technique.

High-intensity focused ultrasound ablation of breast cancer

The noninvasive ablation of tumors with high-intensity focused ultrasound (HIFU) energy has received increasingly widespread interest. The temperature within the focal volume of an ultrasound beam is rapidly raised to cytotoxic levels. HIFU can selectively ablate a targeted tumor at depth without any damage to surrounding or overlying tissues. Animal studies have shown that HIFU ablation is safe and effective for the treatment of implanted breast malignancies. The results from early clinical trials (Phase I and II) are encouraging, suggesting that HIFU is a promising treatment for small breast cancer. Once oncologic efficacy data from large-scale randomized clinical trials are available, HIFU ablation may become an attractive treatment option for patients with small breast cancer, especially the elderly.

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

Background

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

Methods

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

Results

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

Conclusions

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

Trial registration

Trial Registration: UMIN000010193

Experimental methods for improved spatial control of thermal lesions in magnetic resonance-guided focused ultrasound ablation

Magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU, or MRgFUS) is a hybrid technology that was developed to provide efficient and tolerable thermal ablation of targeted tumors or other pathologic tissues, while preserving the normal surrounding structures. Fast 3-D ablation strategies are feasible with the newly available phased-array HIFU transducers. However, unlike fixed heating sources for interstitial ablation (radiofrequency electrode, microwave applicator, infra-red laser applicator), HIFU uses propagating waves. Therefore, the main challenge is to avoid thermo-acoustical adverse effects, such as energy deposition at reflecting interfaces and thermal drift of the focal lesion toward the near field. We report here our investigations on some novel experimental solutions to solve, or at least to alleviate, these generally known tolerability problems in HIFU-based therapy. Online multiplanar MR thermometry was the main investigational tool extensively used in this study to identify the problems and to assess the efficacy of the tested solutions. We present an improved method to cancel the beam reflection at the exit window (i.e., tissue-to-air interface) by creating a multilayer protection, to dissipate the residual HIFU beam by bulk scattering. This study evaluates selective de-activation of transducer elements to reduce the collateral heating at bone surfaces in the far field, mainly during automatically controlled volumetric ablation. We also explore, using hybrid US/MR simultaneous imaging, the feasibility of using disruptive boiling at the focus, both as a far-field self-shielding technique and as an enhanced ablation strategy (i.e., boiling core controlled HIFU ablation).

Design and characterization of a laterally mounted phased-array transducer breast-specific MRgHIFU device with integrated 11-channel receiver array

PURPOSE

This work presents the design and preliminary evaluation of a new laterally mounted phased-array MRI-guided high-intensity focused ultrasound (MRgHIFU) system with an integrated 11-channel phased-array radio frequency (RF) coil intended for breast cancer treatment. The design goals for the system included the ability to treat the majority of tumor locations, to increase the MR image's signal-to-noise ratio (SNR) throughout the treatment volume and to provide adequate comfort for the patient.

METHODS

In order to treat the majority of the breast volume, the device was designed such that the treated breast is suspended in a 17-cm diameter treatment cylinder. A laterally shooting 1-MHz, 256-element phased-array ultrasound transducer with flexible positioning is mounted outside the treatment cylinder. This configuration achieves a reduced water volume to minimize RF coil loading effects, to position the coils closer to the breast for increased signal sensitivity, and to reduce the MR image noise associated with using water as the coupling fluid. This design uses an 11-channel phased-array RF coil that is placed on the outer surface of the cylinder surrounding the breast. Mechanical positioning of the transducer and electronic steering of the focal spot enable placement of the ultrasound focus at arbitrary locations throughout the suspended breast. The treatment platform allows the patient to lie prone in a face-down position. The system was tested for comfort with 18 normal volunteers and SNR capabilities in one normal volunteer and for heating accuracy and stability in homogeneous phantom and inhomogeneous ex vivo porcine tissue.

RESULTS

There was a 61% increase in mean relative SNR achieved in a homogeneous phantom using the 11-channel RF coil when compared to using only a single-loop coil around the chest wall. The repeatability of the system's energy delivery in a single location was excellent, with less than 3% variability between repeated temperature measurements at the same location. The execution of a continuously sonicated, predefined 48-point, 8-min trajectory path resulted in an ablation volume of 8.17 cm(3), with one standard deviation of 0.35 cm(3) between inhomogeneous ex vivo tissue samples. Comfort testing resulted in negligible side effects for all volunteers.

CONCLUSIONS

The initial results suggest that this new device will potentially be suitable for MRgHIFU treatment in a wide range of breast sizes and tumor locations.

High-intensity focused ultrasound: advances in technology and experimental trials support enhanced utility of focused ultrasound surgery in oncology

High-intensity focused ultrasound (HIFU) is a rapidly maturing technology with diverse clinical applications. In the field of oncology, the use of HIFU to non-invasively cause tissue necrosis in a defined target, a technique known as focused ultrasound surgery (FUS), has considerable potential for tumour ablation. In this article, we outline the development and underlying principles of HIFU, overview the limitations and commercially available equipment for FUS, then summarise some of the recent technological advances and experimental clinical trials that we predict will have a positive impact on extending the role of FUS in cancer therapy.

Magnetic resonance image-guided versus ultrasound-guided high-intensity focused ultrasound in the treatment of breast cancer

Image-guided high-intensity focused ultrasound (HIFU) has been used for more than ten years, primarily in the treatment of liver and prostate cancers. HIFU has the advantages of precise cancer ablation and excellent protection of healthy tissue. Breast cancer is a common cancer in women. HIFU therapy, in combination with other therapies, has the potential to improve both oncologic and cosmetic outcomes for breast cancer patients by providing a curative therapy that conserves mammary shape. Currently, HIFU therapy is not commonly used in breast cancer treatment, and efforts to promote the application of HIFU is expected. In this article, we compare different image-guided models for HIFU and reviewed the status, drawbacks, and potential of HIFU therapy for breast cancer.

MR-guided high-intensity focused ultrasound ablation of breast cancer with a dedicated breast platform

Optimizing the treatment of breast cancer remains a major topic of interest. In current clinical practice, breast-conserving therapy is the standard of care for patients with localized breast cancer. Technological developments have fueled interest in less invasive breast cancer treatment. Magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) is a completely noninvasive ablation technique. Focused beams of ultrasound are used for ablation of the target lesion without disrupting the skin and subcutaneous tissues in the beam path. MRI is an excellent imaging method for tumor targeting, treatment monitoring, and evaluation of treatment results. The combination of HIFU and MR imaging offers an opportunity for image-guided ablation of breast cancer. Previous studies of MR-HIFU in breast cancer patients reported a limited efficacy, which hampered the clinical translation of this technique. These prior studies were performed without an MR-HIFU system specifically developed for breast cancer treatment. In this article, a novel and dedicated MR-HIFU breast platform is presented. This system has been designed for safe and effective MR-HIFU ablation of breast cancer. Furthermore, both clinical and technical challenges are discussed, which have to be solved before MR-HIFU ablation of breast cancer can be implemented in routine clinical practice.

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.

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.

Temperature dependence of the optoacoustic transformation efficiency in ex vivo tissues for application in monitoring thermal therapies

The calibration dependencies of the optoacoustic (OA) transformation efficiency on tissue temperature are obtained for the application in OA temperature monitoring during thermal therapies. Accurate measurement of the OA signal amplitude versus temperature is performed in different ex vivo tissues in the temperature range 25°C to 80°C. The investigated tissues were selected to represent different structural components: chicken breast (skeletal muscle), porcine lard (fatty tissue), and porcine liver (richly perfused tissue). Backward mode of the OA signal detection and a narrow probe laser beam were used in the experiments to avoid the influence of changes in light scattering with tissue coagulation on the OA signal amplitude. Measurements were performed in heating and cooling regimes. Characteristic behavior of the OA signal amplitude temperature dependences in different temperature ranges were described in terms of changes in different structural components of the tissue samples. The accuracy of temperature reconstruction from the obtained calibration dependencies for the investigated tissue types is evaluated.

Modeling focused ultrasound exposure for the optimal control of thermal dose distribution

Preclinical studies indicate that focused ultrasound at exposure conditions close to the threshold for thermal damage can increase drug delivery at the focal region. Although these results are promising, the optimal control of temperature still remains a challenge. To address this issue, computer-simulated ultrasound treatments have been performed. When the treatments are delivered without taking into account the cooling effect exerted by the blood flow, the resulting thermal dose is highly variable with regions of thermal damage, regions of underdosage close to the vessels, and areas in between these two extremes. When the power deposition is adjusted so that the peak thermal dose remains close to the threshold for thermal damage, the thermal dose is more uniformly distributed but under-dosage is still visible around the thermally significant vessels. The results of these simulations suggest that, for focused ultrasound, as for other delivery methods, the only way to control temperature is to adjust the average energy deposition to compensate for the presence of thermally significant vessels in the target area. By doing this, we have shown that it is possible to reduce the temperature heterogeneity observed in focused ultrasound thermal treatments.