Pathological changes in human malignant carcinoma treated with high-intensity focused ultrasound

Extracardiac Ablation of the Left Ventricular Septum in Beating Canine Hearts Using High-Intensity Focused Ultrasound

BACKGROUND

High-intensity focused ultrasound (HIFU) produces immediate focal lesions without direct tissue contact. Previously, we reported the HIFU potential for cardiac ablation. The purpose of this study was to evaluate the possibility of myocardial ablation in the left ventricle of beating dog hearts with monitoring by 2-dimensional echocardiography.

METHODS

The operating frequency and the acoustic intensity were 5.25 MHz and 23 kW/cm(2), and the focal length and diameter were 3.3 mm axial and 0.37 mm wide at a distance of 35 mm from the transducer. Three dogs underwent a left-sided thoracotomy. The right ventricular surface was coupled with the transducer. The timing of the HIFU exposure was set during the early systolic phase using an electrocardiographic triggering system. The focal point was set in the left ventricular septum using 2-dimensional echocardiography mounted in the HIFU transducer. Ultrasound energy was delivered for 0.2 seconds. For each dog, we created 18 lesions. Exposures were performed 20, 30, or 40 times. Lesion size was assessed by manually measuring its length and width.

RESULTS

All lesions except one were clearly visible. The histologic lesion area was 18.7 +/- 8.3, 26.3 +/- 8.7, and 35.5 +/- 15.7 mm(2) (20, 30, and 40 times, respectively). The intraclass correlation coefficients were found to be 0.72, 0.63, 0.75, and 0.73 for lesion length, width, area, and depth, respectively.

CONCLUSION

HIFU can be used to create targeted, well-demarcated thermal lesions in the ventricular septum myocardium during cardiac contraction.

The antivascular action of physiotherapy ultrasound on a murine tumor: role of a microbubble contrast agent

This study investigated whether a microbubble-containing ultrasound contrast agent had a role in the antivascular action of physiotherapy ultrasound on tumor neovasculature. Ultrasound images (B-mode and contrast-enhanced power Doppler [0.02 mL Definity]) were made of 22 murine melanomas (K1735(22)). The tumor was insonated (I(SATA) = 1.7 W cm(-2), 1 MHz, continuous output) for 3 min and the power Doppler observations of the pre- and postinsonation tumor vascularities were analyzed. Significant reductions (p = 0.005 for analyses of color-weighted fractional area) in vascularity occurred when a contrast-enhanced power Doppler study occurred before insonation. Vascularity was unchanged in tumors without a pretherapy Doppler study. Histologic studies revealed tissue structural changes that correlated with the ultrasound findings. The underlying etiology of the interaction between the physiotherapy ultrasound beam, the microbubble-containing contrast agent and the tumor neovasculature is unknown. It was concluded that contrast agents play an important role in the antivascular effects induced by physiotherapy ultrasound.

Plasmonic photothermal therapy (PPTT) using gold nanoparticles

The use of lasers, over the past few decades, has emerged to be highly promising for cancer therapy modalities, most commonly the photothermal therapy method, which employs light absorbing dyes for achieving the photothermal damage of tumors, and the photodynamic therapy, which employs chemical photosensitizers that generate singlet oxygen that is capable of tumor destruction. However, recent advances in the field of nanoscience have seen the emergence of noble metal nanostructures with unique photophysical properties, well suited for applications in cancer phototherapy. Noble metal nanoparticles, on account of the phenomenon of surface plasmon resonance, possess strongly enhanced visible and near-infrared light absorption, several orders of magnitude more intense compared to conventional laser phototherapy agents. The use of plasmonic nanoparticles as highly enhanced photoabsorbing agents has thus introduced a much more selective and efficient cancer therapy strategy, viz. plasmonic photothermal therapy (PPTT). The synthetic tunability of the optothermal properties and the bio-targeting abilities of the plasmonic gold nanostructures make the PPTT method furthermore promising. In this review, we discuss the development of the PPTT method with special emphasis on the recent in vitro and in vivo success using gold nanospheres coupled with visible lasers and gold nanorods and silica-gold nanoshells coupled with near-infrared lasers.

Thermal therapy for breast tumors by using a cylindrical ultrasound phased array with multifocus pattern scanning: a preliminary numerical study

The purpose of this study is to investigate the feasibility of using a 1 MHz cylindrical ultrasound phased array with multifocus pattern scanning to produce uniform heating for breast tumor thermal therapy. The breast was submerged in water and surrounded by the cylindrical ultrasound phased array. A multifocus pattern was generated and electrically scanned by the phased array to enlarge the treatment lesion in single heating. To prevent overheating normal tissues, a large planning target volume (PTV) would be divided into several planes with several subunits on each plane and sequentially treated with a cooling phase between two successive heatings of the subunit. Heating results for different target temperatures (T(tgt)), blood perfusion rates and sizes of the PTV have been studied. Furthermore, a superficial breast tumor with different water temperatures was also studied. Results indicated that a higher target temperature would produce a slightly larger thermal lesion, and a higher blood perfusion rate would not affect the heating lesion size but increase the heating time significantly. The acoustic power deposition and temperature elevations in ribs can be minimized by orienting the acoustic beam from the ultrasound phased array approximately parallel to the ribs. In addition, a large acoustic window on the convex-shaped breast surface for the proposed ultrasound phased array and the cooling effect of water would prevent the skin overheating for the production of a lesion at any desired location. This study demonstrated that the proposed cylindrical ultrasound phased array can provide effective heating for breast tumor thermal therapy without overheating the skin and ribs within a reasonable treatment time.

Host antitumour immune responses to HIFU ablation

The ideal cancer therapy not only induces the death of all localized tumour cells without damage to surrounding normal tissue, but also activates a systemic antitumour immunity. High-intensity focused ultrasound (HIFU) has the potential to be such a treatment, as it can non-invasively ablate a targeted tumour below the skin surface, and may subsequently augment host antitumour immunity. In addition to thermal and cavitation effects, which act directly and locally on the tumour, there is increasing evidence linking systemic anti-tumour immune response to HIFU ablation. This may provide micro-metastatic control and long-term tumour resistance for cancer patients. The goal of this article is to review the emerging pre-clinical and clinical results suggesting that HIFU ablation may enhance host anti-tumour immunity, and to discuss its potential mechanisms. It is concluded that the systemic immune response induced by thermal ablation may play an important role in local recurrence and metastasis control after HIFU treatment.

High intensity focused ultrasound: physical principles and devices

High intensity focused ultrasound (HIFU) is gaining rapid clinical acceptance as a treatment modality enabling non-invasive tissue heating and ablation for numerous applications. HIFU treatments are usually carried out in a single session, often as a day case procedure, with the patient either fully conscious, lightly sedated or under light general anaesthesia. A major advantage of HIFU over other thermal ablation techniques is that there is no necessity for the transcutaneous insertion of probes into the target tissue. The high powered focused beams employed are generated from sources placed either outside the body (for treatment of tumours of the liver, kidney, breast, uterus, pancreas and bone) or in the rectum (for treatment of the prostate), and are designed to enable rapid heating of a target tissue volume, while leaving tissue in the ultrasound propagation path relatively unaffected. Given the wide-ranging applicability of HIFU, numerous extra-corporeal, transrectal and interstitial devices have been designed to optimise application-specific treatment delivery. Their principle of operation is described here, alongside an overview of the physical mechanisms governing HIFU propagation and HIFU-induced heating. Present methods of characterising HIFU fields and of quantifying HIFU exposure and its associated effects are also addressed.

A review of magnetic resonance imaging-guided focused ultrasound surgery of uterine fibroids

Uterine fibroids are a significant cause of morbidity for women of reproductive age. Over the past decade, minimally invasive treatment options are becoming increasingly popular. A new, Food and Drug Administration-approved noninvasive treatment option is magnetic resonance-guided focused ultrasound surgery, which has the potential to become a treatment of choice for selected patients. We review the technical aspects of the procedure of magnetic resonance-guided focused ultrasound surgery for treatment of uterine fibroids, potential difficulties with treatment planning, and clinical trial results to date. We also describe current developments in treatment imaging and treatment optimization.

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

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

Magnetic Resonance–Guided Focused Ultrasound Surgery for the Noninvasive Curative Ablation of Tumors and Palliative Treatments: A Review

This article reviews and discusses the up-to-date data on and feasibility of focused ultrasound surgery. This technique uses high-energy ultrasound beams that can be directed to penetrate through the skin and various soft tissues, focus on the target, and destroy tumors by increasing the temperature at the targeted tissue volume. The boundaries of the treatment area are sharply demarcated (focused) without causing damage to the surrounding organs. Although the idea of using sound waves to ablate tumors was first demonstrated in the 1940 s, only recent developments have enabled this technology to become more controlled and, hence, more feasible. The major breakthrough toward its clinical use came with coupling the thermal ablative process to advanced imaging. The development of magnetic resonance as the foundation to guide and evaluate the end results of focused ultrasound surgery treatment, the image guidance of the ultrasound beam, and the development of a reliable method for tissue temperature measurement and real-time feedback of the extent of tissue destruction have pushed this novel technology forward in oncological practice.

High-intensity focused ultrasound principles, current uses, and potential for the future

High-intensity focused ultrasound (HIFU) continues to be a very attractive option for minimally invasive procedures. Using well-established principles, this ablative therapy can be used to treat a number of benign and malignant diseases with few side effects. During the last 15 years, there has been an enormous amount of work, both laboratory based and in the form of clinical trials, aimed at developing devices that can deliver treatments with safe and effective outcomes. In this article, we aim to outline the principles of HIFU, describe the current commercially available machines and their applications, and discuss the role of HIFU in the future.

Extracorporeal Ablation of Uterine Fibroids With High-Intensity Focused Ultrasound

OBJECTIVE

The purpose of this study was to evaluate the therapeutic efficacy of high-intensity focused ultrasound (HIFU) in the treatment of uterine fibroids by using imaging and histopathologic examination.

METHODS

From May 2004 to June 2005, 119 consecutive patients with 187 uterine fibroids were treated with HIFU. Sixty-two fibroids received ultrasonographically guided needle puncture biopsy 1 week before and after HIFU treatment, respectively, to confirm the diagnosis and to assess the early therapeutic efficacy. Hematoxylin-eosin staining and electron microscopy were performed to characterize more subtle phenotypic changes to determine treatment success. Immediate therapeutic effects were assessed at follow-up with Doppler ultrasonography and computed tomography or magnetic resonance imaging. All patients were followed for 6 to 12 months to observe long-term therapeutic effects. Fibroid mean diameters, volumes, and reduction rates 1, 3, 6, and 12 months after HIFU treatment were calculated and compared with 1-way analysis of variance and Student-Newman-Keuls tests.

RESULTS

No severe complications were observed after HIFU ablation. Fifty-one (82.3%) of 62 biopsy specimens revealed obvious signs of necrosis under light microscopy, and more subtle changes in cellular structure that indicated nonviability could be found in 60 specimens (96.8%) under electron microscopy. However, viable cells still could be found in 16 specimens (25.8%). Follow-up images showed absence or reduction of blood supply in the lesions after HIFU ablation. Median reductions in tumor size as a percentage of initial tumor volume at 1, 3, 6, and 12 months after HIFU treatment were 21.2%, 29.6%, 44.8%, and 48.7%, respectively.

CONCLUSIONS

Imaging and histopathologic evidence directly validate HIFU ablation as an effective treatment of uterine fibroids.

Quality assurance and system stability of a clinical MRI-guided focused ultrasound system: four-year experience

To retrospectively evaluate the four-year experience of a quality assurance method for a MRI-guided focused ultrasound system that uses temperature maps acquired during heating in an ultrasound/MRI phantom. This quality assurance method was performed before 148 clinical uterine fibroid thermal ablation treatments. The stability of the peak temperature rise, the targeting accuracy, the shape of the heated zone, and the noise level in the imaging was evaluated. The peak temperature rise was mostly stable for the first three years. An increase in heating was observed when the system was replaced after year three. Detection of this increase was taken into account in the subsequent clinical treatments. A small secondary hotspot was detected by the temperature maps and was seen to be resolved after system calibration. The average standard deviation in unheated regions of the phantom in the temperature maps was 0.5 +/- 0.2 degrees C; it was less than 1 degrees C in all but one procedure. The average initial targeting error was 2.8 +/- 1.8 and 2.8 +/- 2.1 mm in two radial directions and 7.7 +/- 2.9 mm along the ultrasound beam direction. The width of the heating profile was consistent over the four years. This simple method to evaluate the performance appeared to be sensitive to small changes in system performance, which was adequately stable over a four-year time period.

Image-guided acoustic hemostasis for hemorrhage in the posterior liver

We investigated the use of ultrasound image-guided high intensity focused ultrasound (HIFU) to stop bleeding from injuries in the posterior liver. A HIFU transducer with focal length of 3.5 cm and frequency of 3.2 MHz was integrated with an intraoperative high-resolution ultrasound-imaging probe. Wedge tissue extractions, 30-mm long, 5-mm wide and 8-mm deep, were made in the posterior liver surface of five pigs to induce bleeding. The device was positioned on the anterior surface of the liver and HIFU was applied using ultrasound image-guidance. Hemostasis was achieved in 66 +/- 18 s (mean +/- standard deviation) for 17 HIFU treatments. During 7 min of sham HIFU treatment, none of the control incisions (n = 7) became hemostatic. Ultrasound image-guided HIFU offers a promising method for hemostasis in surgical settings in which the hemorrhage site is hidden and/or not accessible.

Effects of ultrasonic exposure parameters on myocardial lesions induced by high-intensity focused ultrasound

OBJECTIVE

This study evaluated variables relevant to creating myocardial lesions using high-intensity focused ultrasound (HIFU). Without an effective means of tracking heart motion, lesion formation in the moving ventricle can be accomplished by intermittent delivery of HIFU energy synchronized by electrocardiographic triggering. In anticipation of future clinical applications, multiple lesions were created by brief HIFU pulses in calf myocardial tissue ex vivo.

METHODS

Experiments used f-number 1.1 spherical cap HIFU transducers operating near 5 MHz with in situ spatial average intensities of 13 and 7.4 kW/cm2 at corresponding depths of 10 and 25 mm in the tissue. The distance from the HIFU transducer to the tissue surface was measured with a 7.5-MHz A-mode transducer coaxial and confocal with the HIFU transducer. After exposures, fresh, unstained tissue was dissected to measure visible lesion length and width. Lesion dimensions were plotted as functions of pulse parameters, cardiac structure, tissue temperature, and focal depth.

RESULTS

Lesion size in ex vivo tissue depended strongly on the total exposure time but did not depend strongly on pulse duration. Lesion width depended strongly on the pulse-to-pulse interval, and lesion width and length depended strongly on the initial tissue temperature.

CONCLUSIONS

High-intensity focused ultrasound creates well-demarcated lesions in ex vivo cardiac muscle without damaging intervening or distal tissue. These initial studies suggest that HIFU offers an effective, noninvasive method for ablating myocardial tissues to treat several important cardiac diseases.

Heat fixation of cancer cells ablated with high-intensity-focused ultrasound in patients with breast cancer

BACKGROUND

High-intensity-focused ultrasound (HIFU) is a noninvasive thermal ablation technique. This study reports the use of histological techniques for the pathological assessment of HIFU effects in patients with breast cancer.

METHODS

Twenty-three patients with biopsy-proven breast cancer underwent HIFU treatment for primary breast lesion. Mastectomy was performed on all patients after HIFU. By using histological examinations, the surgical specimens were assessed to explore HIFU effects on breast cancer.

RESULTS

Coagulation necrosis of targeted tumors was confirmed by microscopy in 23 patients. Tumor cells presented typical characteristics of coagulation necrosis in the peripheral region of the ablated tumor in all patients. However, in 11 of 23 patients, hematoxylin and eosin staining showed normal cellular structure in the central ablated tumor. By using electronic microscopy and nicotinamide adenine dinucleotide-diaphorase stain, those who had normal-appearing cancer cells were not viable.

CONCLUSIONS

HIFU can cause the heat fixation of ablated tumor through thermal effect.

Magnetic resonance-guided focused ultrasound surgery (MRgFUS): Ablation of liver tissue in a porcine model

BACKGROUND

Liver surgery is technically demanding and is considered a major procedure with relatively high morbidity rates. Magnetic resonance-guided focused ultrasound surgery (MRgFUS) uses focused ultrasonic energy to create a heat coagulation lesion, which can be achieved in a totally controlled, very accurate manner (<1 mm). The aim of this study was to evaluate the safety and accuracy of non-invasive focal ablation of liver tissue achieved by consecutive MRgFUS sonications.

MATERIALS AND METHODS

Six MRgFUS procedures were performed in five pigs under general anesthesia, with the ExAblate 2000 system (InSightec, Israel). Real-time imaging and temperature mapping (Signa Twinspeed 1.5T, GEHC, USA) enabled the immediate evaluation of the results of each sonication. Different foci were chosen within the liver. These mock lesions were ablated by several sonications, each of them performed during 20-30 s of apnea. Between sonications, the pigs were normally ventilated. The pigs were sacrificed 3-21 days after the procedure and their livers were examined.

RESULTS

The MRgFUS created complete tissue destruction of mock lesions in different areas of the pig's liver. The lesion sizes in each animal varied according to the number of sonications used and the extent of overlap between adjacent sonications. The lesion ranged in size from 1.5 cm x 1.5 cm x 2.0 cm to 5.5 cm x 4.5 cm x 2.0 cm. There was no morbidity.

CONCLUSIONS

MRgFUS under general anesthesia is a safe, completely non-invasive technology for the ablation of liver tissue. Liver tissue can be ablated in a very accurate manner, based on the pre-treatment planning on the MR images. The MR imaging characteristics, including real-time temperature mapping, enable real-time control of every step of the ablation process. Mechanical ventilation with intermittent periods of apnea is a technique that overcomes the problem of the respiratory movements of the liver.

Measurement of high intensity focused ultrasound fields by a fiber optic probe hydrophone

The acoustic fields of a high intensity focused ultrasound (HIFU) transducer operating either at its fundamental (1.1 MHz) or third harmonic (3.3 MHz) frequency were measured by a fiber optic probe hydrophone (FOPH). At 1.1 MHz when the electric power applied to the transducer was increased from 1.6 to 125 W, the peak positive/negative pressures at the focus were measured to be p⁺=1.7–23.3 MPa and p⁻=−1.2–−10.0 MPa. The corresponding spatial-peak pulse-average (I_SPPA) and spatial-average pulse-average (I_SAPA) intensities were I_SPPA=77–6000 W/cm² and I_SAPA=35–4365 W/cm². Nonlinear propagation with harmonics generation was dominant at high intensities, leading to a reduced −6 dB beam size (L×W) of the compressional wave (11.5×1.8–8.8×1.04 mm) but an increased beam size of the rarefactional wave (12.5×1.6–13.2×2.0 mm). Enhancement ratio of absorbed power density in water increased from 1.0 to 3.0. In comparison, the HIFU transducer working at 3.3 MHz produced higher peak pressures (p⁺=3.0–35.1 MPa and p⁻=−2.5–−13.8 MPa) with smaller beam size (0.5×4 mm). Overall, FOPH was found to be a convenient and reliable tool for HIFU exposimetry measurement.

Extracorporeal high intensity focused ultrasound in the treatment of patients with solid malignancy

The ideal treatment of localized cancer should cause the complete death of tumor cells without damage to surrounding normal tissue. High intensity focused ultrasound (HIFU) is such a potential treatment, which can induce complete coagulation necrosis of a targeted tumor, at depth, through the intact skin. The concept of using HIFU as a non-invasive therapy has attracted attention in medicine for 60 years. Recently, it has received increasing interest as a promising modality for the treatment of localized solid malignancies. The goal of this article is to introduce recent clinical developments in the use of extracorporeal HIFU ablation for solid tumors, including those of liver, breast, bone, kidney, pancreas, soft tissue, and uterus. It describes the physical principles and ablative mechanisms, three-dimensional therapeutic regimes, and medical imaging used in HIFU. Currently, large numbers of patients with solid malignancy are already treated using HIFU, and short-term clinical results are very encouraging. However, large-scale randomized clinical trials are necessary to evaluate long-term efficacy of HIFU treatment for solid malignancies. It is concluded that this non-invasive ablation can be considered as a conventional therapy for widespread clinical use only when the results from prospective, randomized clinical trials worldwide are available.

Breast focused ultrasound surgery with magnetic resonance guidance

This paper will review the experience and current applications of magnetic resonance-guided focused ultrasound surgery (MRgFUS) for treatment of breast tumors. Because of the efficient screening mammography programs, most of the breast cancers diagnosed today in the United States and European Union are in early stage and are treated with limited surgery. The MRgFUS may offer an alternative treatment option to conventional surgical lumpectomy with the advantage of being a noninvasive procedure and potentially achieving a better cosmetic outcome. Selection of appropriate patients is of paramount importance. Additional studies are needed to determine the effectiveness of the MRgFUS tumor ablation and define its role as a replacement for surgical lumpectomy.

The affection on the tissue lesions of difference frequency in dual-frequency high-intensity focused ultrasound (HIFU)

The lesions induced by dual-frequency high-intensity focused ultrasound (HIFU) in freshly excised porcine livers were investigated and compared with the lesions induced by conventional single-frequency HIFU. The results have shown that using different exposure time resulted in lesions of different sizes in both dual-frequency and single-frequency HIFU modes at the same intensity level (ISAL = 808 W cm(-2)), but the dimensions of lesions in dual-frequency mode were obviously larger than those in single-frequency mode. A much possible explanation was suggested for the results and the possibilities of applications in the future were also discussed in brief.

Cavitation-enhanced ultrasound thermal therapy by combined low- and high-frequency ultrasound exposure

This paper demonstrates a novel approach for enhancing ultrasound-induced heating by the introduction of acoustic cavitation using simultaneous sonication with low- and high-frequency ultrasound. A spherical focused transducer (566 or 1155 kHz) was used to generate the thermal lesions, and a low-frequency planar transducer (40 or 28 kHz) was used to enhance the bubble activity. Ex vivo fresh porcine muscles were used as the target of ultrasound ablation. The emitted signals and the signals backscattered from the bubble activity were also recorded during the heating process by a PVDF-type needle hydrophone, and thermocouples were inserted to measure temperatures. Compared with the lesions formed by a single focused transducer, the size of the lesions generated by this approach were as much as 140% larger along the axial direction and 200% larger along the radial direction for combined 566- and 40-kHz sonication. They were 47% and 66% larger along the axial and radial directions, respectively, for combined 1155- and 28-kHz sonication. Cavitation activities enhanced by low-frequency ultrasound were confirmed by the presence of subharmonics in the spectrum and temperature increase as a result of increased tissue absorption. These observations imply that cavitation-enhanced lesions can be generated without reducing the penetration ability; they also show the advantage of producing larger and more uniform thermal lesions by multiple sonications. This technique provides an easy and effective way to achieve cavitation-enhanced heating, and may be useful for generating large and deep-seated thermal lesions.

Histopathological observations of the antivascular effects of physiotherapy ultrasound on a murine neoplasm

This study evaluates the histopathological changes that follow insonation of a neoplasm with physiotherapy ultrasound. In 27 mice (C3HV/HeN strain), a subcutaneous melanoma (K1735(22)) was insonated with continuous physiotherapy ultrasound (1 MHz; spatial-average-temporal-average = 2.3 W cm(-2)). Analyses of contrast enhanced (0.1 mL Optison) power Doppler observations showed that insonation significantly (p < 0.05) increased the avascular area in the neoplasm. The predominant acute effect of insonating the neoplasm was an apparently irreparable dilation of the tumor capillaries with associated intercellular oedema; other immediate effects were haemorrage and increased intercellular fluid. Liquefactive necrosis of neoplastic cells was a delayed effect. There was a high correlation (R2 = 0.91) between the percent area affected on histologic examination and the percent increase in avascularity of the neoplasm in the Doppler study. In conclusion, physiotherapy ultrasound produced histologic changes in the tumor vasculature that were consistent with observations made by contrast enhanced power Doppler ultrasound.

Effects of nonlinear propagation, cavitation, and boiling in lesion formation by high intensity focused ultrasound in a gel phantom

The importance of nonlinear acoustic wave propagation and ultrasound-induced cavitation in the acceleration of thermal lesion production by high intensity focused ultrasound was investigated experimentally and theoretically in a transparent protein-containing gel. A numerical model that accounted for nonlinear acoustic propagation was used to simulate experimental conditions. Various exposure regimes with equal total ultrasound energy but variable peak acoustic pressure were studied for single lesions and lesion stripes obtained by moving the transducer. Static overpressure was applied to suppress cavitation. Strong enhancement of lesion production was observed for high amplitude waves and was supported by modeling. Through overpressure experiments it was shown that both nonlinear propagation and cavitation mechanisms participate in accelerating lesion inception and growth. Using B-mode ultrasound, cavitation was observed at normal ambient pressure as weakly enhanced echogenicity in the focal region, but was not detected with overpressure. Formation of tadpole-shaped lesions, shifted toward the transducer, was always observed to be due to boiling. Boiling bubbles were visible in the gel and were evident as strongly echogenic regions in B-mode images. These experiments indicate that nonlinear propagation and cavitation accelerate heating, but no lesion displacement or distortion was observed in the absence of boiling.

The use of a micro-bubble agent to enhance rabbit liver destruction using high intensity focused ultrasound

Liver tissues in New Zealand rabbits were ablated using high intensity focused ultrasound (HIFU, 14300 W/cm(2), 1.0 MHz). The animals were intravenously administered 0.2 ml of micro-bubble agent in the experimental (n=20) group and an isovolumetric normal saline solution in the control (n=27) group before HIFU treatment which was performed as a linear scan. In both groups, the preselected tissue volumes were destroyed without harming the overlying tissues. Necrosis rate (NR, cm(3)/s) was used to reflect the ablation efficiency, which was the tissue volume of occurring coagulative necrosis per 1s HIFU exposure. NR was improved in the experimental group (0.0570+/-0.0433 vs 0.0120+/-0.0122, P=0.0002). Pathological studies confirmed that there were no residual intact targets within the exposed volume. These findings suggested that the introduction of the micro-bubble agent enhanced HIFU liver destruction.

Magnetic resonance-guided focused ultrasound surgery (MRgFUS). Four ablation treatments of a single canine hepatocellular adenoma

BACKGROUND

Canine hepatocellular adenomas are benign, well-differentiated, primary hepatic tumors. Surgical resection is technically demanding and is considered a major procedure with relatively high morbidity rates. Magnetic resonance-guided focused ultrasound surgery (MRgFUS) uses focused ultrasonic energy to non-invasively create a heat-coagulated lesion deep within the body. This effect can be achieved in a controlled, accurate manner. The aim of this study was to evaluate the safety, accuracy and efficacy of non-invasive focal ablation of tissue volumes of a canine benign liver tumour by consecutive MRgFUS sonications.

MATERIALS AND METHODS

Four MRgFUS procedures were performed in a 10-year-old, male, mixed large breed dog (45 kg) under general anaesthesia. The exact location and volume of the ablated areas were planned on the MR images. Real-time MR imaging and temperature mapping enabled the immediate evaluation of the effect of each sonication. Different areas were chosen within the tumour. These volumes of tumoral tissue were ablated by multiple sonications. To allow accurate targeting and quality imaging, sonications were performed during 20-30 s of apnoea. Between the sonications the dog was normally ventilated. The dog was operated 21 days after the fourth ablative procedure. The tumour was resected and histopathologically examined.

RESULTS

The MRgFUS created necrosis with contiguous areas of complete tissue destruction within the liver tumour, in full accordance with the planning. A focal thermal injury to the cartilage of the right lower ribs was noted after the fourth treatment. This lesion became infected and was treated surgically. Ten months after the last treatment the dog is well and healthy.

CONCLUSIONS

Focused ultrasound ablation of liver tumoral tissue with MR guidance under general anaesthesia and controlled apnoea is a safe and accurate treatment modality. Its main advantage is that it is a completely non-invasive image-guided treatment. The ablation of significant volumes of a highly vascular liver tumoral tissue was achieved. Such tissue can be ablated in a very accurate manner, exactly according to the pretreatment planning on the MR images. The MR imaging characteristics, including real-time temperature mapping, enable real-time control of every step of the ablation process. Mechanical ventilation with intermittent apnoea periods overcomes the problem of the respiratory movements of the liver. Care must be taken to avoid the passage of the ultrasound beam through energy-absorbing calcified tissue.

Miniaturized ultrasound arrays for interstitial ablation and imaging

A potential alternative to extracorporeal, noninvasive HIFU therapy is minimally invasive intense ultrasound ablation that can be performed laparoscopically or percutaneously. An approach to minimally invasive ablation of soft tissue using miniaturized linear ultrasound arrays is presented here. Recently developed 32-element arrays with aperture 2.3 x 49 mm, therapy frequency 3.1 MHz, pulse-echo bandwidths >42% and surface acoustic energy density >80 W/cm2, are described. These arrays are integrated into a probe assembly, including a coupling balloon and piercing tip, suitable for interstitial ablation. An integrated electronic control system allows therapy planning and automated treatment guided by real-time interstitial B-scan imaging. Image quality, challenging because of limited probe dimensions and channel count, is aided by signal processing techniques that improve image definition and contrast, resulting in image quality comparable to typical transabdominal ultrasound imaging. Ablation results from ex vivo and in vivo experiments on mammalian liver tissue show that this approach is capable of ablation rates and volumes relevant to clinical applications of soft tissue ablation such as treatment of liver cancer.

MR imaging-controlled focused ultrasound ablation: a noninvasive image-guided surgery

The history of MR-guided FUS demonstrates the need for merging advanced therapy technology with advanced imaging. Without the ability of MR imaging to localize the tumor margins and without the temperature-sensitive imaging that provides the closed-loop control of energy deposition, this method is inadequate for most clinical applications. Given these limitations,high-intensity focused ultrasound initially appeared to have a narrow application area and was not able to compete with other surgical or ablation methods. Today, MR imaging-guided FUS has become a safe and effective means of performing probe-delivered thermal ablations and minimally invasive surgery. Moreover, it has the potential to replace treatments that use ionizing radiation such as radiosurgery and brachytherapy. Although the cost of integrating"big ticket" MR imaging systems with complex and expensive phased arrays is high, this expenditure will largely be offset by eliminating hospitalization and anesthesia and by reducing complications. In effect, an investment in this emerging technology will ultimately redound to the benefit of the health care delivery system and, most important, to the patient. The FUS system provides a safe, repeatable treatment approach for benign tumors (eg, uterine fibroid and breast fibroadenoma) that do not require an aggressive approach. MR-guided FUS can also be used for debulking cancerous tissue. It has already been tested as a breast cancer treatment; its application for other malignancies in the brain, liver, and prostate is under development. MR-guided FUS offers an attractive alternative to conventional surgery because it incorporates intraoperative MR imaging, which provides far more precise target definition than is possible with the surgeon's direct visualization of the lesion. MR-guided FUS is undeniably the most promising interventional MR imaging method in the field of image-guided therapy today. It is applicable not only in the thermal coagulative treatment of tumors but also in several other medical situations for which invasive surgery or radiation may not be treatment options. The use of FUS for treating vascular malformation or functional disorders of the brain is also exciting. It is uniquely applicable for image-guided therapy using targeted drug delivery methods and gene therapy. Further advances in this technology will no doubt improve energy deposition and reduce treatment times. In the near future, FUS will offer a viable alternative to conventional surgery and radiation therapy; in the longer-term, it may also enable a host of targeted treatment methods aimed at eradicating or arresting heretofore intractable diseases such as certain brain malignancies and forms of epilepsy.

Gel phantom for use in high-intensity focused ultrasound dosimetry

An optically transparent phantom was developed for use in high-intensity focused ultrasound (US), or HIFU, dosimetry studies. The phantom is composed of polyacrylamide hydrogel, embedded with bovine serum albumin (BSA) that becomes optically opaque when denatured. Acoustic and optical properties of the phantom were characterized as a function of BSA concentration and temperature. The speed of sound (1544 m/s) and acoustic impedance (1.6 MRayls) were similar to the values in soft tissue. The attenuation coefficient was approximately 8 times lower than that of soft tissues (0.02 Np/cm/MHz for 9% BSA). The nonlinear (B/A) coefficient was similar to the value in water. HIFU lesions were readily seen during formation in the phantom. In US B-mode images, the HIFU lesions were observed as hyperechoic regions only if the cavitation activity was present. The phantom can be used for fast characterization and calibration of US-image guided HIFU devices before animal or clinical studies.

Thermal-based treatment options for localized prostate cancer

It seems clear that thermal-based therapies of prostate cancer have the potential to completely eradicate the prostate gland. Technical modifications continue to improve our ability to use these modalities more effectively, which can be seen in the ever decreasing morbidity from damage to adjacent structures. These treatments offer potential major advantages over surgery and radiation-based treatment modalities.

Bulk ablation of soft tissue with intense ultrasound: modeling and experiments

Methods for the bulk ablation of soft tissue using intense ultrasound, with potential applications in the thermal treatment of focal tumors, are presented. An approximate analytic model for bulk ablation predicts the progress of ablation based on tissue properties, spatially averaged ultrasonic heat deposition, and perfusion. The approximate model allows the prediction of threshold acoustic powers required for ablation in vivo as well as the comparison of cases with different starting temperatures and perfusion characteristics, such as typical in vivo and ex vivo experiments. In a full three-dimensional numerical model, heat deposition from array transducers is computed using the Fresnel approximation and heat transfer in tissue is computed by finite differences, accounting for heating changes caused by boiling and thermal dose-dependent absorption. Similar ablation trends due to perfusion effects are predicted by both the simple analytic model and the full numerical model. Comparisons with experimental results show the efficacy of both models in predicting tissue ablation effects. Phenomena illustrated by the simulations and experiments include power thresholds for in vivo ablation, differences between in vivo and ex vivo lesioning for comparable source conditions, the effect of tissue boiling and absorption changes on ablation depth, and the performance of a continuous rotational scanning method suitable for interstitial bulk ablation of soft tissue.

Image guided tumour ablation

Several different technologies have been employed for the local ablation of tissue by thermal techniques. At the present time the most widely favoured technique is radiofrequency ablation (RFA) but developments in other techniques, e.g. microwave may change this. In many countries RFA or percutaneous ethanol injection (PEI) are accepted therapies for patients with Childs Pugh Class A or B cirrhosis and early hepatocellular carcinoma (HCC). Results for RFA in large series of patients with liver metastases from colon cancer are very promising. Five-year survival rates of 26% from the time of first ablation and 30% from the diagnosis of liver metastases for patients with limited (<6, <5 cm) liver disease who are not surgical candidates compares well with post resection series where 5-year survival rates vary between 29% and 39% in operable candidates. Sufficient experience has now been gained in lung and renal ablation to show that these are minimally invasive techniques which can produce effective tumour destruction with a limited morbidity. More novel areas for ablation such as adrenal or pelvic recurrence are being explored.

MRI-guided focused ultrasound surgery of uterine leiomyomas

Uterine fibroids are the most common pelvic tumors in women and are a significant cause of morbidity for women of reproductive age. Today, there are a variety of less invasive alternatives available to hysterectomy, such as myomectomy, hormonal therapy, uterine artery embolization, and more recently magnetic resonance-guided focused ultrasound surgery (MRgFUS). With this technique, ultrasound waves are focused through intact skin of the anterior abdominal wall resulting in localized thermal tissue ablation, monitored by online MR temperature control. By using an effective combination of image guidance and energy delivery, MRgFUS therefore allows for preservation of uterine function while obviating the need for a minimally invasive procedure or surgery.

MR-Guided Interventions of the Breast

Techniques and instrumentation are now widely available that enable interventional MR-guided preoperative needle localization and lesion marking. Minimally invasive MR-guided core biopsy techniques have been demonstrated but remain limited for small lesions and will be facilitated by the development of biopsy instruments that can be directly visualized using MR imaging. MR-guided tumor ablation is beginning to be evaluated in a few centers. It holds promise as new treatment modality in the continuing trend toward greater breast conservation in the local therapy of breast cancer. Further studies are needed to document the ability of MR-guided ablation to control the margins of a tumor as effectively as surgery. Patients with an extensive in situ intra-ductal component may pose a significant hurdle because the extent of ductal carcinoma in situ maybe underestimated on breast MR images. Ultimately, the success of MR-guided thermal ablation depends on the ability of MR imaging to map the extent of heating during the procedure so that the procedure can be performed to achieve complete control of the tumor margins. It is unfortunate that the conventional method for MR thermometry--the proton resonance frequency shift method--does not work in fat or in voxels with a mix of fat and glandular tissue and, hence, has limited applicability in the breast. Other methods, including measurement of T1 and T2, are being investigated as alternatives.

Feasibility of US-guided high-intensity focused ultrasound treatment in patients with advanced pancreatic cancer: initial experience

The study was approved by the university ethics committee, and informed consent was obtained from all patients. The purpose of this study was to prospectively evaluate ultrasonographically guided high-intensity focused ultrasound in the treatment of patients with advanced-stage pancreatic cancer. Eight patients underwent high-intensity focused ultrasound ablation, and laboratory and radiologic examinations were performed after intervention. Changes in symptoms and survival time were noted at follow-up. No complications were observed, and preexisting severe back pain disappeared after intervention. Follow-up images revealed an absence of tumor blood supply and shrinkage of the ablated tumor. Four patients died, and four patients were alive at the time of this writing, with a median survival time of 11.25 months. The authors conclude that high-intensity focused ultrasound ablation is safe and feasible in the treatment of advanced pancreatic cancer.

Extracorporeal high intensity focused ultrasound treatment for patients with breast cancer

PURPOSE

To investigate the safety, efficacy and feasibility of using high-intensity focused ultrasound (HIFU) as a non-invasive treatment for patients with breast cancer.

PATIENTS AND METHODS

Twenty-two patients with breast cancer were enrolled into this non-randomized prospective trial. Disease TNM stage was classified as stage I in 4 patients, stage II(A) in 9 patients, stage II(B) in 8 patients, and stage IV in 1 patient. Tumor size ranged from 2 to 4.8 cm in diameter (mean 3.4 cm). All patients received chemotherapy, radiation and tamoxifen, following HIFU for the primary lesions. Outcome measures included radiological and pathologic assessment of the treated tumor, cosmesis, and local recurrence. A cumulative survival rate is calculated by using the Kaplan-Meier method.

RESULTS

No severe complications were encountered after HIFU. Post-operative imaging demonstrated positive response and regression of all treated lesions. Follow-up biopsy revealed coagulation necrosis of target tumor and subsequent replacement by fibroblastic tissue. After a median follow-up of 54.8 months, 1 patient died, 1 was lost to follow-up, and 20 were still alive. Two of 22 patients developed local recurrence. Five-year disease-free survival and recurrence-free survival were 95% and 89%, respectively. Cosmetic result was judged as good to excellent in 94% of patients.

CONCLUSIONS

HIFU treatment is safe, effective, and feasible for patients with breast cancer. But, large-scale, multiple-center clinical trials will be needed to determine the future role of this novel modality.

Advanced hepatocellular carcinoma: treatment with high-intensity focused ultrasound ablation combined with transcatheter arterial embolization

PURPOSE

To evaluate ultrasonographically (US)-guided high-intensity focused ultrasound ablation combined with transcatheter arterial chemoembolization (TACE) in the treatment of stage IVA hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained. From November 1998 to May 2000, 50 consecutive patients with stage IVA HCC (TNM classification, T4N0-1M0) were alternately enrolled in one of two treatment groups: group 1 (n = 26), in which TACE was performed alone, and group 2 (n = 24), in which transcutaneous ablation of HCC with high-intensity focused ultrasound was performed 2-4 weeks after TACE. The tumors were 4-14 cm in diameter (mean, 10.5 cm). Immediate therapeutic effects were assessed at follow-up with Doppler US and computed tomography or magnetic resonance imaging. All patients were followed up for 3-24 months (mean, 8 months) to observe long-term therapeutic effects and complications in both groups. Tumor reduction rates, median survival time, and cumulative survival rates in both groups were calculated by using the unpaired Student t test and Kaplan-Meier method.

RESULTS

No severe complication was observed after focused ultrasound ablation, and no unexpected side effects were noted after TACE. Follow-up images showed absence or reduction of blood supply in the lesions after focused ultrasound ablation when compared with blood supply after TACE alone. The median survival time was 11.3 months in group 2 and 4.0 months in group 1 (P = .004). The 6-month survival rate was 80.4%-85.4% in group 2 and 13.2% in group 1 (P = .002), and the 1-year survival rate was 42.9% and 0%, respectively. Median reductions in tumor size as a percentage of initial tumor volume at 1, 3, 6, and 12 months after treatment, respectively, were 28.6%, 35.0%, 50.0%, and 50.0% in group 2 and 4.8%, 7.7%, 10.0%, and 0% in group 1 (P < .01).

CONCLUSION

The combination of high-intensity focused ultrasound ablation and TACE is a promising approach in patients with advanced-stage HCC, but large-scale randomized clinical trials are necessary for confirmation.

Direct thermal dose control of constrained focused ultrasound treatments: phantom and in vivo evaluation

The first treatment control system that explicitly and automatically balances the efficacy and safety goals of noninvasive thermal therapies is described, and its performance is evaluated in phantoms and in vivo using ultrasound heating with a fixed, focused transducer. The treatment efficacy is quantified in terms of thermal dose delivered to the target. The developed feedback thermal dose controller has a cascade structure with the main nonlinear dose controller continuously generating the reference temperature trajectory for the secondary, constrained, model predictive temperature controller. The control system ensures thermal safety of the normal tissue by automatically complying with user-specified constraints on the maximum allowable normal tissue temperatures. To reflect hardware limitations and to prevent cavitation, constraints on the maximum transducer power can also be imposed. It is shown that the developed controller can be used to achieve the minimum-time delivery of the desired thermal dose to the target without violating safety constraints, which is a novel and clinically desirable feature. The developed controller is model based, and requires patient- and site-specific models for its operation. These models were obtained during pre-treatment identification experiments. In our implementation, predictive models, internally used by the automatic treatment controller, are dynamically updated each time new temperature measurements become available. The adaptability of internal models safeguards against adverse effects of modelling errors, and ensures robust performance of the control system in the presence of a priori unknown treatment disturbances. The successful validation with two experimental models of considerably different thermal and ultrasound properties suggests the applicability of the developed treatment control system to different anatomical sites.

Vascular effects induced by combined 1-MHz ultrasound and microbubble contrast agent treatments in vivo

Previous in vivo studies have demonstrated that microvessel hemorrhages and alterations of endothelial permeability can be produced in tissues containing microbubble-based ultrasound contrast agents when those tissues are exposed to MHz-frequency pulsed ultrasound of sufficient pressure amplitudes. The general hypothesis guiding this research was that acoustic (viz., inertial) cavitation, rather than thermal insult, is the dominant mechanism by which such effects arise. We report the results of testing five specific hypotheses in an in vivo rabbit auricular blood vessel model: (1) acoustic cavitation nucleated by microbubble contrast agent can damage the endothelia of veins at relatively low spatial-peak temporal-average intensities, (2) such damage will be proportional to the peak negative pressure amplitude of the insonifying pulses, (3) damage will be confined largely to the intimal surface, with sparing of perivascular tissues, (4) greater damage will occur to the endothelial cells on the side of the vessel distal to the source transducer than on the proximal side and (5) ultrasound/contrast agent-induced endothelial damage can be inherently thrombogenic, or can aid sclerotherapeutic thrombogenesis through the application of otherwise subtherapeutic doses of thrombogenic drugs. Auricular vessels were exposed to 1-MHz focused ultrasound of variable peak pressure amplitude using low duty factor, fixed pulse parameters, with or without infusion of a shelled microbubble contrast agent. Extravasation of Evans blue dye and erythrocytes was assessed at the macroscopic level. Endothelial damage was assessed via scanning electron microscopy (SEM) image analysis. The hypotheses were supported by the data. We discuss potential therapeutic applications of vessel occlusion, e.g., occlusion of at-risk gastric varices.

High-intensity focused ultrasound in the treatment of solid tumours

Traditionally, surgery has been the only cure for many solid tumours. Technological advances have catalysed a shift from open surgery towards less invasive techniques. Laparoscopic surgery and minimally invasive techniques continue to evolve, but for decades high-intensity focused ultrasound has promised to deliver the ultimate objective - truly non-invasive tumour ablation. Only now, however, with recent improvements in imaging, has this objective finally emerged as a real clinical possibility.

Effects of high intensity focused ultrasound on vascular endothelial growth factor in melanoma bearing mice

This study was to investigate the effects of high intensity focused ultrasound on vascular endothelial growth factor. A B16 melanoma model was adopted in our study. Melanoma bearing mice were randomly divided into two groups: HIFU group and surgery group. While the control group was only injected with isovolumetric normal saline solution and treated as the surgery group. We detected VEGF both in tissues and sera through immunohistochemical method and ELISA respectively. Tissues were sampled pre- and at the 3rd day post-operation in HIFU group and blood samples were taken pre- and at the 1st, 3rd, and 7th day post-operation in all the groups. As a result, in the tissues, VEGF was expressed in 80% melanomas, but none was detected in the targeted area after HIFU treatment. In the sera, there was a decreasing tendency of serum-VEGF concentrations in group HIFU and surgery after operation, while that in the control group increased after operation. The levels in the HIFU group on day 1, 3, and 7 postoperatively were all lower than that in the surgery group respectively (79.16 pg/ml vs 91.59 pg/ml; 33.64 pg/ml vs 49.39 pg/ml; 30.37 pg/ml vs 46.68 pg/ml), but there wasn't any significant difference (P > 0.05). So HIFU can destroy VEGF in the targeted area and maybe have less of an effect on serum-VEGF than surgery.

In vitro ablation of cardiac valves using high-intensity focused ultrasound

The purpose of this study was to evaluate the possibility of using high-intensity focused ultrasound (US), or HIFU, to create lesions in cardiac valves in vitro. Calf mitral valves and aortic valves were examined. Focused US energy was applied with an operating frequency of 4.67 MHz at a nominal acoustic power of 58 W for 0.2, 0.3 and 0.4 s at 4-s intervals. Mitral valve perforation was achieved with 20.8 +/- 3.7 exposures of 0.2 s, 15.4 +/- 2.1 exposures of 0.3 s or 11.2 +/- 2.3 exposures of 0.4 s. Aortic valve perforation was achieved with 13.3 +/- 2.4 exposures of 0.2 s, 10.3 +/- 2.2 exposures of 0.3 s or 8.4 +/- 1.8 exposures of 0.4 s. The mean diameter of the perforated area was 1.09 +/- 0.11 mm. The lesions were slightly discolored and coagulation of tissue around the perforation was observed. HIFU was successful in perforating cardiac valves. With further refinement, HIFU may prove useful for valvulotomy or valvuloplasty.

Extracorporeal high intensity focused ultrasound ablation in the treatment of patients with large hepatocellular carcinoma

BACKGROUND

High intensity focused ultrasound (HIFU) is a noninvasive treatment modality that induces complete coagulative necrosis of a deep tumor through the intact skin. The current study was conducted to determine the safety, efficacy, and feasibility of extracorporeal HIFU in the treatment of patients with hepatocellular carcinoma (HCC).

METHODS

A total of 55 patients with HCC with cirrhosis were enrolled in this prospective, nonrandomized clinical trial. Among them, 51 patients had unresectable HCC. Tumor size ranged from 4 to 14 cm in diameter with mean diameter of 8.14 cm. According to tumor, node, metastasis (TNM) classification, 15 patients corresponded to stage II, 16 to stage IIIA, and 24 to IIIC. All patients had HIFU, and the median number of HIFU session was 1.69. Safety and efficacy of HIFU were assessed in this trial.

RESULTS

No severe side effect was observed in the patients treated with HIFU. Follow-up imaging showed an absence of tumor vascular supply and the shrinkage of treated lesions. Serum alpha-fetoprotein returned to normal level in 34% of patients. The overall survival rates at 6, 12, and 18 months were 86.1%, 61.5%, and 35.3%, respectively. The survival rates were significantly higher in patients in stage II than those in stage IIIA (P = .0132) and in stage IIIC (P = .0265).

CONCLUSION

As a noninvasive therapy, HIFU appears to be effective, safe, and feasible in the treatment of patients with HCC. It may play an important role in the ablation of large tumors.

Noninvasive thermal ablation of hepatocellular carcinoma by using magnetic resonance imaging-guided focused ultrasound

A number of minimally invasive methods have been tested for the thermal ablation of liver tumors as an alternative to surgical resection. The use of focused ultrasound transducers to ablate deep tumors offers the first completely noninvasive alternative to these techniques. By increasing the flexibility of this technology with modern phased-array transducer design and by combining it with magnetic resonance imaging for targeting and online guidance, a powerful tool results with the potential to offer treatment to a larger population of patients, to reduce trauma to the patient, and to reduce the cost of treatment. In this article, we review previous work with focused ultrasound in the liver and recent experimental results with magnetic resonance imaging guidance.

In vivo feasibility of image-guided transvaginal focused ultrasound therapy for the treatment of intracavitary fibroids

OBJECTIVE

To determine the feasibility of uterine tissue ablation in vivo using a transvaginal focused ultrasound applicator guided by ultrasound imaging.

DESIGN

Randomized in vivo animal study.

SETTING

Academic research environment.

ANIMAL(S)

Healthy anesthetized sheep.

INTERVENTION(S)

Uterine treatment location was determined using a computerized targeting system. Five sonications 10 seconds in duration and averaging 2,000 W/cm(2) of focal ultrasound intensity were applied in each animal's uterus. Animals were euthanized either immediately or 2, 7, or 30 days post-treatment.

MAIN OUTCOME MEASURE(S)

Gross and microscopic analysis of the dissected uterus was used to quantitatively and qualitatively determine the ablated region and treatment side effects.

RESULT(S)

Treatments resulted in coagulative necrosis. Histopathological analysis showed that over 7 days, inflammatory cells appeared and smooth muscle bundles regenerated. By day 30, treated tissues healed and scar tissue formed. None of the animals showed abnormal behavior or medical problems. Complications in three animals were damage to the vaginal wall and colon, possibly due to inadequate applicator cooling and an empty bladder during treatment.

CONCLUSION(S)

Transvaginal image-guided high-intensity focused ultrasound has potential for treating uterine fibroids. Further safety testing of this treatment will prepare it for human use.

Activated anti-tumor immunity in cancer patients after high intensity focused ultrasound ablation

T cell-mediated immune responses represent the main cellular antitumor immunity in cancer patients. Recent studies have shown that that both surgical procedure and radiation therapy could cause the functional suppression of lymphocyte-mediated cellular immunity. The purpose of current study is to evaluate whether high intensity focused ultrasound (HIFU) might change a systemic antitumor immunity, particularly T lymphocyte-mediated immunity in cancer patients. A total of 16 patients with solid malignancies were treated with HIFU. Among them, six patients had osteosarcoma (Enneking stage, II(B)4, III(B) 2), five had hepatocellular carcinoma (TNM stage, III 3, IV 2), and five had renal cell carcinoma (TNM stage, III 2, IV 3). Using flow cytometry technique, T lymphocyte and subset, B lymphocyte and natural killer cell (NK) in the peripheral blood were measured in these patients on the day before HIFU and 7 to 10 d after HIFU. The statistical significance of any observed difference is evaluated by Student's t-test. The results showed a significance increase in the population of CD4(+) lymphocytes (p < 0.01) and the ratio of CD4(+) /CD8(+) (p < 0.05) in the circulation of cancer patients after HIFU treatment. The abnormal levels of CD3(+) lymphocytes returned toward the normal range in two patients, CD4(+)/CD8(+) ratio in 3, CD19(+) lymphocytes in one and cytotoxic NK in one, respectively, in comparison to control values. It is concluded that HIFU could enhance a systemic antitumor cellular immunity in addition to local tumor destruction in patients with solid malignancies.