An image-guided high intensity focused ultrasound device for uterine fibroids treatment

Delivery of liposomal doxorubicin (Doxil) in a breast cancer tumor model: investigation of potential enhancement by pulsed-high intensity focused ultrasound exposure

RATIONALE AND OBJECTIVES

To investigate the potential of using pulsed high-intensity focused ultrasound (HIFU) exposures to enhance the delivery, and hence therapeutic effect of liposomal doxorubicin (Doxil) in a murine breast cancer tumor model.

MATERIALS AND METHODS

Tumors were grown in the bilateral flanks of mice using a mammary adenocarcinoma cell line. Experiments consisted of exposing one of two tumors to pulsed-HIFU, followed by tail vein injections of Doxil. Tumor growth rates were monitored, and assays carried out for doxorubicin concentration in these tumors as well as in a second (squamous cell carcinoma) tumor model and in muscle. Laser scanning confocal microscopy was used with fluorescent probes to observe both the uptake of polystyrene nanoparticles and dilation of exposed blood vessels. Additional experiments involving histologic analysis and real-time temperature measurements were performed to determine the safety of the exposures.

RESULTS

Pulsed-HIFU exposures were shown to be safe, producing no apparent deleterious effects in the tumors. The exposures, however, were not found to enhance the delivery of Doxil, and consequently did not allow for lower doses for obtaining tumor regression. Imaging with a fluorescent dextran showed blood vessels to be dilated as a result of the exposures. Experiments with polystyrene nanoparticles of similar size to the liposomes showed a greater abundance to be present in the treated tumors.

CONCLUSION

Although past studies have shown the advantages of pulsed-HIFU exposures for enhancing delivery, this was not observed with the liposomes, apparently because of their inherent ability to preferentially accumulate into tumors on their own. Potential mechanisms for enhanced uptake of non-liposomal nanoparticles are discussed.

Annular phased-array high-intensity focused ultrasound device for image-guided therapy of uterine fibroids

An ultrasound (US), image-guided high-intensity focused ultrasound (HIFU) device was developed for noninvasive ablation of uterine fibroids. The HIFU device was an annular phased array, with a focal depth range of 30-60 mm, a natural focus of 50 mm, and a resonant frequency of 3 MHz. The in-house control software was developed to operate the HIFU electronics drive system for inducing tissue coagulation at different distances from the array. A novel imaging algorithm was developed to minimize the HIFU-induced noise in the US images. The device was able to produce lesions in bovine serum albumin-embedded polyacrylamide gels and excised pig liver. The lesions could be seen on the US images as hyperechoic regions. Depths ranging from 30 to 60 mm were sonicated at acoustic intensities of 4100 and 6100 W/cm2 for 15 s each, with the latter producing average lesion volumes at least 63% larger than the former. Tissue sonication patterns that began distal to the transducer produced longer lesions than those that began proximally. The variation in lesion dimensions indicates the possible development of HIFU protocols that increase HIFU throughput and shorten tumor treatment times.

Uterine fibroids: diffusion-weighted MR imaging for monitoring therapy with focused ultrasound surgery--preliminary study

PURPOSE

To prospectively determine the feasibility of using diffusion-weighted (DW) imaging and apparent diffusion coefficient (ADC) mapping before (baseline) and after treatment and at 6-month follow-up to monitor magnetic resonance (MR) image-guided focused ultrasound surgical ablation of uterine fibroids.

MATERIALS AND METHODS

Informed consent was obtained from patients before treatment with our study protocol, as approved by the institutional review board, and the study complied with the Health Insurance Portability and Accountability Act. Fourteen patients (mean age, 46 years +/- 5 [standard deviation]) who underwent DW imaging were enrolled in this study, and 12 of 14 completed the inclusive MR examination with DW imaging at 6-month follow-up. Treatment was performed by one radiologist with a modified MR image-guided focused ultrasound surgical system coupled with a 1.5-T MR imager. Pre- and posttreatment and 6-month follow-up MR images were obtained by using phase-sensitive T1-weighted fast spoiled gradient-recalled acquisition, T1-weighted contrast material-enhanced, and DW imaging sequences. Total treatment time was 1-3 hours. Trace ADC maps were constructed for quantitative analysis. Regions of interest localized to areas of hyperintensity on DW images were drawn on postcontrast images, and quantitative statistics were obtained from treated and nontreated uterine tissue before and after treatment and at 6-month follow-up. Statistical analysis was performed with analysis of variance. Differences with P < .05 were considered statistically significant.

RESULTS

T1-weighted contrast-enhancing fibroids selected for treatment had no hyperintense or hypointense signal intensity changes on the DW images or ADC maps before treatment. Considerably increased signal intensity changes that were localized within the treated areas were noted on DW images. Mean baseline ADC value in fibroids was 1504 mm(-6)/sec2 +/- 290. Posttreatment ADC values for nontreated fibroid tissue (1685 mm(-6)/sec2 +/- 468) differed from posttreatment ADC values for fibroid tissue (1078 mm(-6)/sec2 +/- 293) (P = .001). A significant difference (P < .001) between ADC values for treated (1905 mm(-6)/sec2 +/- 446) and nontreated (1437 mm(-6)/sec2 +/- 270) fibroid tissue at 6-month follow-up was observed.

CONCLUSION

DW imaging and ADC mapping are feasible for identification of ablated tissue after focused ultrasound treatment of uterine fibroids.

Extracorporeal application of high-intensity focused ultrasound for prostatic tissue ablation

OBJECTIVE

To investigate the efficacy and safety of extracorporeal prostatic tissue ablation using high-intensity focused ultrasound (HIFU) in vivo in animals, and in a clinical feasibility study in men, as this is an investigational minimally invasive treatment alternative for locally confined prostatic carcinoma, but may have significant side-effects.

PATIENTS, MATERIALS AND METHODS

Ultrasound (1.04 MHz excitation frequency) was generated by an extracorporeal cylindrical piezo-ceramic element and focused by a paraboloidal reflector to a focal size of 32 x 4 mm. The focal distance and aperture diameter were both 100 mm. HIFU was applied extracorporeally at different intensities and pulse duration (up to 6 s) to 11 dog prostates in vivo (median intensity 1192 W/cm2) and eight patients (median intensity 3278 W/cm2, range 2384-3576) under general anaesthesia. The lesions were assessed macroscopically and histologically after HIFU and any side-effects evaluated.

RESULTS

Thermoablation was feasible in vivo and in all patients. Macroscopic analysis and histology showed sharply demarcated coagulative necrosis. Side-effects, including skin and rectal burns, occurred only after transvesical application in the in vivo study. There were no side-effects in patients after perineal application.

CONCLUSION

Extracorporeal HIFU is technically feasible and induces sharply demarcated tissue damage in the prostate. From the early results of this phase 1 study, the perineal approach seems to be safe.

Hyperecho in ultrasound images of HIFU therapy: involvement of cavitation

High-intensity focused ultrasound (US), or HIFU, treatment of soft tissues has been shown to result in a hyperechoic region in B-mode US images. We report on detecting cavitation in vivo in correlation with the appearance of a hyperechoic region. The US system consisted of a HIFU transducer (3.3 MHz), a broadband A-mode transducer for active and passive cavitation detection and an US-imaging probe that were all confocal and synchronized. HIFU, at in situ intensities of 220 to 1710 W/cm(2), was applied for 10 s to pig muscles in vivo. Active and passive cavitation detection results showed a strong correlation between the onset of cavitation and the appearance of a hyperechoic region. Passive cavitation detection results showed that inertial cavitation typically occurred prior (within 0.5 s) to the appearance of a hyperechoic region. The observed cavitation activity confirms that bubbles are present during the formation of a hyperechoic region at the HIFU focus.

High-intensity focused ultrasound for localized thyroid-tissue ablation: preliminary experimental animal study

OBJECTIVE

Thyroid surgery is common and complications are not rare. High-intensity focused ultrasound (HIFU) could be a possible minimally invasive alternative to surgery. The aim of this study was to assess the feasibility of using HIFU to obtain localized ablation of thyroid tissue without affecting neighboring structures.

METHODS

The ewe was chosen as the model because its thyroid is easily accessible, with a size comparable to the human gland. An HIFU device designed to treat human prostate cancer was used. Eight ewes were anesthetised and their thyroids were ablated with ultrasound-guided HIFU. HIFU was generated by a 3-MHz spherical piezocomposite transducer that delivered an average of 24 (range, 9-44) ultrasound pulses per lobe covering a mean volume of 0.7 cm(3) (range, 0.2-1.8).

RESULTS

Ewes were sacrificed 6-13 days after HIFU treatment and the anterior part of the neck was fixed in formalin before macroscopic and microscopic examinations. Adverse events occurred mainly for the first treated ewes before the energy delivered to the thyroid tissues was fully mastered: one animal died 3 days after HIFU, most probably because of inhalation pneumonia; the ultrasound beam hit adjacent organs in three animals. As expected, typical histologic lesions of the thyroid were obtained: central coagulative necrosis with ghost vesicular structures, disappearance of the nuclei, and cytoplasmic flocculation. At the periphery of the necrotic zone, a cell reaction was observed with fibroblastic granulation tissue, mononuclear cell infiltrate and regenerating thyroid tissue.

CONCLUSION

The results of this preliminary study confirm the possibility of using HIFU in order to destroy a defined area in thyroid tissue. Future experiments in ewes will be focused on the safety of the method by refining the HIFU parameters and by developing a new equipment specially built for the thyroid.

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.

Uterine myomas: an overview of development, clinical features, and management

OBJECTIVE

To review the biology and the pathophysiology of uterine myomas, focus on options for management, and emphasize principles that will render the decision-making process as logical as possible.

DESIGN

Literature review and synthesis of the authors' experience and philosophy.

RESULTS

Uterine myomas are the most common solid pelvic tumors in women. There is increasing evidence that they have a genetic basis and that their growth is related to genetic predisposition, hormonal influences, and various growth factors. Treatment choices are wide and include pharmacologic, surgical, and radiographically directed intervention. Most myomas can be followed serially with surveillance for development of symptoms or progressive growth.

CONCLUSION

The past century has witnessed development of highly sophisticated diagnostic and therapeutic technology for myomas. The tools currently at our disposal permit greater management flexibility with safe options, which must be tailored to the individual clinical situation.

Perspectives in clinical uses of high-intensity focused ultrasound

Focused ultrasound holds promise in a large number of therapeutic applications. It has long been known that high intensity focused ultrasound can kill tissue through coagulative necrosis. However, it is only in recent years that practical clinical applications are becoming possible, with the development of high power ultrasound phased arrays and noninvasive monitoring methods. These technologies, combined with more sophisticated treatment planning methods allow noninvasive focusing in areas such as the brain, that were once thought to be unreachable. Meanwhile, exciting investigations are underway in microbubble-enhanced heating which could significantly reduce treatment times. These developments have promoted an increase in the number of potential applications by providing valuable new tools for medical research. This paper provides an overview of the scientific and engineering advances that are allowing the growth in clinical focused ultrasound applications. It also discusses some of these prospective applications, including the treatment of brain disorders and targeted drug delivery.

High-intensity focused ultrasound in the treatment of postpartum hemorrhage: an animal model

OBJECTIVE

To investigate the use of high-intensity focused ultrasound (HIFUS) to reduce uterine artery blood flow in ewes in the postpartum period.

METHODS

HIFUS was applied to the uterine arteries of seven ewes in the postpartum period. Arterial flow velocities were measured before and after the procedure at the site of HIFUS application (target), as well as 3 cm upstream and 3 cm downstream from the target. The uterine arteries were then removed for macroscopic and histological examination.

RESULTS

Maximum flow velocities in the target area increased after the procedure by 350% and those upstream from the target decreased by 65%. Macroscopically, the vessel diameter was shown to have reduced at the site of HIFUS application. Microscopically, both the endothelium and media showed thermal lesions. Tissues surrounding the arteries were macroscopically and microscopically normal.

CONCLUSION

Exposure of uterine arteries to HIFUS reduces the vessel diameter and thus induces a dramatic increase in the maximum flow velocities within the target area. HIFUS may have a role in the treatment of postpartum hemorrhage.

Pilot point temperature regulation for thermal lesion control during ultrasound thermal therapy

The fundamental goal of ultrasound thermal therapy is to provide proper thermal lesion formations for effective tumour treatment. The quality of the therapy depends mostly on its positional precision. To date, most ultrasound thermal therapy treatments have focused on the formation of power or temperature patterns. The non-linear and time-delay effects of thermal dose formation prohibit direct control of the thermal dose distribution. In the paper, the control of thermal lesions by regulation of the temperature of a pilot point is proposed. This scheme utilises the high correlation between temperature elevation and thermal dose at the forward boundary of thermal lesions. To verify the feasibility, a 2D ultrasound phased array system was used to generate thermal lesions of various sizes, and the temperature elevation required to generate a thermal dose threshold was investigated. Results showed that the required temperature elevation was found to be a reasonably constant value of 52.5 degrees C under differing conditions when the focal area was small. When the focal area under consideration was large, the required temperature elevation became a monotonic function of blood perfusion rate, ranging from 49.2 to 52.5 degrees C. When the reference temperature of the pilot point was set at a conservative value (52.5 degrees C), the thermal lesions were controlled precisely under a wide range of blood perfusion and power pattern changes, tested by using a more realistic model that takes into account thermal-induced attenuation and blood perfusion changes. This changed the complex thermal dose control problem into a simple temperature regulation problem, which makes implementation of thermal lesion control easier, giving the scheme a high potential for application to current ultrasound thermal therapy systems.

Smooth muscle tumors of uncertain malignant potential and leiomyosarcomas of the uterus: MR findings

PURPOSE

To study the MR characteristics of nonbenign uterine smooth muscle tumors.

MATERIALS AND METHODS

Nine patients with pathologically proven leiomyosarcomas, and three patients with smooth muscle tumors of uncertain malignant potential (SMTUMP) were included in this study. Twelve cases of benign uterine leiomyomas and variants, in which gynecologists suspected leiomyosarcomas, were also analyzed. In each case we studied the size, location, signal intensity, and contrast enhancement of the tumors.

RESULTS

Nine of the 12 nonbenign characters had more than 50% of high-intensity areas on T2-weighted images (T2WI), and some hyperintense foci on T1-weighted images (T1WI). In the contrast study, nine of 12 nonbenign characters had well-demarcated unenhanced areas. On the other hand, only two of 12 benign characters showed such a signal intensity pattern, and none of them had a pocket-like unenhanced area.

CONCLUSION

Although there were some exceptions, more than 50% of high signal on T2WI, and the presence of any small high-signal areas on T1WI with unenhanced pockets were considered MR-suggestive for SMTUMPs and leiomyosarcomas.

Treatment of uterine fibroid tumors in an in situ rat model using high-intensity focused ultrasound

OBJECTIVE

To determine the efficacy and safety of high-intensity focused ultrasound (HIFU) for the treatment of uterine fibroid tumors in an in situ animal model.

DESIGN

High-intensity focused ultrasound was applied intraoperatively to uterine fibroid tumors in rats.

SETTING

Department of Bioengineering, and Applied Physics Laboratory, University of Washington, Seattle, Washington.

ANIMAL(S)

Thirty-five tumors in 27 Eker rats that had spontaneous in situ uterine fibroids were randomly assigned into two groups receiving HIFU (n = 29) or sham (n = 6) treatments.

INTERVENTION(S)

Animals were anesthetized, and tumors were exposed surgically. The HIFU was applied at 3.5 MHz in 10-second bursts to produce coagulative necrosis lesions (3 mm by 10 mm), spaced 5 mm apart. Sham treatments consisted of exposing the tumors, and handling them similarly to those in the HIFU treatment group, but HIFU was not applied.

MAIN OUTCOME MEASURE(S)

Tumor volume was measured every week transabdominally using B-mode ultrasound imaging. Gross examination and histological analysis were performed after euthanasia.

RESULT(S)

More than half of the tumors in the HIFU treatment group showed significant tumor volume reduction. The average tumor volume in the sham treatment group increased 40-fold. Gross and histological analysis showed coagulative necrosis of tumor cells in the HIFU treatment group.

CONCLUSION(S)

The HIFU may provide an effective and safe method of treating uterine fibroid tumors.