Image-guided high intensity focused ultrasound treatment for uterine leiomyomata

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Image-guided high intensity focused ultrasound treatment for uterine leiomyomata

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Title: Image-guided high intensity focused ultrasound treatment for uterine leiomyomata
Author: Chan, Arthur Ho-Yin
Abstract: High Intensity Focused Ultrasound, or HIFU, is capable of treating tissue deep in the body without the need for surgery. With this premise, an ultrasound image-guided HIFU device has been developed for treating submucosal uterine fibroids, which are benign tumors common in women of reproductive age. Fibroids may cause bleeding, discomfort, and lead to infertility, and is the largest indication for hysterectomy. HIFU treatment has the potential for women to retain their uterus while suppressing symptomatic fibroids.The device was designed based on the female anatomy. It consisted of a commercially available abdominal image probe and a transvaginal HIFU transducer operating at 4.0 MHz. A piezoelectric crystal affixed to an aluminum lens focused ultrasound energy at a fixed distance of 4 cm from the transducer. A graphite embedded epoxy matching layer placed in front of the lens increased the transducer efficiency by approximately 6%. The HIFU transducer was mechanically aligned to the image probe such that the HIFU focus was in the image plane allowing image-guided therapy. A latex condom filled with circulated water covered the transducer providing a sterile covering, acoustic coupling, and transducer cooling. A targeting system using position sensors mounted on the device was used to track the location of the HIFU focus relative to the ultrasound image. Computer software tracked the HIFU focus location and superimposed a visual target on the ultrasound image based on the data acquired by the position sensors.The device was characterized using acoustic measurement techniques of hydrophone field mapping and radiation force balance. Image-guided therapy was then performed in vitro in a tissue-mimicking phantom and in turkey breast tissue. Treated regions, or lesions, were created at the intended location, and appeared in the ultrasound image as hyperechoic spots above a specific intensity threshold. An ergonomic study without treatment, using human volunteers, was performed. The HIFU transducer, uterus, and pelvic structures were visualized in the ultrasound image. There was no patient discomfort when the device was placed in situ.The device was used to create lesions in vivo in sheep uterus. Gross and microscopic analysis was performed for 4 different time periods post-treatment. A full bladder and adequate transducer cooling were needed for a successful treatment. During treatment, lesions were visible as hyperechoic spots at HIFU intensities above 2200 W/cm2. HIFU treated areas were coagulative necrosis lesions consisting of a necrotic center surrounded by a ring of blood congestion. Over a period of 30 days, necrotic tissue was phagocytosed by macrophages, ablated myometrium was partially regenerated, and scar tissue formed in the treated area.Image-guided HIFU has the potential to become a minimally-invasive treatment option for women with symptomatic uterine fibroids.
Description: Thesis (Ph. D.)--University of Washington, 2003

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