title: Biological and physical mechanisms of HIFU-induced hyperecho in ultrasound images.
abstract: Guidance and monitoring of high intensity focused ultrasound (HIFU) therapy, using ultrasound imaging, has primarily utilized formation of a hyperechoic region at the HIFU focus. We investigated biologic and physical mechanisms of a hyperecho, as well as safety of this phenomenon, using thermal, acoustic and light microscopy observations. Single, short-duration HIFU pulses (30-60 ms) were able to produce a hyperechoic region at the HIFU focus, 2 cm deep in a rabbit thigh muscle. When hyperechoic regions appeared, inertial cavitation was detected in vivo using a custom-made passive cavitation detection system. Light micrographs showed a large number of cavities (approximately 100/mm3), 1-10 microm in diameter, in a cytoplasm of cells located at the HIFU focus. Blood congestion was observed around a focal region, indicating an injury of microvasculature. Cellular necrosis was observed at 2 d after the treatment, while healing, scar tissue formation and regeneration were observed at 7 d and 14 d. The results indicate that a possibility of adverse tissue effects has to be taken into consideration when the hyperecho formation, induced by very-short HIFU pulses, is used for pretreatment targeting.
authors.affiliation: Department of Bioengineering, University of Washington, Seattle, WA, USA.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Rabkin
authors.forename: Vesna
authors.initials: V
authors.lastname: Zderic
authors.forename: Lawrence A
authors.initials: LA
authors.lastname: Crum
authors.forename: Shahram
authors.initials: S
authors.lastname: Vaezy
mesh_terms: D000162:Acoustics; D000818:Animals; D045423:Microbubbles; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging* / Q000473:pathology; D009336:Necrosis / Q000209:etiology; D011817:Rabbits; D013552:Swine; D013696:Temperature; D014464:Ultrasonic Therapy / Q000009:adverse effects / Q000379:methods*; D014463:Ultrasonography; D014945:Wound Healing