title: HIFU focusing efficiency and a twin annular array source for prostate treatment.
abstract: A measure of focusing efficiency is introduced for high-intensity, focused ultrasound (HIFU). The measure consists of the fraction of the total acoustic power emitted that linearly propagates through a circle located at the focus. The medium is absorption-free water, and power is computed using pressure and the normal component of velocity. 3 MHz phased-array designs involving different element layouts and curvatures are placed in square apertures of length 2.2 cm. The acoustic fields of these devices then are propagated to on-axis foci. The resulting focal efficiencies then are calculated using a two wavelength (0.1 cm) radius circle. Among these array designs, an annular array with 27 wavelength-wide rings then is extended to be the basis of a twin phased-array device for prostate hyperthermia treatment. The two annular arrays are attached to door-like hinges to allow for joint two-dimensional focusing. The focusing efficiency of this device then is compared to rectangular element-array devices with the same 5.4 by 2.2 cm source extent. With the addition of absorption and finite-amplitude distortion, the heating rate and temperature rise produced by the twin annular device in prostate tissue is considered. As a final look at the potential of annular array-based designs, three larger 2 MHz devices are briefly considered for abdominal treatment.
authors.affiliation: tchrist7@rochester.rr.com
authors.forename: Ted
authors.initials: T
authors.lastname: Christopher
mesh_terms: D003198:Computer Simulation; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D008297:Male; D008954:Models, Biological; D011471:Prostatic Neoplasms / Q000503:physiopathology* / Q000628:therapy*; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods; D012542:Scattering, Radiation; D014159:Transducers; D014464:Ultrasonic Therapy / Q000295:instrumentation* / Q000379:methods