DESIGN AND OPTIMIZATION OF AN APERIODIC ULTRASOUND PHASED-ARRAY FOR INTRACAVITARY PROSTATE THERMAL THERAPIES

A 57 element aperiodic linear phased array was designed and constructe d to investigate the feasibility of using transrectal ultrasound for t he thermal therapeutic treatment of prostate cancer and benign prostat ic hyperplasia. A method of reducing grating lobe levels by using opti mized random distributions of unequally sized elements is introduced. Using this technique, array periodicity is avoided, making it feasible to use larger elements and hence fewer elements and amplifier channel s, while still achieving acceptable power field patterns. Acoustic pow er field simulations determined that the grating lobe levels associate d with selected aperiodic element distributions were approximately 30% -45% less than those associated with periodic element spacing and the same average element width. Or by using aperiodic rather than periodic element distributions, the average element width could be increased b y approximately 20%-35% (similar to lambda/4.4), while maintaining a c onstant grating lobe level. Prior to construction of the 57 element ar ray, the power capabilities of this type of array were demonstrated wi th a 16 element aperiodic phased array, which delivered over 28 W of a coustical power per cm of array length while focused. The power field patterns produced by the 57 element array closely matched the field pa tterns predicted by the theoretical model used in the simulations. The array produced acceptable power field patterns for foci at depths up to 5 cm and up to 2 cm off the center axis, in addition to producing m ultiple foci simultaneously. Based on the power capabilities and field patterns, this aperiodic array design has the potential to be incorpo rated into a clinical heating device as a means of delivering thermal therapies to the prostate and other target volumes close to body cavit ies. (C) 1996 American Association of Physicists in Medicine.