title: The concentric-ring phased-array hyperthermia applicator: problems associated with directly synthesized annular heating patterns.
abstract: The authors investigate the synthesis of different size annular patterns and examine the relative intensities produced in the ultrasonic field proximal and distal to the focal plane. Computer simulations using a concentric-ring array are presented and discussed. The size and position of the synthesized annular patterns are varied by adjusting the phase and amplitude of the driving signal to each array element. It is demonstrated that annular patterns need to be larger than a limiting size (R(s)) to avoid excessive energy accumulation along the array axis. Analysis and computer simulations demonstrate that smaller size annual patterns (r</=R(s)) are always associated with intense hot spots along the axis (beyond the focal plane). On the other hand, simulated temperature distributions associated with large patterns (r>/=R(s)) show that while therapeutic temperatures are reached at the periphery, the tumor center temperature cannot be evenly raised.
authors.affiliation: Bioacoustics Res. Lab., Illinois Univ., Urbana, IL.
authors.forename: M S
authors.initials: MS
authors.lastname: Ibbini
authors.forename: C A
authors.initials: CA
authors.lastname: Cain