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Title:Analysis of Power Deposition Patterns and Ultrasonic Phased Arrays for Localized Hyperthermia
Author(s):Ocheltree, Kenneth Blair
Department / Program:Electrical Engineering
Discipline:Electrical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Electronics and Electrical
Abstract:This thesis examines theoretically the determination of the desired power deposition pattern for localized hyperthermic treatment and the potential for providing precision local hyperthermia by using ultrasonic phased arrays. A method for calculating ultrasonic fields and examples of field patterns produced by square ultrasonic sources are presented. Temperature distributions are calculated from power deposition patterns by using a finite difference solution to the bioheat transfer equation. The combination of these two methods allows calculation of temperature distributions produced by a given applicator design.
The power deposition patterns that are required to uniformly raise (and maintain) the temperature throughout the tumor to hyperthermic levels are examined. A method is discussed which uses the steady state bioheat transfer equation and the desired temperature distribution in normal and tumor tissues to calculate the desired steady state power deposition pattern. This approach is demonstrated analytically for half-space, cylindrical, and spherical tumor models. Transient power deposition patterns are derived from the time dependent bioheat transfer equation, and analytical solutions are developed for half-space and spherical tumor models. A three dimensional numerical method is presented which allows calculation of time dependent power deposition patterns for arbitrarily shaped tumors.
A method is discussed which uses the steady state bioheat transfer equation and the desired temperature distributions in normal and tumor tissues to aid in ferromagnetic seed placement and ultrasonic scan path determination. Methods for forming the required power deposition patterns using practical hyperthermia systems are examined. The design considerations for an ultrasonic hyperthermia phased array are discussed.
An examination is made of an ultrasonic stacked linear phased array applicator for hyperthermia designed for deep heating. The power deposition pattern for this applicator is compared to that for a fixed focus applicator for a circular scan path. The high intensity necessary for generating hyperthermia by scanning a focal region and the large number of focal locations required to cover a typical tumor volume limit the applicability of phased array focal scanning. A method is presented for producing enlarged foci with a phased array so that the required number of scan locations is significantly reduced.
Issue Date:1987
Description:227 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1987.
Other Identifier(s):(UMI)AAI8721727
Date Available in IDEALS:2014-12-15
Date Deposited:1987

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