In this continuing study SRI proposes to model, fabricate and validae ultrasound tissue-equivalent phantoms of the pig kidney. The thermal response of these phantoms during and after hyperthermic exposure to ultrasound will be compared with the results of modeling and of measuring the thermal response of the kidney in the anesthetized pig when it is heated by the same applicators. SRI will develop numerical models based on the bioheat transfer equation and its modified form that includes incomplete counter-current heat exchange in artery-vein pairs. The performance of a prototypical phantom will be predicted by each model using the finite difference technique and the known SAR pattern of an ultrasound applicator. The parameters of the models will be adjusted to approximate the measured response of the live pig kidney to hyperthermia induced by the same applicator. Conditions will be sought under which the predicted performance of the prototypical phantom differs in the two numerical models. If these conditions are physiologically significant, they will guide and constrain the design of the physical phantoms. In addition to providing data with which the performance of the phantoms can be compared, the further objective of the animal experiments to be performed at Stanford University is to quantify and evaluate the effects of varying blood flow on the three-dimensional temperature distributions induced by ultrasound in pig kidney. This information will be useful and necessary for the clinical application of ultrasound-induced localized hyperthermia to treatment of tumors of soft tissues in general and kidney tumors in particular. Temporal and spatial temperature profiles will be measured under conditions of normal and subnormal blood flow rates. Temperature distributions will be correlated with local blood flow rates and emitted ultrasonic power levels. SRI proposes to continue to develop new tissue-equivalent materials capable of simulating the ultrasonic energy absorptive and thermal transport of kidney cortex and to devise means of perfusing tissue-equivalent materials to simulate heat loss due to blood flow. Dynamic phantoms will then be fabricated and evaluated; temporal and spatial temperature profiles will be recorded during heating, steady-state, and cooling phases with known perfusate flow rates and temperatures and known ultrasonic power input. A microcomputer-based temperature monitoring system capable of monitoring 100 temperature sensors will be further refined to facilitate this study. Temperature distributions will also be determined my means of a thermographic camera. The resulting models, phantoms and new knowledge will provide means for evaluating the effectiveness of ultrasound applicators, will facilitate validation of computer models of hyperthermia, and thus will aid in treatment planning.
NIH ExPorter
NIH ExPorter