R. M. Arthur, W. L. Straube and E. G. Moros, "Noninvasive Temperature Estimation Based on the Energy of Backscattered Ultrasound", Invited Talk, Proceedings of the 20th Annual Meeting of the North American Hyperthermia Society (NAHS), Reno, Nevada, April, 2002.

Abstract

A noninvasive method for volumetrically determining temperature distribution during treatment would greatly enhance the ability to uniformly heat tumors at therapeutic levels.  Ultrasound is an attractive modality for this purpose.  We investigated changes in backscattered energy (CBE) with temperature from tissue inhomogeneities in the form of small (subwavelength) scatterers.  Our predicted changes in backscattered energy were matched by in vitro measurements in bovine liver samples.  We examined the results of studying CBE in tissue regions with multiple scatterers, of isolated individual scatterers, and in collections of individual scatterers.  The latter appears to have the most potential.  We measured the CBE from 37 to 50 ^oC with a focused circular transducer with a center frequency of 7.5 MHz.  The standard deviation of the CBE of 120 scatterers from 4 bovine liver samples increased nearly monotonically with temperature.  The curve was well matched by a second-degree polynomial, which had a correlation coefficient of 0.998.  The 120 scatterers came from 24 sites that were contained in a total insonified volume of less than 1 cm³.  These results suggest our approach may be capable of 0.5 ^oC accuracy and 1 cm³ resolution conveniently and at low cost.  Because our approach exploits the inhomogeneities present in tissue, we believe that if it is successful in vitro, it holds promise for in vivo application.

Supported in part by NIH R21 CA90531