William L. Straube, R. Martin Arthur, and Jason W. Trobaugh, "Noninvasive Temperature Monitoring Using Change in Backscattered Energy for Clinically Relevant Heating Scenarios", Proceedings 2007 Annual Meeting of the Society for Thermal Heating, Bethesda, MD, 6-8 April 2006, p. 40.

Abstract

Background: We have previously shown that the change in backscattered ultrasound energy (CBE) from heated tissue tracks with temperature and shows promise for utilization as a method for non-invasively monitoring thermal therapies. The heating methodology we have used until now, however, has been water baths that allow uniform heating of in vitro or in vivo tissues. This set up is not clinically relevant as patients are heated with local devices that induce considerable temperature heterogeneity.
Methods: In order to move to a more realistic heating set up we have looked into coupling CBE measuring devices (Terason 3000, Teratech Corp.) with clinically relevant devices that produce heterogeneous heating: the Small Animal Heating Ultrasound System (SAHUS) and a clinical ultrasound heating system, the Sonotherm 1000 (Labthermics Technologies, Inc.). The coupling of the CBE measurement device to tissue samples or patients is complicated by maintaining a water path between tissue, the measurement device and the heating device. Also, ultrasound from the heating devices causes interference in the CBE measurement data. This noise must be filtered from data in order to analyze CBE during heating.
Results: Using either orthogonal or oblique angles between the direction of the interrogating ultrasound beam for CBE measurement and the ultrasound beam used for heating we have been able to image and analyze data measured during the heating of tissue in living mice (SAHUS) and a human (Sontherm 1000). Interference from the heating ultrasound can be partially filtered from CBE data to reduce noise from stray ultrasound. Interference was reduced by 50 dB from RF CBE data collected while heating with the Sonotherm, a device which produces continuous square waves. Data collected from narrow band continuous wave sinusoidal devices such as the SAHUS should be easier to filter and analyze. Measurements and analysis with the Sonotherm and SAHUS on tissue samples will be presented.
Conclusions: This work is a significant step towards experimentation which will further the measurement of CBE in clinically relevant heating scenarios.

Support: R21-CA90531, R01-CA107558 from NIH and the Wilkinson Trust at Washington University in St. Louis.