R. M. Arthur, W. L. Straube, J. W. Trobaugh and E. G. Moros, "3D In Vitro Estimation of Temperature Using the Change in Backscattered Ultrasonic Energy", IEEE Transactions on UFFC, in review.
Temperature imaging with a noninvasive modality to monitor the heating of tumors during hyperthermia treatment is an attractive alternative to sparse invasive measurement. Previously, we predicted monotonic changes in backscattered energy (CBE) of ultrasound with temperature for certain sub-wavelength scatterers. We also measured CBE values similar to our predictions in bovine liver, turkey breast muscle, and pork rib muscle in two-dimensional in vitro studies and in nude mice during 2D in vivo studies. To extend these studies to three dimensions, we compensated for motion and measured CBE in turkey breast muscle. 3D datasets were assembled from images formed by a phased-array imager with a 7.5 MHz linear probe moved in 0.6 cm steps in elevation during uniform heating from 37 to 45oC in 0.5oC increments. We used cross-correlation as a similarity measure in RF signals to automatically track feature displacement as a function of temperature. Feature displacement was non-uniform. Envelopes of image regions, compensated for non-rigid motion, were found with the Hilbert transform then smoothed with a 3x3 running average filter before forming the backscattered energy at each pixel. CBE in 3D motion-compensated images was nearly linear with an average sensitivity of 0.30 dB/oC. 3D estimation of temperature in separate tissue regions had errors with a maximum standard deviation of about 0.5oC with a 1 cm3 spatial resolution. Success of CBE temperature estimation based on 3D non-rigid tracking and compensation for real and apparent motion of image features could serve as the foundation for the eventual generation of 3D temperature maps in soft tissue in a noninvasive, convenient, and low-cost way in clinical hyperthermia.
Keywords: Diagnostic ultrasound,
hyperthermia, motion compensation, temperature imaging, ultrasonic thermometry
Support: National Institutes of Health grants R01-CA107588 and R21-CA90531 from the National Cancer Institute and the Wilkinson Trust at Washington University in St. Louis.