R. M. Arthur, W. L. Straube, J. W. Trobaugh and E. G. Moros, "In vivo change in ultrasonic backscattered energy with temperature
in motion-compensated images", Int. J. Hyperthermia, Vol. 24, No.5, pp. 389–398, 2008.

Abstract

Ultrasound is an attractive modality for non-invasive imaging to monitor temperature of tumorous regions undergoing hyperthermia therapy. 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 both 1D and 2D in in vitro studies. To corroborate those results in perfused, living tissue, we measured CBE in both normal tissue and in implanted human tumors (HT29 colon cancer line) in 7 nude mice. Images were formed by a phased-array imager with a 7.5 MHz linear probe during homogeneous heating from 37 to 45^oC in 0.5^oC steps and from body temperature to 43^oC during heterogeneous heating. 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 with a maximum value of 1mm across all specimens during homogeneous heating, and 0.2 mm during heterogeneous heating. 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. Means of both the positive and negative changes in the BE images were evaluated. CBE was monotonic and accumulated to 4–5 dB during homogeneous heating to 45^oC and 3–4 dB during heterogenous heating to 43^oC.  These results are consistent with our previous in vitro measurements and support the use of CBE for temperature estimation in vivo during hyperthermia.

Keywords:  Diagnostic ultrasound, hyperthermia, in vivo study, non-invasive 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.