Investigation of proton density for measuring tissue temperature

Abstract

To examine the temperature dependence of the proton density (PD) in both adipose and muscle tissues, and the application of the PD as a thermometry parameter in breast tissues. Porcine fat samples and bovine muscle samples were successively heated to temperatures ranging from 30 degrees C to 76 degrees C and then cooled. They were then imaged with a dual-echo spin-echo sequence. T1 and T2 effects were carefully corrected from the images. The apparent PD (APD) in regions of interest (ROIs) and the sum of the APD in all pixels (Sum_APD) were measured and analyzed by linear regression. APD in adipose tissue is linear and reversible, and changes with a 0.3%/ degrees C to 0.45%/ degrees C temperature variation. The temperature coefficient of Sum_APD in adipose tissue is approximately 0.29%/ degrees C, as predicted from the Boltzmann distribution. However, the results in muscle tissue are more variable. There is an offset in both APD and Sum_APD between heating and cooling phases, as well as different temperature coefficients between these two phases. The Sum_APD in adipose tissue validates the 1/T dependence on temperature. The APD is a potentially useful parameter for fat thermometry; however, its application in muscle tissue requires further investigation.