T1 and T2 temperature dependence of female human breast adipose tissue at 1.5 T: groundwork for monitoring thermal therapies in the breast

The T-1 and T-2 temperature dependence of female breast adipose tissue was investigated at 1.5 T in order to evaluate the applicability of relaxation-based MR thermometry in fat for the monitoring of thermal therapies in the breast. Relaxation times T-1, T-2 and T-2TSE (the apparent T-2 measured using a turbo spin echo readout sequence) were measured in seven fresh adipose breast samples for temperatures from 25 to 65 degrees C. Spectral water suppression was used to reduce the influence of the residual water signal. The temperature dependence of the relaxation times was characterized. The expected maximum temperature measurement errors based on average calibration lines were calculated. In addition, the heating-cooling reversibility was investigated for two samples. The T-1 and T-2TSE temperature (T) dependence could be fitted well with an exponential function of 1/T. A linear relationship between T-2 and temperature was found. The temperature coefficients (mean +/- inter-sample standard deviation) of T-1 and T-2TSE increased from 25 degrees C (dT(1)/dT = 5.35 +/- 0.08 ms/degrees C, dT(2TSE)/dT = 3.82 +/- 0.06 ms/degrees C) to 65 degrees C (dT(1)/dT = 9.50 +/- 0.16 ms/degrees C, dT(2TSE)/dT = 7.99 +/- 0.38 ms/degrees C). The temperature coefficient of T-2 was 0.90 +/- 0.03 ms/degrees C. The temperature-induced changes in the relaxation times were found to be reversible after heating to 65 degrees C. Given the small inter-sample variation of the temperature coefficients, relaxation-based MR thermometry appears to be feasible in breast adipose tissue, and may be used as an adjunct to proton resonance frequency shift (PRFS) thermometry in aqueous tissue (glandular + tumor). Copyright (c) 2015 John Wiley & Sons, Ltd.