T1 relaxation time at 0.2 Tesla for monitoring regional hyperthermia: Feasibility study in muscle and adipose tissue

Abstract

The purpose of this study was to characterize T1, particularly in the hyperthermia temperature range (ca. 37-44°C), in order to control regional hyperthermia with MR monitoring using 0.2 Tesla, and to improve T1 mapping. A single-slice and a new multislice "T One by Multiple Read-Out Pulses" (TOMROP) pulse sequence were used for fast T1 mapping in a clinical MRI hyperthermia hybrid system. Temporal stability, temperature sensitivity, and reversibility of T1 were investigated in a polyamidacryl gel phantom and in samples of muscle and adipose tissues from turkey and pig, and verified in patients. In the gel phantom a high linear correlation between T1 and temperature (R2 = 0.97) was observed. In muscle and adipose tissue, T1 and temperature had a linear relationship below a breakpoint of 43°C. Above this breakpoint muscle tissue showed irreversible tissue changes; these effects were not visible in adipose tissue. The ex vivo results were confirmed in vivo under clinical conditions. T1 mapping allows the characterization of hyperthermia-related tissue response in healthy tissue. T1, in combination with fast mapping, is suitable for controlling regional hyperthermia at 0.2 T within the hybrid system. © 2002 Wiley-Liss, Inc.