Two-point method for T-2 estimation with optimized gradient-echo sequence

Relaxation times estimation methods play a central role in various problems , such as magnetic resonance (MR) hardware calibration, tissue characteriza tion, or temperature measurement. Previous studies have proposed optimizati on criteria to estimate the relaxation time T-1 faster than with a multipoi nt method leading to two-point methods. In this paper, the class of optimiz ed two-point methods is extended to gradient-echo (GE) sequence offering ne w advantages over spin-echo (SE) or inversion recovery (IR) sequences. Two GE acquisitions, with optimal flip angles theta 1 and theta 2 minimizing bo th the total scan time and the variance in the computed T-1 image were appl ied to estimate T-1, and the results were compared with those of SE sequenc e,vith optimized paired repetition times T-R1 and T-R2. First, phantom stud ies were carried out with five tissue-like samples on a 0.5 T scanner. Then in vivo, human brain T-1 image were calculated using both optimized GE and SE two-point methods. More precise T-1 GE estimates than those for SE were found thanks to high signal-to-noise ratio (SNR) per unit of time, but wit h a small bias. These results also concern the temperature variation measur ement methods, based on T-1 estimation. Preliminary experimental data for t emperature measurement are given. (C) 1999 Elsevier Science Inc.