Optimized precision of inversion-recovery T1 measurements for constrained scan time

Optimization of inversion-recovery (IR) measurements of T, relaxation times has focused on the efficiency of T-1 estimation (precision per unit time), without explicit consideration of the total experimental time. With the modified fast IR method, the repetition time (TR) is constant and each inversion time (TI) must be less than TR. For a fixed total experimental time in the absence of signal averaging, TR and the longest TI time must decrease as more TI times are added. This article investigates the number of TI times and their values to optimize the precision of T-1 measurements when time constraints preclude signal averaging and limit the largest TI that can be acquired. If the longest TI is less than approximately three times the longest T-1 of interest, then precision is optimum with only four TI times. Suggestions are given for selecting the optimum TI times for 1-16-fold ranges of T-1 times relative to a given maximum T-1. (C) 2004Wiley-Liss, Inc.