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

Optimization of inversion-recovery (IR) measurements of T1 relaxation times has focused on the efficiency of T1 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 T1 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 T1 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 T1 times relative to a given maximum T1.