Optimizing saturation-recovery measurements of the longitudinal relaxation rate under time constraints

Abstract

The saturation-recovery method using two and three recovery times is studied for conditions in which the sum of recovery times is 1.5T1 to 3T1, where T1 is the longitudinal relaxation time. These conditions can reduce scan time considerably for long T1 species and make longitudinal relaxation rate R1 (R1 = 1/T 1) mapping for body fluids clinically feasible. Monte Carlo computer simulation is carried out to determine the ideal set of recovery times under various constraints of the sum of recovery times. The ideal set is found to be approximately invariant to the signal-to-noise ratio. For the three-point method, two of the recovery times should be set the same or approximately the same and should be shorter than the third one. Only marginal improvements in accuracy and precision can be achieved by the three-point method over the two-point method under a common constraint of the sum of recovery times. Three-dimensional, high resolution, whole-brain saturation-recovery scans on volunteers with a fast-spin-echo technique (XETA) and completed in a scan time of 10 min generated R1 measurements of cerebrospinal fluid (T 1 ∼ 4 s) in agreement with the computer simulation and literature results, which demonstrates the clinical feasibility of applying the twopoint saturation-recovery method for R1 mapping for long relaxation components. © 2009 Wiley-Liss, Inc.