Optimizing the precision in T1 relaxation estimation using limited flip angles

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Abstract
In this article we describe the precision in the estimation of the spin–lattice relaxation time TI from MRI signals acquired for various flip angles with the repetition time TR held constant. We review the estimation procedure itself and present a model for the propagation of noise in the signal into the calculated TI. This model is verified by both Monte Carlo simulations and experimental data taken on image phantoms. Based on this model, we find that for a given TR/TI there exist two optimal flip angles that will minimize the uncertainty in the estimated TI. We also show how two optimal angles can be selected for a given range of TR/TI values. In addition, T1 estimation using the two optimal angles can be comparable to or better than using multiple evenly spaced angles. Finally, in an initial comparison with the two‐point saturation recovery method of calculating T1, results for equal total scanning time TRTot suggest that for T1 > 0.5 TRTot, the limited flip angle approach gives better TI precision whereas for TI < 0.5 TRTot, the saturation recovery approach is better. © Academic Press, Inc.