OPTIMUM FLIP-ANGLES FOR EXCITING NMR WITH UNCERTAIN T-1 VALUES

T-1 is often ill-determined. This means that an Ernst angle excitation often cannot be precisely defined for the simple pulse and acquire experiment. Here, published P-31 T-1 values of metabolites in human muscle, liver, heart, and brain are archived, some new data on heart and brain added, and overall confidence intervals determined. Strategies for setting the flip-angle based on the confidence intervals are examined, and an optimum flip-angle derived which minimizes the signal loss relative to what could have been realized if T-1 were precisely known. With such optimized pulses, signal loss can be limited to less than or equal to 14% for up to a 10-fold variation in T-1, with TR less than or equal to T-1. The effect that an uncertainty in T-1 by a factor of two has on the saturation corrected signal is limited to less than or equal to 20% in the optimum flip-angle experiment. Adiabatic B-1-independent rotation phase-cycled (BIRP) excitation pulses are ideal as optimum flip-angle pulses as they can be prescribed without calibration.