Time-efficient relaxation measurements by 31P MR fingerprinting in human brain at 7T

PurposeThe goal of the study is to develop 31P spectroscopic MRF at 7T to measure T1 and T2 relaxation times simultaneously and to compare time efficiency and test-retest reproducibility of MRF with conventional inversion recovery and multi-TE methods. MethodsA 31P MRF scheme was designed based on a balanced steady-state free precession type sequence. Dictionary was generated using the Bloch equations. B0 map was acquired experimentally and incorporated into the dictionary. 7 phantoms with different T1 and T2 relaxation times were prepared for MRF validation. Simulations were performed to evaluate estimation bias. 7 volunteers were scanned twice using both MRF and the conventional methods to evaluate the reproducibility. ResultsIn phantom measurements, T1 and T2 values between MRF and conventional methods demonstrated a good agreement with Pearsons correlation coefficients of 0.99 and 0.97, respectively. In in vivo experiments, estimated T1 by MRF were in good agreement with those measured by the inversion recovery and in the literature. On the other hand, estimated T2 values by MRF were shorter than those measured by the multi-TE method. 31P MRF method can reduce the acquisition time by 15 min providing less than 10% of mean CV for T1 estimations and less than 20% of mean CV for T2 estimations of metabolites. ConclusionOur results shows the feasibility of simultaneous T1 and T2 measurement of 31P metabolites in human brain using MRF at 7T. High reproducibility can be achieved especially for T1 measurement with 40% time reduction over conventional methods.