Simultaneous estimation of PD, T1, T2, T2*, and ΔB0 using magnetic resonance fingerprinting with background gradient compensation

Purpose: This study aims to estimate PD, T-1, T-2, T-2*, and Delta B-0 simultaneously using magnetic resonance fingerprinting (MRF) with compensation of the linearly varying background field. Methods: MRF based on fast imaging with steady-state precession (FISP) and multi-echo spoiled gradient (SPGR) schemes are alternatively used, which encode T2 and T-2*, respectively. Simulations are performed to determine the appropriate ratio of the FISP and SPGR sections with respect to the T-2 and T-2* accuracy. Additionally, background field inhomogeneity (G(z)) compensation using z-shim gradients are incorporated into the SPGR section and the dictionary. The background field compensation is tested in the phantom experiment under well-shimmed and poor-shimmed conditions. An in vivo experiment is performed and the estimated parameters are compared before and after Gz compensation. Results: The T-1, T-2, and T-2* values from the phantom results are in good agreement with the reference methods under well-shimmed condition. The underestimated T-2 and T-2* values under poor-shimmed condition are recovered by Gz compensation and the parameters are also in good agreement with the reference methods. In the human brain, T-2 and T-2* values are restored by Gz compensation in regions where the magnetic field is particularly inhomogeneous, such as near the sinus and ear canals. Conclusions: The proposed FISP and SPGR combined MRF provides a simultaneous estimation of PD, T-1, T-2, T-2*, and Delta B-0. By incorporating field inhomogeneity as a gradient term into both the sequence and dictionary, T-2 and T-2* values can be restored where field inhomogeneity exists.