Simultaneous estimation of PD, T , T , T , and ∆B using magnetic resonance fingerprinting with background gradient compensation.

PURPOSE

This study aims to estimate PD, T , T , T , and B 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 T and T , respectively. Simulations are performed to determine the appropriate ratio of the FISP and SPGR sections with respect to the T and T accuracy. Additionally, background field inhomogeneity (G ) 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 G compensation.

RESULTS

The T , T , and T values from the phantom results are in good agreement with the reference methods under well-shimmed condition. The underestimated T and T values under poor-shimmed condition are recovered by G compensation and the parameters are also in good agreement with the reference methods. In the human brain, T and T values are restored by G 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 , T , T , and B . By incorporating field inhomogeneity as a gradient term into both the sequence and dictionary, T and T values can be restored where field inhomogeneity exists.