Simultaneous estimation of PD, T 1 , T 2 , T 2 * , and ∆B 0 using magnetic resonance fingerprinting with background gradient compensation.

Purpose: This study aims to estimate PD, T ₁ , T ₂ , T ₂ ^* , and Δ 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 T ₂ 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 G _z 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 G _z 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 G _z 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 Δ 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.
(© 2018 International Society for Magnetic Resonance in Medicine.)