MR fingerprinting with simultaneous T1, T2, and fat signal fraction estimation with integrated B0 correction reduces bias in water T1 and T2 estimates

Purpose: MR fingerprinting (MRF) sequences permit efficient T-1 and T-2 estimation in cranial and extracranial regions, but these areas may include substantial fat signals that bias T-1 and T-2 estimates. MRI fat signal fraction estimation is also a topic of active research in itself, but may be complicated by B-0 heterogeneity and blurring during spiral k-space acquisitions, which are commonly used for MRF. An MRF method is proposed that separates fat and water signals, estimates water T-1 and T-2, and accounts for B-0 effects with spiral blurring correction, in a single sequence. Theory and methods: A k-space-based fat-water separation method is further extended to unbalanced steady-state free precession MRF with swept echo time. Repeated application of this k-space fat-water separation to demodulated forms of the measured data allows a B-0 map and correction to be approximated. The method is compared with MRF without fat separation across a broad range of fat signal fractions (FSFs), water T(1)s and T(2)s, and under heterogeneous static fields in simulations, phantoms, and in vivo. Results: The proposed method's FSF estimates had a concordance correlation coefficient of 0.990 with conventional measurements, and reduced biases in the T-1 and T-2 estimates due to fat signal relative to other MRF sequences by several hundred ms. The B-0 correction improved the FSF, T-1, and T-2 estimation compared to those estimates without correction. Conclusion: The proposed method improves MRF water T-1 and T-2 estimation in the presence of fat and provides accurate FSF estimation with inline B-0 correction.