Low‐rank inversion reconstruction for through‐plane accelerated radial MR fingerprinting applied to relaxometry at 0. 35 T

Purpose To reduce scan time, methods to accelerate phase‐encoded/non‐Cartesian MR fingerprinting (MRF) acquisitions for variable density spiral acquisitions have recently been developed. These methods are not applicable to MRF acquisitions, wherein a single k‐space spoke is acquired per frame. Therefore, we propose a low‐rank inversion method to resolve MRF contrast dynamics from through‐plane accelerated Cartesian/radial measurements applied to quantitative relaxation‐time mapping on a 0.35T system. Methods An algorithm was implemented to reconstruct through‐plane aliased low‐rank images describing the contrast dynamics occurring because of the transient‐state MRF acquisition. T 1 and T 2 times from accelerated acquisitions were compared with those from unaccelerated linear reconstructions in a standardized system phantom and within in vivo brain and prostate experiments on a hybrid 0.35T MRI/linear accelerator. Results No significant differences between T 1 and T 2 times for the accelerated reconstructions were observed compared to fully sampled acquisitions ( p  = 0.41 and p  = 0.36, respectively). The mean absolute errors in T 1 and T 2 were 5.6% and 2.9%, respectively, between the full and accelerated acquisitions. The SDs in T 1 and T 2 decreased with the advanced accelerated reconstruction compared with the unaccelerated reconstruction ( p  = 0.02 and p  = 0.03, respectively). The quality of the T 1 and T 2 maps generated with the proposed approach are comparable to those obtained using the unaccelerated data sets. Conclusions Through‐plane accelerated MRF with radial k‐space coverage was demonstrated at a low field strength of 0.35 T. This method enabled 3D T 1 and T 2 mapping at 0.35 T with a 3‐min scan.