Accelerating Parameter Mapping with a Locally Low Rank Constraint

PurposeTo accelerate MR parameter mapping using a locally low rank (LLR) constraint, and the combination of parallel imaging and the LLR constraint. Theory and MethodsAn LLR method is developed for MR parameter mapping and compared with a globally low rank method in a multiecho spin-echo T-2 mapping experiment. For acquisition with coil arrays, a combined LLR and parallel imaging method is proposed. The proposed method is evaluated in a variable flip angle T-1 mapping experiment and compared with the LLR method and parallel imaging alone. ResultsIn the multiecho spin-echo T-2 mapping experiment, the LLR method is more accurate than the globally low rank method for acceleration factors 2 and 3, especially for tissues with high T-2 values. Variable flip angle T-1 mapping is achieved by acquiring datasets with 10 flip angles, each dataset accelerated by a factor of 6, and reconstructed by the proposed method with a small normalized root mean square error of 0.025. ConclusionsThe LLR method is likely superior to the globally low rank method for MR parameter mapping. The proposed combined LLR and parallel imaging method has better performance than the two methods alone, especially with highly accelerated acquisition. Magn Reson Med 73:655-661, 2015. (c) 2014 Wiley Periodicals, Inc.