Accelerated MP2RAGE imaging using Cartesian phyllotaxis readout and compressed sensing reconstruction

Purpose: MP2RAGE T₁ -weighted imaging has been shown to be beneficial for various applications, mainly because of its good grey-white matter contrast, its B₁ -robustness and ability to derive T₁ maps. Even using parallel imaging, the method requires long acquisition times, especially at high resolution. This work aims at accelerating MP2RAGE imaging using compressed sensing.

Methods: A pseudo-phyllotactic Cartesian MP2RAGE readout was implemented allowing for flexible reordering and undersampling factors. The sampling pattern was first optimized based on fully sampled data and a compressed sensing reconstruction. Changes in contrast ratios, automated brain segmentation results, and quantitative T₁ values were used for benchmarking. In vivo undersampled data from eleven healthy subjects were then acquired using a 4-fold acceleration with the optimized sampling pattern. The resulting images were compared to the standard parallel imaging MP2RAGE protocol by visual inspection and using the above quality metrics.

Results: The application of incoherent undersampling and iterative compressed sensing reconstruction on MP2RAGE acquisitions allows for a 57% time reduction (corresponding to 4-fold undersampling with maintained reference lines, TA = 3:35 minutes) compared to the reference protocol using parallel imaging (GRAPPAx3 acceleration, TA = 8:22 minutes) while obtaining images with similar image quality, morphometric (volume differences = [0.07 ± 1.2-3.8 ± 1.9]%) and T₁ -mapping outcomes (T₁ error = [6 ± 5.1-37 ± 12.3] ms depending on the different structures).

Conclusion: A whole-brain MP2RAGE acquisition is feasible with compressed sensing in less than 4 minutes without appreciably compromising image quality.