Super-resolution of sodium images from simultaneous 1H MRF/23Na MRI acquisition

In this work, we introduce a super-resolution method that generates a high-resolution (HR) sodium (Na-23) image from simultaneously acquired low-resolution (LR) Na-23 density-weighted MRI and HR proton density, T-1, and T-2 maps from proton (H-1) MR fingerprinting in the brain at 7 T. The core of our method is a partial least squares regression between the HR (H-1) images and the LR (Na-23) image. An iterative loop and deconvolution with the point spread function of each acquired image were included in the algorithm to generate a final HR Na-23 image without losing features from the LR Na-23 image. The method was applied to simultaneously acquired HR proton and LR sodium data with in-plane resolution ratios between sodium and proton data of 3.8 and 1.9 and the same slice thickness. Four volunteers were scanned to evaluate the method's performance. For the data with a resolution ratio of 3.8, the mean absolute difference between the generated and ground truth HR Na-23 images was in the range of 1.5%-7.2% of the ground truth with a multiscale structural similarity index (M-SSIM) of 0.93 +/- 0.03. For the data with a resolution ratio of 1.9, the mean absolute difference was in the range of 4.8%-6.3% with an M-SSIM of 0.95 +/- 0.01.