Accelerated 3D metabolite T 1 mapping of the brain using variable‐flip‐angle SPICE

Purpose To develop a practical method to enable 3D T 1 mapping of brain metabolites. Theory and Methods Due to the high dimensionality of the imaging problem underlying metabolite T 1 mapping, measurement of metabolite T 1 values has been currently limited to a single voxel or slice. This work achieved 3D metabolite T 1 mapping by leveraging a recent ultrafast MRSI technique called SPICE (spectroscopic imaging by exploiting spatiospectral correlation). The Ernst‐angle FID MRSI data acquisition used in SPICE was extended to variable flip angles, with variable‐density sparse sampling for efficient encoding of metabolite T 1 information. In data processing, a novel generalized series model was used to remove water and subcutaneous lipid signals; a low‐rank tensor model with prelearned subspaces was used to reconstruct the variable‐flip‐angle metabolite signals jointly from the noisy data. Results The proposed method was evaluated using both phantom and healthy subject data. Phantom experimental results demonstrated that high‐quality 3D metabolite T 1 maps could be obtained and used for correction of T 1 saturation effects. In vivo experimental results showed metabolite T 1 maps with a large spatial coverage of 240 × 240 × 72 mm 3 and good reproducibility coefficients (< 11%) in a 14.5‐min scan. The metabolite T 1 times obtained ranged from 0.99 to 1.44 s in gray matter and from 1.00 to 1.35 s in white matter. Conclusion We successfully demonstrated the feasibility of 3D metabolite T 1 mapping within a clinically acceptable scan time. The proposed method may prove useful for both T 1 mapping of brain metabolites and correcting the T 1 ‐weighting effects in quantitative metabolic imaging.