Blip up‐down acquisition for spin‐ and gradient‐echo imaging (<scp>BUDA‐SAGE</scp>) with self‐supervised denoising enables efficient <scp>T₂</scp>, <scp>T₂</scp>*, para‐ and dia‐magnetic susceptibility mapping

Abstract

Purpose To rapidly obtain high resolution T 2 , T 2 *, and quantitative susceptibility mapping (QSM) source separation maps with whole‐brain coverage and high geometric fidelity. Methods We propose Blip Up‐Down Acquisition for Spin And Gradient Echo imaging (BUDA‐SAGE), an efficient EPI sequence for quantitative mapping. The acquisition includes multiple T 2 *‐, T 2 ′‐, and T 2 ‐weighted contrasts. We alternate the phase‐encoding polarities across the interleaved shots in this multi‐shot navigator‐free acquisition. A field map estimated from interim reconstructions was incorporated into the joint multi‐shot EPI reconstruction with a structured low rank constraint to eliminate distortion. A self‐supervised neural network (NN), MR‐Self2Self (MR‐S2S), was used to perform denoising to boost SNR. Using Slider encoding allowed us to reach 1 mm isotropic resolution by performing super‐resolution reconstruction on volumes acquired with 2 mm slice thickness. Quantitative T 2 (=1/R 2 ) and T 2 * (=1/R 2 *) maps were obtained using Bloch dictionary matching on the reconstructed echoes. QSM was estimated using nonlinear dipole inversion on the gradient echoes. Starting from the estimated R 2 /R 2 * maps, R 2 ′ information was derived and used in source separation QSM reconstruction, which provided additional para‐ and dia‐magnetic susceptibility maps. Results In vivo results demonstrate the ability of BUDA‐SAGE to provide whole‐brain, distortion‐free, high‐resolution, multi‐contrast images and quantitative T 2 /T 2 * maps, as well as yielding para‐ and dia‐magnetic susceptibility maps. Estimated quantitative maps showed comparable values to conventional mapping methods in phantom and in vivo measurements. Conclusion BUDA‐SAGE acquisition with self‐supervised denoising and Slider encoding enables rapid, distortion‐free, whole‐brain T 2 /T 2 * mapping at 1 mm isotropic resolution under 90 s.