3D multi-phase balanced non-steady-state free precession acquisition for multi-parameter mapping.

Abstract

Objective: This study presents the 3D MP-b-nSSFP sequence for multi-parametric mapping.

Methods: We evaluate several aspects of the 3D implementation, like the type of RF pulse (selective/non-selective), the readout duration, the undersampling pattern, and the acceleration factor. We use undersampled scans with subspace-constrained reconstruction and extended spiral readouts to achieve clinically acceptable scan times. The repeatability and accuracy of the $T_1$ and $T_2$ maps are compared with a reference technique in phantom and three volunteer scans.

Results: Compared with selective refocusing pulses, we observe lower bias with non-selective pulses, despite modeling the spatially varying effect of the pulses in the fitting process. $T_1$ and $T_2$ maps obtained from phantom scans were comparable to the nominal values and those from reference scans. $T_1$ values in vivo were underestimated compared to the reference scan. The maps with an acquisition matrix of $256\times 256\times 44$ and resolution $1\times 1\times 3$ ${\text{mm}}^3$ were acquired in 11 min.

Conclusion: We show that 3D MP-b-nSSFP can be used for multi-parameter mapping within clinically acceptable scan time. Phantom scans show results in good agreement with reference scan results. However, the in vivo scan underestimated $T_1$ .