MULTI-parametric MR imaging with fLEXible design (MULTIPLEX)

Abstract

Purpose: To introduce a gradient echo (GRE) -based method, namely MULTIPLEX, for single-scan 3D multi-parametric MRI with high resolution, signal-to-noise ratio (SNR), accuracy, efficiency, and acquisition flexibility.

Theory: With a comprehensive design with dual-repetition time (TR), dual flip angle (FA), multi-echo, and optional flow modulation features, the MULTIPLEX signals contain information on radiofrequency (RF) B_1t fields, proton density, T₁ , susceptibility and blood flows, facilitating multiple qualitative images and parametric maps.

Methods: MULTIPLEX was evaluated on system phantom and human brains, via visual inspection for image contrasts and quality or quantitative evaluation via simulation, phantom scans and literature comparison. Region-of-interest (ROI) analysis was performed on parametric maps of the system phantom and brain scans, extracting the mean and SD of the T₁ , $T_2\ast$ , proton density (PD), and/or quantitative susceptibility mapping (QSM) values for comparison with reference values or literature.

Results: One MULTIPLEX scan offers multiple sets of images, including but not limited to: composited PDW/T₁ W/ $T_2\ast$ W, aT₁ W, SWI, MRA (optional), B_1t map, T₁ map, $T_2\ast$ / $R_2\ast$ maps, PD map, and QSM. The quantitative error of phantom T₁ , $T_2\ast$ and PD mapping were <5%, and those in brain scans were in good agreement with literature. MULTIPLEX scan times for high resolution (0.68 × 0.68 × 2 mm³ ) whole brain coverage were about 7.5 min, while processing times were <1 min. With flow modulation, additional MRA images can be obtained without affecting the quality or accuracy of other images.

Conclusion: The proposed MUTLIPLEX method possesses great potential for multi-parametric MR imaging.

Keywords: AFI; GRE; MDI; aT1W; multi-parametric; qMRI.