Fast and accurate T2 mapping using Bloch simulations and low-rank plus sparse matrix decomposition

Abstract

Purpose: MRI's T₂ relaxation time is one of the key contrast mechanisms for clinical diagnosis and prognosis of pathologies. Mapping this relaxation time, however, involves extensive scan times, which are needed to collect quantitative data, thereby impeding its integration into clinical routine. This study employs a low-rank plus sparse (L + S) signal decomposition approach in order to reconstruct accurate T₂-maps from highly undersampled multi-echo spin-echo (MESE) MRI data.

Methods: Two new algorithms are presented: the first uses standard L + S approach, where both L and S are iteratively updated. The second technique, dubbed SPArse and fixed RanK (SPARK), uses a fixed-rank L, under the assumption that most MESE information is found in the L component and that this rank can be pre-calculated. The utility of these new techniques is demonstrated on in vivo brain and calf data at x2 to x6 acceleration factors.

Results: Accelerated T₂ maps showed improved accuracy compared to fully sampled ground truth maps, when using L + S and SPARK techniques vis-à-vis standard GRAPPA acceleration.

Conclusion: SPARK provides accurate T₂ maps with increased robustness to the selection of reconstruction parameters making it suitable to a wide range of applications and facilitating the use of quantitative T₂ information in clinical settings.

Keywords: Accelerated MRI; L + S; Model-based reconstruction; Quantitative MRI; Relaxation; T(2)-mapping.