Accelerated T2 mapping combining parallel MRI and model-based reconstruction: GRAPPATINI

Abstract

Background: Quantitative T₂ measurements are sensitive to intra- and extracellular water accumulation and myelin loss. Therefore, quantitative T₂ promises to be a good biomarker of disease. However, T₂ measurements require long acquisition times.

Purpose: To accelerate T₂ quantification and subsequent generation of synthetic T₂ -weighted (T₂ -w) image contrast for clinical research and routine. To that end, a recently developed model-based approach for rapid T₂ and M₀ quantification (MARTINI) based on undersampling k-space, was extended by parallel imaging (GRAPPA) to enable high-resolution T₂ mapping with access to T₂ -w images in less than 2 minutes acquisition time for the entire brain.

Study type: Prospective cross-sectional study.

Subjects/phantom: Fourteen healthy subjects and a multipurpose phantom.

Field strength/sequence: Carr-Purcell-Meiboom-Gill sequence at a 3T scanner.

Assessment: The accuracy and reproducibility of the accelerated T₂ quantification was assessed. Validations comprised MRI studies on a phantom as well as the brain, knee, prostate, and liver from healthy volunteers. Synthetic T₂ -w images were generated from computed T₂ and M₀ maps and compared to conventional fast spin-echo (SE) images.

Statistical tests: Root mean square distance (RMSD) to the reference method and region of interest analysis.

Results: The combination of MARTINI and GRAPPA (GRAPPATINI) lead to a 10-fold accelerated T₂ mapping protocol with 1:44 minutes acquisition time and full brain coverage. The RMSD of GRAPPATINI increases less (4.3%) than a 10-fold MARTINI reconstruction (37.6%) in comparison to the reference. Reproducibility tests showed low standard deviation (SD) of T₂ values in regions of interest between scan and rescan (<0.4 msec) and across subjects (<4 msec).

Data conclusion: GRAPPATINI provides highly reproducible and fast whole-brain T₂ maps and arbitrary synthetic T₂ -w images in clinically compatible acquisition times of less than 2 minutes. These abilities are expected to support more widespread clinical applications of quantitative T₂ mapping.

Level of evidence: 2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2018;48:359-368.

Keywords: T2 mapping; model-based reconstruction; parametric mapping; quantitative MRI.