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

Quantitative T <sub>2</sub> measurements are sensitive to intra- and extracellular water accumulation and myelin loss. Therefore, quantitative T <sub>2</sub> promises to be a good biomarker of disease. However, T <sub>2</sub> measurements require long acquisition times. To accelerate T <sub>2</sub> quantification and subsequent generation of synthetic T <sub>2</sub> -weighted (T <sub>2</sub> -w) image contrast for clinical research and routine. To that end, a recently developed model-based approach for rapid T <sub>2</sub> and M <sub>0</sub> quantification (MARTINI) based on undersampling k-space, was extended by parallel imaging (GRAPPA) to enable high-resolution T <sub>2</sub> mapping with access to T <sub>2</sub> -w images in less than 2 minutes acquisition time for the entire brain. Prospective cross-sectional study. Fourteen healthy subjects and a multipurpose phantom. Carr-Purcell-Meiboom-Gill sequence at a 3T scanner. The accuracy and reproducibility of the accelerated T <sub>2</sub> quantification was assessed. Validations comprised MRI studies on a phantom as well as the brain, knee, prostate, and liver from healthy volunteers. Synthetic T <sub>2</sub> -w images were generated from computed T <sub>2</sub> and M <sub>0</sub> maps and compared to conventional fast spin-echo (SE) images. Root mean square distance (RMSD) to the reference method and region of interest analysis. The combination of MARTINI and GRAPPA (GRAPPATINI) lead to a 10-fold accelerated T <sub>2</sub> 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 T <sub>2</sub> values in regions of interest between scan and rescan (<0.4 msec) and across subjects (<4 msec). GRAPPATINI provides highly reproducible and fast whole-brain T <sub>2</sub> maps and arbitrary synthetic T <sub>2</sub> -w images in clinically compatible acquisition times of less than 2 minutes. These abilities are expected to support more widespread clinical applications of quantitative T <sub>2</sub> mapping. 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018