Purpose: Quantitative relaxometry in the abdomen is challenging due to respiratory, pulsative, and peristaltic motion. We present an implementation of free-breathing MR-fingerprinting and study improvements in image quality as a function of reconstruction.
Methods: The acquisition method relies on golden-angle radial sampling combined with a varying flip-angle (FA), gradient-spoiled, SSFP MRF sequence. The imaging sequence consists of an inversion pulse followed by the varying FA train and a delay time (Td) to allow for relaxation to thermal equilibrium. The exam parameters were: TR/TE/TI=8/4/15 ms, FOV=25x25cm2, matrix=224x224, and slice thickness=5mm. Two FA schedules were studied. The number of spokes/dynamic was varied in the range [1 2 3 4 5 10] while Td was varied in the range [0.1 1 10] seconds. Golden-angle radial sparse parallel (GRASP) reconstruction was implemented with total variation (tTV) or principal-component analysis (tPCA) as regularization functions in the temporal domain. Template matching was used for T1/T2 calculations. The quantitative maps derived from tTV-GRASP, tPCA-GRASP, and conventional gridding were compared using a NIST phantom with known T1/T2 values. Image quality was also compared in a healthy volunteer during a free-breathing (FB) and (BH) acquisition.
Results: The bias for T1 and T2 was comparable in parameters calculated with gridding and tTV-GRASP, and larger for tPCA-GRASP reconstructions. For T1, we find an approximately two-fold decrease in the standard deviation of maps calculated with tTV-GRASP compared to gridding and tPCA-GRASP. For T2, tTV-GRASP and tPCA-GRASP generated maps with comparable uncertainty but improved when compared to gridding. The improvements were dependent on the number of spokes/dynamic, Td, and FA schedule.
Conclusion: GRASP provides a feasible method for free-breathing MR-fingerprinting with improved image quality and reduced sensitivity to artifacts from physiologic motion.
Not Applicable / None Entered.