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In this work, we propose a free-breathing magnetic resonance fingerprintingmethod that can be used to obtain $B_1^+$-robust quantitative maps of theabdomen in a clinically acceptable time. A three-dimensional MR fingerprintingsequence with a radial stack-of-stars trajectory was implemented forquantitative abdominal imaging. The k-space acquisition ordering was adjustedto improve motion-robustness. The flip angle pattern was optimized using theCram\'er-Rao Lower Bound, and the encoding efficiency of sequences with 300,600, 900, and 1800 flip angles was evaluated. To validate the sequence, amovable multicompartment phantom was developed. Reference multiparametric mapswere acquired under stationary conditions using a previously validated MRFmethod. Periodic motion of the phantom was used to investigate themotion-robustness of the proposed sequence. The best performing sequence length(600 flip angles) was used to image the abdomen during a free-breathingvolunteer scan. When using a series of 600 or more flip angles, the estimated$T_1$ values in the stationary phantom showed good agreement with the referencescan. Phantom experiments revealed that motion-related artefacts can appear inthe quantitative maps, and confirmed that a motion-robust k-space ordering isessential in preventing these artefacts. The in vivo scan demonstrated that theproposed sequence can produce clean parameter maps while the subject breathesfreely. Using this sequence, it is possible to generate $B_1^+$-robustquantitative maps of proton density, $T_1$, and $B_1^+$ under free-breathingconditions at a clinically usable resolution within 5 minutes.

Optimization of MR Fingerprinting for Free-Breathing Quantitative Abdominal Imaging