Cardiac MR Fingerprinting at 0.55T Using a Deep Image Prior for Joint T1, T2, and M0 Mapping.

BACKGROUND: 0.55T systems offer unique advantages and may support expanded access to cardiac MRI. PURPOSE: To assess the feasibility of 0.55T cardiac MR Fingerprinting (MRF), leveraging a deep image prior reconstruction to mitigate noise. STUDY TYPE: Phantom and prospective in vivo assessment. POPULATION: ISMRM/NIST MRI system phantom and 18 healthy subjects (11 female; ages 28 ± 8 years). FIELD STRENGTH AND SEQUENCES: MRF, modified Look-Locker inversion recovery (MOLLI), and T2-prepared balanced steady state free precession (T2-bSSFP) at 0.55T. ASSESSMENT: MRF T1 and T2 maps were reconstructed using (1) a low-rank technique with sparse and locally low-rank regularization (SLLR-MRF) and (2) a deep image prior (DIP-MRF). Accuracy and precision of MRF and conventional sequences were evaluated in a phantom. In vivo performance of MRF was evaluated in the 18 healthy subjects, with 7 subjects also undergoing conventional mapping. Myocardial T1 and T2 values were compared among methods and image quality scored by three readers (2, 3, and 4 years of experience) on a 5-point scale. STATISTICAL TESTS: Linear regression, Bland-Altman, intraclass correlation coefficient, and one-way ANOVA with p < 0.05 considered significant. RESULTS: Mean measurements in the left ventricular septum were 671 ± 31 ms (MOLLI), 761 ± 147 ms (SLLR-MRF), and 686 ± 39 ms (DIP-MRF) for T1, and 63.5 ± 5.7 ms (T2-bSSFP), 47.5 ± 12.7 ms (SLLR-MRF), and 45.2 ± 4.5 ms (DIP-MRF) for T2. Compared to conventional mapping, DIP-MRF exhibited significantly lower T2 but no differences in T1 (p > 0.99). Standard deviations within the myocardium were significantly lower with DIP-MRF compared to SLLR-MRF (39 vs. 147 ms for T1 and 4.5 vs. 12.7 ms for T2). Overall image quality ratings were significantly lower for SLLR-MRF (T1: 2.3, T2: 2.9), which were significantly lower compared to conventional mapping methods (T1: 3.4, T2: 3.9), and DIP-MRF (T1: 3.8, T2: 4.1) received higher scores. DATA CONCLUSION: This study demonstrated the feasibility of cardiac MRF on a commercial 0.55T system, enabled by a deep image prior reconstruction for denoising. EVIDENCE LEVEL: 2. STAGE OF TECHNICAL EFFICACY: 1.