3D Phase Contrast Using Balanced Steady‐State Free Precession ( PC ‐ SSFP ) for Improved 4D Flow at Clinical Field Strengths

PURPOSE: 4D flow MRI provides comprehensive evaluation of cardiovascular flow. One major limitation of intracardiac 4D flow is poor blood-myocardial contrast. 2D phase contrast using balanced steady state free precession (PC-SSFP) methods have been demonstrated to provide accurate velocity, with enhanced contrast and SNR. In this work, we extended our 2D PC-SSFP to 4D flow at clinical field strengths, and tested it for diastolic evaluation. METHODS: The 4D flow sequence with four-point encoding was modified to have 0th and 1st moment gradient nulling over each TR to achieve bSSFP contrast. Pixel-wise velocities were validated in a flow phantom at 3 T. Mitral inflow peak velocity (E, A, e') and stroke volume (SV) were compared in 14 scan (13 healthy subjects at 3 T, with one subject scanned again at 1.5 T) with standard 2D and 4D flow GRE methods. RESULTS: In phantom study, 4D flow bSSFP strongly agreed with GRE, with r > 0.9 in all three directions. Significantly improved SNR (42.4 ± 24.7 vs. 16.9 ± 8.5) and blood-tissue CNR (9.7 ± 3.3 vs. 2.3 ± 1.5) were found in vivo. 4D flow bSSFP measured comparable E (limits of agreement 1.3 ± 14.6 cm/s, r = 0.88), A (0.3 ± 11.3 cm/s, r = 0.95), e' (1.3 ± 3.4 cm/s, r = 0.71), and SV (-2.6 ± 9.7 mL, r = 0.91) vs. GRE approach, and showed similar agreement with 2D methods (r = 0.64-0.91). A study at 1.5 T suggested its potential applicability at lower field strength, with reduced susceptibility to off-resonance artifacts. CONCLUSION: Our 4D flow bSSFP method is feasible, achieving improved SNR, CNR, and accurately measuring mitral velocity and volume at clinical field strengths.