Evaluating rapid water excitation techniques for 5D whole-heart fat-suppressed free-running cardiac MRI at 1.5T scanner
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Background
Balanced steady-state free precession (bSSFP) sequences offer high SNR and excellent tissue contrast for whole-heart MRI. However, inadequate fat suppression can introduce artifacts, particularly with non-Cartesian readouts. This study aimed to compare novel rapid water-excitation (WE) pulses for 3D radial whole-heart free-running MRI at 1.5T, specifically Binomial Off-Resonant Rectangular (BORR), Lipid Insensitive Binomial Off-Resonant RF Excitation (LIBRE), and Lipid Insensitive Binomial Off-Resonant (LIBOR) pulses, alongside a Fast Interrupted Steady-State (FISS) and non-fat suppressed free-running bSSFP sequence.
Methods
Three free-running MRI protocols (BORR, LIBRE, LIBOR) were optimized for fat suppression at 1.5T using a phantom. These protocols, along with FISS and non-fat suppressed bSSFP, were tested in phantom and five volunteers, with each acquisition lasting 3min and 41sec.
SNR and CNR Water-Fat were measured in phantom data, while SNR and CNR Blood-Myocardium were assessed in volunteers using static gridded reconstructions. Motion-resolved reconstructions were used for qualitative assessments. SAR values were measured for each sequence, and statistical differences were analyzed using one-way ANOVA (p < 0.05). The pulse with the best combination of high SNR and low SAR was identified for further applications.
Results
In phantom studies, LIBOR had the highest CNR Water-Fat (276.8 ± 2.5), followed by LIBRE (268.1 ± 2.6), BORR (249.9 ± 2.2), and FISS (212.7 ± 2.7), though these differences were not statistically significant (p > 0.05). FISS showed the highest SAR (1.41 W.kg -1 ), while LIBOR had the lowest (0.23 W.kg -1 ). In volunteers, BORR had the highest SNR in the ventricular blood pool (17.0 ± 1.5), and LIBRE had the highest CNR Blood-Fat (29.4 ± 9.3). FISS had the highest CNR Blood-Myocardium (29.0 ± 8.9), but the differences were not significant (p > 0.05). LIBOR consistently had the lowest SAR (0.26 W.kg -1 ).
Conclusion
This study compared various fat-signal-suppression approaches in 3D contrast-free whole-heart free-running bSSFP MRI at 1.5T. Although the sequences performed similarly in SNR and CNR, LIBOR offered the lowest SAR, making it a promising candidate for future whole-heart MRI applications, particularly where RF energy deposition is a concern.
