Purpose: To accelerate cardiac cine at 7 tesla using simultaneous multi-slice (SMS) acquisition with self-calibration to resolve misalignment between calibration and imaging data due to breathing motion.
Methods: A spoiled-gradient echo cine sequence was modified with radiofrequency phase-cycled SMS excitations. A Fourier encoding strategy was applied along the cardiac phase dimension to allow for slice untangling and split-slice GRAPPA calibration. Split-slice GRAPPA was coupled with regular GRAPPA (SMS-GRAPPA) and L1-SPIRiT (SMS-L1SPIRiT) for image reconstruction. 3-slice SMS cine MRI was evaluated in ten subjects against single-slice cine MRI in terms of SNR and contrast-to-noise ratio and slice leakage.
Results: SNR decreased significantly from 10.1 ± 7.1 for single-slice cine to 7.4 ± 2.8 for SMS-GRAPPA (P = 0.02) and was recovered to 9.0 ± 4.5 with SMS-L1SPIRiT (P = 0.02). Contrast to noise ratio decreased significantly from 14.5 ± 8.1 for single-slice cine to 5.6 ± 3.6 for SMS-GRAPPA (P < 0.0001) and increased slightly but significantly back to 6.7 ± 4.4 for SMS-L1SPIRiT (P = 0.03). Specific absorption rate restrictions imposed a reduced nominal flip angle (-37 ± 7%, P = 0.02) for 3-slice SMS excitations compared to single-slice acquisitions. SMS slice leakage increased significantly from apex (8.6 ± 6.5 %) to base (13.1 ± 4.1 %, P = 0.03) in the left ventricle.
Conclusion: Three-fold acceleration of cine at 7T was achieved using the proposed SMS technique. Fourier encoding self-calibration and regularized image reconstruction enabled simultaneous acquisition of three slices without significant SNR decrease but significant CNR decrease linked to the reduced nominal excitation flip angle.
Keywords: 7 tesla cardiac MR (CMR); Fourier encoding; cardiac function MRI (cine); simultaneous multi-slice (SMS); ultrahigh field MRI.
© 2018 International Society for Magnetic Resonance in Medicine.