Spatially and velocity selective magnetization preparation for non-contrast-enhanced peripheral MR angiography.
Academic Article
Overview
abstract
PURPOSE: To develop spatially and velocity selective (SVS) magnetization preparation pulses for non-contrast-enhanced peripheral MR angiography (MRA) with comparisons to velocity-selective (VS) MRA. METHODS: VS preparation pulses were designed by concatenating multiple excitation steps, each of which was a combination of a hard RF pulse, VS unipolar gradient pulses, and refocusing RF pulses. SVS preparation pulses were designed by replacing the hard RF pulse with a sinc-shaped RF pulse combined with a symmetric tripolar gradient pulse (which does not perturb the velocity encoding by the VS unipolar gradient pulses). Numerical simulations were performed to verify the intended hybrid excitation selectivity of SVS pulses taking account of tissue relaxation, magnetic field errors and eddy currents. In vivo experiments were performed in healthy subjects to verify the hybrid excitation selectivity as well as to demonstrate the visualization of the entire peripheral arteries using 6-station protocols. RESULTS: As demonstrated by numerical simulations, SVS preparation yielded a notch-shaped longitudinal magnetization (Mz )-velocity response within the spatial stopband (same as VS preparation) and preserved the Mz of spins outside the stopband regardless of its velocity. We confirmed these observations also through in vivo tests with good agreement in normalized arterial and muscle signal intensities. In 6-station peripheral MRA experiments, the proposed SVS-MRA yielded significantly higher arterial signal-to-noise ratio (51.6 ± 14.3 versus 38.9 ± 10.9; p<0.001) and contrast-to-noise ratio (41.2 ± 13.0 versus 31.3 ± 10.5; p < 0.001) compared with VS-MRA. CONCLUSION: The proposed SVS-MRA improves arterial SNR and CNR compared with VS-MRA by mitigating undesired pre-saturation of arterial blood upstream the imaging field-of-view.
