Off-resonance-robust velocity-selective magnetization preparation for non-contrast-enhanced peripheral MR angiography

To develop a new velocity-selective (VS) excitation pulse sequence which is robust to field inhomogeneity, and demonstrate its application to non-contrast-enhanced peripheral MR angiography (MRA).

The off-resonance-robust VS saturation pulse is designed by incorporating 180° refocusing pulses into the k-space-based reference design and tailoring sequence parameters in a velocity region of interest. The VS saturation pulse is used as magnetization preparation for non-contrast-enhanced peripheral MRA to suppress background tissues but not arterial blood based on their velocities. Non-contrast-enhanced peripheral MRA using the proposed VS preparation was tested in healthy volunteers and a patient with arterial stenosis.

Calf angiograms obtained using the new VS preparation show more uniform background suppression than the reference VS preparation, as demonstrated by larger mean values and smaller standard deviations of artery-to-vein and artery-to-muscle contrast-to-noise ratios (71.0 ± 11.4 and 75.3 ± 12.1 versus 61.7 ± 22.7 and 58.5 ± 27.8). Two-station peripheral MRA using the new VS preparation identifies stenosis of the femoral and popliteal arteries in the patient, as validated by digital subtraction angiography.

Non-contrast-enhanced MRA using the new VS magnetization preparation can reliably provide high angiographic contrast in the lower extremities with significantly improved immunity to field inhomogeneity.