Whole-Neck Non-Contrast-Enhanced MR Angiography Using Velocity Selective Magnetization Preparation

Abstract

This study aimed to optimize velocity-selective magnetic resonance angiography (VS-MRA) protocols for whole-neck angiography and demonstrate its feasibility in healthy subjects with comparisons to clinical 3D time-of-flight (TOF) angiography. To help optimize VS-MRA protocols, 2D phase-contrast (PC) flow imaging and 3D B0 and B1 field mappings were performed on five healthy volunteers. Based on these measurements, a slab-selective (SS) inversion preparation was applied prior to a VS saturation preparation to further suppress venous blood, while the VS preparation pulse was designed with compensation for field offsets. VS-MRA and 3D TOF were performed on six healthy subjects, and relative contrast ratios (CRs) between artery and muscle signals were calculated for twenty arterial regions for comparisons. The pre-compensated VS pulse improved the visualization of the subclavian arteries and suppression of background tissues, which involved large B0 and B1 field errors. The combination of SS and VS preparations effectively suppressed venous blood. While the relative CR values were 0.78 ± 0.08 and 0.72 ± 0.10 for VS-MRA and 3D TOF, respectively, over the twenty segments, VS-MRA outperformed 3D TOF in visualizing arterial segments of a small size or with a horizontal orientation, such as subclavian, facial, and occipital arteries. The proposed neck VS-MRA with the field-error-compensated VS preparation combined with the SS preparation is feasible and superior to 3D TOF in visualizing small and/or horizontally oriented arterial segments.

Spatially and velocity‐selective magnetization preparation for noncontrast‐enhanced peripheral MR angiography

“…First, to confirm the intended excitation selectivity in spatial and velocity dimensions, MRA scans were performed on two subjects using VS preparation, SVS preparation, or without any preparation. The MRA pulse sequence was electrocardiographically triggered, and consisted of a VS or SVS preparation pulse played after a cardiac trigger delay (TD), a postpreparation delay (TI), a spectral‐selective fat saturation pulse, and a segmented 3D gradient‐echo readout with square‐spiral centric view order 27 . This magnetization‐prepared segmented acquisition was repeated every cardiac cycle.…”

“…The MRA pulse sequence was electrocardiographically triggered, and consisted of a VS or SVS preparation pulse played after a cardiac trigger delay (TD), a postpreparation delay (TI), a spectral-selective fat saturation pulse, and a segmented 3D gradient-echo readout with square-spiral centric view order. 27 This magnetization-prepared segmented acquisition was repeated every cardiac cycle. Scan parameters included scan orientation = coronal, TD = 230-280 ms (as determined by scout phase-contrast flow measurements), TI = 80 ms, flip angle = 10 , spatial resolution = 1.2 Â 1.2 Â 1.3 mm 3 (in the order of S/I, R/L, and A/P directions), FOV = 380 Â 380 Â 135 mm 3 , TE/TR = 3.1/6.5 ms, readout bandwidth = 330 Hz/pixel, and number of views per acquisition = 42.…”

Variable-Density Velocity-Selective Magnetization Preparation for Non-Contrast-Enhanced Peripheral MR Angiography

“…This was followed by a spectral-selective fat saturation pulse and a segmented 3D gradient-echo (GRE) with square-spiral sampling trajectory (Fig. 2) [24,27]. This set of pulse sequences was repeated every two cardiac cycles.…”

“…To address these issues, various solutions have been developed, including multi-refocusing schemes, periodic shifting of spatial responses, and numerically optimized excitation pulses [17][18][19][20]. VS-MRA has shown feasibility for various vascular regions, including the renal, abdominal, peripheral, cerebral, pedal, and carotid arteries [13,14,17,[21][22][23][24].…”