Brain MR perfusion-weighted imaging with alternate ascending/descending directional navigation

In this study, a new arterial spin labeling technique that requires no separate spin preparation pulse was developed. Sequential two-dimensional slices were acquired in ascending and descending orders by turns using balanced steady state free precession for pair-wise subtraction. Simulation studies showed this new technique, alternate ascending/descending directional navigation (ALADDIN), has high sensitivity to both slow- (1-10 cm/sec) and fast-moving (>10 cm/sec) blood because of the presence of multiple labeling planes proximal to imaging planes and sensitivity of balanced steady state free precession to initial magnetization differences. ALADDIN provided high-resolution multislice perfusion-weighted images in ∼3 min. About 80-90% of signals in a slice were ascribed to spins saturated in the four prior slices. Three to five edge slices on each side of imaging group were affected by transient magnetization transfer effects and incomplete T₁ recovery between successive acquisitions. ALADDIN signals were dependent on many imaging parameters, implying room for improvement. Sagittal and coronal ALADDIN images demonstrated perfusion direction in gray matter regions was mostly from center to lateral, anterior, or posterior, whereas that in some white matter regions was reversed. ALADDIN is likely useful for many studies requiring perfusion-weighted imaging with short scan time, insensitiveness to arterial transit time, directional information, high resolution, and/or wide coverage.