Time-resolved vessel-selective digital subtraction MR angiography of the cerebral vasculature with arterial spin labeling

Purpose: To demonstrate an arterial spin-labeling (ASL) magnetic resonance (MR) angiographic technique that covers the entire cerebral vasculature and yields transparent-background, time-resolved hemodynamic, and vessel-specific information similar to that obtained with x-ray digital subtraction angiography (DSA) without the use of exogenous contrast agents. Materials and Methods: Prior institutional review board approval and written informed consent were obtained for this HIPAA-compliant study in which 12 healthy volunteers (five women, seven men; age range, 21-62 years; average age, 28 years) underwent imaging. An ASL technique in which variable labeling durations are used to acquire hemodynamic in-flow information and a vessel-selective pulsed-continuous ASL technique were tested. Region-of-interest signal intensities in various vessel segments were averaged across subjects and used to quantitatively compare images. For comparison, a standard time of flight (TOF) acquisition was performed in the circle of Willis. Results: Inflow temporal resolution of 200 msec was demonstrated, revealing arterial transit times of 750, 950, and 1100 msec to consecutive segments of the middle cerebral artery from distal to the circle of Willis to deep regions of the midbrain. Selective labeling resulted in an average of eight-fold suppression of contralateral vessels relative to the labeled vessel. Signal-to-noise ratios and contrast-to-noise ratios on maximum intensity projection images obtained with 88-second volumetric acquisitions (60 ± 15 [standard deviation] and 57 ± 15, respectively) and 11-second single-projection acquisitions (19 ± 5 and 17 ± 5, respectively) were comparable with standard TOF acquisitions, in which a 2.7-fold longer imaging duration for a 2.6-fold lower pixel area was used. Normal variations of the vasculature were identified with ASL angiography. Conclusion: ASL angiography can be used to acquire hemodynamic vessel-specific information similar to that obtained with x-ray DSA.