Time-resolved Vessel-selective Digital Subtraction MR Angiography of the Cerebral Vasculature with Arterial Spin Labeling

Abstract

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-specifi c 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 (fi ve 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 infl ow 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 fl ight (TOF) acquisition was performed in the circle of Willis. Results:Infl ow 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 eightfold 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 6 15 [standard deviation] and 57 6 15, respectively) and 11-second single-projection acquisitions (19 6 5 and 17 6 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 identifi ed with ASL angiography. Conclusion:ASL angiography can be used to acquire hemodynamic vessel-specifi c information similar to that obtained with x-ray DSA.q RSNA, 2010

Reduced resolution transit delay prescan for quantitative continuous arterial spin labeling perfusion imaging

“…The first is that the local transit delay due to flow in the very small vessels is much smaller than the delay from the labeling plane. Our measured transit delays to tissue are not much larger than transit delays within the major vessel branches performed with an ASL angiography technique (43). ASL-based measures of arterial blood volume, an indicator of transit delay since transit delay is blood volume divided by blood flow, suggest that 80% of the arterial blood volume vanishes when dephasing gradients that crush velocities greater than 4 cm/s are applied (44).…”

Optimization of 4D vessel‐selective arterial spin labeling angiography using balanced steady‐state free precession and vessel‐encoding

“…Second, it yields highly vessel‐selective angiograms: the average signal contamination in this study was 1.9 ± 2.0%, which is considerably lower than the average value of 12 ± 7% reported by Robson et al . using single‐artery selective PCASL. This has the advantage of reducing ambiguity in the resulting images: for example, signal present in vessels not normally supplied by the labeled artery can be more confidently ascribed to collateral flow rather than signal contamination.…”

“…For vessel‐selective applications, the ASL preparation can be modified to label blood flowing through an individual artery . However, such methods are not SNR efficient where multiple arteries are of interest, since labeled blood signal is confined to a single artery on any given acquisition: for example, to generate four vessel‐selective angiograms of the brain‐feeding arteries, the measured signal y can be described using the equations of Wong as where R ICA , L ICA , R VA , L VA , and S represent the blood signals arising from the right and left internal carotid arteries, the right and left vertebral arteries, and static tissue, respectively.…”

A novel magnetic resonance imaging approach to collateral flow imaging in ischemic stroke

“…This map can provide information about collateral circulation with good intra-and interobserver agreement. 13 However, ASL techniques have several limitations, including the short half-life of the ASL tracer (the period the magnetic label lasts) and the lack of a threshold for ASL measurement of ischemic penumbra. In addition, collateral flow information as assessed by a collateral flow map derived from MRP has prognostic value in acute ischemic stroke with a major artery occlusion.…”

“…[11][12][13][14][15] In this study, we applied a novel MR imaging (MRI) technique employing DSC-MRP source data to visualize leptomeningeal collateral circulation in acute ischemic stroke with a major artery occlusion. [11][12][13][14][15] In this study, we applied a novel MR imaging (MRI) technique employing DSC-MRP source data to visualize leptomeningeal collateral circulation in acute ischemic stroke with a major artery occlusion.…”