Arterial Spin-Labeling in Routine Clinical Practice, Part 2: Hypoperfusion Patterns

Carotid occlusion and tissue at risk. Axial contrast-enhanced spoiled gradient-recalled-echo image (left) shows chronic occlusion of the left internal carotid artery (arrow). FLAIR (center) shows no evidence of ischemia. Flow asymmetry on the ASL CBF map (ellipse) represents tissue at risk in the left cerebral hemisphere.

Encephalomalacia. Axial T2-weighted image shows high signal intensity in the frontal lobes representing the remote bilateral anterior cerebral artery (ACA) territory infarcts (yellow arrows). ASL CBF map reveals corresponding focal decrease in flow in the ACA territories (white arrows).

Localized hypoperfusion in temporal lobe epilepsy. Interictal ASL CBF map in a 37-year-old woman demonstrates low signal intensity in the right lateral temporal lobe (arrow) and right hippocampus. Electroencephalography confirmed a right temporal seizure focus.

Hypoperfused tumor on ASL. Axial (left) and coronal (center) gadolinium-enhanced T1-weighted images demonstrate a heterogeneously enhancing mass invading the third and lateral ventricles (yellow arrows). ASL (right) shows regional hypoperfusion within the more cystic portion of the tumor (white arrow). The solid portions show hyperperfusion on ASL (arrowhead). The tumor proved to be a pituitary macroadenoma at surgery.

Paradoxically low signal intensity on ASL. T2*-weighted gradient-recall image reveals a calcified mass arising from the left sphenoid wing. The mass showed avid contrast enhancement (not shown) consistent with meningioma. Despite the enhancement, ASL CBF map shows no increased flow within the tumor (arrow). Underlying hyperperfusion may be masked by competing susceptibility effects.

Hypoperfused glioma on ASL. Coronal FLAIR (upper left) and axial T2 (upper right) images demonstrate a high-signal-intensity mass in the left thalamus (white arrows). Minimal enhancement is seen after contrast (lower left), with corresponding low perfusion on the CBF map (white arrow, bottom right). The rim of normal perfusion (arrowheads) corresponds to the residual normal tissue in the adjacent thalamus.

Blood products on ASL. Axial unenhanced CT scan reveals acute parenchymal hemorrhage in the right frontal lobe (yellow arrow). Focal loss of signal intensity on the ASL CBF map (white arrow) corresponds to the area of hemorrhage. Note flow asymmetry with decreased signal intensity throughout the right hemisphere.

A, Toxoplasmosis on ASL. Decreased perfusion to a toxoplasmosis abscess. Ring-enhancing lesion is demonstrated on corresponding postgadolinium T1-weighted image (arrow). The edema surrounding the abscess decreases the perfusion of the white matter, accentuating the normal perfusion of the adjacent gyri. The area of high signal intensity on ASL surrounding the abscess (arrowhead) represents the normal adjacent gray matter. B, Toxoplasmosis on ASL. Axial T2-weighted image (left) shows a mass with vasogenic edema in the left frontal lobe (arrow). Corresponding ASL image (right) shows diffusely decreased perfusion in the lesion and adjacent white matter (arrow).

Steal phenomenon associated with AVM. ASL CBF map shows characteristic hyperperfusion corresponding to the AVM (arrow). Also seen is a regional zone of hypoperfusion representing the associated steal phenomenon (arrowhead).

Cerebral atrophy as a cause of globally decreased ASL signal intensity. T2-weighted image (left) reveals advanced cerebral volume loss, ex vacuo ventricular enlargement, and white matter hyperintensities. ASL map demonstrates poor perfusion signal intensity throughout.