Arterial spin labeling and dynamic susceptibility contrast CBF MRI in postischemic hyperperfusion, hypercapnia, and after mannitol injection

Abstract

Arterial spin labeling (ASL) and dynamic susceptibility contrast (DSC) magnetic resonance imaging (MRI) are widely used to image cerebral blood flow (CBF) in stroke. This study examined how changes in tissue spin-lattice relaxation-time constant ( T1), blood-brain barrier (BBB) permeability, and transit time affect CBF quantification by ASL and DSC in postischemic hyperperfusion in the same animals. In Group I ( n = 6), embolic stroke rats imaged 48hours after stroke showed regional hyperperfusion. In normal pixels, ASL- and DSC-CBF linearly correlated pixel-by-pixel. In hyperperfusion pixels, ASL-CBF was significantly higher than DSC-CBF pixel-by-pixel (by 25%). T1 increased from 1.76 ± 0.14 seconds in normal pixels to 1.93 ± 0.17 seconds in hyperperfusion pixels. Arterial transit time decreased from 300 milliseconds in normal pixels to 200 milliseconds in hyperperfusion pixels. Δ R2* profiles showed contrast-agent leakages in the hyperperfusion regions. In Group II ( n = 3) in which hypercapnic inhalation was used to increase CBF without BBB disruption, CBF increased overall but ASL- and DSC-CBF remained linearly correlated. In Group III ( n = 3) in which mannitol was used to break the BBB, ASL-CBF was significantly higher than DSC-CBF. We concluded that in normal tissue, ASL and DSC provide comparable quantitative CBF, whereas in postischemic hyperperfusion, ASL-CBF and DSC-CBF differed significantly because ischemia-induced changes in T1 and BBB permeability affected the two methods differently.