Magnetic Resonance Perfusion Imaging in Acute Ischemic Stroke Using Continuous Arterial Spin Labeling

Abstract

Background and Purpose-Continuous arterial spin-labeled perfusion MRI (CASL-PI) uses electromagnetically labeled arterial blood water as a diffusible tracer to noninvasively measure cerebral blood flow (CBF). We hypothesized that CASL-PI could detect perfusion deficits and perfusion/diffusion mismatches and predict outcome in acute ischemic stroke. Methods-We studied 15 patients with acute ischemic stroke within 24 hours of symptom onset. With the use of a 6-minute imaging protocol, CASL-PI was measured at 1.5 T in 8-mm contiguous supratentorial slices with a 3.75-mm in-plane resolution. Diffusion-weighted images were also obtained. Visual inspection for perfusion deficits, perfusion/diffusion mismatches, and effects of delayed arterial transit was performed. CBF in predetermined vascular territories was quantified by transformation into Talairach space. Regional CBF values were correlated with National Institutes of Health Stroke Scale (NIHSS) score on admission and Rankin Scale (RS) score at 30 days. Results-Interpretable CASL-PI images were obtained in all patients. Perfusion deficits were consistent with symptoms and/or diffusion-weighted imaging abnormalities. Eleven patients had hypoperfusion, 3 had normal perfusion, and 1 had relative hyperperfusion. Perfusion/diffusion mismatches were present in 8 patients. Delayed arterial transit effect was present in 7 patients; serial imaging in 2 of them showed that the delayed arterial transit area did not succumb to infarction. CBF in the affected hemisphere correlated with NIHSS and RS scores (Pϭ0.037 and Pϭ0.003, Spearman rank correlation). The interhemispheric percent difference in middle cerebral artery CBF correlated with NIHSS and RS scores (Pϭ0.007 and Pϭ0.0002, respectively). Conclusions-CASL-PI

Effect of Mild Cognitive Impairment and APOE Genotype on Resting Cerebral Blood Flow and its Association with Cognition

“…For each subject, a mean ASL image was formed from the average difference of the control and tag images using surround subtraction to create an uncorrected perfusion time series, and slice timing delays were accounted for, making the inversion time (TI2) slice specific (Liu and Wong, 2005). This mean ASL image was then converted to absolute units of CBF (mL/100 g tissue per minute) using an estimate of the equilibrium magnetization of CSF as a reference signal (Chalela et al, 2000). This resulted in a calibrated perfusion value for each voxel.…”

Arterial spin labeling measurement of cerebral perfusion in children with sickle cell disease

“…where CBF is the flow in mL/g/sec, DM is the difference between the control and labeled image intensities, w is the postlabeling delay, T1 a is the T1 of arterial blood (1.70 sec for Hct ¼ 0.4), TE is the echo time (14 msec), T2* a is the T2* of arterial blood (50 msec) (21), r is the density of brain tissue (1.05 g/mL) (22), M 0a is the equilibrium magnetization of arterial blood for which an average scanner value was used that was calculated according to Chalela et al (23), a the labeling efficiency (0.85 for p-CASL), T1 b is the T1 of brain tissue (1.24 sec), d is the transit time from the labeling region to the tissue compartment (tissue arrival time) (assumed to be 1500 msec), and t is the tagging duration (1650 msec) (15,24,25).…”

Assessment of functional development in normal infant brain using arterial spin labeled perfusion MRI

“…The 3 ASL image pairs were averaged and smoothed with a 3-D isotropical kernel of size 6mm. CBF values were derived from the averaged ASL image pair using a modified one-compartment model (Chalela et al, 2000). CBF maps showing spuriously low values (<20 ml/100g/min for whole brain) suggested ineffective labeling and were discarded.…”