Multiple Inflow Pulsed Arterial Spin-Labeling Reveals Delays in the Arterial Arrival Time in Minor Stroke and Transient Ischemic Attack

Abstract

SUMMARY:Our purpose was to use multiple inflow pulsed ASL to investigate whether hemodynamic AAT information is sensitive to hemispheric asymmetry in acute ischemia. The cohorts included 15 patients with acute minor stroke or TIA and 15 age-matched controls. Patients were scanned by using a stroke MR imaging protocol at a median time of 74 hours. DWI lesion volumes were small and functional impairment was low; however, perfusion abnormalities were evident. Prolonged AAT values were more likely to reside in the affected hemisphere (significant when compared with controls, P Ͻ .048). An advantage of this ASL technique is the ability to use AAT information in addition to CBF to characterize ischemia. ABBREVIATIONS:AAT ϭ arterial arrival time; ASL ϭ arterial spin-labeling; AUH ϭ area under the histogram; CBF ϭ cerebral blood flow; DSC ϭ dynamic susceptibility contrast; DWI ϭ diffusionweighted imaging; FMRIB ϭ Functional MRI of the Brain; GRASE ϭ gradient and spin-echo; ICA ϭ internal carotid artery; MCA ϭ middle cerebral artery; NIHSS ϭ National Institutes of Health Stroke Scale; PASL ϭ pulsed arterial spin-labeling; TIA ϭ transient ischemic attack A SL is a noninvasive MR imaging technique capable of providing perfusion information without the use of gadolinium-based contrast agents. ASL relies on contrast by magnetically labeling blood water and detecting the signal intensity as a tracer bolus; it has shown promise in clinical studies involving acute stroke 1,2 and ICA occlusion. 3,4 The shortcomings of the ASL techniques include the following: 1) limited brain coverage, 2) low signal intensity-to-noise ratio, and 3) accounting for delays in AAT (the time duration for blood to move from tagging to imaging locations). The current study attempts to address each of these issues.An acute cerebrovascular event may increase the AAT by the following mechanisms: Labeled blood must travel via either collateral pathways of the circle of Willis or secondary collateral pathways, such as those that are provided by leptomeningeal vessels. Labeled blood that remains in the largevessel intravascular space at the time of imaging, due to an insufficient postlabel delay as in continuous ASL or an insufficient TI as in pulsed ASL, will affect the CBF image.2 A recent ICA occlusion study highlighted the relevance of AAT in clinical perfusion ASL. 5 The goal in the current study is to demonstrate the clinical utility of a whole-brain 3D-GRASE-PASL implementation with multiple-inflow periods to derive maps of CBF and AAT in patients with minor stroke/TIA. Analogous to hemodynamic timing parameters used in DSC perfusion for acute stroke diagnosis, AAT maps, hypothetically, can be used to characterize the extent of perfusion abnormalities. TechniqueMR imaging data were collected on a 3T scanner (Tim Trio; Siemens, Erlangen, Germany) with a 12-channel head receive coil in a 2-cohort study: 1) 15 patients with acute minor stroke or TIA, and 2) 15 agematched controls. Carotid Doppler sonography was performed on patients only. Relevant sequen...

Hemodynamic Alterations in Vertebrobasilar Large Artery Disease Assessed by Arterial Spin-Labeling MR Imaging

“…These results extend the work of previous clinical ASL studies 2,[5][6][7][19][20][21] by showing that CBF is reduced in the VB circulation in patients compared with controls. Significance of ASL fitting was assessed voxelwise using the 95% confidence intervals produced from the ASL model fitting.…”

“…This approach is justified for healthy patients but might be problematic in cerebrovascular diseases where arterial flow is atypical or delayed, as in the case of ischemic scenarios. 2,4 Recent work illustrates the value of multiple inflow ASL to extract both CBF and ATT information [5][6][7] The current study focused on symptomatic VB circulation. In contrast to carotid circulation, the impact of stenotic disease on brain perfusion in VB circulation has not been reported in the literature thus far.…”

Visualization of Altered Neurovascular Coupling in Chronic Stroke Patients using Multimodal Functional MRI

“…Clinically, ASL has been used to show perfusion deficits in acute (MacIntosh et al, 2010b) and chronic (Brumm et al, 2010) stroke and VASO has been successfully applied in studies of ischemic steno-occlusive disease (Donahue et al, 2009c(Donahue et al, , 2010. However, no fMRI activation studies have directly compared BOLD with these new fMRI techniques, nor evaluated their feasibility or added value in chronic stroke.…”

Cerebral Perfusion Long Term after Therapeutic Occlusion of the Internal Carotid Artery in Patients Who Tolerated Angiographic Balloon Test Occlusion

“…In addition to the previous work by Bokkers et al, 16,29 Hendrikse et al, 30 and Macintosh et al, 17 this study demonstrates the feasibility of ASL with multiple TIs to measure perfusion and its temporal characteristics. Whereas previous studies included symptomatic patient populations, this study was the first to assess cerebral perfusion and its temporal characteristics in an asymptomatic patient population in whom increased delay time particularly is a reflection of the elongated route via collateral pathways.…”

“…14,15 Bokkers et al 16 were the first to use this technique in patients with symptomatic carotid artery occlusion and measured significant differences in CBF and timing parameters between hemispheres ipsilateral and contralateral to the occlusion side. Recently, a similar technique was used by Macintosh et al, 17 who found that prolonged arterial arrival times resided in the affected hemisphere of patients with minor stroke or transient ischemic attack, though functional impairment and lesions on diffusion-weighted imaging were limited.…”