Raw Arterial Spin Labeling Data Can Help Identify Arterial Occlusion in Acute Ischemic Stroke

Abstract

A rterial spin labeling (ASL) is one of the most recent magnetic resonance imaging (MRI) sequences used to assess brain perfusion noninvasively. It can be used in the acute phase of ischemic stroke (IS) to identify ischemic penumbra. 1 In patients in acute phase of IS, thrombus assessment is of major clinical relevance because the presence and location of the thrombus may determine therapeutic strategy. 2 An arterial bright signal (ABS), at the level of vascular occlusions, can be observed on raw data of ASL sequence performed for stroke.The aim of this study is to evaluate the relevance of this MRI sign in patients admitted for IS. Patients and MethodsWith the approval of the local ethics committee, we retrospectively analyzed MRI sequences of patients with an IS suspicion admitted in the Department of Neuroradiology (University Hospital of Martinique) from December 2011 to August 2014. MRI (GE Optima MR450W 1.5 T) was performed within 6 hours from stroke onset and included diffusion weighted imaging sequence, echo planar imaging T2* (EPI T2*), fluid attenuated inversion recovery (FLAIR) and MR angiography (Willis time of flight (TOF)). ASL sequence was performed only in case of doubtful diffusion weighted imaging or to highlight a mismatch before a thrombolytic treatment.ASL scans were performed using a pseudocontinuous mode with a repetition time of 4554 ms, an echo time of 10 ms, a postlabeling delay of 1525 ms, and a total acquisition time of 4 minutes.Main judgment criteria were the assessment and the concordance of ABS compared with other sequences (TOF, EPI T2*, and FLAIR).Moreover, a vessel occlusion was diagnosed if an artery was missing on Willis TOF. An intra-arterial clot could be diagnosed on T2* (as a focal hyposignal) and on FLAIR sequences (as a focal hypersignal). ABS was diagnosed according to 2 different patterns upstream of a hypoperfused territory: spot-like (rounded or oval, with sharp edges, on a vascular path) or vessel-like (linear hypersignal on an artery path).One neuroradiologist (AA), with 11 years of experience, first analyzed ASL data while being blinded to clinical data and other sequences. After this first analysis, ABS was definitely graded as 0 if absent or 1 if present and its grading remained unmodified thereon. Other MRI sequence findings (diffusion weighted imaging, occlusion on Willis TOF, clot on T2*, clot on FLAIR) were also studied and graded in a similar manner.A radiology resident, with a 6-month experience in neuroradiology, independently repeated the whole data analysis process in the same conditions.A stroke was considered ongoing in case of the detection of an area of restricted diffusion, identified while being blinded to ASL results.The absence of stroke diagnosis was made if no restricted diffusion area was observed, while still blinded to ASL results. This was further corroborated by clinical data and computed tomography or MRI follow-up for 1 week after patient admission for IS suspicion. Statistical AnalysisInterobserver variability for ABS was assessed usi...

Brain perfusion magnetic resonance imaging using pseudocontinuous arterial spin labeling in 314 dogs and cats

“…In our study, age did not clearly emerge as a variable influencing optimal PLD in dogs. In humans, the well‐documented positive correlation between age and PLD is illustrated by the progressive increase in PLD from 1025 ms in children to 3025 ms in elderly people 19‐26,38‐42 . Our findings suggest that age might not influence arterial blood velocity and ATT in dogs as it does in humans.…”

“…The major limitations of these techniques are IV injection of an exogenous contrast agent and, with CT and nuclear medicine techniques, exposure to ionizing radiation. Since the early 1990s, a noninvasive MRI technique to assess brain perfusion has emerged first in neurosciences research and then in clinical neuroimaging: arterial spin labeling (ASL) 2‐4,11‐28 . Arterial spin labeling uses arterial blood water as a freely diffusible endogenous flow tracer.…”

ASL and susceptibility-weighted imaging contribution to the management of acute ischaemic stroke

“…This bright vessel sign corresponds to an accumulation of protons in labelled arterial blood immediately upstream from the arterial occlusion. The sensitivity of the bright vessel sign would be superior to that of the susceptibility vessel sign [36–38]. The bright vessel sign can also reveal certain distal arterial occlusions not initially detected on the vascular sequences, e.g.…”

Role of the intact hemisphere in determining the rehabilitation potential in the acute period of ischemic stroke: a diffusion and perfusion model

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