Assessing Cerebrovascular Reactivity in Carotid Steno-Occlusive Disease Using MRI BOLD and ASL Techniques

Abstract

Impaired cerebrovascular reactivity (CVR), a predictive factor of imminent stroke, has been shown to be associated with carotid steno-occlusive disease. Magnetic resonance imaging (MRI) techniques, such as blood oxygenation level-dependent (BOLD) and arterial spin labeling (ASL), have emerged as promising noninvasive tools to evaluate altered CVR with whole-brain coverage, when combined with a vasoactive stimulus, such as respiratory task or injection of acetazolamide. Under normal cerebrovascular conditions, CVR has been shown to be globally and homogenously distributed between hemispheres, but with differences among cerebral regions. Such differences can be explained by anatomical specificities and different biochemical mechanisms responsible for vascular regulation. In patients with carotid steno-occlusive disease, studies have shown that MRI techniques can detect impaired CVR in brain tissue supplied by the affected artery. Moreover, resulting CVR estimations have been well correlated to those obtained with more established techniques, indicating that BOLD and ASL are robust and reliable methods to assess CVR in patients with cerebrovascular diseases. Therefore, the present paper aims to review recent studies which use BOLD and ASL to evaluate CVR, in healthy individuals and in patients with carotid steno-occlusive disease, providing a source of information regarding the obtained results and the methodological difficulties.

Vascular Dysfunction in Leukoaraiosis

“…49 CVR may be more sensitive than resting blood flow metrics for the following reasons: CBF measures can be normal due to the action of vascular autoregulation, CBV is difficult to quantitate accurately, and transit time measures can be increased but with normal CVR, with collaterals that maintain normal resting blood flow. 50 Our study is limited in several respects. First, our measure of CVR is based on the percentage BOLD change per millimeter of mercury P ET CO 2 .…”

Cerebrovascular reactivity measured with arterial spin labeling and blood oxygen level dependent techniques

“…However, the tasks usually require subjects to be co-operative and cued and results are also prone to intra-subject variability. Further, BH may induce a mixed hypercapnic-hypoxic state during which the CMRO 2 level is not constant [16]. Quantification of CVR based on well-validated hypercapnic BOLD measurement alone has been reported recently, with a slight drop of CMRO 2 levels observed during hypercapnia [17, 18].…”

“…Integration of the two techniques into a single scan session is straightforward, and had been implemented under hypercapnia and/or hyperoxia calibration studies [28]. Coupling between direct CBF and the BOLD signal, as well as resulted CBF and BOLD CVR changes under hypercapnia, have been investigated in various animal and human studies [8, 16]. Using a vessel-encoded ASL technique with simultaneous acquisitions of BOLD and CBF data, a close correlation has further been reported during hyperoxia [29], though with lower sensitivity in BOLD reactivity compared to CBF reactivity.…”

Arterial Spin Labeling and Blood Oxygen Level-Dependent MRI Cerebrovascular Reactivity in Cerebrovascular Disease: A Systematic Review and Meta-Analysis

“…This allows interested clinicians or researchers working within this field to get a comprehensive overview of the available data. A previously published review did look into the BOLD and ASL CVR MRI studies performed in carotid steno-occlusive disease, but they did not provide a systematic overview of the resulting BOLD and ASL CVR results [70] . Also, in our review, data are presented for different subgroups of cerebrovascular disease: stroke, stenosis, occlusion and MMD respectively.…”