Vascular Steal Explains Early Paradoxical Blood Oxygen Level-Dependent Cerebrovascular Response in Brain Regions with Delayed Arterial Transit Times

Abstract

Introduction: Blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) during manipulation of inhaled carbon dioxide (CO₂) can be used to measure cerebrovascular reactivity (CVR) and map regions of exhausted cerebrovascular reserve. These regions exhibit a reduced or negative BOLD response to inhaled CO₂. In this study, we sought to clarify the mechanism behind the negative BOLD response by investigating its time delay (TD). Dynamic susceptibility contrast (DSC) MRI with the injection of a contrast agent was used as the gold standard in order to provide measurement of the blood arrival time to which CVR TD could be compared. We hypothesize that if negative BOLD responses are the result of a steal phenomenon, they should be synchronized with positive BOLD responses from healthy brain tissue, even though the blood arrival time would be delayed. Methods: On a 3-tesla MRI system, BOLD CVR and DSC images were collected in a group of 19 patients with steno-occlusive cerebrovascular disease. For each patient, we generated a CVR magnitude map by regressing the BOLD signal with the end-tidal partial pressure of CO₂ (P_ETCO₂), and a CVR TD map by extracting the time of maximum cross-correlation between the BOLD signal and P_ETCO₂. In addition, a blood arrival time map was generated by fitting the DSC signal with a gamma variate function. ROI masks corresponding to varying degrees of reactivity were constructed. Within these masks, the mean CVR magnitude, CVR TD and DSC blood arrival time were extracted and averaged over the 19 patients. CVR magnitude and CVR TD were then plotted against DSC blood arrival time. Results: The results show that CVR magnitude is highly correlated to DSC blood arrival time. As expected, the most compromised tissues with the longest blood arrival time have the lowest (most negative) CVR magnitude. However, CVR TD shows a noncontinuous relationship with DSC blood arrival time. CVR TD is well correlated to DSC blood arrival time (p < 0.0001) for tissue of positive reactivity, but fails to maintain this trend for tissue of negative reactivity. Regions with negative reactivity have similar CVR TD than healthy regions. Conclusion: These results support the hypothesis that negative reactivity is the result of a steal phenomenon, lowering the BOLD signal as soon as healthier parts of the brain start to react and augment their blood flow. BOLD CVR MRI is capable of identifying this steal distribution, which has particular diagnostic significance as it represents an actual reduction in flow to already compromised tissue.

The Effects of Perturbed Cerebral Blood Flow and Cerebrovascular Reactivity on Structural MRI and Behavioral Readouts in Mild Traumatic Brain Injury

“…Such a blood-stealing phenomenon has been observed in ischemic stroke, and ischemic cerebrovascular disease. [30][31][32] Attenuated CBF responses to vasodilation have been reported using both the CCI 33,34 and fluid percussion injury models. 35 However, negative CBF responses to hypercapnia have not been reported previously.…”

Iterative analysis of cerebrovascular reactivity dynamic response by temporal decomposition

“…Furthermore, Delay corr also shows a better correspondence to bolus arrival time (BAT) in Dynamic Susceptibility (DSC) MRI or Arterial Spin Labeling (ASL) (Donahue et al., 2014; MacIntosh et al., 2010; Poublanc et al., 2013). Poublanc et al.…”

“…a voxel‐wise CO 2 shift (Delay maxcorr ) which has been proposed by Poublanc et al., 2013 (Blockley et al., 2011; Poublanc et al., 2013) and…”

“…To better model true CVR response, investigators (Blockley, Driver, Francis, Fisher, & Gowland, 2011; Donahue et al., 2015; Geranmayeh, Wise, Leech, & Murphy, 2015; Halani, Kwinta, Golestani, Khatamian, & Chen, 2015; Poublanc et al., 2013) have aimed to define the arterial arrival time of PaCO 2 by applying maximum Pearson product‐moment correlation coefficient between CO 2 and BOLD signal response, assuming a constant rate of vascular dynamic response over the brain. In this instance, the delay inducing the maximum correlation is considered the arterial arrival time.…”

BOLD delay times using group delay in sickle cell disease

“…During this state, there are systematic autonomic cerebrovascular responses, such as vasodilation and increases in respiration rate, heart rate, cerebral blood volume, and cerebral blood flow (CBF), to compensate for reduced inspired oxygen. 7,8 …”