Assessing Cerebrovascular Reactivity Abnormality by Comparison to a Reference Atlas

Abstract

Attribution of vascular pathophysiology to reductions in cerebrovascular reactivity (CVR) is confounded by subjective assessment and the normal variation between anatomic regions. This study aimed to develop an objective scoring assessment of abnormality. CVR was measured as the ratio of the blood-oxygen-level-dependent magnetic resonance signal response divided by an increase in CO 2 , standardized to eliminate variability. A reference normal atlas was generated by coregistering the CVR maps from 46 healthy subjects into a standard space and calculating the mean and standard deviation (s.d.) of CVR for each voxel. Example CVR studies from 10 patients with cerebral vasculopathy were assessed for abnormality, by normalizing each patient's CVR to the same standard space as the atlas, and assigning a z-score to each voxel relative to the mean and s.d. of the corresponding atlas voxel. Z-scores were color coded and superimposed on their anatomic scans to form CVR z-maps. We found the CVR z-maps provided an objective evaluation of abnormality, enhancing our appreciation of the extent and distribution of pathophysiology compared with CVR maps alone. We concluded that CVR z-maps provide an objective, improved form of evaluation for comparisons of voxel-specific CVR between subjects, and across tests sites.

Iterative analysis of cerebrovascular reactivity dynamic response by temporal decomposition

“…(2014), Sobczyk, Battisti‐Charbonney, Poublanc, et al. (2014) we determined the voxel to be abnormal with | z score | > 2σ. For clarification only abnormal voxels are presented with a color‐coded overlay (−2σ = blue, +2σ = red).…”

“…Another technique for static or time independent CVR calculations is implementation of a controlled ramp protocol (Mutch et al., 2012; Sobczyk, Battisti‐Charbonney, Fierstra, et al., 2014; Sobczyk, Battisti‐Charbonney, Poublanc et al., 2014). Under controlled CO 2 changes it can be argued that a ramp protocol with a slowly progressive CO 2 increase can induce vascular dilatation throughout the brain with enough delay to level out DTP.…”

“…(2014), Sobczyk, Battisti‐Charbonney, Poublanc, et al. (2014) and Poublanc, Crawley, Sobczyk, Montandon, et al. (2015), have previously defined the approach to generate CVR reference atlases, with increased sensitivity for impaired CVR.…”

“…a global CO 2 shift for the whole‐brain (Delay global ), the most commonly used method (Bhogal et al., 2015; Sobczyk, Battisti‐Charbonney, Fierstra, et al., 2014; Sobczyk, Battisti‐Charbonney, Poublanc, et al., 2014). …”

“…After creation of each reference atlas with standard deviation, we calculated the Z scores on a voxel‐wise basis as followed (Sobczyk, Battisti‐Charbonney, Fierstra, et al., 2014, Sobczyk, Battisti‐Charbonney, Poublanc, et al., 2014):$z-\text{score}=\frac{X-\mathit{\mu }}{\mathrm{italic\sigma }}$ …”