Cerebrovascular Reactivity Assays Collateral Function in Carotid Stenosis

Area of Science:

• Neuroimaging
• Vascular Neurology
• Cardiovascular Imaging

Background:

• Collateral blood flow is crucial for managing stroke risk in carotid artery stenosis (CAS).
• Assessing collateral flow with traditional imaging methods shows poor observer agreement.
• Blood-oxygen-level-dependent (BOLD) MRI can measure cerebrovascular reactivity (CVR) as a surrogate for cerebral blood flow reserve.

Purpose of the Study:

• To investigate if functional collateral flow, indicated by normalized ipsilateral CVR, exists in patients with hemodynamically significant CAS.
• To evaluate CVR as a potential marker for assessing collateral blood flow in CAS patients.

Main Methods:

• 55 patients with varying degrees of CAS were analyzed using BOLD MRI during a hypercapnic challenge to measure CVR.
• CVR was calculated as the change in BOLD signal relative to end-tidal CO2 (Δ BOLD/Δ PETCO2).
• CVR values were normalized using z-scores against a healthy control atlas and averaged over gray and white matter in the middle cerebral artery territory.

Main Results:

• CVR varied across all CAS severity groups, generally decreasing with increased stenosis.
• Ipsilateral CVR was reduced in all CAS groups, even those with <50% stenosis.
• A significant portion of patients exhibited normal CVR despite varying degrees of stenosis, including complete occlusion, highlighting individual variability.

Conclusions:

• Carotid artery stenosis generally reduces downstream vascular reserve.
• The extent of collateralization in CAS is highly variable and not solely predictable by the degree of stenosis.
• CVR measured by BOLD MRI appears to be a more reliable indicator of recruitable collateral blood flow than the degree of stenosis itself.