BOLD Imaging

Home page Description: 
Functional imaging measures changes in blood flow.
Posted On: November 29, 2016
Image Caption: 
Conference attendee, Kevin Sam, Postdoctoral Fellow. Supervisor: Dr. David Mikulis, Krembil
Conference: The 8th International Society of Vascular Behavioural and Cognitive Disorders (VasCog), October 12-15, 2016, Amsterdam, Netherlands

Conference Highlight: VasCog 2016 covered neuroimaging and epidemiological aspects of vascular burden in dementia. It featured research on mechanisms of cerebral blood flow in small vessel disease.

Conference Article:
     Blood oxygen level-development (BOLD) functional imaging is a technology that measures changes in brain blood flow, which is representative of neuronal activity. According to the literature, it remains controversial whether blood flow is controlled by the activity of astrocytes or capillary pericytes on arteriole smooth muscle. At this year’s VasCog, it was demonstrated that glutamate and neuronal activity release chemical messengers, such as the prostaglandin E2, that dilate capillaries by actively relaxing pericytes. Therefore, a significant finding presented at the conference was that pericytes are major regulators of cerebral blood flow and may be the factor enabling BOLD imaging.

     Radiological highlights from VasCog included the optimization of imaging small vessel disease (SVD). The presence of thalamic lesions is used to help diagnose vascular dementia. The literature  advocates the use of T2-weighted imaging and fluid-attenuated inversion recovery images to detect ischemic lesions in vascular dementia in older adults; however, it was shown that these images are not reliable in detecting thalamic and cerebellar lesions.

     Another significant finding is the standardization of cerebrovascular reactivity (CVR) measurements. CVR refers to the body’s ability to alter blood flow in response to a vasoactive stimulus. It is currently not possible to perform a formal meta-analysis of CVR in cerebral SVD due to heterogeneity of the vasoactive stimulus used, the stimulus duration, tolerability of safety of the stimulus, and analysis methods. At VasCog, a standardized measurement of CVR was proposed. Individual BOLD MRI CVR scans may be normalized by scoring them to a reference atlas, thus yielding a Z-score and interval-difference Z-score for cross-sectional datasets. Longitudinal assessment of SVD progression can be performed by the generation of interval-difference Z-scores. This enables standardized CVR data to be compared consistently across individuals, over time and institutions.