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To describe the neuroimaging and other methods for assessing vascular contributions to neurodegeneration in the Comprehensive Assessment of Neurodegeneration and Dementia (COMPASS-ND) study, a Canadian multi-center, prospective longitudinal cohort study, including reliability and feasibility in the first 200 participants.
COMPASS-ND includes persons with Alzheimer’s disease (AD; n = 150), Parkinson’s disease (PD) and Lewy body dementias (LBDs) (200), mixed dementia (200), mild cognitive impairment (MCI; 400), subcortical ischemic vascular MCI (V-MCI; 200), subjective cognitive impairment (SCI; 300), and cognitively intact elderly controls (660). Magnetic resonance imaging (MRI) was acquired according to the validated Canadian Dementia Imaging Protocol and visually reviewed by either of two experienced readers blinded to clinical characteristics. Other relevant assessments include history of vascular disease and risk factors, blood pressure, height and weight, cholesterol, glucose, and hemoglobin A1c.
Analyzable data were obtained in 197/200 of whom 18 of whom were clinically diagnosed with V-MCI or mixed dementia. The overall prevalence of infarcts was 24.9%, microbleeds was 24.6%, and high white matter hyperintensity (WMH) was 31.0%. MRI evidence of a potential vascular contribution to neurodegeneration was seen in 12.9%–40.0% of participants clinically diagnosed with another condition such as AD. Inter-rater reliability was good to excellent.
COMPASS-ND will be a useful platform to study vascular brain injury and its association with risk factors, biomarkers, and cognitive and functional decline across multiple age-related neurodegenerative diseases. Initial findings show that MRI-defined vascular brain injury is common in all cognitive syndromes and is under-recognized clinically.
Of the metals that are commonly present in the human brain, it is considered that only iron in the form of ferritin and hemosiderin is present in sufficient quantities and appropriate oxidation state to be visualized by magnetic resonance imaging (MRI). Histology has shown that cerebral microbleeds (CMBs) contain hemosiderin deposits, a paramagnetic substance. In attempts to quantify the actual susceptibility distribution, many different models have been proposed, which relate measurable MRI effects to the underlying susceptibility distribution. However, for the detection of CMBs it is probably sufficient to use qualitative techniques with a high sensitivity to magnetic field inhomogeneities to provide information on the location and approximate size of the CMB. This chapter describes some possible technical developments to discriminate between some of the different origins of signal loss. The introduction of higher-field scanners and the development of new sequences can provide increased sensitivity for the detection of CMBs.
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