WHIte MAtter Hyperintensity Shape and Glymphatics

Overview

In a society with increased life expectancy, the economic, social and personal burden of dementia increases. Dementia is often caused by a combination of neurovascular and neurodegenerative diseases. Impaired brain clearance is suggested to be closely related to dementia development, as waste products (e.g. amyloid beta) accumulate in the brain, leading to neurodegeneration. Cerebral small vessel disease (SVD) is the most common neurovascular disease that even contributes to about 45% of dementia pathophysiology in patients with a diagnosis of Alzheimer's dementia. White matter hyperintensities of presumed vascular origin (WMH) are the key brain MRI manifestation of cerebral SVD. There is evidence that the currently known and MRI-visible WMH are landmarks of an already progressed stage of the underlying pathology. The pathophysiology of WMH has been attributed to multiple underlying mechanisms, such as hypoperfusion, defective cerebrovascular reactivity and blood-brain barrier dysfunction. Furthermore, different anatomical locations and different types of WMH are related to different underlying pathological changes. Using ultra-high field 7T MR imaging techniques WMH lesions can be detected with a higher sensitivity and resolution than on 3T MRI. The hypothesis is that different pathological mechanisms of cerebral SVD lead to variations in WMH shape. Moreover, the brain clearance ('glymphatic') system of the brain appears to be tightly connected to dementia pathology. Thus, novel markers of glymphatic activity could aid to describe and understand the pathology.

Aim: The overall aim is to study how different pathological mechanisms in cerebral SVD influence WMH shape. Primary objective: To study the association of a more complex WMH shape with abnormalities in small vessel morphology. Secondary objectives: To study the association between WMH shape and cognition/other cerebral small vessel disease markers. To study the association of novel MRI markers of glymphatics with cerebral SVD markers and cognition. Study design: Cross-sectional study that will be conducted at the Leiden University Medical Center (LUMC). Patients will be included from the LUMC or the Alrijne Hospital Leiden. The study contains 3T and 7T MRI scans, as well as neuropsychological assessments. The data will be analyzed by performing association analysis. Study population: Patients of the memory/geriatric clinic that are over 65 years of age. Main study parameter/endpoint: In order to postulate underlying mechanisms related to WMH shape variations the investigators will study the association between a more complex WMH shape and structural and functional markers of cerebral SVD (such as lacunes and microbleeds). WMH shape is assessed as follows: Convexity, solidity, concavity index, and fractal dimension are calculated for periventricular/confluent WMH. A lower convexity and solidity, and higher concavity index and fractal dimension indicate a more irregular shape of periventricular/confluent WMH. For deep WMH, fractal dimension and eccentricity are determined. A higher eccentricity and fractal dimension indicate a more complex shape of deep WMH. Other study parameters: The investigators want to investigate WMH shape parameters and the association with cognition (mini-mental state exam, clinical dementia rating and cognitive domain scores). Another endpoint is to investigate if different WMH phenotypes can be identified (by machine learning models). Moreover, the association between SVD markers/cognition and novel glymphatics markers (such as size of perivascular spaces, CSF mobility and 4th ventricle CSF flow dynamics) will be investigated. Nature and extent of the burden and risks associated with participation, benefit and group relatedness: The participants will not directly benefit from the results of the study. However, their contribution to the study will add important information about the pathophysiology of the cerebrovascular pathology that contributes to dementia. Therefore, it is not possible to study the research question in a different population group. The ultra-high field 7T MRI system is widely used in a research setting and since its first introduction in the 1990s no serious adverse events have been reported. Important temporary side-effects are vertigo, nausea and involuntary eye motion due to forces on ion currents in the semicircular loops. As all MRI scans are performed within a maximum of 60 minutes and without any contrast agents, the participant burden is seen as a non-substantial burden.