Speaker: Dr. Henry Mak, Clinical Associate Professor, Department of Diagnostic Radiology, The University of Hong Kong

Date: Wednesday, 20 July 2016
Time: 16:00-18:00
Venue: Room 802, Meng Wah Complex 8/F, HKU

Abstract

SWI is more sensitive than conventional gradient-echo technique for the detection of blood products. Both T2-weighted magnitude and phase information are employed to emphasize the magnetic susceptibility differences of various tissues or substances, such as blood products, iron, and calcification, by post-processing the magnitude images with a phase mask. Its role as a biomarker of Cerebral Amyloid Angiopathy (CAA), in detection of microbleeds and evaluation of iron loading in dementia will be discussed in this talk.

CA A is a vascular disease associated with stroke, especially recurrent hemorrhagic stroke. However, its presentation is variable, depending on the severity, and might not be diagnosed until autopsy. Autopsy studies show moderate to severe CAA with an age-dependent prevalence of 8% (age 75 to 84) to 12% (age of 84) and has a higher prevalence in patients with Alzheimer’s disease.

CAA is well-known to manifest as amyloid protein deposits in small arteries. As the beta-amyloid protein build up within the elastic lamina of vessel walls, vessels loose elasticity and become fragile. Fragile vessels are more easily damaged, and tiny hemorrhages (cerebral microbleeds) occur in and around the arteriole vessel wall. A post-mortem 3T MR imaging study revealed that hypointensities in the lobar areas identified with SWI correspond to a variety of abnormalities related to CAA in dementia patients. The authors suggested the use of SWI as a biomarker of CAA. However, a recent 3T SWI study showed high small hypointense foci in patients with vascular dementia, AD and dementia with Lewy bodies (DLB), and there was a significant lobar (versus basal ganglia/thalamus or infratentorial region) predilection for AD, DLB, and frontotemporal lobar dementia (FTLD).

Oxidative damage of the human brain has been shown to be strongly related to aging and AD, and the pathophysiologic role of tissue iron has been implicated. Detection of iron deposition in aging, mild cognitive impairment and AD has been reported using MRI, but further validation of these findings is warranted.