Cerebral microbleed detection and mapping: principles, methodological aspects and rationale in vascular dementia

Cerebral microbleeds (CMBs) have emerged as an important new imaging manifestation of sporadic cerebral small vessel diseases - mainly hypertensive arteriopathy and cerebral amyloid angiopathy - which are highly prevalent in the elderly and have a critical role in vascular cognitive impairment and dementia. With the development of MRI techniques that are exquisitely sensitive to the products of bleeding, including T2*-weighted gradient-recalled echo (T2*-GRE) and susceptibility-weighted imaging (SWI), CMBs have been detected in ever-increasing numbers of patients, including those with vascular cognitive impairment and dementia, as well as in population-based samples of healthy elderly people. Our increased ability to image CMBs and hence to see the development and progression of cerebral small vessel disease raises many clinical and pathophysiological questions about the mechanisms, diagnosis and monitoring of cognitive impairment. In order to tackle these questions, it is important to be able to reliably detect, define and map CMBs in the brains of elderly people. In this review, we consider radiological detection methods, criteria for defining CMBs (including a practical approach to the identification of CMB "mimics"), and the use of standardised rating scales. We also briefly discuss the potential for automatically detecting and quantitatively mapping CMBs in future.