Understanding haemodynamics in neurodegenerative disease

In this thesis, the haemodynamic, functional and structural changes in Alzheimer's Disease, Huntington's Disease and Multiple Sclerosis are assessed at 7T. Across all chapters, there is a focus on the use of Arterial Spin Labelling (ASL) to provide haemodynamic measures of perfusion (or cerebral blood flow) and transit time (TT) to provide a useful marker of disease. Arterial Spin Labelling (ASL) has the advantage that it is a non-invasive method to measure perfusion using magnetic resonance imaging (MRI). Clinically, perfusion is assessed using contrast-enhanced techniques which requires the intravenous administration of an exogenous gadolinium-based contrast agent, such as Prohance-TM and Gadovist-TM. Contrast-enhanced techniques typically provide higher SNR than ASL methods, however the non-invasive nature of ASL makes it a safe method suited for repeated measures in any subjects, including those with poor renal clearance. Additionally, gadolinium contrast agents have been shown to accumulate in neuronal tissue, and until the clinical significance of this is determined, contrast-enhanced scans should be performed with caution. In Chapter 5, arterial spin labelling is used to assess cerebral perfusion in a patient group with Alzheimer's Disease (AD) and compared with an age-matched healthy control group (HC). Functional MRI (fMRI) is used to assess functional connectivity within the default mode network (DMN) and measures compared between the AD and HC group. In addition, high resolution structural data is acquired to assess the effects of atrophy in AD. Results demonstrate a significant decrease in grey matter perfusion and a significant increase in grey matter transit time in the AD group compared the HC group. A trend showing a decrease in functional connectivity in the DMN was found in the AD group as compared to the HC group. As expected, significant grey matter loss and cortical thinning were observed in the AD group compared to the HC group. Secondly, haemodynamic and vascular changes in a Huntington's Disease (HD) patient group are assessed and compared with healthy age matched controls (HC). Phase contrast angiography is used to assess vessel density and vessel radius distributions between the two groups. Structural data was also acquired to assess grey matter volume and cortical thickness differences between the two groups. A significant reduction in perfusion was found in grey matter, putamen and the caudate in the HD group compared to the HC group. The ASL transit time was found to be significantly increased in the caudate and putamen in the HD group compared to the HC group. Phase contrast angiography data showed an increase in the frequency of smaller vessels (0.15-0.35mm) in the HD group compared to the HC group, whereas larger vessels appeared more frequently in the HC group. A significant reduction in grey matter volume was also observed in the HD group compared to the HC group, which manifested as thinning of the cortical ribbon. In the final study of this thesis, high spatial resolution arterial spin labelling is used to assess perfusion inside cortical lesions and compare with perfusion in surrounding normal appearing grey matter in a Multiple Sclerosis (MS) patient group. Grey matter perfusion as a function of distance from the cortical lesions was also assessed. It was found that cortical lesions have reduced perfusion compared to surrounding normal appearing grey matter. Perfusion increased and stabilised immediately outside of the cortical lesion itself, suggesting that the perfusion deficit observed is highly spatially localised