Cerebral small vessel disease (SVD) is associated with increased risks of stroke and dementia, however the mechanisms remain unclear. Low cerebral blood flow (CBF) has long been suggested and accepted, but clinical evidence is conflicting. On the other hand, growing evidence suggests that increased intracranial pulsatility due to vascular stiffening might be an alternative mechanism. Pulse-gated phase-contrast MRI is an imaging technique that allows measuring of CBF contemporaneously with pulsatility in multiple vessels and cerebrospinal fluid (CSF) spaces. The overall aim of this thesis was to provide an overview of existing clinical evidence on both hypotheses, to test the reproducibility of CBF and pulsatility measures in phase-contrast MRI, and to explore the relationship between CBF and intracranial pulsatility and SVD features in a group of patients with minor stroke and SVD changes on brain imaging. I first systematically reviewed and meta-analysed clinical studies that have assessed CBF or intracranial pulsatility in SVD patients. There were 38 studies (n=4006) on CBF and 27 (n=3356) on intracranial pulsatility. Most were cross-sectional, and longitudinal studies were scarce. There were large heterogeneities in patient characteristics and indices used particularly for measuring and calculating pulsatility. Methods to reduce bias such as blinding and the expertise of structural image readers were generally poorly reported, and many studies did not account for the impact of confounding factors (e.g. age, vascular risk factors and disease severity) on CBF or pulsatility. Evidence for falling CBF predating SVD was not supported by longitudinal studies; high pulsatility in one large artery such as internal carotid arteries (ICA) or middle cerebral arteries might be related to SVD, but studies that measured arteries, veins and CSF in the same patients were very limited and the reliability of some pulsatility measures, especially in CSF, needs to be tested. In order to test the reproducibility of the CBF and intracranial pulsatility measures, I repeated 2D phase-contrast MRI scans of vessels and CSF on healthy volunteers during two visits. I also compared the ICA pulsatility index derived from the MRI flow waveform to that from the Doppler ultrasound velocity waveform in patients with minor stroke and SVD features. In 10 heathy volunteers (age 35.2±9.78 years), the reproducibility of CBF and vascular pulsatility indices was good, with within-subject coefficients of variability (CV) less than 10%; whereas CSF flow and pulsatility measures were generally less reproducible (CV>20%). In 56 patients (age 67.8±8.27 years), the ICA pulsatility indices in Doppler ultrasound and MRI were acceptably well-correlated (r=0.5, p
