Alterations to the integrity of the blood brain barrier (BBB) appear to be mechanistically important in the development of neurodegenerative disease. Traditionally, BBB integrity is measured by investigating the transfer of intravascular contrast agents, such as gadolinium or evans blue, into the brain parenchyma. Alternative, non-invasive, MRI techniques have been proposed that harness arterial spin labelling sequences to assess the permeability of the BBB to water, potentially yielding a sensitive marker of subtle pathological changes. In this lecture I will review these non-invasive techniques and how they have been applied to investigate abnormalities to BBB integrity in disease.
TARGET AUDIENCE
Those with an interest in: ·
OUTCOME/OBJECTIVES
Attendees will better understand how to perform and interpret studies that aim to assess the integrity/permeability of the blood brain barrier (BBB) using non-contrast MRI techniques.
As such, I will describe how arterial spin labelling (ASL) methods are combined with different contrast mechanisms during the image readout in order to separate the intravascular and extravascular distribution of labelled spins. These contrast mechanisms include relaxometry, diffusion weighting (IVIM) and magnetisation transfer. In doing so, these techniques aim to assess the rate of flux of water from the blood, across the BBB, and into the tissue, as a surrogate index of BBB permeability to water.
I will describe how these measurements may yield valuable biomarkers for a wide spectrum of brain disorders, but also their implications for accurate cerebral blood flow (CBF) quantification using ASL techniques.
Finally I will summarise the progress made using these non-invasive techniques to assess changes in BBB permeability to water including Alzheimer’s disease, brain tumours, sleep apnea and ageing.