Brain perfusion imaging
Perfusion MRI gives access to information on the capillary microcirculation of tissue. The main quantitative parameters measured are blood volumes and temporal data (transit time, time to contrast peak…).
The ultimate goal of perfusion MRI is to measure or assess the blood flow irrigating the explored organ, expressed in milliliters per 100 gram of tissue per minute. This flow corresponds to microcirculatory tissue perfusion rather than the flow of the main vascular axes.
Differentiating between perfused and non-perfused tissue relies on the use of an intra-vascular tracer that is either:
- exogenous: an injected contrast agent (generally non diffusible, i.e. only present in the vascular space and that will not cross the normal blood-brain barrier).
- or endogenous: by tracing the hydrogen nuclei of the water circulating in the blood (in this case, the tracer is diffusible, i.e. there is an exchange between intra- and extravascular compartments).