How can we measure blood flow?
Two brain imaging techniques, PET and fMRI, measure blood flow through the brain. Active areas of the brain use more energy and so need a greater supply of oxygen and glucose. More blood is directed to these areas to meet the demands of the active neurons. PET tracks blood flow by using labelled chemicals, while fMRI monitors the oxygen content of the blood.
What is fMRI?
What is PET?
Scientists have used PET to investigate what different areas of the brain do, how the brain develops and how drugs affect it. The information gathered from PET scans can be added to MRI images from the same person - this provides a better idea of exactly where the activity is taking place. PET scans can detect changes due to brain damage, epilepsy, Alzheimer's disease and brain tumours, often earlier than is possible using other methods. But PET is an expensive and time-consuming technique.
How does PET work?
A PET scan detects radioactively labelled molecules (such as oxygen or glucose), which will be used by active neurons in the brain. The radioactive substance is injected into the patient's blood where it gives off positrons, which break down to produce gamma rays. A gamma ray detector traces the flow of blood around the body.