The ability to measure brain functions non-invasively is important both for clinical diagnoses and research in neurology and psychology. Two main imaging techniques are used: positron emission tomography (PET), which reveals metabolic processes in the brain; and activity of different brain regions is measured on the basis of the cells’ oxygen consumption by magnetic resonance imaging (MRI). A direct comparison of PET and MRI measurements was previously difficult because each had to be performed in a separate machine. Scientists have now successfully combined both methods.