Functional magnetic resonance imaging

The development of anatomical neuroimaging enabled the in vivo visualisation of neuropathology in conditions such as stroke, facilitating differential diagnoses and early treatment. Since then scanning techniques have gone beyond structural detail to provide images relating to human brain function, and in the past decade these techniques have been joined by an impressive new imaging tool, functional magnetic resonance imaging (functional MRI). This has a spatial resolution within the millimetre scale and can capture responses in the brain occurring over a few seconds, although reconstruction and processing of the raw data commonly occur after scanning. Functional MRI is non-invasive and safe. It does not require radioactive tracer substances, unlike positron emission tomography (PET) or single photon emission tomography (SPET), and uses the brain's natural haemodynamic response to neural activity as an endogenous tracer. It can be carried out during the same session as routine magnetic resonance imaging in a clinical scanner. These features are making it increasingly popular in neuropsychiatric research.

The commonest form of functional MRI is blood oxygenation level dependent (BOLD) imaging.1 The BOLD signal depends on the ratio of oxygenated to deoxygenated haemoglobin. In regions of neuronal activity this ratio changes as increased flow of oxygenated blood temporarily surpasses consumption, decreasing the level of paramagnetic deoxyhaemoglobin. These localised changes cause increases in magnetic resonance signal, which are used …