What is Functional MRI (fMRI)?

Functional MRI (fMRI) is the use of MRI to detect localized changes in brain activity, usually in the form of changes in cerebral metabolism, blood flow, volume, or oxygenation in response to task activation. In other words, Functional MRI provides images of brain activity in response to various stimuli. These changes are interrelated and may have opposite effects. For instance, an increase in blood flow increases oxygenation, whereas an increase in metabolism decreases it. The most common ways of detection is measuring the changes in the magnetic susceptibility of haemoglobin. Oxygenated blood is diamagnetic and deoxygenated blood is paramagnetic. The differences lead to a detection method called blood oxygen level dependent contrast (BOLD).

Because these changes are very small, images before and after task initiation are subtracted from each other and the resultant difference image is overlaid on a standard image. Special care is taken when obtaining these images because the effect is small and can be corrupted by several source of noise. Normally, hundreds of images are taken for each plane position and statistical analysis is used to produce the final image. Source of noise errors are thermal noise, head movement and respiratory and cardiac cycles.

Application of Functional MRI (fMRI)

Functional MRI has been used widely to map regions of the brain connected to stimuli, activities and higher-level cognition.

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