About Functional MRI

Functional MRI (fMRI), also called blood oxygen level dependent (BOLD) imaging, is a non-invasive tool for mapping brain function. The technique makes use of the differences in blood oxygenation levels when areas of the brain are recruited for a particular cognitive task. When oxygen molecules bind with the hemoglobin carried in the blood, the magnetic properties of the hemoglobin change. Deoxyhemoglobin is paramagnetic, while oxyhemoglobin is diamagnetic. The oxygenated blood will therefore produce an increased MRI signal intensity, which can be detected by acquiring images both while the task is being performed and during a resting state.

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In a typical fMRI session, the subject is asked to alternately perform a given cognitive task, such as finger tapping, and a control task. Statistical comparisons are made between the images from both datasets in order to determine which areas of the brain are involved in the task. In a typical fMRI session at the IRC, the durations of the cognitive task and the control task are 30 seconds each, and each task is performed five times, so that the total scan time is 5 minutes. As an image is acquired every 3 seconds, there are a total of 100 images acquired: 50 for the cognitive task, and 50 for the control task.

fMRI has both research and clinical applications. Projects currently underway at the IRC include a mapping of language distribution in normal pediatric subjects, and use of fMRI for presurgical planning for neurosurgery patients.