Fmri

Functional magnetic resonance imaging or fMRI is a neuroimaging technique that measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area of the brain is in use, blood flow to that region also increases.

Overview

The primary form of fMRI uses the Blood-oxygen-level dependent (BOLD) contrast, discovered by Seiji Ogawa. This is a type of specialized brain and body scan used to map neural activity in the brain or spinal cord of humans or other animals by imaging the change in blood flow (hemodynamic response) related to energy use by brain cells. Since the early 1990s, fMRI has come to dominate the brain mapping field due to its low invasiveness, lack of radiation exposure, and relatively wide availability.

History

The fMRI concept builds on the earlier MRI scanning technology and the discovery of properties of oxygen-rich blood. MRI brain scans use a strong, permanent, static magnetic field to align nuclei in the brain region being studied. Another magnetic field, the gradient field, is then applied to spatially locate different nuclei. Finally, a radio frequency (RF) field is applied to kick the nuclei to higher magnetization levels, with the RF field then turned off to allow the nuclei to relax back to the original magnetization level, producing a signal that can be detected and turned into an image.

Applications

fMRI has been used to produce activation maps of cognitively normal individuals and patients with various neurological and psychiatric disorders. It can also be used to guide neurosurgery, and to monitor brain responses to therapies.

Limitations

While fMRI is a powerful tool, it is important to remember that it measures neuronal activity indirectly by blood flow changes. It does not measure neuronal activity directly and relies on the assumption that changes in blood flow are related to neuronal activity.

See also

• Magnetic resonance imaging
• Neuroimaging
• Blood-oxygen-level dependent

References

Fmri Resources
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