fMRI is a special application of
MRI used to look at
brain function,
more or less. As the various parts of the brain work, they
demand freshly
oxygenated
blood; the sudden
perfusion of blood to a particular brain area in response to increased
workload causes the
magnetic susceptibility of that brain area to ever so slightly change --
In other words, the
signal emitted by any particular piece of brain will
fluctuate over
time depending on its supply of oxygenated blood and the rate at which it
metabolilizes that supply.
The cool part is this: if you know what your particular brain is thinking about at any given time during the scan (i.e., you give the brain some interesting cognitive task to do,) you can associate brain the signal changes you see with the task that the brain is working on.
The most common application of fMRI is in research, usually cognitive neuroscience research. Psychiatrists and radiologists also use fMRI methods in the hopes that they may be some day developed to the point they can be used to diagnose or even treat disesase.
And the BEST part is that fMRI requires *really* powerful magnets, fiber optic button boxes and ton's of NIH dollars.