How SPECT Differs
from MRI, fMRI,
and PET

A SPECT scan is similar to an MRI study in that both can show 3D images and slices of the brain. However, whereas MRI shows the physical anatomy or structure of the brain, SPECT shows how the brain actually works. PET, another nuclear imaging technique, is very similar to SPECT but is a more costly imagining technique.

Both SPECT and PET scans show areas of the brain that are healthy, overactive, or underactive. MRI does not give any information on function. A newer version of MRI, functional MRI or fMRI, is also capable of showing brain activity and is used extensively in scientific research on brain function. fMRI shows instantaneous neural activity to see how the brain responds to a specific stimulus. With SPECT, we see brain activity averaged over a few minutes so it is better at showing the state of someone's brain at rest or during a concentration task, rather than just a moment in time. For both fMRI and PET, the images are acquired when a patient lies in the camera, which can be uncomfortable, noisy, and anxiety provoking. For SPECT, the image occurs when a patient is in the injection room, making the procedure more reliable and easier to do.