Functional magnetic resonance imaging
From Psy3241
Contents |
General
Functional magnetic resonance imaging (fMRI) is a fairly new noninvasive procedure that allows doctors and researchers to maps changes in the hemodynamics (blood flow) of the brain. This mapping can occur because of the increase of blood flow that accompanies neural activity in the brain.
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Procedure
The patient lies on a table and is pushed into the tube of the scanner. While inside, certain images can be projected on a screen that is visible to the patient. Depending on the images desired by the researchers, the patient may be asked to perform certain tasks that are hypothesized to activate specific parts of the brain. Thirty images are required to complete the testing: the first and last ten images serve as baseline conditions, while the middle ten images during the experimental task. In general, the testing lasts approximately 90 seconds.
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The machine itself uses a magnetic field and radio waves to take pictures of specific slices of the brain. When performing a task, as mentioned, certain parts of the brain activate, which is indicated by expanding blood vessels, chemical changes, and changes in the delivery of oxygen.
Specific imaging and experimental techniques vary from place to place because, as of yet, there is not a commercial package of software that generalizes the procedure.
Uses
Examine the brain's anatomy
Identify parts of the brain that could be responsible for certain functions
Help assess the effects of illness and injury to the brain
Monitor growth and function of brain tumors
In the future
fMRI has great potential for planning brain surgery; this potential is illustrated in the following image.
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The left image shows the patient's brain prior to the surgery, and it clearly shows an area of the brain essential for speech. In the image on the right, one can see that the part of the brain that included the tumor has been removed, but the speech area remains. The doctors involved in the surgery report that the patient expressed absolutely no deficit in speech.
There is a problem with this procedure, however, in that the speech area of the brain was identified using tasks known to activate parts of the brain known to be associated with speech. But what of parts that are unknown and that these tasks do not activate? Herein lies a major limitation.
