Functional Magnetic Resonance Imaging (fMRI) examination is an imaging method developed to show regional, time-varying changes in brain metabolism, in other words, changing in areas of the brain that are active during a task.
How it works
Oxygen is delivered to brain cells – neurons by hemoglobin in capillary red blood cells. When neuronal activity increases there is an increased demand for oxygen and the local response is an increase in blood flow to regions of increased neural activity. Hemoglobin is diamagnetic when oxygenated but paramagnetic when deoxygenated. This difference in magnetic properties leads to small differences in the MR signal of blood depending on the degree of oxygenation. Since blood oxygenation varies according to the levels of neural activity these differences can be used to detect brain activity. This form of MRI is known as blood oxygenation level dependent (BOLD) imaging. The idea that changes in blood oxygenation could drive measurable signal changes in brain MR images was introduced by Ogawa and colleagues in 1990. More…
fMRI is becoming the diagnostic method of choice for learning how a normal, diseased or injured brain is working, as well as for assessing the potential risks of surgery or other invasive treatments of the brain.
When is it used?
fMRI may be used to examine your brain’s anatomy, determine which parts of the brain are handling critical functions such as thought, speech, sensation and movement. This process is called brain mapping. fMRI is used to evaluate the effects in case of stroke, degenerative disease (Alzheimer’s) or guide brain treatment (surgical, radiation therapy). It also helps to monitor the growth of brain tumors and detect abnormalities within the brain that cannot be found with other imaging techniques.
Rules, by which you should prepare for the examination, are basically the same as for classical MRI. About how to prepare for an MRI examination you can read more here. During the fMRI examination, you will perform simple tasks during the imaging process, such as tapping your toes or fingers, reading, listening to an audio recording, pursing your lips, wiggling your tongue, viewing pictures and/or playing word games. These tasks will cause increased metabolic activity in the responsible areas of the brain. Increased activity results in expanding blood vessels, chemical changes and the delivery of extra oxygen that will be recorded on fMRI images.