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Functional Magnetic Resonance Imaging (fMRI)

fMRI Scan

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Research and studies conducted by:
Dr. Nolan Altman and Dr. Byron Bernal of the Radiology Department

Functional Magnetic Resonance Imaging is a new procedure that shows us how the brain works.

Up to now we have had the computed-tomography-scan and magnetic resonance exams (Do the acronyms CT-Scan and MRI look more familiar to you?) to see the brain anatomy. These exams produce images that show the surface and the inner parts of the brain as in the best pictures of a scholarly book. But the function of the brain could not be assessed with these tools. For this purpose we used to deal with electro-encephalograms, also named EEG, and more sophisticated procedures like evoked potentials, a sort of electrical detection of the activity of the cortex. And these exams are not images of the brain. Instead they are a representation of groups of waves produced by the electrical activity of the cortex averaged at a given point. The bigger the wave (or the higher its frequency) the more the activity.

Medical information about fMRI scan

Functional magnetic resonance imaging (fMRI) is a development of MRI techniques that allows visualization of brain functions related to specific tasks. The study does not require any substance to be administered since it is based on the indigenous brain vascular response, requiring only cooperation for periods ranging from 15 to 60 minutes.

To date, several tasks have been utilized for mapping the brain cortex. Simple tasks include stimuli based on presentation of light, colors, tones, chords, music, syllables, movement of fingers and basic sensory perceptions. More complex and refined experiments have been implemented to map subtle cognitive functions. Currently, there is a vast armamentarium for mapping memory, attention, inhibition, face recognition, sensory discrimination, fear, etc. However, most fMRI work has been directed in mapping language. Language mapping has been performed in children and adults. Reading, listening to meaningful text, generating words, making semantic decisions, are the most frequent paradigms described in the abundant current literature on fMRI. The technique has received ample acceptance among neuroscientists interested in epilepsy for the potential it has to become a tool to replace the Wada test.

Functional MRI is based on small signal changes that result from the following cascade of events. A task elicits activation in one or several brain areas. These areas increase their metabolic demands, suffer vasodilatation, and alter their levels of deoxyhemoglobin and oxyhemoglobin. Since deoxyhemoglobin is a paramagnetic molecule, it influences the phase of local proton-spins, altering the source signal that is converted into images. Therefore, the image is a representation of local changes of levels of deoxyhemoglobin, related to the brain region performing a task.

Although fMRI is almost risk-free, it cannot be performed in patients with claustrophobia, metal implants, wires and pace-makers. Patients with vagal nerve stimulators, or dental braces, may be included. However, some degradation of the images is expected.

 

Image of MRI of headMRI. Horizontal cut of the head done a little bit over the level of the ears. Do you recognize the eyes here? They are located in the superior aspect of the image. Both hemispheres are divided by the middle line. The left hemisphere appears at the right of the image. The white matter is... White, yes. The cortex is gray. The red area shows strong activation of cortex working in language comprehension. The anterior yellow and green areas are zones that are less active.

 

  

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