For explaining functional fMRI in an easy and simple manner, it can be said that fMRI is similar to MRI in the sense that it involves MRI machine and produces scans similar to MRI except it highlights the "functional brain" area . It is based on the principle that when an area of the brain is in use, the blood flow to that region increases. So, the neuronal activity changes the blood flow ( Hemodynamic Response) and which, in turn, changes the magnetization between oxygen -rich and oxygen-poor blood. f MRI uses the blood-oxygen level dependent ( BOLD) contrast and maps the neuronal activity by imaging the changes in hemodynamic response of a brain area when a patient performs an activity.
When a person is told to perform some activity or a stimulus is received by a patient ( Paradigm) , the neurons corresponding to that functional area of the brain become active , local blood flow to those brain regions increases , and oxygen rich ( oxygenated) blood displaces oxygen- depleted ( deoxygenated) blood around 2 seconds later. his rises to peak over 4-6 seconds , before falling back to original level. Deoxygenated Hemoglobin (dHB) is more magnetic ( paramagnetic) than oxygenated Hb , which is virtually resistant to magnetism ( diamagnetic). This difference to magnetism can lead to an improved MR signal and which can be mapped to show which neurons are active at a time.
Neurosurgeons may use fMRI for pre-surgical planning for lesions close to eloquent area of the brain, e.g., motor area. Similarly , language , memory areas can be mapped.
fMRI had also been used in research, effect of stroke, brain injury on brain functions , effect of drugs, lie-detection, etc.
Sources:
Radiopedia.org
Wikipedia.org
When a person is told to perform some activity or a stimulus is received by a patient ( Paradigm) , the neurons corresponding to that functional area of the brain become active , local blood flow to those brain regions increases , and oxygen rich ( oxygenated) blood displaces oxygen- depleted ( deoxygenated) blood around 2 seconds later. his rises to peak over 4-6 seconds , before falling back to original level. Deoxygenated Hemoglobin (dHB) is more magnetic ( paramagnetic) than oxygenated Hb , which is virtually resistant to magnetism ( diamagnetic). This difference to magnetism can lead to an improved MR signal and which can be mapped to show which neurons are active at a time.
Neurosurgeons may use fMRI for pre-surgical planning for lesions close to eloquent area of the brain, e.g., motor area. Similarly , language , memory areas can be mapped.
fMRI had also been used in research, effect of stroke, brain injury on brain functions , effect of drugs, lie-detection, etc.
The activity performed or stimulus received by the patient is termed a paradigm, and each is designed to elicit a specific cortical response. The four common stimuli are: visual , motor, speech and memory paradigm.
Study/ testing designs in fMRI:
Block design
uses repeated blocks of activity (paradigm) separated by blocks
of inactivity of alternative activity. This is by far the most
frequently used study design in clinical fMRI.
Event related design
involves individual events rather than blocks, and can be randomly distributed
during the study. Sources:
Radiopedia.org
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