Functional magnetic resonance imaging
Functional magnetic resonance imaging (fMRI) is an advanced imaging technique derived from traditional magnetic resonance imaging (MRI), primarily used to monitor and visualize real-time metabolic changes within the brain. Developed in the early 1990s, fMRI enables researchers and clinicians to observe brain activity in response to specific tasks or questions, facilitating the understanding of normal brain functions through a process referred to as "brain mapping." This technique is considered safer than x-rays or computed tomography (CT) scans since it does not use ionizing radiation, and it can provide high-quality images that help differentiate between healthy and abnormal brain tissues.
The fMRI process relies on the blood oxygenation level dependent (BOLD) effect, where changes in blood flow and oxygen levels in specific brain areas are measured, allowing for insights into brain activity. During an fMRI scan, individuals may perform tasks or respond to stimuli while being monitored, with the resulting images reflecting the dynamic activity of various brain regions. Despite its advantages, fMRI has limitations, such as its inability to pinpoint individual neuron activity and susceptibility to motion artifacts. Furthermore, the interpretation of fMRI data can be complex and sometimes misleading, prompting ongoing research to refine the technique and enhance its applications in understanding diverse psychological and neurological phenomena.
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Functional magnetic resonance imaging
Magnetic resonance imaging (MRI) is a radiological technique that uses electromagnetism, not radiation, to examine the body’s internal structures. Functional magnetic resonance imaging (fMRI), developed in the early 1990s, is an MRI procedure used to view and measure real-time metabolic changes occurring deep in the brain. Like other imaging procedures, fMRI is used to help diagnose injuries and disorders, and to assess the brain prior to surgery.
Unique to fMRI is the ability to observe a person’s brain activity as the individual responds to various simple questions or tasks. Consequently, fMRI has launched research into normal brain function, known as “brain mapping,” and helped determine whether a patient is comatose or vegetative.
Overview
As compared to x-rays and computed tomography (CT) scans, which both use radiation, fMRI is much safer for the patient or research subject and may offer higher-quality images that, in diagnosis, can help distinguish between abnormal and normal tissues.
An MRI scanner consists of a circular magnet surrounding a tube into which the patient or subject slides on a moveable exam table. Electrical current is run through wire coils inside the machine to create a magnetic field. In fMRI, the magnetic field realigns the protons of hydrogen atoms found in water (H2O), and all together the nuclei emit a magnetic signal that a computer records and translates into images. Signal strength varies depending on where the hydrogen atoms are, making it possible to “map” their locations in the brain.
During an fMRI scan, the patient or subject periodically must perform small physical tasks or respond to simple questions to activate specific areas of the brain. For some experiments or tests, audiovisual information may be presented through goggles and/or headphones.
Most fMRI scans are based on the blood oxygenation level dependent (BOLD) effect. When the individual engages in an activity, blood flow increases to the responsible brain area(s). Meanwhile, blood oxygen levels briefly decrease, then surge in response to higher demand, and ultimately return to normal. Blood varies in its ability to be magnetized, giving a stronger magnetic signal when it is oxygen-rich. These changes in blood flow, blood oxygen level, and the corresponding magnetic shifts enable fMRI equipment to record brain activity in a given area. As of 2012, no fMRI technique could measure the number of neurons that are activated (firing) or determine what, if any, effect the active area has on its neighbors. According to a study published in the Journal of Neuroscience in August 2014, researchers found that blood flow levels in the brain did not always correspond with an increase in neural activity and recommended caution in interpreting the results of brain scans.
Movement can distort fMRI images, so braces are used to immobilize the head during scans. Similarly, metal in implanted devices and other objects can interfere with signals, resulting in lower-quality images. The cost, size constraints, and session duration of fMRI further limit its use. Its use in research has also been questioned. It only identifies activity in broad, general areas of the brain, has lent itself to causational assertions about correlated events, and relies on statistical methods that can be easily misinterpreted. Researchers are trying to devise better fMRI-based techniques to record neuron-level signal changes, detect changes more quickly, and increase the signal-to-noise ratio to improve data collection.
Studies using fMRI have explored such clinical topics as motor and sensory function, speech processing, and epileptic seizures. Learning, memory, language, pain, and emotion are among the many psychological phenomena that researchers are attempting to understand using fMRI.
Bibliography
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