Blood-oxygenation-level–dependent imaging, or BOLD-contrast imaging, is a method used in functional magnetic resonance imaging (fMRI) to observe the Blood-oxygenation-level in different areas of the brain or other organs, which are found to be active at any given time.
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👉 Blood-oxygen-level dependent in the context of Resting state fMRI
Resting state fMRI (rs-fMRI or R-fMRI), also referred to as task-independent fMRI or task-free fMRI, is a method of functional magnetic resonance imaging (fMRI) that is used in brain mapping to evaluate regional interactions that occur in a resting or task-negative state, when an explicit task is not being performed. A number of resting-state brain networks have been identified, one of which is the default mode network. These brain networks are observed through changes in blood flow in the brain which creates what is referred to as a blood-oxygen-level dependent (BOLD) signal that can be measured using fMRI.
Because brain activity is intrinsic, present even in the absence of an externally prompted task, any brain region will have spontaneous fluctuations in BOLD signal. The resting state approach is useful to explore the brain's functional organization and to examine if it is altered in neurological or mental disorders. Because of the resting state aspect of this imaging, data can be collected from a range of patient groups including people with intellectual disabilities, pediatric groups, and even those that are unconscious. Resting-state functional connectivity research has revealed a number of networks which are consistently found in healthy subjects, different stages of consciousness and across species, and represent specific patterns of synchronous activity.
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Blood-oxygen-level dependent in the context of Functional magnetic resonance imaging
Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled: When an area of the brain is in use, blood flow to that region increases.
The primary form of fMRI uses the blood-oxygen-level dependent (BOLD) contrast, discovered by Seiji Ogawa and his colleagues in 1990. This is a type of specialized brain and body scan used to map neural activity in the brain or spinal cord of humans or other animals by imaging the change in blood flow (hemodynamic response) related to energy use by nerve cells. Since the early 1990s, fMRI has come to dominate brain mapping research because it is noninvasive, typically requiring no injections, surgery, or the ingestion of substances such as radioactive tracers as in positron emission tomography. Data acquired using fMRI, however, is frequently corrupted by noise from various sources; hence, statistical procedures are used to extract the underlying signal. The resulting brain activation can be graphically represented by color-coding the strength of activation across the brain or the specific region studied. The technique can localize activity to within millimeters but, using standard techniques, no better than within a window of a few seconds. Other methods of obtaining contrast are arterial spin labeling and diffusion MRI. Diffusion MRI is similar to BOLD fMRI but provides contrast based on the magnitude of diffusion of water molecules in the brain.
Blood-oxygen-level dependent in the context of Seiji Ogawa
Seiji Ogawa (小川 誠二 Ogawa Seiji, born January 19, 1934) is a Japanese biophysicist and neuroscientist known for discovering the technique that underlies Functional Magnetic Resonance Imaging (fMRI). He is regarded as the father of modern functional brain imaging. He determined that the changes in blood oxygen levels cause its magnetic resonance imaging properties to change, allowing a map of blood, and hence, functional, activity in the brain to be created. This map reflected which neurons of the brain responded with electrochemical signals to mental processes. He was the first scientist who demonstrated that the functional brain imaging is dependent on the oxygenation status of the blood, the BOLD effect. The technique was therefore called blood oxygenation level-dependent or BOLD contrast. Functional MRI (fMRI) has been used to map the visual, auditory, and sensory regions and moving toward higher brain functions such as cognitive functions in the brain.
In 2020, Ogawa was appointed as Osaka University Distinguished Honorary Professor. He is the second scholar to receive this title after Nobel Prize winner Yoichiro Nambu.