Recent trend was focused on identification of brain regions involved with characteristic oxygenation-sensitive MRI response function. Still there is paucity in information of metabolic requirements and hemodynamic response in different brain functions. For that, blood flow provides the substrates. Increased neuronal activity needs the metabolic support. fMRI and conventional neurophysiological techniques have been in use to localize the specific functions of the human brain. Last decade was an excitement for clinical application of 1.5 T-7.0 T clinical scanners to observe functional activity of visual cortex, the motor cortex and Broca's area of speech and language-related activities. Deoxyhemoglobin acts as paramagnetic endogenous contrast agent and alters the T2* weighted magnetic resonance image signal and serves as the source of the signal for fMRI. Historically, these observations initially were supported by reports on local reduction in deoxyhemoglobin due to increased blood flow without change in oxygen extraction. In fact, all task performances such as arousal, attention, alertness, adaptation, sleep, or consciousness that affect the vascular hemodynamics do interfere with oxygenation-sensitive mapping by fMRI techniques.
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Neurovascular and neurometabolic coupling establishes the critical link between a focal change in neuronal activity and MRI-detectable observations.
#Scholar one human brain mapping registration
The paper reviews the physiological basis of fMRI signal origin and contrast mechanisms with state-of-art fMRI segmentation and registration algorithms to identify cortical visual response and event related cortical areas associated with neurophysiological measurements and potential image post-processing directions in future. Presently, fMRI serves as non-invasive imaging of neurophysiological activities of brain that depend more on physiological characteristics of brain. Later fMRI applications extended the understanding of neuronal and motor activities associated with different brain regional functions. High resolution, noninvasive neural activity by a blood oxygen level dependent signal has tremendous potentials for assessing the neurological status and neurosurgical risk. It extended brain anatomical imaging to map structures and specific function of human brain. Functional magnetic resonance imaging (fMRI) was introduced to map the changes in brain local blood flow and oxygenation or hemodynamics that correspond to regional neuronal activity of brain accompanying metabolic events. Recent investigations focused on specific brain regional and functional specificity to delineate the specific distribution of neural activities at a given moment in the brain as a whole. Latest developments are reviewed for clinical applications of fMRI along with other different neurophysiological and imaging modalities. This review article summarizes the physiological basis of fMRI signal, its origin, contrast enhancement, physical factors, anatomical labeling by segmentation, registration approaches with examples of visual and motor activity in brain.
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Registration algorithms provide geometric features using two or more imaging modalities to assure clinically useful neuronal and motor information of brain activation. Segmentation algorithms provide brain surface-based analysis, automated anatomical labeling of cortical fields in magnetic resonance data sets based on oxygen metabolic state. Image processing is performed by segmentation and registration methods. Functional magnetic resonance imaging (fMRI) is recently developing as imaging modality used for mapping hemodynamics of neuronal and motor event related tissue blood oxygen level dependence (BOLD) in terms of brain activation.