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The cause is thought to be thermoelastic expansion of portions of auditory apparatus, and the generally accepted mechanism is rapid (but minuscule, in the range of 10 −5 °C) heating of brain by each pulse, and the resulting pressure wave traveling through the skull to the cochlea.
Since the early 1990s, fMRI has come to dominate brain mapping research because it does not involve the use of injections, surgery, the ingestion of substances, or exposure to ionizing radiation. [5] This measure is frequently corrupted by noise from various sources; hence, statistical procedures are used to extract the underlying signal.
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.
Averaging is necessary because of the complex spectral structures and relatively low concentrations of many brain metabolites, which result in a low signal-to-noise ratio (SNR) in MRS of a living brain. fMRS differs from MRS by acquiring not one but multiple spectra at different time points while the participant is inside the MRI scanner.
Noise in fMRI can arise from a variety of different factors including heart beat, changes in the blood brain barrier, characteristics of the acquiring scanner, or unintended effects of analysis. Some researchers have proposed that the variability in functional connectivity in fMRI studies is consistent with the variability that one would expect ...
Electroencephalogram or EEG can be used to measure the brain since the signal-to-noise ratio is poor, so noise produced by the brain can be detected in vivo. Local field potentials can be used to test the noise present in large neuronal networks. This measure of voltage can be used to determine the interconnectivity by the level of noise. [10]
This is most marked with high-field machines, [40] and rapid-imaging techniques in which sound pressure levels may reach 120 dB(A) (equivalent to a jet engine at take-off), [41] and therefore, appropriate ear protection is essential for anyone inside the MRI scanner room during the examination. [42]
Modern 3 Tesla clinical MRI scanner.. Magnetic resonance imaging (MRI) is a medical imaging technique mostly used in radiology and nuclear medicine in order to investigate the anatomy and physiology of the body, and to detect pathologies including tumors, inflammation, neurological conditions such as stroke, disorders of muscles and joints, and abnormalities in the heart and blood vessels ...