Magnetic field changes in the human brain due to swallowing or speaking

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Abstract
Variations in the magnetic field in the human brain caused by the processes of swallowing or speaking are measured. In both processes, motion of the pharyngeal muscles, especially the tongue and jaw, alter the susceptibility‐induced magnetic field distribution at the brain slice being imaged. This leads to image warping, compromising the analysis of a time series of images, such as in functional magnetic resonance imaging (fMRI). These dynamic changes are assessed by acquiring a time series of images using a gradient‐echo asymmetric‐spin‐echo sequence (GREASE), a technique in which two images are acquired for each excitation–one during the gradient echo, and one during the latter part of the spin echo. The NMR phase difference between the two images is a measure of the magnetic field distribution. A series of brain images, acquired with this sequence while the subject either swallows or speaks, indicated negative magnetic field changes of up to O.087 ppm in the inferior region of the brain for both speaking and swallowing, and in some speech, additional positive changes of up to O.056 ppm in the frontal region of the brain were indicated.