Moiré fringes
Moiré fringes are an interference pattern most commonly seen when acquiring gradient echo images using the body coil.
Because of lack of perfect homogeneity of the main magnetic field from one side of the body to the other, aliasing of one side of the body to the other results in superimposition of signals of different phases that alternatively add and cancel. This causes the banding appearance similar to the effect of looking through two screen windows.
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Physics and Imaging Technology: MRI
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