Moire Fringes

Moire fringes are an interference pattern most commonly seen when doing gradient echo images with the body coil as shown in the figure.
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 and is similar to the effect of looking though two screen windows.