Bright and dark ripples (bands, lines, rings) adjacent to and paralleling high-contrast interfaces. It is due to the inability of truncated Fourier series or finite number of sine waves to perfectly describe a square wave (step-like change in signal). It is usually more pronounced in the phase encoding direction. The ripples have constant periodicity for a given axis and uniform decay. The periodicity depends on the acquisition matrix. Gibbs phenomenon refers to the 8.95% signal overshoot at a signal boundary that occurs with an infinite Fourier series and is due to the lack of convergence of the Fourier integral at point of function discontinuity.