HARP (algorithm)
![Demonstration of the HARP processing of a tagged cardiac MRI slice. (a) An MR image with vertical SPAMM tags. (b) shows the magnitude of its Fourier transform. By extracting the spectral peak inside the circle, a complex image is produced with a magnitude (c) and a phase (d).](/Images/godic/202501/17/HARP_Algorithm_Processing3204.png")
![Result of HARP tracking of a tagged cardiac MRI slice.](/Images/godic/202501/17/HARP_Tracking3204.png"){kind=tracking}
Harmonic phase (HARP) algorithm is a medical image analysis technique capable of extracting and processing motion information from tagged magnetic resonance image (MRI) sequences. It was initially developed by N. F. Osman and J. L. Prince at the Image Analysis and Communications Laboratory at Johns Hopkins University. The method uses spectral peaks in the Fourier domain of tagged MRI, calculating the phase images of their inverse Fourier transforms, which are called harmonic phase (HARP) images. The motion of material points through time is then tracked, under the assumption that the HARP value of a fixed material point is time-invariant. The method is fast and accurate, and has been accepted as one of the most popular tagged MRI analysis methods in medical image processing.