Phase difference images, obtained by comparing data from motion-sensitized and -unsensitized spin-echo sequences, can be used to study intravoxel coherent motions. The resulting images, which have been routinely used to study fast flowing blood, may potentially yield information about perfused flows and bulk tissue motion. The likely limitations and potential of this technique applied to the central nervous system are reviewed with reference to parallel studies of intravoxel incoherent motion.