1. A computer-implemented method for determining a contrast arrival phase in a plurality of temporal phases of an image of tissue, comprising the steps of: establishing in a region of interest, within the image of the tissue, intensity statistics for voxels in each of the plurality of phases; receiving a pre-contrast intensity threshold value of the statistics; preselecting the voxels within the region of interest based upon temporal enhancement characteristics for each of the voxels; computing statistics for predetermined dynamic phases from the preselected voxels; determining a cutoff threshold based on the statistics; determining by a computer, a relative change in statistics for each of the predetermined dynamic phases with respect to the cutoff threshold by determining the contrast arrival phase as a function of temporal increase in frequency of the preselected voxels having post-contrast signal intensity values that exceed the pre-contrast signal intensity threshold value; and reporting the contrast arrival phase to an output device based upon the determined relative change.