1. A method, comprising: (a) overlaying a grid on a set of dynamic positron emission tomography (PET), single photon emission computed tomography (SPECT), computed tomography (CT) or magnetic resonance (MR) data collected from a subject, so as to define a set of voxels defining a plurality of cluster seeds; (b) extracting a respective time activity curve (TAC) for dynamic PET or SPECT data or time varying signals in the case of dynamic CT or MR data, for each voxel based on the data; (c) selecting a subset of the cluster seeds defined by the grid as initial cluster centroids of a set of clusters; (d) assigning each TAC to a respective cluster in the set of clusters containing a nearest one of the cluster centroids in a time-activity coordinate system; (e) extracting a respective average TAC for each cluster after step (d); (f) generating a parametric image based on the respective average TACs of step (e); (g) repeating steps (c) to (f) one or more times using respectively different subsets of the cluster seeds; and (h) averaging the parametric images generated by each realization of steps (c) to (f).