Systems and methods (200) for characterizing spatial distortions in location data determined by an imaging system (102), for example as employed in imaged guided therapy A three dimensional phantom (104) is custom formed (204, 206, 210, 212, 214) for a desired imaging space (120) of a given imaging system (102) The phantom (104) includes a large plurality of control points (105) fixed rigidly in space to a high degree of known accuracy The phantom (104) is fixed to a stereotactic frame (108) defining a known calibrated reference or zero and imaged (216) An algorithm (218) customized for the phantom (104) determines the spatial locations of the control points (105). A (comparison 220) is made between the known and the determined spatial locations for at least a subset of the control points(105) The (comparison 220) results in indicia for any determined spatial distortions observed.