a method for evaluating the spatial resolution of a volumetric medical imaging system comprises imaging an image phantom including a sphere surrounded by a uniform medium . the image phantom is imaged and the resulting volumetric data set is used to generate an edge response function in three dimensions . differentiating the edge response function produces a plane spread function . the method simultaneously measures the spatial resolution in all directions , providing a bulk measurement resolution . alternatively , the edge response function may be assembled in a manner so as to independently measure the axial and trans - axial resolution of the volumetric imaging system .