Abstract: Automated testing of the resolution capability of medical imagers, such as ultrasound scanners, magnetic resonance imagers and computed tomography equipment, is carried out using phantoms having coplanar arrays of target objects, such as spheres, the locations of which are precisely known. Images of the phantom at positions containing background material and the target spheres are taken, digitized and processed to determine in the digitized images the locations of the target spheres by making use of the known location and spacing of the spheres. Lesion signal-to-noise ratios are then calculated at the now located positions of the target spheres in the image, and this information may be utilized to determine thresholds for detectability that allow evaluation of the performance of the imager being utilized.