In image-guided surgeries (IGSs) and radiology, images are the main source of information. As image data provide the differentiation between normal and abnormal tissues in the human, the images need to be reliable and they need to provide accurate spatial representation of the patient. This research concentrates on the accuracy assessment of IGS devices in general and then specifically on the spatial accuracy of a common magnetic resonance (MR) imager and a mobile three-dimensional surgical computed tomography (CT) scanner. The accuracy assessment tool had been designed to be universal and to enable its use in the hospital setting. In this study, it was used in detecting the spatial accuracy of a commercial surgical CT scanner, the O-arm, and a 1.5-T MR imager. The results show the tendency of magnetic resonance imaging to produce slight decreases in spatial accuracy toward the fringes of the images from the isocenter. Furthermore, the results indicate that the accuracy of both scanners was within pixel size and thus highly accurate in the region of surgical interest of this study.