Analysis and correction of spatial distortions produced by the gamma camera.

Two types of distortions are produced by the gamma camera. One is nonuniform sensitivity re sponse over the detecting area. The second is spatial distortion; that is, the displacement from their true positions of the xand y-coordinates of a scintilla tion. This component of camera image distortion arises in the resolution and transfer of the xand y-coordinates of a scintillation and results in a non linear relationship between the object and the image. The existence of spatial distortions in cameraproduced radionuclide images is well known and has been recognized and observed by several workers (1-6). Today because of the present emphasis on com puter processing and analysis of the data image, gamma cameras are commonly interfaced to digital computers. This affords an opportunity to quantita tively analyze the inherent distortions introduced by the camera-computer system to any clinical image and to correct them by digital techniques. Nonuniform sensitivity of the camera system may be analyzed by uniformly irradiating the detecting crys tal and corrected by storing a digitized matrix of correction factors for subsequent application to any data matrix (7). Corrections for sensitivity distor tion are applied routinely to digitized images by some laboratories. However, spatial distortions produced by the gamma camera are not currently corrected. The purpose of this study is to determine and evalu ate the spatial distortions in radionuclide images caused by a gamma camera and to develop a method for routine correction of these errors by digital com putation.