BASIC SCIENCES PHYSICS AND RADIATION BIOLOGY Correction for Out-of-Focal-Plane Blurring in a Simulated Multiplane Tomographie

A technique has been developed to remove out-of-focal-plane blurring from co ronal and axial images made using a multiplane tomographic scanner. The tech nique uses a combined smoothing and differential operator that is applied to the axial images. It has been tested using computer-simulated images, with favorable results. The usefulness of the technique in a real system has yet to be deter mined. J NucÃ-Med 20:1194-1196, 1979 Since its initial development (1,2) the multiplane tomographic scanner has proved to be a useful clinical tool, providing coronal images of superior diagnostic quality (3-6). An inherent problem with the scanner, however, is that, although activity in specified coronal planes can be sharply focused and activity in other planes blurred, the out-of-focus activity is still superimposed on the focused planes. This out-of-focal-plane blurring is evident clinically on liver scans, where lesions in a given liver plane may be obscured by overlying activity (3). Interest has developed (7,8) in the use of a multiplane tomographic scanner combined with a computer to provide axial and other sectional images as well as those in the coronal plane. Axial imaging would be helpful both because it could provide better information on the depth distribution of radiotracer in the body, and because the gamma images produced could be compatible with transmission CT images. Out-of-focal-plane blurring will appear on axial images as two cones of activity meeting at each source location, with the cone's apical angle equal to the acceptance angle of the collimator used (7). Out-of-focal-plane blurring results from the use of back projection in the reconstruction of images. The two cones of activity noted in axial imaging are in fact