Coded aperture imaging of gamma-ray sources with an off-axis rotating slit

The rotating slit is a time-varying coded aperture that can be used advantageously with a scintillation camera in imaging of static radioactive objects. The coded image obtained from an on-axis slit conveys no tomographic information, but when the slit is displaced away from the axis of rotation, tomographic information can be obtained. From one set of coded images, each plane of a 3-D object can be brought in focus by shift operations and a computed-tomography algorithm. Inverse filtering is necessary to remove the side lobes of the point spread function. The intrinsic resolution of the camera, the slit width, the filter function, and the display all affect the lateral resolution, while the object distance, the off-axis distance of the slit, and the lateral resolution determine the longitudinal resolution of the system.