Imaging with rotating slit apertures and rotating collimators.

The statistical quality of conventional nuclear medical imagery is limited by the small signal collected through low-efficiency conventional apertures. Coded-aperture imaging overcomes this by employing a two-step process in which the object is first efficiently detected as an "encoded" form which does not resemble the object, and then filtered (or "decoded") to form an image. We present here the imaging properties of a class of time-modulated coded apertures which, unlike most coded apertures, encode projections of the object rather than the object itself. These coded apertures can reconstruct a volume object nontomographically, tomographically (one plane focused), or three-dimensionally. We describe a new decoding algorithm that reconstructs the object from its planar projections. Results of noise calculations are given, and the noise performance of these coded-aperture systems is compared to that of conventional counterparts. A hybrid slit-pinhole system which combines the imaging advantages of a rotating slit and a pinhole is described. A new scintillation detector which accurately measures the position of an event in one dimension only is presented, and its use in our coded-aperture system is outlined. Finally, results of imaging test objects and animals are given.

High-resolution computed tomography of the normal rat nephrogram.

This study describes a unique, film-recorded computed tomography (CT) system and its use in studying contrast flow between anatomic compartments of the rat kidney. The CT apparatus, composed of a microfocal spot tube, rotating animal carrier, film-cassette translator, and control electronics, was used to expose "sinograms" of 3:1 magnification through the kidneys of normal rats prior to and 2, 15, 30, 60, and 120 minutes after intravenous contrast injection. Microdensitometry and computer reconstruction resulted in CT images representing 1-mm thick coronal sections with lateral resolution of 150 micron. With this novel technique of ultrahigh-resolution CT, temporal alterations in absorption coefficient of cortical and medullary nephrographic components were depicted for contrast flow study in our small animal model.

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.