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.
Using a unique, magnifying computed tomography scanner, we have evaluated the renal excretion of iodinated radiographic contrast material in 3 normal rats and 5 rats with glycerol-induced acute renal failure. Computed tomography scans were performed on each animal prior to and 2, 15, 30, 60, and 120 min following the intravenous administration of contrast material. Normal rats showed a greater concentration of contrast material in the medulla than in the cortex; excretion of contrast material was virtually completed within 60 min. All rats affected with acute renal failure manifested an initially greater concentration of contrast material in the cortex than in the medulla. Later scans showed very variable patterns of contrast material excretion, with no significant contrast material reaching the medulla in 2 animals, and delayed excretion poor syntax in the other 3 animals.
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