Comparative resolution of single gamma counting and coincidence counting in focusing collimator scanning systems
High resolution radioisotope scanning systems have been restricted in general to: (1) focusing collimators, and (2) positron coincidence scanning. If the nuclear decay process includes the nearly simultaneous emission of the gammas in cascade with the direct transition highly forbidden or if, as for I/sup 125/ and Hg/sup 197/, electron capture occurs, following which a gamma ray and a characteristic K x-ray are emitted, a third type of scanning may be carried out. By setting the pulse height window of any standard scanner at the summed energy either of the two gammas or of the gamma and x-ray, only coincidences will be recorded, and an essentially composite type of scanning, namely, focusing collimator coincidence scanning (FCCS), becomes possible. Although improved resolution for FCCS has already been demonstrated under special experimental conditions in order to investigate the range of applicability of the scanning method and to indicate appropriate collimator design, a general theoretical analysis has been attempted. As will be seen in detail, a general analytic comparison of the resolutions obtainable with single gamma scanning and with FCCS is not likely to be possible. All of the problems associated with characterizing collimator detector performance in single gamma scanning are compounded by coincidence considerations. The inherent three-dimensionality of FCCS makes the theoretical resolution of the method quite different, for example, in hot spot scanning against a cold background (brain scans) as contrasted with searching for cold regions embedded in a radioactive volume (liver scans).
- OSTI ID:
- 6926295
- Journal Information:
- Trans. N.Y. Acad. Sci.; (United States), Vol. 30:4
- Country of Publication:
- United States
- Language:
- English
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