Dependence Of The Computerized Tomography (CT) Number - Electron Density Relationship On Patient Size And X-Ray Beam Filtration For Fan Beam CT Scanners

M. E. Masterson; C. L. Thomason; R. McGary; M. A. Hunt; L. D. Simpson; D. W. Miller; J. S. Laughlin

doi:10.1117/12.931818

16 July 1981 Dependence Of The Computerized Tomography (CT) Number - Electron Density Relationship On Patient Size And X-Ray Beam Filtration For Fan Beam CT Scanners

M. E. Masterson, C. L. Thomason, R. McGary, M. A. Hunt, L. D. Simpson, D. W. Miller, J. S. Laughlin

Author Affiliations +

Proceedings Volume 0273, Application of Optical Instrumentation in Medicine IX; (1981) https://doi.org/10.1117/12.931818
Event: Application of Optical Instrumentation in Medicine, 1981, San Francisco, United States

Abstract

The applicability of quantitative information contained in CT scans to diagnostic radiology and to radiation therapy treatment planning and the heterogeneity problem has been recognized by members of the radiological community and by manufacturers. Determination of the relationship between electron density and CT number is important for these applications. As CT technology has evolved, CT number generation has changed. CT number variation was limited in the early water bag systems. However, later generation "air" scanners may exhibit variation in CT numbers across a reconstructed image which are re-lated to positioning within the scan circle and scan field size. Results of experimental investigations using tissue-equivalent phantoms of different cross-sectional shapes and areas on the Technicare Delta 2020 are presented. Investigations also cover the effect of "shaped" and "flat" x-ray beam filters. A variation in CT number is demonstrated on this fan beam geometry scanner for phantoms of different sizes and for different scan circle diameters. An explanation of these effects is given. Differences of as much as 20% in determination of tissue electron density relative to water under different experimental conditions are obtained and reported. A family of curves (electron density vs. CT number) is presented for different patient cross-sectional areas and different scanner settings.

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M. E. Masterson, C. L. Thomason, R. McGary, M. A. Hunt, L. D. Simpson, D. W. Miller, and J. S. Laughlin "Dependence Of The Computerized Tomography (CT) Number - Electron Density Relationship On Patient Size And X-Ray Beam Filtration For Fan Beam CT Scanners", Proc. SPIE 0273, Application of Optical Instrumentation in Medicine IX, (16 July 1981); https://doi.org/10.1117/12.931818

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