Digitally Controlled Beam Attenuator

W. W. Peppler; B. Kudva; J. T. Dobbins III; C. S. Lee; M. S. Van Lysel; B. H. Hasegawa; C. A. Mistretta

doi:10.1117/12.933815

29 December 1982 Digitally Controlled Beam Attenuator

W. W. Peppler, B. Kudva, J. T. Dobbins III, C. S. Lee, M. S. Van Lysel, B. H. Hasegawa, C. A. Mistretta

Proceedings Volume 0347, Application of Optical Instrumentation in Medicine X; (1982) https://doi.org/10.1117/12.933815
Event: Application of Optical Instrumentation in Medicine X, 1982, New Orleans, United States

Abstract

In digital fluorographic techniques the video camera must accommodate a wide dynamic range due to the large variation in the subject thickness within the field of view. Typically exposure factors and the optical aperture are selected such that the maximum video signal is obtained in the most transmissive region of the subject. Consequently, it has been shown that the signal-to-noise ratio is severely reduced in the dark regions. We have developed a prototype digital beam attenuator (DBA) which will alleviate this and some related problems in digital fluorography. The prototype DBA consists of a 6x6 array of pistons which are individually controlled. A membrane containing an attenuating solu-tion of (CeC1₃) in water and the piston matrix are placed between the x-ray tube and the subject. Under digital control the pistons are moved into the attenuating material in order to adjust the beam intensity over each of the 36 cells. The DBA control unit which digitizes the image during patient positioning will direct the pistons under hydraulic control to produce a uniform x-ray field exiting the subject. The pistons were designed to produce very little structural background in the image. In subtraction studies any structure would be cancelled. For non-subtraction studies such as cine-cardiology we are considering higher cell densities (eg. 64x64). Due to the narrow range of transmission provided by the DBA, in such studies ultra-high contrast films could be used to produce a high resolution quasi-subtraction display. Additional benefits of the DBA are: 1) reduced dose to the bright image areas when the dark areas are properly exposed. 2) improved scatter and glare to primary ratios, leading to improved contrast in the dark areas.

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W. W. Peppler, B. Kudva, J. T. Dobbins III, C. S. Lee, M. S. Van Lysel, B. H. Hasegawa, and C. A. Mistretta "Digitally Controlled Beam Attenuator", Proc. SPIE 0347, Application of Optical Instrumentation in Medicine X, (29 December 1982); https://doi.org/10.1117/12.933815

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