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Resolution and contrast reduction
Author(s) -
Shuping Ralph E.,
Judy Philip F.
Publication year - 1978
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.594459
Subject(s) - microdensitometer , magnification , pinhole (optics) , opacity , radiography , optics , resolution (logic) , contrast (vision) , reduction (mathematics) , image resolution , medicine , mathematics , surgery , physics , computer science , artificial intelligence , geometry
Lack of resolution (unsharpness) can reduce contrast in diagnostic radiography if the proper conditions of magnification and unsharpness are met. To describe this phenomenon, a modification of the contrast reduction factor (CRF) was introduced which used the response function of a semi‐opaque edge to predict contrast reduction for small bar‐shaped objects. To predict CRF, unsharpness is employed as a single‐term description of resolution and is obtained experimentally from the edge response function. The unsharpness term is defined as the distance over which the response goes from 16.5% to 83.5% of the maximum. Measured and predicted CRFs were compared and the CRF concept was found to be an excellent predictor of contrast reduction. The individual components of unsharpness were determined experimentally and the sum‐of‐squares rule predicted adequately their combination. Three methods to measure unsharpness were compared: (a) the ICRU prescription using pinhole radiographs of the focal spot, (b) one‐dimensional integration of the focal‐spot pinhole radiograph, and (c) the unsharpness term produced by a semi‐opaque edge. The latter two were measured using a microdensitometer.