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Tytuł:
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Wiener spectrum of radiographic systems: comparison of different evaluation methods.
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Autorzy:
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Bregant P; Servizio di Fisica Sanitaria, A.S.S.N. 1, Trieste.
De Denaro M
De Guarrini F
Borasi G
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Źródło:
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La Radiologia medica [Radiol Med] 1997 May; Vol. 93 (5), pp. 613-7.
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Typ publikacji:
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Comparative Study; Journal Article
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Język:
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English
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Imprint Name(s):
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Publication: Milan : Springer Milan
Original Publication: Torino [etc.] Minerva medica.
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MeSH Terms:
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Radiography/*methods
Physical Phenomena ; Physics
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Entry Date(s):
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Date Created: 19970501 Date Completed: 19970902 Latest Revision: 20081121
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Update Code:
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20240104
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PMID:
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9251741
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The noise power spectrum, or Wiener spectrum, of the radiographic mottle is a fundamental quantity in film-screen image quality evaluation. In this paper, using a high-quality computerized microdensitometer, two different acquisition and calculation methods for noise evaluation are compared. The first one is the classic (unidimensional) method used in film noise evaluation: a long and narrow slit (10 x 400 microns2) is used to delimit the microdensitometer light beam and the transmission data are collected by scanning the sample in a rectilinear pattern. A section of the two-dimensional Wiener spectrum is thus obtained. The second (two-dimensional) method is similar to that used in digital image noise evaluation: a square slit is used on the microdensitometer window and data are collected by scanning the sample on a square pattern. To evaluate the effect of different sampling frequencies, our data were acquired both selecting a 50 x 50 microns2 square slit and a 20 x 20 microns2 square slit. The two-dimensional Wiener spectrum thus obtained is then reduced to a unidimensional function. The measurements were made on two different films (Kodak Ortho G e Kodak T-MAT G) exposed with the same screen (Kodak Lanex Regular). These films have the same sensitivity but a different emulsion structure. One film (Ortho G) is made of irregular halide silver grains and the other (T-MAT G) of tabular grains. A satisfactory agreement between the two procedures was found which makes the comparison of data from the laboratories using microdensitometers and those using TV-grabbing system for film-screen evaluation meaningful.