Comparison of image quality in optical and radiographic magnification techniques for fine-detail skeletal radiography: effect of object thickness Page: 4 of 38
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Both hand and knee phantoms were selected so that the bone images
for thin and thick parts of the body, respectively, could be examined.
It has generally been believed that optical magnification used with
fine-grain direct x-ray film is superior to radiographic magnification;
it will be shown that this is not always true.
Exposing conditions for the two techniques applied to radiography
of the hand are illustrated in Fig. 1. With the optical magnification
technique, Kodak Industrial Type M film and a large focal spot of
1.2 mm nominal size are used. The average distance of bone structures
in the hand from the film was estimated from lateral radiographs to be
24 nm, which corresponds to a geometric magnification of 1.02 at a
120 cm focal spot-to-film distance. In optical magnification for the
hand, 50 instead of 65 kVp are used for routine clinical examinations.
However, since the lowest setting for the microfocus x-ray tube
(Siemens Bi 125/3/50 RG) employed for radiographic magnification is
65 kVp, the same value is used in this study for the optical magnifica-
tion so that the comparison of the two techniques is not made more
difficult by a contrast change in the input x-ray patterns. With the
radiographic magnification technique, a 4x geanetric magnification and
a slow screen-film system (Kodak RP film with DuPont Detail screens)
with a microfocus tube having a 50 ndcron nominal focal spot size are
used. These technical parameters for radiographic magnification were
chosen on the basis of preliminary -studies and are not necessarily
optimal. The speed of RP-Detail is approximately 40 times greater than
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Doi, K.; Genant, H.K. & Rossmann, K. Comparison of image quality in optical and radiographic magnification techniques for fine-detail skeletal radiography: effect of object thickness, article, January 1, 1974; United States. (https://digital.library.unt.edu/ark:/67531/metadc1021083/m1/4/: accessed April 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.