RELATION BETWEEN RADIOGRAPHIC MOTTLE FOR DOUBLE AND SINGLE EMULSIONS

The radiographic density fluctuations produced by using dual screen-fi lm systems are designated as the radiographic mottle. The density fluc tuation of the radiographic mottle for the double emulsions at a densi ty of the double emulsions consists of those for the front and back em ulsions on a radiograph. However, the relation between the Wiener spec tra of the radiographic mottle for the double and single emulsions had not been studied. Hence we compared the Wiener spectra of the radiogr aphic mottle for the double emulsions with the sum of those for the fr ont and back emulsions on the same radiographs and with the sum of tho se for the emulsions at the same densities. At all densities of more t han 0.62 for lower spatial frequencies (less than or equal to 1 mm(-1) ), the Wiener spectral values of the radiographic mottle for the doubl e emulsions were greater than the sum of those for the front and back emulsions for both comparisons on the same radiographs and at the same densities. In order to investigate the reason of the above phenomena, we separated the Wiener spectral values of the radiographic mottle fo r various densities into those of the three factors, i.e., quantum mot tle, structure mottle, and film granularity, and performed the same co mparisons as the radiographic mottle. Also, to explain the results for the three factors, we obtained the Wiener spectral values of the spat ial fluctuations of the light exposure or the fluorescence intensity a nd the gradients of the characteristic curves of the film for the doub le and single emulsions of the x-ray film. As a result of the investig ation, we found that the phenomena on the radiographic mottle were cau sed by that (1) on the same radiographs the squares of the gradients o f the characteristic curves for the double emulsions were about 5.3 ti mes as great as those for the single emulsion at densities of more tha n 0.62 of the double emulsions, and (2) at the same density of more th an 0.62 those were more than about 2.2 times as great as those for the single emulsion. (C) 1998 American Association of Physicists in Medic ine.