Dual-film cassette technique for studying the effect of radiographic image quality on diagnostic accuracy

In order to investigate the relationship between diagnostic accuracy and radiographic image quality, we have developed a dual-film cassette which produces two radiographs simultaneously with a single exposure. One of these radiographs is of standard quality; the second is of lower quality because of degraded spatial resolution and a significantly lower exposure. We have studied the basic physical properties of the standard and low-dose screen-film systems which we use in the dual-film cassette by comparing their beam hardening, scatter fractions, contrasts, modulation transfer functions (MTFs), and Wiener spectra. The x-ray spectrum incident on the low-dose system contained more high-energy photons than that incident on the standard system, and the scatter fractions for the low-dose system were slightly less than or comparable to those for the standard system. While the radiographic contrast produced by the two systems were generally comparable, the standard system had a slightly higher contrast than the low-dose system in some cases. The MTF of the low-dose system was considerably lower than that of the standard system, and the low-dose system had a noise level considerably greater than did the standard system. Phantom images and clinical radiographs indicated that, for the low-dose system, the image quality degraded significantly.