METHOD OF SIMULATED SCREEN SENSITOMETRY FOR ASYMMETRIC, LOW CROSSOVERMEDICAL X-RAY-FILMS

Recognition of the importance of performing simulated screen-light sen sitometry of medical x-ray films for the purpose of processor quality control has increased over the past several years. As a result there i s a greater need to provide new techniques for performing simulated sc reen-light sensitometry. Medical films with reduced intensifying scree n-light crossover intended to achieve reduced blur and higher spatial resolution pose particular problems in doing simulated screen-light se nsitometry if care is not taken to choose a proper simulated light sen sitometer with the capability of simultaneous double-sided exposures. Misleading and incorrect sensitometric data can be obtained for film c ontrast evaluation if a single side exposure is used. Asymmetric, near -zero crossover films pose even greater problems as proper orientation of the film and proper degree of light output asymmetry need be achie ved in order to obtain correct sensitometry. The films used in this st udy were three double emulsion films varying in crossover from 3% to 2 4%. Of the two very-low-crossover films, one had symmetric emulsion la yers while the second featured emulsion layers which were asymmetric i n terms of contrast and speed. Sensitometric data show several curve s hapes with significant distortions, depending on orientation, for the asymmetric, low-crossover film when exposed using a single-sided expos ure. Only by using a double-sided exposure and an appropriate neutral density filter to simulate the degree of screen-light asymmetry in thi s system could one achieve a characteristic curve comparable to that a chieved by inverse square sensitometry.