Comparative image quality of 105 mm and conventional spot films

The image qualities of 105 mm film (Cronex MRF-21) and a conventional screen-film (Hi-Plus/Cronex 4) were compared for gastrointestinal studies, a high-contrast-resolution procedure, using a General Electric MPX 100/Fluoricon 300 x-ray system. The high contrast resolution was determined at a location approximating the midplane of an average-sized patient (20 cm). Films were made for each image-intensifier mode (9, 6, and 4.5 inch [22.9, 15.2, and 11.4 cm]) and compared with the conventional screen-film for contrast transfer (modulation-transfer function) and maximum cutoff frequency. The effects of unsharpness caused by patient motion were included in the analysis. The patient entrance exposure was measured for each technique. In the absence of patient motion, the cutoff frequencies for the spot films in the 9, 6, and 4.5 inch (22.9, 15.2, and 11.4 cm) modes were 2.1, 2.3, and 2.4 line pairs/mm, respectively. The cutoff frequency for the conventional spot-film was 2.0 line pairs/mm. The modulation-transfer functions for the 105 mm films in the 9, 6, and 4.5 inch (22.9, 15.2, and 11.4 cm) modes were found to be equal to or superior to those of the conventional screen-film for all degrees of patient motion. The 6 inch (15.2 cm), 105 mm films were found to have the best overall performance. These results were achieved with a reduction in radiation dose of 55%.