Experimental Study for Influence of Film-Screen Combination on Image Quality

ABSTRACT

PURPOSE: In determining image quality of mammography,many factors are related. Selection of film and screen is one of them. Authors took phantom images of nine film-screen combinations under properly controlled conditions and compared them to evaluate their image qualities. In addition, KVp, mAs and surface dose were evaluated at each combination to deterrhine proper exposure conditions. MATERIALS AND METHODS: Using phantom,images of nine film-screen combinations composed of Fuji MI-NC, UM-MA, UM-MH films and Fuji Fine,Medium, Kodak Min-R screeens were taken. Phantom(Ackermann Mammochip Phantom) was composed of simulations for microcalcifications, fibers, nodules, lymph nodes, breast tissue and breast cancer masses. For phantom of 4.5 cm compressed breast equivalent, 28 KVp was used. For 1.5 and 3.0 cm equivalant phantoms, 24 KVp and 26 KVp was used. At each KVp, mammographic images were taken at various mAs. Among images taken by this process, best images were selected and then, according to scoring method, comparison of image quality for each combination was done. With dosimation strip, surface doses for various conditions were evaluated. RESULTS: Combination of Fuji UM-MA film and Fuji Fine screen showed best image quality regardless of KVp or phantom thickness. For the best image, 10 mAs with 26 KVp was most ideal while mAs with 24 KVp was optimal for equivalent phantom of 3.0 cm thickness breast. At this condition, surface dose was less than other combinations when combinations involving UM-MH films were used. On the other hand,when combinations involving MI-NC films were used, surface dose was higher than others. CONCLUSION: Using phantom, image quality of film-screen combinations could be evaluated and compared. Such process can contribute to best quality image with decreased exposure and can play a role in quality asurance program.