Characterization of the reciprocity law failure in three mammography screen-film systems

The purpose of this project was to quantify reciprocity law failure (RLF) f or mammography screen-film systems. Three widely used screen-film systems w ere evaluated: the Kodak MinR 2000 system, Fuji UM Mammo Fine screen and Fu ji UM MA HC film, and Agfa MR Detail screen and Agfa Mammoray MR5 film. The legit algorithm that Linearizes logistic curve shapes was utilized to char acterize film sensitometric response. Different values of mammographic phan tom thickness, tube current, and kVp were used to vary screen-film exposure rates. RLF was quantified by examining the dependence of legit parameters (maximum and minimum film density, curve shift, and slope) on exposure rate . The shift of the legit curve was found to be a good indicator of the scre en-film system speed, while the slope of the legit curve is affected by the RLF. RLF leads to changes in film contrast as well as speed. For the range of exposure rates measured (50-fold), screen-film contrast and speed varie d by factors of 2 and 3.5, respectively. Film contrast decreased as exposur e rate increased. The greatest changes were observed with the Kodak MinR 20 00 screen-film system. (C) 1999 American Association of Physicists in Medic ine. [S0094-2405(99)01905-7].