Receptor dose in digital fluorography: a comparison between theory and practice

A method of identifying the dose per image when quantum mottle no longer do minates the image statistics is presented as a first step towards quantitat ive optimization in native and subtracted digital fluorography. The method is based on measurements of threshold contrast over a range of receptor dos es and the application of a simple model of the threshold contrast detectio n task to estimate the magnitude of system noise sources. The point at whic h system and quantum noise sources are equal in magnitude is proposed as th e practical upper limit for dose per image. The method is applied to a typi cal digital fluorography system and the results are placed into the context of the range of dose per image values found from a regional survey of digi tal fluorography units. While there is broad agreement between the dose per image values in the survey with values predicted from the experimental met hod, the considerable spread in survey doses suggests there are instances w here the use of a high dose per image is unjustified.