Inverse-square sensitometry for low kVp techniques is limited by air attenuation and beam hardening. It is thus difficult to obtain accurate H and D curves for mammographic screen-film combinations at technique factors used clinically. Methods are described for the determination of characteristic curves at low x-ray energies which provide composite intensity-scale curves using small changes in source-to-receptor distance and concomitant changes in either exposure time, beam attenuation, or kVp. H and D curves obtained at low kVp's using the various sensitometric approaches are compared with those obtained using inverse-square sensitometry; the relative merits of the different methods are discussed.
Daniel R. Bednarek,
"Methods Of Sensitometry For Low Energy Radiography," Optical Engineering 21(1), 211105 (1 February 1982). https://doi.org/10.1117/12.7972867