[Image quality and optical density in mammography: study on phantoms].

Optical densisty (od) is an important factor for image quality in mammography. We studied the effect of o.d. on the image score with two phantoms (Contrast Detail MAMmography phantom (CDMAM), University Hospital Nijmegen, The Netherlands and breast-equivalent phantom (MTM 100) made by CIRS in the United States). We also evaluated the doses required to obtain the blackening considered from measurements made with thermoluminescent pastilles. Two series of exposure were performed at 28 kV with mAs ranging from 25 to 100 to obtain a range of o.d. varying between 0.72 and 2.67. Image scores were then evaluated for each negative by calculating the mean of five different readers. The study showed a clear increase of the image score with o.d. These observations were consistent with other studies. For the two phantoms and the screen-film combination used, the maximum quality was obtained for an o.d. of 1.6, but the drawback of negatives at high o.d. is increase of the irradiation dose from 5,4 to 7,2 mGy when the o.d. increases from 1.30 to 1.70.