IMAGE QUALITY AND OPTICAL-DENSITY IN MAMM OGRAPHY - STUDY ON PHANTOM

Optical densisty (od) is an important factor for image quality in mamm ography. We studied the effect of o.d. on the image score with two pha ntoms (Contrast Detail MAMmography phantom (CDMAM), University Hospita l Nijmegen, The Netherlands and breast-equivalent phantom (MTM 100) ma de by CIRS in the United States). We also evaluated the doses required to obtain the blackening considered from measurements made with therm oluminescent 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 bet ween 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 c onsistent 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 irradi ation dose from 5,4 to 7,2 mGy when the o.d. increases from 1.30 to 1. 70.