The authors have developed an experimental method for simultaneous determination of dose and image parameters in mammography. A global and objective quality concept, the image quality index, is proposed and its reliability demonstrated by tests of reproducibility. Objective quality tests and subjective evaluation by radiologists showed good correlation.

Superposable radiographs of lower molar areas were obtained by means of a specially designed film holder and a gnathostat maintained in a constant position with respect to long-cone radiological equipement. A quantitative evaluation of the bone mass in the interradicular area was obtained by scanning the area under a photodensitometer. A photodensitometric scan of the image of an aluminium wedge adapted to each radiograph was also performed. This allowed the transformation, with the aid of a computer, of the photodensitometric recording of bone into a tracing of mm of aluminium equivalents. The reproducibility and precision of the method were verified by comparing magnifications of repeated radiographs, by photodensitometric readings of radiographs developed in different batches and by repeated quantitative readings of the same film. The method allowed one, for instance, to follow quantitatively the healing of a radiographically visible periapical lesion. It was also used to evaluate quantitatively, in the interradicular area, bone changes which could not be seen with the marked eye.

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The performance of a radiological system can be evaluated on the one hand by an objective determination of the quality of the produced image and, on the other hand, by the dose delivered to the patient. In order to measure these two factors in a single exposure a Kodak breast phantom has been modified so as to simulate the breast absorption. The dose distribution is measured with thermoluminescent detectors. By consideration of a theoretical model of the X -ray imaging in mammography, a single quality factor is computed from the contrast, the spatial resolution and the noise measured on the phantom image. We present results obtained in various working conditions, i.e. variable X -ray tube voltages, use of different screen -film combinations, use of a grid.

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