Digital radiography: a quantitative approach

'Full-text:' In a radiograph the value of each pixel is related to the material thickness crossed by the x-rays. Using this relationship, an object can be characterized by parameters such as depth, surface and volume. Assuming a locally linear detector response and using a radiograph of reference object, the quantitative thickness map of object can be obtained by applying offset and gain corrections. However, for an acquisition system composed of cooled CCD camera optically coupled to a scintillator screen, the radiographic image formation process generates some bias which prevent from obtaining the quantitative information: non uniformity of the x-ray source, beam hardening, Compton scattering, scintillator screen, optical system response. In a first section, we propose a complete model of the radiographic image formation process taking account of these biases. In a second section, we present an inversion scheme of this model for a single material object, which enables to obtain the thickness map of the object crossed by the x-rays. (author)