Evaluation of a YAG:Ce scintillation crystal based CCD X-ray imaging detector with the Medipix2 detector

Abstract

Over the last decades the traditional photographic films used in radiology are being replaced by digital X-ray imaging sensors in many applications. The main advantages of these systems are their detection efficiency of image acquisition and the ability to directly digitally transfer and enhance obtained images. In this paper we characterize and evaluate the X-ray imaging performance of a YAG:Ce single crystal scintillator. The scintillator converts X-rays into visible light that is collected by an optical camera. The camera uses a CCD sensor with the size of 36x24 mm2 and with 4050 x 2630 pixels of 9x9 μm2 pitch, and is equipped with a macro objective. The semiconductor pixel detector Medipix2 was used for the evaluation of the imaging capabilities of this imaging system. The imaging capability is evaluated in terms of several basic characteristics: spatial resolution, edge response function, signal to noise ratio and contrast to noise ratio. A microfocus X-ray tube was used for high spatial resolution measurements in order to minimize the influence of the X-ray tube spot size. Measurements were done using an edge phantom, step wedge phantom and low contrast fibres. The corresponding measurements for all phantoms were done under identical conditions in order to assure comparability. The results measured by the CCD camera demonstrate the possibilities of sensitive X-ray radiography imaging with high spatial resolution.