Preliminary study to optimize the irradiation condition for future application in small animal CT

In digital imaging the ability to detect low contrast details is an aim that must be pursued. In order to achieve this result we have developed an acquisition system based on silicon pixel detector. The detector is a matrix of 256x256 square pixels of 55 μm size. It is bump-bonded to a readout chip developed by the Medipix2 Collaboration [X. Llopart, et al., IEEE Trans. Nucl. Sci, NS-49 (5) (2002) 2279]. To see the low contrast details with this system, it is necessary to reduce inside the image the fluctuations of pixel-to-pixel counts, down to statistical fluctuations. This has been achieved equalizing the phantom image with a high statistics flat field acquired in the same irradiation condition. We have studied the dependence of the image uniformity for different flat field and we have investigated the dependence of the image quality on the thickness of the phantom and on the energy window selected inside the incident spectrum