Method of X-ray transmission radiography is available for 100 years and it is one of the fastest and easiest ways to study the internal structures of the tissue, samples or body. Advances in semiconductor technology in last years makes possible to fabricate new types of X-ray detectors (e.g. Medipix2 photon counting chip). Compared to the film technique it brings real-time information about the studied object with high resolution, high sensitivity and broad dynamic range. These semiconductor-based imaging systems become important as new tools in the field of small animal imaging for cancer research and for observation of the dynamic processes inside the organism. It opens up new possibilities for researchers to perform non-invasively studies of the tissue for mutations or pathologies and to monitor disease progression and response to therapy.