Assessment of a new CT system for small animals

We have developed an X-ray cone beam tomograph for in vivo small-animal imaging using a flat panel detector (CMOS technology with a columnar CsI scintillator plate) and a microfocus X-ray source in a geometric configuration with 1.6 magnification and 7.5 cm2 field of view. This work presents an initial characterization of this new system. We measured the detector modulation transfer function (MTF), detector stability, system resolution, the quality of the reconstructed tomographic images and radiated dose. The system resolution was measured following the standard test method ASTM E1696-95. For image quality evaluation, we assessed signal to noise ratio (SNR) and contrast to noise ratio (CNR) with respect to radiated dose. Measurements have been performed on Hounsfield-calibrated images of quantitative phantoms. Effective dose studies have been performed introducing TLD dosimeters in representative organs (ICRU criteria) of euthanized laboratory rats for different imaging protocols. Noise measurements indicate that 50 HU can be achieved at a dose of 10 cGy. Effective dose in standard research methods is below 200 mSv, confirming that the system is appropriate for in vivo imaging. Maximum spatial resolution achieved is better than 50 microns. Experimental results on image quality phantoms as well as on in-vivo studies show that the use of CMOS flat panel is a good choice in terms of quality with respect to radiated dose.