Characterization of the imaging performance of a micro-CT system based on the photon counting XPAD3/Si hybrid pixel detectors

We characterize the imaging performance of the micro computed tomography (micro-CT) prototype PIXSCAN equipped with an x-ray photon counting camera based on XPAD3/Si hybrid pixel detectors. The camera, which is composed of eight distinctive horizontal modules, permits the performance of whole-body mouse scans. Photon counting supplied by hybrid pixels guarantees acquisitions at a Poisson noise level exclusively determined by the detected photon statistics. First, we characterize the performance of the imaging system while assessing its linearity, noise, spatial resolution and low contrast detectability estimated from scans of appropriate phantoms. Then, we show CT images of mice data acquired either in vivo or post mortem, without or with an injection of iodine as a contrast agent. Although hybrid pixels guarantee a minimal noise to the images, the limited detection efficiency of Si sensors impairs detected photon statistics and therefore the improvement in contrast-to-noise ratio for standard tomographic imaging. Indeed, the most innovative potential of the PIXSCAN prototype is its capacity to perform spectral tomographic imaging and fast dynamic imaging. The first is thanks to the possibility of setting an energy threshold on the detected photons, and the second is thanks to its fast acquisition rate (till 500 images/s). We present some examples of these imaging methods applied to mice and discuss their main limiting factors.