A tabletop clinical x-ray CT scanner with energy-resolving photon counting detectors

Photon counting x-ray detectors (PCXDs) are an emerging technology in x-ray computed tomography (CT) as they have the potential to overcome some of the most significant limitations of current CT with energy integrating detectors. Among these are: insufficient tissue contrast, relatively high radiation dose, tissue non-specificity, and the non-quantitative nature. In contrast, CT with PCXDs has shown promise in producing higher contrast, tissue specific, quantitative images at lower dose. Novel applications for PCXDs include k-edge and functional imaging and material decomposition. A limiting factor, however, is the high photon flux that occurs in clinical applications resulting in signal pulse pile up in the detector. Faster detectors and new strategies for data corrections and image reconstruction algorithms are needed to overcome these limitations. A research tabletop x-ray CT scanner was developed with the following aims: 1) to characterize and calibrate the PCXD; 2) to acquire CT projection data under conditions similar to those of clinical CT; and 3) to reconstruct images using correction schemes specific for PCXDs. The scanner employs a commercial clinical x-ray tube, a PCXD with two energy thresholds, and allows scanning of objects of up to 40 cm in diameter. This paper presents measurements of detector quantities crucial for data corrections and calibration, such as energy response, deadtime, and count rates. Reconstructed CT images are presented and qualitative results from material decomposition are shown.