Detectors working in photon counting mode offer an interesting alternative to the common charge integrating detectors for computed tomography (CT), because they can potentially measure the energy of every detected X-ray photons and achieve better image contrast sensitivity for a given dose. Unfortunately, most current X-ray detectors suffer from limited count rate capability, due either to a long charge migration time in semiconductor and gas detectors, or to a slow decay time in ceramic scintillators. To overcome these difficulties, we propose to use pixel detectors based on fast light emitting inorganic scintillators individually coupled to avalanche photodiodes with parallel, low-noise, fast digital processing electronics to provide real time single event detection and recording. The proposed detector was investigated with 2 × 2 × 10 mm3 Lu1.9Y0.1SiO5 (LYSO), a fast decay time (40 ns), heavy (7.19 g/cc) scintillator that is also suitable for coincidence detection of annihilation radiation (511 keV) in positron emission tomography (PET). Therefore, the detector characteristics make it a good candidate for implementation in a combined PET/CT dual-modality scanner. Although only coarse spectral analysis is possible in the X-ray energy range, it is demonstrated that appropriate CT images for anatomical localization can be obtained at very low dose in counting mode using a PET/CT simulator set up for small animal imaging. Data are reported on CT image resolution, noise, contrast and dose.