As low-dose computed tomography becomes a hot issue in the field of clinical x-ray imaging, photon counting detectors
have drawn great attention as alternative x-ray image sensors. Even though photon-counting image sensors have several
advantages over the integration-type sensors, such as low noise and high DQE, they are known to be more sensitive to
the various experimental conditions like temperature and electric drift. Particularly, time-varying detector response
during the CT scan is troublesome in photon-counting-detector-based CTs. To overcome the time-varying behavior of
the image sensor during the CT scan, we developed a flat-field correction method together with an automated scanning
mechanism. We acquired the flat-field images and projection data every view alternatively. When we took the flat-field
image, we moved down the imaging sample away from the field-of-view with aid of computer controlled linear
positioning stage. Then, we corrected the flat-field effects view-by-view with the flat-field image taken at given view.
With a CdTe photon-counting image sensor (XRI-UNO, IMATEK), we took CT images of small bugs. The CT images
reconstructed with the proposed flat-field correction method were much superior to the ones reconstructed with the
conventional flat-field correction method.