Image Number 11 for United States Patent #5684855.
Only an umbra of an X-ray beam is allowed to enter a designated detecting device arrays of an X-ray detector, whereby stable and good X-ray detection signals and images are provided. Even if a focal spot in an X-ray tube shifts, occurrence of artifacts or shifts of CT numbers is prevented to improve image quality. An X-ray CT scanner comprises an X-ray tube and X-ray detector, which are opposed to each other with a patient lying down on a couchtop between them, and a pre-collimator inserted between the X-ray tube and patient for restricting the width in a slice direction of an X-ray beam irradiated by the X-ray tube. The X-ray detector consists of, for example, a two-dimensional detector in which a plurality of detecting device arrays are arranged in the slice direction, each detecting device array including a plurality of detecting channels. The scanner further comprises a unit for controlling the pre-collimator in a manner that a detecting device array designated among the plurality of detecting device arrays receives only an umbra of the X-ray beam. An X-ray CT image is reconstructed using data detected by the designated detecting device arrays.