Patent ID: 8184768

Claim:
An X-ray CT apparatus configured to reconstruct an image from projection data obtained in a scan by radiation and detection of an X-ray, the X-ray CT apparatus comprising: a setting part configured to set an imaging condition for a real scan or a prep scan, which is scanning by a resolution lower than the real scan; an X-ray tube having a filament, an anode, and generators arranged opposite to each other across a path heading from the filament to the anode and configured to output an electric field or a magnetic field onto the path to focus an electron beam heading from the filament to the anode in accordance with the output under the imaging condition set by the setting part, the X-ray tube being configured to radiate the X-ray; a detector configured to detect the X-ray radiated from the X-ray tube; a reconstructing part configured to reconstruct an image from the projection data based on the detection by the detector; an acquiring part configured to determine a CT value from the image reconstructed by the reconstructing part; a determining part configured to determine whether the CT value is included within a reference range; and a controller configured to control an intensity of the output of the generators with reference to a result of the determination by the determining part to change a focal point size of the electron beam to a different size depending on the imaging condition during the scan, while continuously switching the scan between the prep scan and the real scan and changing the focal point size.