Patent ID: 7154988

Claim:
An X-ray computed tomography apparatus comprising: an X-ray tube configured to generate X-rays diverging in channel and slice directions; a collimator which has an aperture that is variable in the slice direction and limits a divergence angle of the X-rays in the slice direction in accordance with the aperture; an X-ray detector which has a plurality of X-ray detection elements for detecting X-rays transmitted through an object to be examined, the plurality of X-ray detection elements being arrayed in the channel and slice directions; an input device configured to set a substantially cylindrical reconstruction area; an image reconstructing unit configured to reconstruct image data within the set reconstruction area on the basis of an output from said X-ray detector; a divergence angle determining unit configured to determine a divergence angle of the X-rays in the slice direction on the basis of a radius and height of the set reconstruction area; and a control unit configured to control the aperture of said collimator in accordance with the determined divergence angle.