Patent ID: 7583778

Claim:
An X-ray CT apparatus comprising: an X-ray source for irradiating an X-ray; an X-ray detector arranged with a plurality of X-ray detector elements and for detecting the X-ray; a rotating unit configured to rotate the X-ray source and the X-ray detector around a subject such that an X-ray path closest to a rotation center of upon rotation of the X-ray source and the X-ray detector is in a position deviated by a first value α d from the rotation center, and the X-ray path and a longitudinal axis of the subject are substantially perpendicular to each other; a collecting unit configured to cause the X-ray detector to collect the X-ray irradiated from the X-ray source; a setting unit configured to set a second value γ d in accordance with the first value α d by looking up a table, including a connection between the X-ray path and a path to backproject projection data based on an output signal of the X-ray detector connected to reduce an aliasing artifact level on an image, and by storing a previous correspondence of the first value α d and the second value γ d , or by operating based on an operation equation, including the connection, defining a relationship between the first value α d and the second value γ d ; a storing unit configured to store the second value γ d set by the setting unit; and a reconstructuring unit configured to perform a backprojection operation on the projection data and to reconstruct the image, wherein the reconstructing unit is configured to upon the backprojection operation, backproject the projection data at least in a vicinity of the rotation center to a position deviated by the second value γ d different from the first value α d from the rotation center so as to reduce an artifact level.