X-ray CT apparatus and X-ray CT backprojection operating method

An X-ray CT apparatus comprising:

• a detector system oppositely arranged with an X-ray source for irradiating an X-ray and an X-ray detector arranging a plurality of X-ray detector elements, by sandwiching a subject such that an X-ray path closest to a rotation center of upon rotation of the detector system is in a position deviated by a first value αd from the rotation center, and the X-ray path and a longitudinal axis of the subject are substantially perpendicular to each other;
• a scanning unit configured to cause the X-ray source to irradiate an X-ray on each view while rotating the X-ray source and the X-ray detector in unison round the subject, and the X-ray detector to collect as collected data transmission data of the X-ray to the subject;
• a setting unit configured to set a second value γd in accordance with the first value αd 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 αd and the second value γd, or by operating based on an operation equation, including the connection, defining a relationship between the first value αd and the second value γd;
• a storing unit configured to store the second value γd set by the setting unit;
• and
• a reconstructing unit configured to process the collected data on each view to thereby obtain the projection data and to perform a backprojection operation on the projection data to thereby reconstruct the image,
• wherein the reconstructing unit is configured such that, the projection data of the X-ray detector element at least in a vicinity of the rotation center upon the backprojection operation is backprojected to a position deviated by the second value γd different from the first value αd from the rotation center so as to reduce the aliasing artifact level.

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 about a rotation center the X-ray source and the X-ray detector in a state opposed to each other 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 αd 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 γd in accordance with the first value αd 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 αd and the second value γd, or by operating based on an operation equation, including the connection, defining a relationship between the first value αd and the second value γd;
• a storing unit configured to store the second value Yd set by the setting unit;
• and
• a reconstructing unit configured to perform a backprojection operation on the projection data and to reconstruct the image,
• wherein the reconstructing unit is configured such that, the projection data of the X-ray detector element at least in a vicinity of the rotation center upon the backprojection operation is backprojected to a position deviated by the second value γd different from the first value αd from the rotation center so as to reduce the aliasing artifact level.

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 about a rotation center the X-ray source and the X-ray detector in a state opposed to each other around a subject such that 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 γd in accordance with the first value αd 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 αd and the second value γd, or by operating based on an operation equation, including the connection, defining a relationship between the first value αd and the second value γd;
• a storing unit configured to store the second value γd set by the setting unit;
• and
• a reconstructing unit configured to perform a backprojection operation on the projection data and to reconstruct the image,
• wherein the reconstructing unit is structured to make a backprojection operation to at least a vicinity of the rotation center on a basis of an assumption that the rotation center has a deviation amount of the second value γd different from the first value αd so as to reduce the aliasing artifact level.

An X-ray CT backprojection operating method carried by an X-ray CT apparatus including a detector system oppositely arranged with an X-ray source for irradiating an X-ray and an X-ray detector arranging a plurality of X-ray detector elements by sandwiching a subject, comprising:

• a scanning step of causing the X-ray source to irradiate an X-ray on each view while rotating the X-ray source and the X-ray detector in unison round the 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 αd from the rotation center, the X-ray path and a longitudinal axis of the subject are substantially perpendicular to each other, and the X-ray detector to collect collected data as transmission data of the X-ray to the subject;
• a setting step of setting a second value γd in accordance with the first value αd 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 αd and the second value γd, or by operating based on an operation equation, including the connection, defining a relationship between the first value αd and the second value γd;
• a storing step of storing the second value γd set by the setting step;
• and
• a reconstructing step of processing the collected data on each view to thereby obtain the projection data and making a backprojection operation on the projection data to thereby reconstruct the image,
• wherein, as for the backprojection operation carried out by the reconstructing step, the projection data of the X-ray detector element at least in a vicinity of the rotation center upon the backprojection operation is backprojected to a position deviated by a second value γd different from the first value αd from the rotation center so as to reduce the aliasing artifact level.