Patent Number: 
Section: claims

1. An aperture position adjusting mechanism in an X-ray CT system capable of adjusting the position of an aperture, comprising: a pair of rails disposed along a direction in which said aperture is to be adjusted, for slidably mounting said aperture, said aperture having an aperture opening for limiting an X-ray irradiation range;  a first shaft that is hollow and is provided with a bore passing in parallel with a center axis of said first shaft at a position offset from said center axis, said first shaft being rotatably supported by a base portion of said aperture orthogonally to said pair of rails;  a second shaft that is received and is rotatably supported within said bore of said first shaft; and  a driving device for rotating said second shaft in reciprocal directions around an eccentric axis offset from a center axis of said second shaft, said mechanism characterized in that:  said aperture is moved along said rails as said second shaft is eccentrically rotated by said driving device and, following said eccentric rotation and in a direction opposite to that of said rotation, said first shaft is eccentrically rotated around the center axis of said bore. 2. A gantry apparatus in an X-ray CT system, comprising the aperture position adjusting mechanism as defined by  claim 1 . claim 1 3. The gantry apparatus as defined by  claim 2 , comprising an X-ray detecting device in which a plurality of detector rows are arranged in a carrying direction of a table for carrying a subject, each of said detector rows having a group of detector elements arranged in a direction orthogonal to said carrying direction. claim 2 4. The gantry apparatus as defined by  claim 3 , wherein the direction in which said aperture is to be adjusted coincides with said carrying direction. claim 3 5. The gantry apparatus as defined by  claim 4 , further comprising a control device for feedback-controlling said driving device so that outputs from detector elements at a predefined position in said detector rows are equalized when the focal position of an X-ray source shifts. claim 4 6. A method of controlling a gantry apparatus in an X-ray CT system comprising: a gantry rotating device for integrally rotating an X-ray detecting device and an X-ray source, said X-ray detecting device comprising a plurality of detector rows arranged in a carrying direction of a table for carrying a subject, each of said detector rows having a group of detector elements arranged in a direction orthogonal to said carrying direction, said X-ray source disposed at a position opposite to said X-ray detecting device across a cavity portion for inserting said table; an aperture having an aperture opening for limiting an irradiation range of X-rays from said X-ray source; and adjusting device for adjusting the position of said aperture in said carrying direction, said adjusting device comprising: a pair of rails disposed along a direction in which said aperture is to be adjusted, for slidably mounting said aperture;  a first shaft that is hollow and is provided with a bore passing in parallel with a center axis of said first shaft at a position offset from said center axis, said first shaft being rotatably supported by a base portion of said aperture orthogonally to said pair of rails;  a second shaft that is received and is rotatably supported within said bore of said first shaft; and  a driving device for rotating said second shaft in reciprocal directions around an eccentric axis offset from a center axis of said second shaft, said method comprising the steps of:  performing a scan for collecting X-ray projection data of the subject during a rotation of said gantry rotating device; and  feedback-controlling said driving device so that outputs from detector elements at a predefined position in said detector rows are equalized when the focal position of the X-ray source shifts during the rotation of said gantry rotating device.