1. A CT imaging method comprising the steps of: determining from tomographic images information representing geometries of contact surfaces between markers and an object to be imaged, the tomographic images being obtained by imaging the object attached with the markers on its reference surfaces by a CT apparatus using an X-ray or radiation; based on the information representing the geometries of the contact surfaces, determining a positional relation between a reference coordinate system of the object and a coordinate system of the CT apparatus; and imaging the object by the CT apparatus and, based on the positional relation, producing bit-map data of a desired portion of the object.