X-ray CT apparatus and method for operating same for reducing the radiation dose to an examiner having a body part exposed to the X-ray beam

A computed tomography apparatus comprising:

• a computed tomography scanner having an x-ray source with a focus from which an x-ray beam emanates, and a radiation detector, at least said focus of said x-ray source being rotatable around a system axis to irradiate an examination subject, disposed in said scanner, from a plurality of different directions, with said radiation detector producing scanning data dependent on x-rays incident thereon from the respective directions;
• a detector arrangement for automatically detecting entry of a body part of an examiner into a first volumetric region covered by said x-ray beam;
• a radiation control arrangement, connected to said detector arrangement, and interacting with at least one of said x-ray radiator and said x-ray beam for, upon detection of entry of a body part of said examiner into said first volumetric region, automatically reducing an effective amount of x-rays in said first volumetric region compared to an effective amount of x-rays in a second volumetric region of a same size and at a same distance from said system axis as said first volumetric region in which no body part of said examiner is disposed;
• and
• a dimensioning control arrangement, connected to said detector arrangement, for automatically setting a size of said first volumetric region dependent on at least one parameter associated with said body part selected from the group of parameters consisting of size, position and movement direction of said body part.