The invention relates to a medical computed tomography apparatus which includes a support construction (1) supporting a substantially ring-shaped O-arm (2), which in turn supports imaging means (21, 22). The cross-section of the outer cover (3) of the O-arm in a direction perpendicular with respect to the central axis of said ring-shaped structure (2) is for its prevailing portion arranged substantially of the shape of an arch of a circle but to comprise a cut, and within the sector covered by the cut the distance from the centre of said arch of a circle to the edge of the outer cover (3) is shorter than within said portion of the outer cover (3) substantially of the shape of an arch of a circle. As to the examination opening (4), it is arranged for its prevailing portion substantially of the shape of an arch of a circle but to comprise an extension, and within the sector covered by the extension the distance from the centre of said arch of a circle to the edge of the examination opening (4) is longer than within said prevailing portion of the examination opening (4) substantially of the shape of an arch of a circle. The imaging means (21, 22) are arranged to be moved within the O-arm at different distances from their centre of rotation.
