The invention relates to a computer tomography scanner comprising a gantry, on the rotor of which one or more displaceable masses are arranged. During rotation of the rotor about a rotation axis, the position of each mass can be changed perpendicular to the rotation axis by means of an adjustment unit. By retaining the rotary momentum of the rotor, the rotational speed is increased when the masses are moved toward the rotation axis, and vice versa. As a result, it is possible to maintain a specific ratio between the heart rate of the examined patient and the rotational speed even if the heart rate of the patient changes during the examination.