[en] The tomographic method of picking up layers of body substances is using an ionographic pick-up chamber filled with a gas to record an X-ray picture. The chamber together with the X-ray source is rotated about a swivel axis lying in the plane of the body layer to be reproduced. By suitable control of the movement of the pick-up chamber the X-rays are penetrating the gas-filled reaction volume always essentially at right angle. The projection in the swivel plane of the body layer to be recorded, being reduced by rotating the X-ray source, is enlarged by increasing the distance between the body layer and the pick-up chamber thus compensating for the reducing effect. If the X-ray source is moved along a straight line parallel to the body layer or on a circular orbit around the swivel axis the distance variation, depending on the angle of traverse, must obey a certain formula. (ORU)