A multi-modality tomography apparatus comprising: a support ring rotatable around an axial shaft in either of two directions; a first X-ray tomography computerized which is supported on a face of the support ring having a hole comprising X-ray detection means and an X-ray emitter adapted to provide a radiation field, a second computer assisted tomography having a different operating principle from the first X-ray tomography computerized comprising at least one tomograph detector system using flat detectors covering most of the field of view, the second computer assisted tomography being supported on the same face of the support ring, characterized in that the first X-ray tomography computerized and the second computer assisted tomography are installed on the face of the support ring in one plane and the first and second tomographs having an overlapping effective field of view, and in that the tomography apparatus further comprises shielding or screening means (16, 17) configured, designed and located to prevent possible interferences of the first tomography in the second tomography or vice versa, and allowing the first and second tomography taking samples of the same region of a subject without moving the subject, wherein the shielding or screening means comprises a first screening means, adapted to screen the said detector system of the second tomography, having upper and lower parts of different geometric shape adapted to the radiation field of the first X-ray tomography at the distal end of said X-ray emitter, that is, the surface of the mentioned upper part of the first screen is substantially parallel to the radiation field of the first tomography and adapted such that it is effective against scattered radiation and prevents interference with the first tomography. a support ring rotatable around an axial shaft in either of two directions; a first X-ray tomography computerized which is supported on a face of the support ring having a hole comprising X-ray detection means and an X-ray emitter adapted to provide a radiation field, a second computer assisted tomography having a different operating principle from the first X-ray tomography computerized comprising at least one tomograph detector system using flat detectors covering most of the field of view, the second computer assisted tomography being supported on the same face of the support ring, characterized in that the first X-ray tomography computerized and the second computer assisted tomography are installed on the face of the support ring in one plane and the first and second tomographs having an overlapping effective field of view, and in that the tomography apparatus further comprises shielding or screening means (16, 17) configured, designed and located to prevent possible interferences of the first tomography in the second tomography or vice versa, and allowing the first and second tomography taking samples of the same region of a subject without moving the subject, wherein the shielding or screening means comprises a first screening means, adapted to screen the said detector system of the second tomography, having upper and lower parts of different geometric shape adapted to the radiation field of the first X-ray tomography at the distal end of said X-ray emitter, that is, the surface of the mentioned upper part of the first screen is substantially parallel to the radiation field of the first tomography and adapted such that it is effective against scattered radiation and prevents interference with the first tomography.