A miniature X-ray tube for intravascular or intracorporeal radiation treatment in living beings is proposed. The X-ray tube comprises a cylindrical housing section with a longitudinal axis. The miniature X-ray tube also comprises a cylindrical or cylindrical-tube-shaped first field emission cathode arranged concentrically about the longitudinal axis in the housing with a plurality of carbon nanotubes which emit electrons radially outward. The miniature X-ray tube also comprises a second field emission cathode in the housing with a plurality of carbon nanotubes which emit electrons in the direction of longitudinal axis. The miniature X-ray tube only emits little heat and is robust against mechanical stresses.