This article describes carbon-nanotube based X-ray technologies for medical research and clinical applications, including an X-ray source, microfocus X-ray tube, microcomputed tomography scanner, stationary digital breast tomosynthesis, microradiotherapy system, and single-cell irradiation system. It first examines electron field emission from carbon nanotubes before discussing carbon-nanotube field emission electron and X-ray technologies in greater detail. It highlights the enormous promise of these systems in commercial and research application for the future in diagnostic medical imaging; in-vivo imaging of small-animal modelsfor pre-clinical cancer studies; security screening; industrial inspection; cancer radiotherapy of small-animal models for pre-clinical cancer studies; and basic cancer research using single-cell irradiation.