An antenna unit for a PET/MRI scanner is disclosed, including a supporting tube in which at least one antenna for MR signals is arranged. In at least one embodiment, the supporting tube has at least one permeable section and one impermeable section, the permeable section of which has a greater permeability to PET quanta than the impermeable section. The antenna unit further includes a screen for radio-frequency signals which is arranged outside of the supporting tube and surrounds the latter. In at least one embodiment, an intermediate layer is arranged between the supporting tube and the screen and, in the region of the permeable section of the supporting tube, is composed of, at least in part, a material which has a permeability to PET quanta comparable to the permeable section.