A medical instrument for magnetic resonance imaging guided radiotherapy includes a magnetic resonance imaging system for acquiring magnetic resonance data from an imaging zone, a radiation source for emitting X-ray or gamma ray radiation directed at a target zone within the imaging zone, wherein the radiation from the radiation source directed to the target zone passes through a radiation window of the magnetic resonance imaging system. The magnetic resonance imaging system includes at least one radiation transparent electrical transmission line, which is configured for transmitting an electrical signal and which extends through the radiation window, wherein the electrical transmission line is provided by a microstrip comprising a conductor line extending parallel to the ground layer, wherein the conductor line and the ground layer are separated from each other by a dielectric substrate.
