The invention relates to a medical examination and/or treatment device for performing image acquisitions and/or radiation- or instrument based treatments in an examination or treatment region, comprising an image acquisition means and/or a treatment means and a patient table wherein a detection means (7) for determining the position of a patient (4) located on the patient table (3) is provided, the detection means comprising a radiation emitter (8) which irradiates the patient (4) in at least one region and emits terahertz radiation (9), at least one radiation receiver (10) detecting reflected terahertz radiation (12), and a processing means (13) processing the receiver signals supplied by the radiation receiver (10), wherein the processing means (13) can generate an image showing the surface of the irradiated patient region on the basis of the receiver signals and the position of the patient region relative to the examination or treatment region (5) can be determined on the basis of said image.
