The invention relates to a medical investigation and/or treatment system comprising: a catheter system, comprising a catheter (1, 7, 9), with a first sensor (4, 11) of an imaging system for optical coherence tomography with an optical fiber via which the light is directed and is radiated in the area of a catheter tip introduced into an area to be investigated, via which fiber reflection light is directed from an illuminated investigation area to a first image processing unit (22), a second sensor (3, 8, 10) of an intravascular ultrasound imaging system to transmit and receive sound pulses which are fed as an electrical signal to a second image processing unit (23), und at least one display unit (24) for presenting the images of the first and second image processing unit (22, 23).