To facilitate imaging of a patient two different image recording methods are to be carried out at the same time. An auxiliary fluid, for example a contrast medium or a tracer, may be introduced into the body in each image recording method. The invention proposes mixing the two auxiliary fluids in situ immediately before dispensing to the patient. For this purpose it provides an injector with which the auxiliary fluids may be mixed and supplied to the patient. Devices for controlling dispensing of fluid from containers connected to the injector to produce a mixed solution may be electronically controlled by a control unit which calculates the total quantities, and optionally sub-quantities, of auxiliary fluids, which are used for a mixed solution, before activating the devices.