or cannot be operated directly and with the necessary precision due to the corresponding coverings to increase the precision of the control measures the invention provides a contactless control system based on gestures of the user in the sterile environment s wherein the gestures are acquired via a portable controller 111 the portable controller 111 can be embodied as a circlet or ring and has one or more inertial sensors 10 which can be acceleration sensors or gyro sensors and are designed to record acceleration data for a body part of the user arm or hand finger or foot etc the acquired acceleration data are forwarded via a wireless interface 11 to a conversion module 20 which is configured to receive the transmitted acceleration data and convert it into instructions i the instructions i being in a format to control the respective medical device 30 the device 30 can be for example a display monitor for displaying the radiological image data wherein the image data are displayed with changes in response to a user input in one embodiment of the invention the conversion module 20 is embodied as a component that is separate from the portable controller 111 and spaced apart therefrom in an alternative embodiment of the invention the conversion module 20 can also be implemented on a further computer on which the program is executed for the control of the device or the image display a first gesture can.