In a method and x-ray device to determine the value of an x-ray tube voltage to generate at least one image of defined tissue to be examined, at least one provided parameter is used that establishes or describes the desired image quality; based on the dependency of the contrast of the defined tissue to be examined on the spectrum of the x-ray radiation or on the value of the tube voltage of the x-ray tube. The tube voltage is determined also based on a contrast-to-noise ratio that is constantly maintained under consideration of the aforementioned parameter such that the dose of x-ray radiation applied to the patient is optimally low upon setting the value of the tube voltage at the x-ray tube and the acquisition of at least one x-ray projection of the defined tissue.