1. Angiographic x-ray diagnostic apparatus, comprising: an x-ray radiator including an x-ray tube; a patient positioning table including a radiation-transparent positioning plate and mattress; an x-ray detector; an imaging system; an image processing unit; and a measuring device connected to the x-ray detector for acquiring output signals of the x-ray detector, the measuring device comprising: a first device for determining a quality value related to a reproduction quality of a clinically relevant object; a second device configured to calculate a local variance of a noise present in a homogenous image region of different x-ray images; and a calculation device for calculating a ratio of the quality value and the local variance of noise.