1. A method for controlling the emission of an X-ray imaging device configured to take images of a patient's body, the method comprising: using the X-ray imaging device with a processing unit comprising a microcomputer implementing the steps of: processing images of the patient's body taken by the X-ray imaging device; calculating information representing a velocity of a medical instrument in the patient's body from the images, wherein the medical instrument is visible in the images; calculating an image quality from the velocity of the medical instrument in the images; and adapting, in real time during imaging, X-ray emission parameters of the X-ray imaging device to (i) obtain the image quality with a minimal X-ray emission dose emitted towards the patient's body, and (ii) adjust the image quality as a function of the velocity of the medical instrument, wherein the image quality is adjusted to increase with an increase in the velocity of the medical instrument.