1. Field of the Invention
The invention concerns a method and system for processing an x-ray image of the type wherein a mathematical correction of the x-ray image is implemented.
2. Description of the Prior Art
In x-ray-based imaging, an x-ray tube with an anode (for example a rotating anode tube) is used as a nearly punctiform x-ray source. In such an x-ray tube, an electron beam in a vacuum housing is accelerated in an electrical field. The electron beam strikes the flat anode made of heavy metal (for example tungsten, molybdenum, rhodium) at a specific angle α. The characteristic bremsstrahlung (braking radiation) thereby arises that exits the anode at an angle of 90 degrees and can be used as imaging radiation. The angle α is optimized as a compromise between the following two criteria: the angle should be as large as possible so that a large area can be exposed with it, and the angle should be as small as possible because the smaller the angle, the larger the electrical focal spot size that can be given the same optical focus size, which allows higher pulse power. The angle is generally selected so that it can expose precisely the required area.
The optical focus size is finite and leads to a blurring of x-ray images. Angular anode tubes additionally have the disadvantage that, due to their special geometric arrangement, the optical focus appears compressed or distorted depending on the viewing direction “seen” from the x-ray detector. An illustration of the variation of the focus geometry in different emission directions relative to the central radiation point of the x-ray beam is shown in FIG. 2. This variation—known as focus astigmatism—leads to different, locally dependent blurrings at the x-ray detector or, respectively, the x-ray image.