Mobile X-ray apparatus and method for determining projection geometries therein

A method for determination of projection geometries in a mobile X-ray apparatus, said mobile X-ray apparatus having an X-ray system comprising an X-ray source and a planar X-ray detector, and a displacement arrangement connected to said X-ray system for displacing said X-ray system relative to a subject, said X-ray system and said displacement arrangement being susceptible to mechanical instabilities, and wherein said displacement arrangement comprises at least one displaceable component for effecting a displacement movement of said X-ray system in at least one displacement direction, said method comprising the steps of:

• adjusting said at least one displacement component to a displacement position to effect said displacement movement of said X-ray system;
• arranging a phantom relative to said X-ray system and penetrating said phantom with an X-ray beam emitted from said X-ray source, and detecting X-rays from said X-ray beam with said X-ray detector after said X-ray beam passes through said phantom;
• picking up a series of 2D projections of said phantom online by moving said X-ray system relative to said phantom;
• evaluating said series of 2D projections of said phantom offline for identifying respective projection geometries for each 2D projection in said series of 2D projections;
• storing said projection geometries for said displacement position of said displaceable component;
• and
• obtaining a further series of 2D projections of said phantom if said displacement position of said displaceable component changes and evaluating said further series of 2D projections offline for identifying respective projection geometries for each 2D projection in said further series of 2D projections, and storing the respective projection geometries for said changed displacement position;
• and
• calculating a 3D image of said subject online using said stored projection geometries of said 2D projections in said series of 2D projections and, if present, using the stored projection geometries of the 2D projections in said further series of 2D projections.