Micro-CT for Minute Objects with Central Ray Determined Using the Projection Data of the Objects

Central ray is the projection of the centre-of-rotation of a computed tomography (CT) system. It is required for all kind of CT image reconstruction algorithms. The current common practice is to determine it by scanning a wire phantom. This is a manual work and very time-consuming. Besides, when a minute object is scanned with large magnification, it usually encounters large errors in the determination of the central ray due to the mechanical movements required. When the source-to-object distance becomes further smaller, it might be even impossible to insert the wire phantom. This paper describes the basic idea of directly using the projection data of an object to be inspected for the determination of the central ray. With this method, the left and right boundary points of the whole-round projection of the object are identified from the sinogram of one slice and the system projection geometry is used to calculate the central ray. This approach significantly simplifies the micro-CT scanning process and saves much operation time as well. The inspections of a small electronic die and a small electric wire-bundle successfully demonstrate the effectiveness of this method.