Image Registration Combining Digital Radiography and Computer-Tomography Image Data

X-Rays are used as reliable technique for today’s quality assurance of safety critical parts, for example in the automotive or in the aerospace industry. Radiography systems are used to ensure a high throughput in the field of hundred percent testing of a batch. In such systems digital images are acquired by using either flat-panel detectors with a high dynamic range or image intensifiers including nearly noiseless, light-sensitive CCDsensors inside. The resulting digital X-Ray images are perspective-projections of the threedimensional density information of the test part onto the two-dimensional picture-plane represented by the dedicated sensor. Due to this projection, structure information and defects may overlap each other. This requires a careful positioning of the test parts to get a penetration of the material as homogeneous as possible. Nevertheless, the three-dimensional spatial information of possible defects is lost in the resulting radiography X-ray image. Also systematic variances of the part (e.g. burr) interfere the defect detection. Therefore sometimes it is hard to decide if possible defects comply to a given specification, i.e. whether a defect in a certain application becomes relevant or not. Computer-Tomography systems (CT-systems) yield tomograms that are representations of certain slices of the three-dimensional density information of the test parts. Thus the spatial location of the structure of the part or of possible defects is clearly visible. Systematic variances of the part can be excluded from regions that belong to the part directly. But the throughput of test parts is less than on a radiography system, because to compute the tomogram several X-Ray image lines from various views have to be acquired. Using a digital Line-Detector-Array (LDA) and a fan-beam X-Ray source leads to a combination of paralleland perspective-projection of the three-dimensional density information onto the picture-plane. This study presents methods for image registration combining digital radiography and computer-tomography image data and is well suited for an appropriate X-Ray testing-system providing radiography images and choosing the layer to compute the tomograms interactively.