Research Of High Dynamic Range X-ray Imaging Technology And System

When one object with large thickness ratio is detected by the X-ray digital imagingtechnology, the traditional imaging mode with fixed tube voltage cannot achieve the completerepresentation of the object’s structure because the phenomenon of overexposure and oweexposure appears in one image, which will lead to the serious lack of the information. Atpresent, people usually adopt some detection methods to resolve this problem, such asthickness or density compensation, local irradiation, imaging device with large chargecapacity or high dynamic range. Although the above methods increase the transmission doseand the costs but is difficult to get the complete visual effect of the object.This paper will study the high dynamic range X-ray imaging technology through thedesign of system control, data acquisition, image fusion, and visualization. The main purposeis to achieve the goal of extending the dynamic range of imaging system. By selecting thethickness segmentation degree of the object and linear scale of gray values from object withsimilar thickness, we used X-ray imaging system with low dynamic range to realize imagingof several object areas with different thickness. Then the features of imaging data fromdifferent object areas were extracted and fused so that we can obtain the X-ray image withhigh dynamic range of the whole object. In order to display the fused X-ray image in thedevice with low dynamic range, we studies gray-scale compression technology of the imagewith high dynamic range. It can compress the dynamic range of the fused image, but enhanceits structure information.The article puts forward to use a high pressure X-ray source with a lineargradient voltage. The voltage can realize a linear gradient adjustment according to the setof kV Tcurve cooperating with the adjustment of exposure time interval of the detector sothat we can acquire X-ray image sequences with different tube voltage intervals rapidly. Bystudying rays with the effect of the object and gray level change rule in X-ray detection process, the thickness repetition rate under adjacent tube voltages, linear proportionalrelationship between different image gray scales and correlation characteristics of tubevoltage intervals are determined. A calculating method based on proportional gain histogramis presented to finish fast calculation of proportional gain coefficient, linear degree and repeatrate between adjacent tube voltages. Also the needed constraint of images acquired underadjacent tube voltage to the thickness repeat rate of the object is raised. It can realizeintelligent control of the second sampling process of original images and extraction of theuseful information of images from areas with different thickness. According to theproportional gain histogram, the scaling values of the needed tube voltage in different areascan be calculated. Based on it, the grey value of each pixel of the image were weighted toobtained a fused image with high dynamic range. Such fusion method can ensure linearrelationship between gray values and the thickness of the object within the scope of certainthickness changes. The fusion experiments results of X-ray images of objects made of asingle or more than one material shows that the presented method is suitable for X-raydetection of objects with different material, thickness distribution and thickness ratio.In order to display the fused image with high dynamic range on device with lowdynamic range, the gray-scale compression algorithm is studied. The image is processed bylogarithmic operation, gradient operation and nonlinear weighted operation. It can compressthe large gradient information, but enhance small gradient information. Then the gradientinformation are reconstructed to obtain gray images. The experiment results show that thecompressed image contains information of different areas of object with different thicknessand can be displayed in device with low dynamic range.