Subtraction Method for X-Ray Imaging of Weakly Absorbing Objects

The X-ray transmission of an object to get information about its internal structure or inhomogeneities is an important method of non-destructive testing. When an object, for example, a connection of polymer pipes for transporting liquids or gases, low absorbs X-rays, the contrast of the X-ray image of the object on the photo film or on digital analogue is relatively low. The aim of the work was to develop a subtractional method for obtaining images of low X-ray absorbing objects with improved contrast using laboratory X-ray sources. In the considered method, an X-ray tube and a digital 2-D X-ray camera for X-ray beam registration are used to capture X-ray images of objects. The object is placed between the X-ray tube and the X-ray camera. The method includes capturing two digital images of the object at different angles of the object orientation to the X-ray beam axis and then processing the images by subtracting them. Images of a number of objects with low absorption of X-rays (bee, polymer mesh, rice grain) were obtained and their computer processing by image subtraction was carried out. X-ray tube BSV-17 with copper anode was used for X-ray transmission of the object, voltage at the anode of the tube – 15 kV, current – 10 mA. A Photonic Science digital X-ray camera was used to capture the X-ray image of the object. The size of the working area of the X-ray camera is 18 × 12 mm2, the number of pixels is 4008 × 2670. The object was placed close to the X-ray camera to improve the resolution of the image. Two images of the object were captured to realise the subtraction, the second image was taken with the object rotated by 5°. The contrast of the original and processed images was calculated. The analysis of the contrast of the resulting images showed that the use of the developed subtraction method allowed to increase the contrast of the image of objects with low absorption of X-rays about two times. The method is reasonably simple in comparison with the well-known phase-contrast method, and it can be used in technical diagnostics in the process of examination of plastic, polymer, composite materials and objects by X-rays.

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