Digital X-ray imaging

Whereas scintillation screens can be used to directly view x-rays passing through the body, the dose to a patient is too high. Instead, scintillation screens are combined with video cameras or electronic intensifier tubes and video cameras. This detection scheme is used in digital radiography where digital x-ray images are recorded, and fluoroscopy where temporal processes are to be followed. 

Analytical electron microscopy permits structural and chemical analyses of catalyst areas nearly 1000 times smaller than those studied by conventional bulk analysis techniques. Quantitative x-ray analyses of bismuth molybdates are shown from lOnm diameter regions to better than 5% relative accuracy for the elements 61 and Mo. Digital x-ray images show qualitative 2-dimensional distributions of elements with a lateral spatial resolution of lOnm in supported Pd catalysts and ZSM-5 zeolites. Fine structure in CuLj 2 edges from electron energy loss spectroscopy indicate d>ether the copper is in the form of Cu metal or Cu oxide. These techniques should prove to be of great utility for the analysis of active phases, promoters, and poisons. 

Analysis of catalyst materials using digital x-ray Images of elements in an AEM offers a method of quickly finding significant areas for analysis. Indeed, Important elements acting as promoters or poisons may not be located at obvious image features at all. 

Figure 5. Pd supported on carbon a) annular dark-field STEM image revealing particles as small 2nm, b) processed digital x-ray image showing that Pd particles 4nm and larger can be imaged using Pd x-rays alone.

Figure 6. Digital x-ray imaging of zeolite ZSM-5 (Si/Al 49,5) thin section a) bright-field STEM image, b) A1 x-ray image smoothed by averaging each pixel with its 8 nearest neighbors. The darker shading within the particle indicates higher A1 content. The circular field is due to the image of the selected area diffraction aperture.

Digital X-ray imaging system An X-ray source coupled to a brightness amplifier and digital camera. This allows contrast improvement for fine detail and image enhancement. 

Fig. 13.1 Principles of Bedescan digital X-ray imaging, (a) in transmission, (b) in reflection.

I. Digital X-ray Mapping. The beam may be controlled by a computer to move within a grid of points on the specimen surface. The beam remains at each point for a pre-set time while an analysis is carried out. With an EDS system, data from several elements may be collected at the same time and a BSE image may also be acquired in the same experiment. Digital X-ray maps may then be displayed for each of the chosen elements in turn. 

This patient is undergoing cerebral angiography. Digital x rays use electronic signals to form visual images, rather than the photographic method of the conventional x ray. 

Dental x-ray images contain more information than might be apparent to the human eye. The loss of detail is due to the low contrast level. After digitizing the image with a sensitive densitometer, the intensities can be rescaled and displayed with greater detail than we would have seen in the original image. 

The dose to which personnel is exposed can be read off the film badge by using thermoluminescence. The thulium-doped calcium sulphate phosphor can measure low doses precisely. The X-ray image in photo stimulable luminescence (PSL) can be processed digitally by stimulating the exposed phosphor with a fight source different from the actual exposure. The PSL intensity has a linear response with respect to X-ray energy. 

Wavelength dispersive X-ray spectrometry (WDS) for a more detailed elemental analysis of samples in the SEM. JEOL Four-Crystal Spectrometer attached to the JSM-35C SEM can be used for l-pm spot analysis, digital and analog line scans, and X-ray image mapping, elements detection from Be to U, minimum detection limit of 0.01% by weight, fully quantitative results by extended cp-p-z. 

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