Tomographic imaging

Despite the relatively poor spatial resolution and quite prolonged measuring times, the method has several advantages. The method is able to "look" into the sample without destroying it, and no microtomy is necessary. Then, it is possible to collect three-dimensional images (tomographs), thus making this method very attractive if three-dimensional information about certain distributions is of interest. 

The radiation dose is very low but can be imaged tomographically using photomultiplier-scintiUator detectors. PET can be used to monitor effects of drugs on metabolism in the brain, e.g. on and off phases in parkinsonism. There are many other applications. 

A diagnostic appheation of NMR in the medical field has been made possible through the development of the NMR imaging (tomographic) technique... 

Johansen GA, Fraystein T, Hjertaker BT and Olsen 0 1996 A dual sensor flow imaging tomographic system, Meas. Sci. Technol, 1, 297-307... 

A. Rougee, K.M. Hanson, and D. Saint-Felix Comparison of 3D Tomographic Algorithms for Vascular Reconstruction. SPIE Vol. 914 Medical Imaging II, 1988, pp. 397-405. 

Cohen, G. and F.A. DiBianca, The use of contrast-detail-dose evaluation of image quality in a computed tomographic scanner. Journal of Computer Assisted Tomography, 1979. 3(2) p. 189-195. 

Among 3D tomographic systems the systems, capable to reconstruct the complete volume image of object for one scanning session, are of interest. 

It seems to be expidiently to develop new scanning geometries, which combining with exact reconstruction methods provide high quality of 3D tomographic images. 

In sections, where exists high probability of presence of defects, on the base formed in the binary type of projections acoustical tomographic images of only defective structure elements of sections is restored. IT of restoring stipulates such operations ... 

For restoring of three-dimensional SD is used stated above approach. Under restoring of tomographic images for the base undertakes a function of three-dimensional total image, which after double differentiation and inverse projecting describes sought SD 8 (1) ... 

Fig. 1. Experimental restored acoustical tomographic images of defects in product sections (a-dififerent density 5p 10%, b- porosity x,y- in mm).

Fig.2. Tomographic (a) and graphic (b, for depth 13 mm) images of relative change of Young s modulus 5E% (average on volume Eo=218,310 Pa) of material in section perpendicular to surface of thick-sheet sample (thickness 26 mm).

A 3D summation tomographic image is generated and layers in any direction may be viewed. Image quality is improved by filters. The method has been proved satisfactory on a high radiographic contrast cylindrical object and on more complex items. 

Tomographic summation images of vertical, horizontal and cylindrical layers were generated by positioning the film in suitable positions. The method has a deficiency when the films have to be positioned close one to the other. Hence for the generation of close or overlapping cuts there is a need for repeated exposures. 

The study presented a new tomographic method based on 3D reconstruction from a single 180 exposure. The method is based on the summation principle and the 3D voxel image is generated almost in real-time. 

Computerized Tomographic Imaging (CT), a well established method in medical diagnostics for 25 years now, also makes its arrival into non-destructive testing since the last decade. 

Principles of Computerized Tomographic Imaging IEEE Press, New York, 1988... 

Considering existing microscopical techniques, one can find that non-destmctive information from the internal stmcture of an object in natural conditions can be obtained by transmission X-ray microscopy. Combination of X-ray transmission technique with tomographical reconstmction allows getting three-dimensional information about the internal microstmcture [1-3]. In this case any internal area can be reconstmcted as a set of flat cross sections which can be used to analyze the two- and three-dimensional morphological parameters [4]. For X-ray methods the contrast in the images is a mixed combination of density and compositional information. In some cases the compositional information can be separated from the density information [5]. Recently there has been a... 

Another important application area is the non-destructive defectoscopy of electronic components. Fig.2a shows an X-ray shadow image of a SMC LED. The 3-dimensional displacement of internal parts can only be visualized non-destructively in the tomographic reconstmction. Reconstructed cross sections through this LED are shown in Fig.2b. In the same way most electronic components in plastic and thin metal cases can be visualized. Even small electronic assemblies like hybrid ICs, magnetic heads, microphones, ABS-sensors can be tested by microtomograpical methods. 

The introscopic image of power reactor fuel assembly reveals the presence the fuel elements, the tomographic image reveals their filling by fuel and location. 

Advanced tomographic sensors for industrial multiphase imaging ... 

BE2-0SS7 Advanced tomographic sensors for industrial multiphase Imaging Or.B.S.Hoyle Univerarty of Leeda... 

The system uses a remote controlled manipulator system whieh scans the volume of interest. It also positions the x-ray source and x-ray camera at different angles relative the crack and create projection images of the craek. By using a tomographic reconstruction of these images a 3-D representation of the crack can be used for analysis and sizing. 

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