J. T. de Assis

X-RAY DIFFRACTION TOMOGRAPHY USING INTERFERENCE EFFECTS

Abstract When the electromagnetic wave excites more than one electron, the coherent scatter from different electrons gives rise to interference effects. X-rays scattered from a crystalline solid can constructively interfere, producing a diffracted beam at well-defined Bragg angles. The aim of this work is to describe a new imaging method based on the detection of diffracted X-rays. Diffraction patterns of polycrystalline solids (lead, silver and copper) were measured. A selective discrimination of a given element in a scanned specimen can be realized by fixing the Bragg angle which produces an interference peak and then, to carry out the computed tomography in the standard mode. The images obtained show the feasibility of this selective tomography

Bone quality analysis using X-ray microtomography and microfluorescence

Bone quality is an evaluation index often applied in order to interpret clinical observations made upon bone health, such as bone mineral density, micro and macro architecture, and mineral content. Conventional inspection techniques do not provide full information on trabecular bone quality. This study shows the high resolution potential and the non-destructive character of X-ray microtomography and microfluorescence upon the application of such techniques for evaluating bone quality. The mineral content assessment was performed by two-dimensional concentration mappings of calcium, zinc, and strontium. The results showed significant changes in bone morphology.

Using the FDK Algorithm to Reconstruct Low Contrast Images Generated by Monte Carlo, Simulation of Sediment Imaging

In geology field, the experimental or computational simulation of the sediment deposition process is widely used to characterize regions and possible findings. Noninvasive methods are the best way to evaluate sediments; in order of not to destroy the information of the sediment deposition structure. The use of computed tomography (CT) techniques to get images of sediments will be evaluated. A CT will be analyzed has a two stage process, the scan of body test to produce a set of X-ray images and the reconstruction step where the set of X-ray images is processed by computational algorithm to generate cross-sectional images of the scanned object. To test the method the X-ray images are generated using the Monte Carlo method with a XRMC tool, and the simulated images are 3D reconstructed using the Feldkamp, David e Kress algorithm. The reconstruction planes and the volume generated in the simulation showed very similar after a visual comparison for all of tested volumes. However a statistical analysis showed that there was no statistical coincidence of the simulated dimensions and reconstruction. The results presented showed the possibility to use CT to study the sediments in tanks or rivers.

Comparison of the GEANT4 releases 8.2 and 9.2 in terms of a pCT reduced calibration curve

The GEANT4 simulations are essential for the development of medical tomography with proton beams — pCT. In the case of thin absorbers the latest releases of GEANT4 generate very similar final spectra which agree well with the results of other popular Monte Carlo codes like TRIM/SRIM, or MCNPX. For thick absorbers, however, the disagreements became evident. In a part, these disagreements are due to the known contradictions in the NIST PSTAR and SRIM reference data. Therefore, it is interesting to compare the GEANT4 results with each other, with experiment, and with diverse code results in a reduced form, which is free from this kind of doubts. In this work such comparison is done within the Reduced Calibration Curve concept elaborated for the proton beam tomography.

Energy Measurements in a Prototype Proton CT Scanner

In proton treatment planning, the use of protons instead of X‐rays for computerized tomography (CT) studies has potential advantages, especially for medical applications. Proton CT requires accurate measurement of the energy loss of protons passing through the object. The resolution of a proton CT scanner is determined by the resolution of the energy loss measurement, which is limited by the inherent energy straggling of protons. An experiment with a doped CsI(Tl) crystal was designed to determine the resolution of the energy loss measurement of protons in the energy range from 40 MeV to 250 MeV experimentally. It was found that, in principle, the resolution of a proton calorimeter is adequate to CT studies with objects of realistic size.