RESUMO
Diffraction-enhanced images have been obtained using two silicon crystals in a non-dispersive set-up at the XRD2 beamline at the Brazilian Synchrotron Light Laboratory (LNLS). A first asymmetrically cut silicon crystal using the (333) reflection vertically expanded the monochromated beam from 1 mm to 20 mm allowing the imaging of the whole sample without movements. A symmetrically cut Si(333) second crystal was used as a Bragg analyzer. Images of biological samples including human tissue were recorded using a direct-conversion CCD detector resulting in enhancement of the contrast compared with absorption-contrast images.
Assuntos
Dente Canino/diagnóstico por imagem , Histerossalpingografia/métodos , Intensificação de Imagem Radiográfica/instrumentação , Intensificação de Imagem Radiográfica/métodos , Tuberculose Pulmonar/diagnóstico por imagem , Difração de Raios X/instrumentação , Difração de Raios X/métodos , Brasil , Estudos de Viabilidade , Humanos , Pulmão/diagnóstico por imagem , Projetos Piloto , Folhas de Planta/anatomia & histologia , Síncrotrons , Árvores/anatomia & histologiaRESUMO
The importance of structure form factors in describing elastic scattering in diagnostic radiology was studied through a Monte Carlo code built to reproduce scattering in large water samples. The code, developed by us, considers all relevant interactions, including multiple scattering and interference due to scattering by the liquid structure. Geometrical conditions and energies similar to those found in radiology were used. The secondary to primary radiation ratio using the usual free atom approximation and the structure form factor was obtained and both approaches were compared. Calculations of radiological parameters such as the angular distribution of photons incident on the detector and the fraction of scattered photons stopped by anti-scattering grids were also performed considering mammography, thorax and abdomen radiography conditions. The results have shown that S(beta)/P depends on the experimental set-up, being more important for low momentum transfers and sample sizes for which the multiple scattering is not expected to be significant, as in the case of mammography. It was also verified that large samples increase the probability of multiple scattering, masking the structure peak in S(beta) and making the sample structure important just for relatively thin samples. Considering mammography-like geometry, the maximum of the S(beta)/P distribution considering structure form factors occurs around 15 degrees while the correspondent maximum without considering the structure factors occurs around 10 degrees for any sample thickness. S(beta)/P is almost independent of the irradiation field, with the maximum remaining at 15 degrees and 10 degrees for the SFF and FAFF, respectively. The cases studied in this paper stress some conditions in which it is mandatory to use SFF, but since it requires no further significant efforts, the SFF approach is recommended as a standard procedure when describing the elastic scattering process in radiology.
Assuntos
Diagnóstico por Imagem/métodos , Espalhamento de Radiação , Mamografia/métodos , Método de Monte Carlo , Fótons , Software , Água , Raios XRESUMO
At low angles the scattering of X-rays in the diagnostic energy range (low-momentum transfer), it is probable that the scattering interaction will be coherent. This coherence gives rise to interference effects resulting in X-ray diffraction patterns that are characteristic of the scattering material. The usefulness of coherent scattering is not limited to crystallography. It can provide information about biological material as well. The interatomic and intermolecular co-operative effects which modify the free-atom coherent scattering process are well known for highly ordered structures such as crystalline materials but are important for amorphous solids and liquids where short-range ordering occurs. X-ray diffraction using synchrotron radiation has became a well established technique. This work introduces a non-destructive synchrotron radiation X-ray diffraction imaging technique. The feasibility of the X-ray diffraction computed microtomography using synchrotron radiation has been investigated. This research was carried out at the X-ray diffraction beam line of the National Synchrotron Light Laboratory supported by the National Council for Scientific and Technological Development (LNLS/CNPq) in Brazil. These experimental patterns were carried out with a 500 microm slit in front of the detector and an 11.101 keV beam (lambda = 1.117 A) monochromatic beam from the double crystal monochromator. The diffracted beam was detected by a fast scintillation detector (10(6) counts s(-1)) designed specifically to meet the needs of high quality X-ray diffraction and synchrotron radiation experiments. The data were recorded at rates of one second per degree of 2theta (angular steps equal to 0.05 +/- 0.01 degrees) and registered by a multichannel analyzer. These experimental data could be used to evaluate the scattering properties of different tissue-substitute (water, lucite, nylon, plastic and polystyrene) and bone-substitute (hydroxyapatite and aluminum) materials. The data are in good agreement with those obtained by other authors, indicating the feasibility of the imaging technique.
Assuntos
Materiais Biomédicos e Odontológicos , Substitutos Ósseos , Tomografia Computadorizada por Raios X/métodos , Difração de Raios X/métodos , Alumínio , Durapatita , Nylons , Plásticos , Polimetil Metacrilato , Poliestirenos , Síncrotrons , ÁguaRESUMO
The angular and energy distributions of photons scattered by water, muscle tissue, and bone were measured at the Physics Institute of the Universidade Federal do Rio de Janeiro using a Ge-detector and a 241Am source of 59.54 keV radiation. Single and double scattering were investigated on samples up to 16 cm in diameter. The results were compared with theoretical calculations of Rayleigh (elastic) and Compton (inelastic) scattering, assuming a simple model for the scattering geometry. The overall agreement between model and experimental results for soft tissue and water allows quantitative predictions based on a simple equation. Some applications are presented.
Assuntos
Fótons , Espalhamento de Radiação , Tomografia Computadorizada por Raios X/estatística & dados numéricos , Fenômenos Biofísicos , Biofísica , Osso e Ossos/diagnóstico por imagem , Humanos , Modelos Estatísticos , Músculos/diagnóstico por imagem , Imagens de Fantasmas , Interpretação de Imagem Radiográfica Assistida por Computador , ÁguaRESUMO
Placas amplificadoras fluorescentes para filmes de raio-X são usadas em radiologia a fim de reduzir a dose de radiação. Estas placas produzem luz visível que aumenta a eficiência do filme. Adicionalmente, raios-X secundários são originados devido à efeito fotoelétrico, espalhamento elástico (Rayleigh( e inelástico (Compton). A taxa de contagem e a distribuição angular destes raios-X foram medidos, mostrando que a razão da radiação secundária pela primária incidente no filme de raio-X é cerca de 20 por cento.
To reduce the radiation dose in radiology, fluorescent intensifying screens for X-ray films are used. They produce visible light which increases the efficiency of the film. ln addition, secondary X-rays arise due to the photoelectric effect, elastic (Rayleigh) and inelastic (Compton) scattering. The counting rate and angular distribution of these X-rays were measured, showing that the ratio of secondary-to-primary radiation incident on the X-ray film is about 20 %