Current Issue : October - December Volume : 2012 Issue Number : 4 Articles : 4 Articles
It is shown that an elementary semi-quantitative approach explains essential\r\nfeatures of the X-ray free-electron laser mechanism, in particular those of the\r\ngain and saturation lengths. Using mathematical methods and derivations\r\nsimpler than complete theories, this treatment reveals the basic physics that\r\ndominates the mechanism and makes it difficult to realise free-electron lasers for\r\nshort wavelengths. This approach can be specifically useful for teachers at\r\ndifferent levels and for colleagues interested in presenting X-ray free-electron\r\nlasers to non-specialized audiences...
Objective: It is well established that computer based models of x-ray imaging systems are basic and very important tools\r\nfor developing and evaluating new emerging x-ray imaging techniques, optimizing technical parameters, and performing\r\nfeasibility studies prior to implementation in clinical practice. Such models are essential for the development and the\r\nestablishment of new breast x-ray imaging modalities that aim to detect and better characterize breast lesions in their early\r\nstage. This work presents a complete software package, called BreastSimulator, dedicated for breast x-ray imaging\r\nresearch.\r\nMethods: The package consists of four modules used to create three-dimensional breast models in compressed and\r\nuncompressed state, simulate x-ray mammographic images and visualize the results of the simulations. The module that is\r\nused to generate breast models, Breast Modeling Module, consists of several sub-modules that are utilized to model the\r\ndifferent breast components: external shape, glandular and adipose tissue, breast lesion, skin, pectoralis and lymphatics.\r\nThe Compression Module is dedicated to simulate the mechanical compression of the breasts. Mammographic projection\r\nimages are obtained with simulation of x-ray photon transport starting from the x-ray source, passing through the breast\r\nmodel and reaching the detector. This is accomplished in the Image Generation Module. Finally, the results of the\r\nsimulations, i.e. breast models and mammographic images can be seen with the Visualization Module.\r\nResults: Here, we demonstrate the application of the software package in conventional and dual-energy mammography as\r\nwell as compression studies, as examples to highlight basic functions and applications of Breast Simulator. The first study\r\naimed to define the optimal pair of ââ?¬Ë?lowââ?¬â?¢ and ââ?¬Ë?highââ?¬â?¢ monochromatic x-ray energies for dual-energy mammography. It\r\ninvolved the synthesis of 225 dual-energy images obtained from combinations of ââ?¬Ë?lowââ?¬â?¢ and ââ?¬Ë?highââ?¬â?¢ energy images acquired\r\nin the energy range 14 to 28 keV. Images were generated from a medium sized dense breast model that contained one\r\ncalcification. The study showed that 17/28 keV incident monoenergetic beams are optimal to obtain maximal calcification\r\ndetectability for this breast. The second study demonstrated the effect of breast compression on the quality of the obtained\r\nmammograms. It included a breast model based on breast CT slices subjected to simulated compression and generation of\r\nmammographic images. Increased image quality is observed for mammograms obtained from breasts with reduced\r\nthickness. The characteristics of the x-ray beams that exit a small dense breast model were investigated in the third study.\r\nFor two mammographic spectra used in mammography imaging, the mean energy of the transmitted x-rays and the mean\r\nexit angle of the scattered radiation increase as the incident x-ray energy increases.\r\nConclusions: We believe that this tool and its functionalities will speed up the development, testing and optimization of\r\nnew breast imaging modalities such as breast tomosynthesis, cone-beam CT and advanced two-dimensional techniques\r\nlike dual-energy as well as specific parts of imaging chain, such as x-ray source, detector and acquisition geometry....
Metals and metalloids play a key role in plant and other biological systems as some of them are essential to living organisms\r\nand all can be toxic at high concentrations. It is therefore important to understand how they are accumulated, complexed\r\nand transported within plants. In situ imaging of metal distribution at physiological relevant concentrations in highly\r\nhydrated biological systems is technically challenging. In the case of roots, this is mainly due to the possibility of artifacts\r\narising during sample preparation such as cross sectioning. Synchrotron x-ray fluorescence microtomography has been\r\nused to obtain virtual cross sections of elemental distributions. However, traditionally this technique requires long data\r\nacquisition times. This has prohibited its application to highly hydrated biological samples which suffer both radiation\r\ndamage and dehydration during extended analysis. However, recent advances in fast detectors coupled with powerful data\r\nacquisition approaches and suitable sample preparation methods can circumvent this problem. We demonstrate the\r\nheightened potential of this technique by imaging the distribution of nickel and zinc in hydrated plant roots. Although 3D\r\ntomography was still impeded by radiation damage, we successfully collected 2D tomograms of hydrated plant roots\r\nexposed to environmentally relevant metal concentrations for short periods of time. To our knowledge, this is the first\r\npublished example of the possibilities offered by a new generation of fast fluorescence detectors to investigate metal and\r\nmetalloid distribution in radiation-sensitive, biological samples....
Recent advancements in magnetic resonance imaging (MRI) have enabled clinical imaging of human cortical bone,\r\nproviding a potentially powerful new means for assessing bone health with molecular-scale sensitivities unavailable to\r\nconventional X-ray-based diagnostics. To this end, 1H nuclear magnetic resonance (NMR) and high-resolution X-ray signals\r\nfrom human cortical bone samples were correlated with mechanical properties of bone. Results showed that 1H NMR\r\nsignals were better predictors of yield stress, peak stress, and pre-yield toughness than were the X-ray derived signals. These\r\n1H NMR signals can, in principle, be extracted from clinical MRI, thus offering the potential for improved clinical assessment\r\nof fracture risk....
Loading....