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Simulation of mammographic x-ray spectra
Abstract
Attempts to simulate Mo-anode spectra for film mammography by using Mo filters with W-anode tubes have been reported by several workers, and others have generated W-like continua for xeromammographic purposes by heavy Al filtration of Mo-anode tubes. In the present work the success of these simulations was tested by Si(Li) spectrometric methods that measured the spectral shapes and the exposure levels. Comparisons of Mo-anode/Al-filter with W-anode/Al-filter combinations were made, and also of W-anode/M-filter with Mo-anode/Mo-folter combinations. In certain circumstance the spectral shape is moderately well simulated but in all cases the useful output is less in the simulations than in the original spectra. The general conclusion is that simulation is always less attractive than direct use of the desired anode.
Bacterial symbionts of insects have been shown to play important roles in host fitness. However, little is known about the bacterial community of Tessaratoma papillosa which is one of the most destructive pests of the well-known fruits Litchi chinensis Sonn and Dimocarpus longan Lour in Oriental Region, especially in South-east Asia and adjacent areas. In this study, we surveyed the bacterial community diversity and dynamics of T. papillosa in all developmental stages with both culture-dependent and culture-independent methods by the third-generation sequencing technology. Five bacterial phyla were identified in seven developmental stages of T. papillosa. Proteobacteria was the dominant phylum and Pantoea was the dominant genus of T. papillosa. The results of alpha and beta diversity analyses showed that egg stage had the most complex bacterial community. Some of different developmental stages showed similarities, which were clustered into three phases: (1) egg stage, (2) early nymph stages (instars 1–3), and (3) late nymph stages (instars 4–5) and adult stage. Functional prediction indicated that the bacterial community played different roles in these three phases. Furthermore, 109 different bacterial strains were isolated and identified from various developmental stages. This study revealed the relationship between the symbiotic bacteria and the development of T. papillosa, and may thus contribute to the biological control techniques of T. papillosa in the future.
The trend in screen-film mammography is toward high-contrast, high-resolution images. In this article technical factors associated with X-ray equipment and/or the screen-film combination which affects radiographic contrast, blurring (unsharpness), and noise will be reviewed. Radiation dose will be discussed in terms of measurement, calculation, and theoretical risk.
Today there are many dedicated mammographic x-ray units available that are capable of providing high-quality screen-film mammograms. Likewise, screen-film combinations designed for mammography are capable of providing images with appropriate contrast, resolution, and noise levels. Proper film processing is most important in order to obtain the appropriate film speed and contrast. A higher-speed screen-film combination designed for mammography can provide mammograms with significantly lower radiation dose, especially for grid and magnification techniques. Designing x-ray units and techniques as well as screen-film combinations with the singular goal of reducing radiation dose will always involve compromises and trade-offs. The key is to always consider optimizing all of the factors that affect image quality: (1) appropriate beam quality, (2) breast compression, (3) consideration of the use of grids, (4) good geometry, (5) selection of an appropriate screen-film combination, and (6) proper film processing. Optimization of all appropriate imaging factors will produce high-quality mammograms at the lowest radiation dose to the patient.
The increasing use of small animals in basic research has spurred interest in new imaging methodologies. Digital subtraction angiography (DSA) offers a particularly appealing approach to functional imaging in the small animal. This study examines the optimal x-ray, molybdenum (Mo) or tungsten (W) target sources, and technique to produce the highest quality small animal functional subtraction angiograms in terms of contrast and signal-difference-to-noise ratio squared (SdNR2). Two limiting conditions were considered-normalization with respect to dose and normalization against tube loading. Image contrast and SdNR2 were simulated using an established x-ray model. DSA images of live rats were taken at two representative tube potentials for the W and Mo sources. Results show that for small animal DSA, the Mo source provides better contrast. However, with digital detectors, SdNR2 is the more relevant figure of merit. The W source operated at kVps >60 achieved a higher SdNR2. The highest SdNR2 was obtained at voltages above 90 kVp. However, operation at the higher potential results in significantly greater dose and tube load and reduced contrast quantization. A reasonable tradeoff can be achieved at tube potentials at the beginning of the performance plateau, around 70 kVp, where the relative gain in SdNR2 is the greatest.
The efficiency of a semi-conductor detector is measured by compairing its response with that of an NaI(Tl) detector of known efficiency when both are exposed to the same flux of gamma-excited fluorescent X-rays. The experimental procedure is outlined and corrections and limitations are discussed. The technique is an inexpensive and convenient way of determining semi-conductor efficiency up to about 100 keV using a single radionuclide source of modest activity and readily-available fluorescers.