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91.
Hemdal B Herrnsdorf L Andersson I Bengtsson G Heddson B Olsson M 《Radiation protection dosimetry》2005,114(1-3):436-443
The Sectra MicroDose Mammography system is based on direct photon counting (with a solid-state detector), and a substantially lower dose to the breast than when using conventional systems can be expected. In this work absorbed dose measurements have been performed for the first unit used in routine mammography screening (at the Hospital of Helsingborg, Sweden). Two European protocols on dosimetry in mammography have been followed. Measurement of half value layer (HVL) cannot be performed as prescribed, but this study has demonstrated that non-invasive measurements of HVL can be performed accurately with a sensitive and well collimated solid-state detector with simultaneous correction for the energy dependence. The average glandular dose for a 50 mm standard breast with 50% glandularity, simulated by 45 mm polymethylmethacrylate, was found to be 0.21 and 0.28 mGy in March and December 2004, respectively. These values are much lower than for any other mammography system on the market today. It has to be stressed that the measurements were made using the current clinical settings and that no systematic optimisation of the relationship between absorbed dose and diagnostic image quality has been performed within the present study. In order to further increase the accuracy of absorbed dose measurements for this unit, the existing dose protocols should be revised to account also for the tungsten/aluminium anode/filter combination, the multi-slit pre-collimator device and the occurrence of a dose profile in the scanning direction. 相似文献
92.
A M?sb?ck J Westerdahl C Ingvar H Olsson N Jonsson 《Canadian Metallurgical Quarterly》1997,79(2):275-283
An in vitro model was established to investigate factors underlying the sensory hyperinnervation of neonatal rat skin wounds that has been observed in vivo (Reynolds and Fitzgerald, J. Comp. Neurol. 358 (1995) 487-489). Explants of normal and wounded rat dorsal foot skin were co-cultured with explants of embryonic chick or newborn rat dorsal root ganglia for 24 h and the number of sensory neurites counted. Explants of skin surrounding a wound made at birth were taken 3 (P3) or 10 (P10) days later and compared with normal skin of the same age. In addition, explants were taken from adult skin wounded 3 and 10 days earlier. At P3, normal skin induced weak neurite outgrowth (mean 13.1 +/- 2.1 neurites per ganglion explant) but skin that had been wounded 3 days earlier, at birth, induced three times more neurite outgrowth (37.8 +/- 3.3). Ten days after wounding at birth, neurite outgrowth was still substantial (40.9 +/- 3.3) although at that age (P10), even normal skin stimulates substantial growth (37.4 +/- 2.9). Normal adult skin also stimulated neurite outgrowth (28.7 +/- 0.45) but this was not increased by wounding 3 or 10 days earlier, and this was enhanced 3 days but not 10 days after wounding. Anti-NGF (nerve growth factor) added to the culture medium blocked the constitutive neurite stimulating activity from normal P10 and adult skin but was ineffective in blocking the neurite stimulating activity produced by neonatal wounding. It is concluded that skin wounding at birth results in release of one or more sensory neurotrophic factors that stimulate rat and chick dorsal root ganglia neurite outgrowth for at least 10 days, but which do not include NGF. 相似文献
93.
Retrofitting older alumina reduction cell lines may be an alternative to a complete line shutdown and replacement with new, modern cells. This may, in turn, extend the time that aging cell lines remain cost effective and profitable, and may also help meet today’s more stringent environmental protection regulations. In this article, practical examples of improvements achieved by cell retrofitting are discussed. 相似文献
94.
The plastic deformation behavior of cast irons, covering the majority of graphite morphologies, has not been comprehensively
studied previously. In this investigation, the effect of graphite morphology and graphite fraction on the plastic deformation
behavior of pearlitic cast irons has been evaluated. The investigation is based on tensile tests performed on various different
cast iron grades, where the graphite morphology and volume fraction have been varied. Pearlitic steel with alloying levels
corresponding to the cast irons were also studied to evaluate how the cast iron matrix behaves in tension without the effects
of the graphite phase. It is concluded that as the roundness of the graphite phase increases, the strain hardening exponent
decreases. This demonstrates that the amount of plastic deformation is higher in the matrix of lamellar cast iron grades compared
to compacted and nodular cast iron grades. Furthermore, this study shows that the strength coefficient in flake graphite cast
irons increases as the graphite fraction decreases due to the weakening effect of the graphite phase. This study presents
relationships between the strain hardening exponent and the strength coefficient and the roundness and fraction of the graphite
phase. Using these correlations to model the plastic part of the stress-strain curves of pearlitic cast irons, we were able
to calculate curves in good agreement with experimentally determined curves, especially for gray cast irons and ductile iron. 相似文献
95.
96.