[en] Based on experimental analysis, the overall point spread function (PSF) of the digital subtraction angiography (DSA) system can be described using three different kinds of PSFs, as follows: (1) a long-range PSF caused by scattered x-ray, (2) a medium-range PSF caused by the veiling glare, and (3) a narrow-range PSF caused by the other elements. The authors have developed the optimum construction method to design a spatial filter for correction of DSA images which were degraded by the narrow-range PSF. In this method, the salient preprocessing feature is that the components caused by the scattered x-ray and the veiling glare are connected before correction is carried out for the narrowing-range PSF. They applied the filter to practical DSA images and confirmed that the spatial resolution was visually improved without introducing extra artifacts

[en] An image network system used in a picture archiving and communication system must minimize image transmission time between pieces of imaging equipment. The authors investigated the change in the transmission time due to the load on the network. They used the following parameters: packet size in the network (16 kB-4 MB), ACR/NEMA network interface transfer rate (100 kB/sec-8 MB-/sec). Their results show that if the network is unoccupied when transmission is initiated, small packets minimize the image transmission time, and if the network is in use, large packets minimize the transmission time. Therefore, their network system has a variable packet size so that they can choose the optimum packet size for adapting to the degree of network usage

[en] Tritium behavior in aquatic organisms through a model food chain was investigated. In this model food chain, tritium in water reaches bacteria or Japanese killifish via diatoms and brine shrimps. Tritium accumulation in these organisms as organic bound form was expressed as the R value which is defined as the ratio of tritium specific activity in lyophilized organisms (μCi/gH) to that in water (μCi/gH). The maximum R values were 0.5 in diatoms: Chaetoceros gracilis, 0.2 in bacteria: Escherichia coli, 0.5 in brine shrimps: Artemia salina, and 0.32 in Japanese killifish: Oryzias latipes under the growing condition in which tritium accumulation was due to tritium in tritiated water and not tritiated foods. Brine shrimps and Japanese killifish were grown from larve to adult in tritiated sea water and were fed on tritiated foods (model food chain). Their R values were 0.70 and 0.67, respectively. Bacteria, which grew in tritiated water by adding the hydrolysate of tritiated brine shrimps, showed a maximum R value at 0.32. The R values of each organ of Japanese killifish and of DNA and the nucleotides purified from brine shrimps growing in tritiated water with or without tritiated food were measured to estimate the tritium distribution in the body or various molecules of the organisms. These results did not indicate concentration of tritium in specific organs or compounds. The changes of specific activity of tritium in these organisms were measured when they were transferred to non-tritiated water. These retention of tritium was not only different among the tissues but also depended on whether or not the organisms were reared with tritiated foods. (author)

[en] Oncogenic transformation of mammalian cells in culture by ionizing radiation has become a useful tool in evaluating induction as a function of radiation quality, dose rate, and dose fractionation. Previous results indicate that whereby fission-spectrum neutrons delivered at low dose rates or in a five-fraction protocol stretched over four days increased the transformation frequency of exposed C₃H 10T1/2 cells compared to single-dose treatments administered at a high dose rate. The authors approach to the question of dose fractionation effects with neutrons is to expose cells to fractionated doses of monoenergetic neutrons that range in energy from 0.22 to 14 MeV. By this protocol, they are able to determine the carcinogenic potential of exposures as a function of neutron energy

[en] Relative biological effectiveness of neutrons has been estimated from epidemiologic data of survivors at Hiroshima and Nagasaki who underwent the momentary exposure to atomic bomb. The radiation risk for the occupational exposure to neutrons at low dose rates or by fractionated doses, e.g., reactor workers, should be determined by biological experiments. (author). 7 refs., 1 fig., 1 tab

No abstract available

[en] Some recent experiments have suggested that, at low doses, fractionation or dose protractionation for neutrons actually increase the transformation rate. It is difficult to draw quantitative conclusions from these data in large part because the fractionated and the unfractionated exposures were not performed concurrently, but several months apart, leaving open the possibility of a change in radiation sensitivity of the cells. A further difficulty in analyzing these early studies is the small number of foci per dose that were observed. In the work reported here, the authors try to eliminate some of the problems discussed above by the following means: firstly, they irradiate sufficient cells to ensure an adequate number of transformed cells-for dose less than 0.5 Gy our target was 20 foci per dose for acute irradiations and 30 foci per dose for fractionated studies. Secondly, in all cases the single and fractionated doses were delivered on the same day with cells from the same culture, so that direct comparisons could be made. They have concluded that at low doses it is reasonably probable that there is an enhancement due to fractionation. Based on this conclusion, they examine whether an enhancement at low doses is understandable based on the data for single acute exposures

[en] The murine severe combined immunodeficient mutation (scid) is characterized by a lack of both B and T cells, due to a deficit in lymphoid variable-(diversity)-joining (V(D)J) rearrangement. Scid cells are highly sensitive to both radiation-induced killing and chromosomal aberrations. Significantly reduced D₀ and n values were demonstrated in scid cells and were similar to ataxia-telangiectasia (AT) cells (a unique human disease conferring whole body radiosensitivity). However, the kinetics of DNA synthesis after irradiation were different between the two cell types. In contrast with the radioresistant DNA synthesis of AT cells, DNA synthesis of scid cells was markedly inhibited after irradiation. The existence of different mutations was also supported by evidence of complementation in somatic cell hybrids between scid cells and AT cells. Results indicate that the radiobiological character of scid is similar to AT but is presumably caused by different mechanisms. (author)

[en] Tritium incorporated into tissues and DNA of mice was studied after daily ingestion of tritiated food or tritiated water. The tritiated food used was a commercial preparation mixed with brine shrimp that had been reared in tritiated sea water. After ingestion of tritiated food or water for up to 22 d, the specific activity of 3H in tissues was measured as tissue-free-water 3H, tissue-bound 3H, and DNA-bound 3H. Carbon-14 glucose was added to food and drinking water to compare the 3H intake from food with that from water. The specific activity of 3H in tissues was then corrected by the specific activity of 14C in tissues to determine the 3H incorporation from the same amount of ingested food and water. DNA-bound 3H after the ingestion of tritiated food was 4.6 times higher than that of tritiated water, while tissue-bound 3H was 2.2 times higher. The radiation dose to liver from 3H incorporated through food was twofold higher than from tritiated water, which was mainly from the high incorporation of 3H into DNA. Our results demonstrated that the dose calculation based on tissue-free-water 3H alone would under-estimate the radiation exposure of the human population exposed to tritiated food

[en] Pepleomycin is a derivative of bleomycin, which is less toxic to the host but possesses greater antitumor activity. Experiments are described herein which Chinese hamster V-79 cells in culture and a murine squamous cell carcinoma in vivo have been used to obtain survival curves for pepleomycin alone or in combination with radiation. In both systems the survival curves for pepleomycin alone are diphasic, and this drug proved to be twice as effective as bleomycin. Further, in contrast to bleomycin, which showed simple additivity with radiation, pepleomycin potentiated radiation injury to the tumor cells both in vivo and in vitro. Therefore, pepleomycin may be superior to bleomycin not only in drug therapy but also in combined modality therapy