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At least 721 records · Page 40Linked to original sources
PubMed1998

A cytokinesis-blocked micronucleus study of the radioadaptive response of lymphocytes of individuals occupationally exposed to chronic doses of radiation.

Human lymphocytes pre-exposed to very low doses of ionizing radiation show an adaptive response, which make these cells less sensitive to subsequent higher exposures. To verify the hypothesis that a similar phenomenon can be induced by occupationally (in vivo) received doses of ionizing radiation, the cytogenetic responses of 24 medical radiation workers to 1 and 2 Gy gamma-irradiation in comparison with 13 non-exposed individuals have been studied. Cytokinesis-blocked micronucleus assay of lymphocytes revealed that although the frequencies of spontaneous micronuclei in radiation workers are more than non-exposed individuals, after 1 and 2 Gy in vitro irradiation of lymphocytes this frequency was found to be lower for radiation workers. The results suggest the existence of an in vivo adaptive response in individuals chronically exposed to low dose radiation. The observation of radioresistance to higher doses of radiation in pre-exposed lymphocytes might be due to initial DNA damage and an induced DNA repair mechanism.

Adult↗
PubMed2005

Clinical evaluation of a new set of image quality criteria for mammography.

The European Commission (EC) quality criteria for screen-film mammography are used as a tool to assess image quality. A new set of criteria was developed and initially tested in a previous study. In the present study, these criteria are further evaluated using screen-film mammograms that have been digitised, manipulated to simulate different image quality levels and reprinted on film. Expert radiologists have evaluated these manipulated images using both the original (EC) and the new criteria. A comparison of three different simulated dose levels reveals that the new criteria yield a larger separation of image criteria scores than the old ones. These results indicate that the new set of image quality criteria has a higher discriminative power than the old set and thus seems to be more suitable for evaluation of image quality in mammography.

Europe↗
PubMed2006

Image quality measurements in radiology.

Image quality measurement methods are reviewed and difficulties in various approaches are highlighted. The main emphasis of the paper is on objective image quality measurements, however, subjective assessment methods are also discussed briefly.

Humans↗
PubMed2006

Segmentation of the posterior ribs in chest radiographs using iterated contextual pixel classification.

The task of segmenting the posterior ribs within the lung fields of standard posteroanterior chest radiographs is considered. To this end, an iterative, pixel-based, supervised, statistical classification method is used, which is called iterated contextual pixel classification (ICPC). Starting from an initial rib segmentation obtained from pixel classification, ICPC updates it by reclassifying every pixel, based on the original features and, additionally, class label information of pixels in the neighborhood of the pixel to be reclassified. The method is evaluated on 30 radiographs taken from the JSRT (Japanese Society of Radiological Technology) database. All posterior ribs within the lung fields in these images have been traced manually by two observers. The first observer's segmentations are set as the gold standard; ICPC is trained using these segmentations. In a sixfold cross-validation experiment, ICPC achieves a classification accuracy of 0.86 +/- 0.06, as compared to 0.94 +/- 0.02 for the second human observer.

Algorithms↗
PubMed2002

High frequency x-ray generator basics.

The purpose of this paper is to present basic functional principles of high frequency x-ray generators. The emphasis is put on physical concepts that determine the engineering solutions to the problem of efficient generation and control of high voltage power required to drive the x-ray tube. The physics of magnetically coupled circuits is discussed first, as a background for the discussion of engineering issues related to high-frequency power transformer design. Attention is paid to physical processes that influence such factors as size, efficiency, and reliability of a high voltage power transformer. The basic electrical circuit of a high frequency generator is analyzed next, with focus on functional principles. This section investigates the role and function of basic components, such as power supply, inverter, and voltage doubler. Essential electronic circuits of generator control are then examined, including regulation of voltage, current and timing of electrical power delivery to the x-ray tube. Finally, issues related to efficient feedback control, including basic design of the AEC circuitry are reviewed.

Electricity↗
PubMed1995

Radiology, physical science, and the emergence of medical physics.

The early development of medical physics as a separate discipline and profession is briefly reviewed. Although both x rays and radioactivity were discovered by physicists, at first the physical investigations of these phenomena, and their medical applications, proceeded along parallel but independent lines. Radiological journals were founded in Britain, Germany, and the U.S. as early as 1896-1897 but it was not until ten years later that papers on radiation physics began to appear regularly. In 1913 the first full-time physicists were appointed to posts in medical schools and hospitals: William Duane in the U.S. and Sydney Russ in Britain. Thereafter the number of physicists engaged in medical applications increased slowly but steadily, and in the 1920s they began to apply the new science of radiation dosimetry to both x ray and radium therapy. The "Hospital Physicists' Association" was founded in Britain in 1943 with 53 members and the "American Association of Physicists in Medicine" followed in 1958 with 127 charter members.

Biophysics↗