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- Carlsson, C.A., et al.
(författare)
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An instrument for measuring ambient dose equivalent, H*(10)
- 1996
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Ingår i: Radiation Protection Dosimetry. - 0144-8420 .- 1742-3406. ; 67:1, s. 33-39
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Tidskriftsartikel (refereegranskat)abstract
- The design and calibration of a small and simple instrument for measuring the ambient dose equivalent, H*(10), in photon fields is described. Comprising a thermoluminescence LiF dosemeter inside a 20 mm diameter PMMA sphere, it is capable of measuring the ambient dose equivalent with a nearly isotropic response. In the interval 0.1-100 mSv and for the energy range 30 keV to 1.25 MeV the energy response is within -31% and +15% relative to that of 137Cs gamma radiation (662 keV). In practical use, it is therefore sufficient to calibrate the instrument in a 137Cs gamma field using the corresponding conversion coefficient H*(10)/Kair taken from tabulations. The possibility of using the instrument to monitor the ambient dose equivalent for energies above 1.25 MeV is discussed and indicates that the range of applicability can be extended to 4.4 MeV with an energy response within -10% relative to 662 keV.
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| 2. |
- Nilsson, Håkan, et al.
(författare)
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Measurements of energy spectra from high dose rate 192Ir sources with a compton scattering spectrometer
- 1994
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Ingår i: Measurement assurance in dosimetry. - 9201001940 ; , s. 289-297
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A Compton scattering spectrometer has been used for spectral measurement of high dose rate (HDR) 192Ir sources. On the basis of the Compton formula a measured distribution of scattered photons is used for the calculation of the primary spectrum leaving the source. The two main reasons for measuring the photon energy distribution from such HDR sources are, firstly, to obtain accurate input for Monte Carlo calculations of the dose distribution and, secondly, to calibrate ionization chambers. The lack of spectral information causes calibration laboratories great difficulties in such work. A third possible reason concerns quality assurance with respect to source impurities, etc. The measured spectrum shows good agreement with the spectrum expected from theoretical considerations.
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| 7. |
- Hammersberg, P., et al.
(författare)
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A theoretical model for determination of the optimal irradiation conditions for computerised tomography
- 1995
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Ingår i: Insight. - 1354-2575 .- 1754-4904. ; 37:12, s. 978-985
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Tidskriftsartikel (refereegranskat)abstract
- Image quality in Computerised Tomography (CT) depends strongly on the quality of the CT-projection data. These depend on sample composition and geometry, contrasting details within the sample and the equipment used, i.e. X-ray spectra, filtration, detector response and geometry. This paper focuses on the problem of selecting the optimal physical parameters to maximise the signal-to-noise in CT projection data (SNRCT) between a contrasting detail and the surrounding sample for CT-scanners equipped with poly-energetic X-ray sources (conventional X-ray tubes) and energy-integrating detector systems (image intensifier and optical video chain). The work includes the derivation and verification ofa theoretical model for SNRCT which can be used for predicting the optimal physical parameters for specific imaging tasks. It is shown that simplified calculations valid for mono-energetic X-ray sources and/or photon counting detectors do not correctly predict the optimal settings. This study also includes measurements of the actual X-ray source and photon transport Monte Carlo simulations of the response of the detector system.
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| 10. |
- Sandborg, Michael, 1961-, et al.
(författare)
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Demonstration of correlations between clinical and physical image quality measures in chest and lumbar spine screen-film radiography
- 2001
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Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 0007-1285 .- 1748-880X. ; 74:882, s. 520-528
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Tidskriftsartikel (refereegranskat)abstract
- The ability to predict clinical image quality from physical measures is useful for optimization in diagnostic radiology. In this work, clinical and physical assessments of image quality are compared and correlations between the two are derived. Clinical assessment has been made by a group of expert radiologists who evaluated fulfilment of the European image criteria for chest and lumbar spine radiography using two scoring methods: image criteria score (ICS) and visual grading analysis score (VGAS). Physical image quality measures were calculated using a Monte Carlo simulation model of the complete imaging system. This model includes a voxelized male anatomy and was used to calculate contrast and signal-to-noise ratio of various important anatomical details and measures of dynamic range. Correlations between the physical image quality measures on the one hand and the ICS and VGAS on the other were sought. 16 chest and 4 lumbar spine imaging system configurations were compared in frontal projection. A statistically significant correlation with clinical image quality was found in chest posteroanterior radiography for the contrast of blood vessels in the retrocardiac area and a measure of useful dynamic range. In lumbar spine anteroposterior radiography, a similar significant correlation with clinical image quality was found between the contrast and signal-to-noise ratio of the trabecular structures in the L1-L5 vertebrae. The significant correlation shows that clinical image quality can, at least in some cases, be predicted from appropriate measures of physical image quality.
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