| 1. |
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| 2. |
- 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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| 3. |
- Dance, David, et al.
(författare)
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Optimisation of the design of antiscatter grids by computer modelling
- 1995
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Ingår i: Radiation Protection Dosimetry. - 0144-8420 .- 1742-3406. ; 57:1, s. 207-210
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Tidskriftsartikel (refereegranskat)abstract
- A Monte Carlo computer program has been developed to model diagnostic radiological examinations, and has been used to study and optimise the design of antiscatter grids. This is important because the use of an inappropriate or poorly designed grid can lead to increased patient dose. Optimal grid parameters may be different for large and small scattering volumes. The program treats the patient as a rectangular block of tissue and takes account of the grid and image receptor. Image quality is measured in terms of contrast and signal-to-noise ratio and patient risk in terms of mean absorbed dose. Test objects of appropriate size and composition are used in the calculation of these image quality parameters. A new performance comparison and optimisation procedure has been developed, and the program has been used to study grid design in screen-film and digital radiology for small, medium and large scattering volumes.
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| 4. |
- Floderus, B
(författare)
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Combined occupational and residential exposures
- 1999
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Ingår i: RADIATION PROTECTION DOSIMETRY. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 83:1-2, s. 93-97
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 5. |
- Helmrot, Ebba, et al.
(författare)
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Scientific instrument for a controlled choice of optimal photon energy in intra-oral radiography
- 1998
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Ingår i: Radiation Protection Dosimetry. - 0144-8420 .- 1742-3406. ; 80:1, s. 321-325
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Tidskriftsartikel (refereegranskat)abstract
- Basic performance parameters are defined and analysed in order to optimise physical image quality in relation to the energy imparted to the patient in dental radiology. Air cavities were embedded in well-defined multimaterial, hard tissue phantoms to represent various objects in dento-maxillo-facial examinations. Basic performance parameters were: object contrast (C), energy imparted (_) to the patient, signal-to-noise ration (SNR), C2/_ (film) and (SNR)2/_ (digital imaging system) as functions of HVL (half-value layer), used to describe the photon energy spectrum. For the film receptor, the performance index C2/_ is maximum (optimal) at HVL values of 1.5-1.7 mm Al in the simulated Incisive, Premolar and Molar examinations. Other imaging tasks (examinations), not simulated here, may require other optimal HVL. For the digital imaging system (Digora) the performance index (SNR)2/_, theoretically calculated, indicates that a lower value of HVL is optimal than with film as receptor. However, due to the limited number of bits (8 bits) in the analogue to digital converter (ADC) contrast resolution is degraded and calls for use of higher photon energies (HVL). Customised optimisations with proper concern for patient category, type of examination, diagnostic task is the ultimate goal of this work. The conclusions stated above give some general advice on the appropriate choice of photon energy spectrum (HVL). In particular situations, it may be necessary to use more dose demanding kV settings (lower HVL) in order to get sufficient image quality for the diagnostic task.
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| 6. |
- Mårdberg, Bertil
(författare)
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Forming homogeneous clusters for differential risk information
- 1996
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Ingår i: Radiation Protection Dosimetry. - 0144-8420 .- 1742-3406. ; 68:3-4, s. 227-230
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Tidskriftsartikel (refereegranskat)abstract
- Latent risk situations are always present in society. General information an these risk situations is supposed to be received differently by different groups of people in the population. In the aftermath of specific accidents different groups presumably have need of specific information about how to act to survive, to avoid injuries, to fmd more information, to obtain facts about the accidents etc. As targets for information these different groups could be defined in different ways. The conventional way is to divide the population according to demographic variables, such as age, sex, occupation etc. Another way would be to structure the population according to dependent Variables measured in different studies. They may concern risk perception, emotional reactions, specific technical knowledge of the accidents, and belief in the information sources. One procedure for forming such groupings of people into homogeneous clusters would be by statistical clustering methods on dependent variables. Examples of such clustering procedures are presented and discussed. Data are from a Norwegian study on the perception of radiation from nuclear accidents and other radiation sources. Speculations are made on different risk information strategies. Elements of a research programme are proposed.
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| 7. |
- Sandborg, Michael, 1961-, et al.
(författare)
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Results from an optimisation of grid design in diagnostic radiology
- 1995
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Ingår i: Radiation Protection Dosimetry. - 0144-8420 .- 1742-3406. ; 57:1, s. 211-215
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Tidskriftsartikel (refereegranskat)abstract
- Results of an optimisation of grid design using a Monte Carlo model of the imaging chain are presented. Patient dose is significantly reduced by changing from aluminium to fibre grid covers and interspaces while keeping contrast constant. Numerous commercial grids have been investigated to identify superior designs. For optimal use, grids with high strip density require thinner lead strips and higher ratios than grids with low strip density. In paediatric radiology, grids with very thin strips (10-20 µm), or an air gap can be considered. In an adult lumbar spine examination, the optimal grid ratios are higher (greater than 15) than in commercial grids. This is particularly accentuated for grids with high strip density, fibre interspaces and in the lateral view. For a given imaging task, it is possible to identify grids of different design that have good performance, provided an appropriate strip width and tube potential are selected.
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| 8. |
- Johansson, L, et al.
(författare)
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Distribution of radioactive caesium in the population of northern Sweden. A follow-up study
- 1999
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Ingår i: Radiation protection dosimetry. - 0144-8420. ; 86:1, s. 59-62
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- After the Chernobyl accident in 1986, the uptake of radioactive caesium has been studied in several population groups in northern Sweden. During the period 1988-1993 the 137Cs content in the population of northern Sweden was followed by measurements of 137Cs concentration in tissue samples from medico-legal autopsies. From these studies an "ecological" half-time for 137Cs in the population was estimated. A follow-up made on samples taken 1995-1996 is presented here. The results from this prolongation of the period indicates a significantly longer half-time. This new half-time gives a better representation of the retention of 137Cs in the population of northern Sweden at times longer from the deposition.
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