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| 2. |
- Gunnarsson, Mikael, et al.
(författare)
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No radiation protection reasons for restrictions on C-14 urea breath tests in children.
- 2002
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Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 1748-880X .- 0007-1285. ; 75:900, s. 982-986
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Tidskriftsartikel (refereegranskat)abstract
- Traditional 14C urea breath tests are normally not used for younger children because the radiation exposure is unknown. High sensitivity accelerator mass spectrometry and an ultra-low amount (440 Bq) of 14C urea were therefore used both to diagnose Helicobacter pylori (HP) infection in seven children, aged 3–6 years, and to make radiation dose estimates. The activity used was 125 times lower than the amount normally used for older children and 250 times lower than that used for adults. Results were compared with previously reported biokinetic and dosimetric data for adults and older children aged 7–14 years. 14C activity concentrations in urine and exhaled air per unit administered activity for younger children (3–6 years) correspond well with those for older children (7–14 years). For a child aged 3–6 years who is HP negative, the urinary bladder wall receives the highest absorbed dose, 0.3 mGy MBq-1. The effective dose is 0.1 mSv MBq-1 for the 3-year-old child and 0.07 mSv MBq-1 for the 6-year-old child. For two children, the 10 min and 20 min post-14C administration samples of exhaled air showed a significantly higher amount of 14C activity than for the rest of the children, that is 6% and 19% of administered activity exhaled per hour compared with 0.3–0.9% (mean 0.5%) of administered activity exhaled per hour indicating that these two children that is were HP positive. For a 3-year-old HP positive child, absorbed dose to the urinary bladder wall was 0.3 mGy MBq-1 and effective dose per unit of administered activity was 0.4 mSv MBq-1. Using 55 kBq, which is a normal amount for older children when liquid scintillation counters are used for measurement, the effective dose will be approximately 6 µSv to a 3-year-old HP negative child and 20 µSv to a HP positive child. Thus there is no reason for restrictions on performing a normal 14C urea breath test, even on young children.
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| 3. |
- Haraldsson, P, et al.
(författare)
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Dose response characteristics and basic dose distribution data for a polymerization-based dosemeter gel evaluated using MR
- 2000
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Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 0007-1285 .- 1748-880X. ; 73:865, s. 58-65
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Tidskriftsartikel (refereegranskat)abstract
- A safe and reproducible mixing procedure for the manufacture of a polymerization-based dosemeter gel evaluated using MRI (PoMRI) is presented. The dose response, obtained by irradiating gel-filled vials with absorbed doses in the interval 0-20 Gy and evaluated with respect to 1/T2, was found to be linear in the interval 0-8 Gy, with a sensitivity of 0.211 s-1Gy-1 (r2 = 0.998) at 1.5 T. Evaluation of the same set of vials with respect to 1/T1 gave a sensitivity of 0.018 s-1Gy-1 (r2 = 0.960). PoMRI and diode data were compared for standard photon and electron treatment beams. A deviation of less than 3% was found between the two methods for central depth dose curves as well as dose profiles (2 mm for electrons in the steep dose gradient regions). The importance of the method used for background correction for the reliability of the results was also evaluated. Barex (with a wall thickness of 1.5 mm) was investigated for use as phantom material and found to be favourable compared with glass. The results obtained in this study show that PoMRI has excellent potential as a 3D detector.
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| 4. |
- Lanhede, B, et al.
(författare)
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The influence of different technique factors on image quality of chest radiographs as evaluated by modified CEC image quality criteria.
- 2002
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Ingår i: The British journal of radiology. - : British Institute of Radiology. - 0007-1285 .- 1748-880X. ; 75:889, s. 38-49
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Tidskriftsartikel (refereegranskat)abstract
- The Commission of the European Communities (CEC) research project "Predictivity and optimisation in medical radiation protection" addressed fundamental operational limitations in existing radiation protection mechanisms. The first part of the project aimed at investigating (1) whether the CEC image quality criteria could be used for optimization of a radiographic process and (2) whether significant differences in image quality based on these criteria could be detected in a controlled project with well known physical and technical parameters. In the present study, chest radiographs on film were produced using healthy volunteers. Four physical/technical parameters were varied in a carefully controlled manner: tube voltage (102 kVp and 141 kVp), nominal speed class (160 and 320), maximum film density (1.3 and 1.8) and method of scatter reduction (grid (R=12) and air gap). The air kerma at the entrance surface was measured for all patients and the risk-related dose H(Golem), based on calculated organ-equivalent dose conversion coefficients and the measured entrance air kerma values, was calculated. Image quality was evaluated by a group of European expert radiologists using a modified version of the CEC quality criteria. For the two density levels, density level 1.8 was significantly better than 1.3 but at the cost of a higher patient radiation exposure. The correlation between the number of fulfilled quality criteria and H(Golem) was generally poor. An air gap technique resulted in lower doses than scatter reduction with a grid but provided comparable image quality. The criteria can be used to highlight optimum radiographic technique in terms of image quality and patient dose, although not unambiguously. A recommendation for good radiographic technique based on a compromise between image quality and risk-related radiation dose to the patient is to use 141 kVp, an air gap, a screen-film system with speed 320 and an optical density of 1.8.
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| 5. |
- McVey, Graham, et al.
(författare)
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A study and optimization of lumbar spine X-ray imaging systems
- 2003
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Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 0007-1285 .- 1748-880X. ; 76:903, s. 177-188
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Tidskriftsartikel (refereegranskat)abstract
- A Monte Carlo program has been developed that incorporates a voxel phantom of an adult patient in a model of the complete X-ray imaging system, including the anti-scatter grid and screen-film receptor. This allows the realistic estimation of patient dose and the corresponding image (optical density map) for a wide range of equipment configurations. This paper focuses on the application of the program to lumbar spine anteroposterior and lateral screen-film examinations. The program has been applied to study the variation of physical image quality measures and effective dose for changing system parameters such as tube voltage, grid design and screen-film system speed. These variations form the basis for optimization of these system parameters. In our approach to optimization, the best systems are those that can match (or come close to) the calculated image quality measure of systems preferred in a recent European clinical trial, but with lower patient dose. The largest dose savings found were 21% for a 400 speed class system with a grid having a strip density of 40 cm-1 and a grid ratio of 16. A further dose saving of 13% was possible when a 600 speed class system was employed. The best systems found from the optimization correspond to those recommended by the European Commission guidelines on image quality criteria for diagnostic radiographic images.
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| 6. |
- 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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| 7. |
- Tingberg, Anders, et al.
(författare)
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Influence of the characteristic curve on the clinical image quality of lumbar spine and chest radiographs.
- 2004
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Ingår i: The British journal of radiology. - : British Institute of Radiology. - 0007-1285 .- 1748-880X. ; 77:915, s. 204-15
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Tidskriftsartikel (refereegranskat)abstract
- The "European Guidelines on Quality Criteria for Diagnostic Radiographic Images" do not address the choice of the film characteristic (H&D) curve, which is an important parameter for the description of a radiographic screen-film system. The image contrast of clinical lumbar spine and chest radiographs was altered by digital image processing techniques, simulating images with different H&D curves, both steeper and flatter than the original. The manipulated images were printed on film for evaluation. Seven experienced radiologists evaluated the clinical image quality by analysing the fulfilment of the European Image Criteria (ICS) and by visual grading analysis (VGA) of in total 224 lumbar spine and 360 chest images. A parallel study of the effect of the H&D curve has also been made using a theoretical model. The contrast (DeltaOD) of relevant anatomical details was calculated, using a Monte Carlo simulation-model of the complete imaging system including a 3D voxel phantom of a patient. Correlations between the calculated contrast and the radiologists' assessment by VGA were sought. The results of the radiologists' assessment show that the quality in selected regions of lumbar spine and chest images can be significantly improved by the use of films with a steeper H&D curve compared with the standard latitude film. Significant (p<0.05) correlations were found between the VGA results and the calculations of the contrast of transverse processes and trabecular details in the lumbar spine vertebrae, and with the contrast of blood vessels in the retrocardiac area of the chest.
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| 8. |
- Dance, David, et al.
(författare)
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Influence of anode/filter material and tube potential on contrast, signal-to-noise ratio and average absorbed dose in mammography: a Monte Carlo study
- 2000
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Ingår i: British Journal of Radiology. - 0007-1285. ; 73, s. 1056-1067
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Tidskriftsartikel (refereegranskat)abstract
- The comparative performance of mammographic X-ray systems that use different anode/filter combinations has been assessed for screen±®lm and digital imaging. Monte Carlo techniques have been used to calculate average glandular dose as well as contrast and signal-tonoise ratio for imaging two test details. Five anode/filter combinations have been studied to establish the potential for dose saving or image quality improvement. For screen±film mammography, it was found that little bene®t is gained by changing from a standard 28 kV molybdenum/molybdenum spectrum for breasts up to 6 cm thick. For thicker breasts, where the tube potential for the standard technique might be increased, 20% improvement in contrast can be achieved without dose penalty using molybdenum/rhodium or rhodium/rhodium spectra, whereas dose savings of more than 50% can be attained whilst maintaining contrast using tungsten/rhodium or rhodium/aluminium spectra. In digital mammography, a molybdenum/ molybdenum spectrum delivers the lowest dose for a 2 cm breast, but gives the highest dose for thicker breasts. Tungsten/rhodium or rhodium/aluminium spectra provide the lowest doses at greater thicknesses. It is concluded that for screen±film mammography, molybdenum/ molybdenum is the spectrum of choice for all but the thickest or most glandular breasts. In digital mammography, an alternative spectrum is preferable for breasts thicker than 2 cm.
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