| 1. |
- Almén, A, et al.
(författare)
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The radiation dose to children from X-ray examinations of the pelvis and the urinary tract
- 1995
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Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 0007-1285 .- 1748-880X. ; 68:810, s. 13-604
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Tidskriftsartikel (refereegranskat)abstract
- X-ray examinations of the pelvis and the urinary tract are frequent examinations of children, in which a large part of the trunk is irradiated. The irradiated volume contains many of the most radiation sensitive organs and tissues. The absorbed dose to children during the examination was estimated from measurements with a dose-area product meter and thermoluminescent dosemeters (TLDs). Entrance surface dose and the dose-area product results are presented. Conversion factors between the entrance surface dose and the organ dose were derived. The energy imparted, organ dose and effective dose were determined. The entrance surface dose for one single exposure varied between 0.32 mGy and 8.6 mGy for the urinary tract examination and between 0.26 mGy and 2.89 mGy per exposure for the pelvis examination. These variations are mainly influenced by the body size of the patient. The number of images taken during one examination varied. For the urinary tract investigation, the average number of exposures was six, while the corresponding number for the pelvis examination was two. The average effective dose for a typical urinary tract investigation ranged from 0.9 mSv to 8.5 mSv and from 0.3 mSv to 1.4 mSv for the pelvis examination. The radiation dose depends greatly on the body size. The recommendations to present the results in relation to age have been followed; however, the variation of body size even within each specified age range is significant. It is suggested that doses should be quoted in relation to a more critical parameter than age.
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| 2. |
- Sundgren, P, et al.
(författare)
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Elevation of the larynx on normal and abnormal cineradiogram
- 1993
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Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 0007-1285 .- 1748-880X. ; 66:789, s. 72-768
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Tidskriftsartikel (refereegranskat)abstract
- The relationship between bolus volume (2.5, 5, 10 and 20 ml) and larynx elevation during swallowing was assessed in 10 non-dysphagic and 10 dysphagic individuals without pharyngeal dysfunction. Laryngeal elevation in different types of pharyngeal dysfunction was assessed in 60 non-dysphagic and 75 dysphagic patients. All subjects were examined with liquid barium and cineradiography at 50 frames/s. The laryngeal elevation was measured at the moment when the bolus reached the level of the valleculae and at maximum elevation. Elevation of the larynx, both the initial and maximal, was not influenced by sex, age or presence of dysphagia. Elevation of the larynx at the moment when the bolus reached the valleculae, when expressed in per cent of maximum elevation, was lower with 10 and 20 ml bolus volumes compared with 2.5 ml bolus volume (p < 0.05) in the 10 dysphagic individuals. Pharyngeal dysfunction was associated with significantly lower initial elevation of the larynx, at the moment when the bolus reached the level of the valleculae, although the maximal laryngeal elevation was normal. Initial elevation was 30% lower (p = 0.03) in patients with aspiration of bolus material into the trachea, 22% lower (p = 0.007) in those with defective closure of the laryngeal vestibule without aspiration and 16% lower (p = 0.06) in those with incoordination of the cricopharyngeal muscle compared with patients without dysfunction.
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| 3. |
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| 4. |
- Sandborg, Michael, 1961-, et al.
(författare)
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Monte Carlo study of grid performance in diagnostic radiology: factors which affect the selection of tube potential and grid ratio
- 1993
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Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 0007-1285 .- 1748-880X. ; 66, s. 1164-1176
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Tidskriftsartikel (refereegranskat)abstract
- A Monte Carlo computational model has been developed for the study of the performance of anti-scatter grids in diagnostic radiology. It is used here to estimate the scatter in the image plane from soft tissue phantoms (representing the patient) and to calculate image contrast and the mean absorbed dose in the phantom. Different scattering conditions, representative of various examinations, have been investigated: adult lumbar spine; small field radiography and fluoroscopy; adult chest and paediatric pelvis and chest. For each scattering condition, the combinations of tube potential and grid ratio have been found which, for a well designed grid, result in the lowest mean absorbed dose in the phantom for a fixed contrast level. In examinations which generate large amounts of scatter, the use of high grid ratios in combination with high tube potentials is favourable with regard to both mean absorbed dose in the phantom and tube charge. When less scatter is generated, either the grid ratio or the tube potential can be varied to achieve the desired contrast level. High grid ratios require shorter exposure times, but need careful alignment in the beam to prevent primary radiation cut-off. It is shown that the air gap technique can be used to reduce patient dose in examinations with small amounts of scatter, but in combinations with a lower tube potential than when a grid is used.
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| 5. |
- Sandborg, Michael, 1961-, et al.
(författare)
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Monte Carlo study of grid performance in diagnostic radiology: task dependent optimisation for screen-film imaging
- 1994
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Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 0007-1285 .- 1748-880X. ; 67, s. 76-85
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Tidskriftsartikel (refereegranskat)abstract
- An optimization of anti-scatter grid design using Monte Carlo techniques in diagnostic radiology is presented. The criterion for optimization was to find the combinations of the grid parameters (lead strip width, grid ratio and strip density) and tube potential which result in the lowest mean absorbed dose in the patient at fixed image contrast. The optimization was performed in three irradiation geometries, representing different scattering conditions (paediatric examinations, and two adult lumbar spine examinations) and was restricted to grids using fibre materials in covers and interspaces. Grid designs currently available were studied, as were designs which use thinner strips (< 30 µm) and higher grid ratios (> 18). It was found that grids with widely different strip densities (strips cm–1) and grid ratios can have good performance provided that they are used with appropriate strip width and tube potential. With increasing amounts of scatter, the optimal grid requires thicker strips and higher grid ratios. Increasing the strip density and using thinner strips and higher grid ratios are generally required. Grids with low strip density (25 strips cm–1) were found to be less sensitive to alterations in strip width. Optimal grids for paediatric radiology require thinner strips (10–20 µm) than those in currently available grids. Grids on the market are best suited for examinations of the adult body in anteroposterior (AP) view. In the adult lateral view, representing the largest scattering volume, higher grid ratios (> 18) than those in existing grids would be optimal. Examples of good grid designs are given for each examination.
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| 6. |
- Sandborg, Michael, 1961-, et al.
(författare)
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Selection of anti-scatter grids for different imaging tasks: the advantage of low atomic number cover and interspace materials
- 1993
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Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 0007-1285 .- 1748-880X. ; 66, s. 1151-1163
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Tidskriftsartikel (refereegranskat)abstract
- A Monte Carlo computer program has been developed for the study of anti-scatter grids used in diagnostic radiology. The program estimates the scatter from soft tissue phantoms representative of either adult or paediatric examinations and uses dose increase, signal-to-noise ratio improvement and contrast improvement factors to study grid performance. It has been used to quantify the advantage of replacing grids with aluminium covers and interspaces by grids using materials of low atomic number for these components. Two approaches are used. First, the aluminium and low atomic number alternatives are compared for five grid ratios at fixed strip density and width and for tube potentials of 50, 70, 100 and 150 kV. Second, 44 commercially available grids are compared for three different imaging situations (lumbar spine, chest and paediatric). The results demonstrate that grids made with carbon fibre cover and cotton fibre interspace result in greater improvements in contrast and signal-to-noise ratio, and lower dose increase factors, than do grids made with aluminium. The dose reduction varies with irradiation conditions and is generally larger at lower tube potentials, higher grid ratios and lower strip densities. A typical reduction in mean absorbed dose in the patient is 30% in an adult lumbar spine (AP view) at 70 kV with a grid with 36 strips per centimetre and ratio 12.
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| 7. |
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| 8. |
- Adrian, Gabriel, et al.
(författare)
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The FLASH effect depends on oxygen concentration
- 2019
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Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 1748-880X .- 0007-1285. ; 93:1106
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: Recent in vivo results have shown prominent tissue sparing effect of radiotherapy with ultra-high dose rates (FLASH) compared to conventional dose rates (CONV). Oxygen depletion has been proposed as the underlying mechanism, but in vitro data to support this have been lacking. The aim of the current study was to compare FLASH to CONV irradiation under different oxygen concentrations in vitro. METHODS: Prostate cancer cells were irradiated at different oxygen concentrations (relative partial pressure ranging between 1.6 and 20%) with a 10 MeV electron beam at a dose rate of either 600 Gy/s (FLASH) or 14 Gy/min (CONV), using a modified clinical linear accelerator. We evaluated the surviving fraction of cells using clonogenic assays after irradiation with doses ranging from 0 to 25 Gy. RESULTS: Under normoxic conditions, no differences between FLASH and CONV irradiation were found. For hypoxic cells (1.6%), the radiation response was similar up to a dose of about 5-10 Gy, above which increased survival was shown for FLASH compared to CONV irradiation. The increased survival was shown to be significant at 18 Gy, and the effect was shown to depend on oxygen concentration. CONCLUSION: The in vitro FLASH effect depends on oxygen concentration. Further studies to characterize and optimize the use of FLASH in order to widen the therapeutic window are indicated. ADVANCES IN KNOWLEDGE: This paper shows in vitro evidence for the role of oxygen concentration underlying the difference between FLASH and CONV irradiation.
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| 9. |
- Al-Okshi, Ayman, et al.
(författare)
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A meta-review of effective doses in dental and maxillofacial cone beam CT using the ROBIS tool.
- 2021
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Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 0007-1285 .- 1748-880X. ; 94:1123
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: To apply the ROBIS tool for assessment of risk of bias (RoB) in systematic reviews (SRs) in a meta-review on effective doses (EDs) in dental and maxillofacial cone beam CT.METHODS: Three electronic databases and reference lists of included SRs were searched. Eligible SRs were classified as having low, high or unclear RoB. Findings of SRs were synthesised and data from primary studies combined to relate ED to field of view (FOV) and operating potential (kV).RESULTS: Seven SRs were included: three displayed low RoB, three high and one had unclear RoB. Only one SR related ED to image quality. Deficiencies in reporting of eligibility criteria, study selection and synthesis of results in SRs were identified. FOV height had a significant relationship with ED, explaining 27.2% of its variability. Median ED for three FOV categories differed significantly. Operating potential had a weak relationship with ED, with no significant difference in median ED between three operating potential groups.CONCLUSION: The ROBIS tool should have a role for meta-reviews of different aspects of radiology. The disappointing results for RoB might be remedied by developing standards to improve the quality of reporting of primary dosimetry studies and of SRs. Future dosimetry studies should always relate ED to image quality or diagnostic accuracy.ADVANCES IN KNOWLEDGE: This meta-review is the first to implement ROBIS for SRs of ED and identified that trustworthiness of some SRs is questionable. The percentage change in average ED per cm increase in FOV height could be calculated, emphasizing the importance of FOV as a determinant of ED in CBCT.
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| 10. |
- Al-Okshi, Ayman, et al.
(författare)
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Effective dose of cone beam computed tomography (CBCT) of the facial skeleton : a systematic review
- 2015
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Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 0007-1285 .- 1748-880X. ; 88:1045
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Forskningsöversikt (refereegranskat)abstract
- Objective: To estimate effective dose of cone beam CT (CBCT) of the facial skeleton with focus on measurement methods and scanning protocols. Methods: A systematic review, which adhered to the preferred reporting items for systematic reviews (PRISMA) Statement, of the literature up to April 2014 was conducted. Data sources included MEDLINE®, The Cochrane Library and Web of Science. A model was developed to underpin data extraction from 38 included studies. Results: Technical specifications of the CBCT units were insufficiently described. Heterogeneity in measurement methods and scanning protocols between studies made comparisons of effective doses of different CBCT units and scanning protocols difficult. Few studies related doses to image quality. Reported effective dose varied across studies, ranging between 9.7 and 197.0 mSv for field of views (FOVs) with height #5cm, between 3.9 and 674.0 mSv for FOVs of heights 5.1–10.0 cm and between 8.8 and 1073.0 mSv for FOVs .10 cm. There was an inconsistency regarding reported effective dose of studies of the same CBCT unit with the same FOV dimensions. Conclusion: The review reveals a need for studies on radiation dosages related to image quality. Reporting quality of future studies has to be improved to facilitate comparison of effective doses obtained from examinations with different CBCT units and scanning protocols. A model with minimum data set on important parameters based on this observation is proposed. Advances in knowledge: Data important when estimating effective dose were insufficiently reported in most studies. A model with minimum data based on this observation is proposed. Few studies related effective dose to image quality.
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