| 1. |
- Lanhede, B., et al.
(författare)
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The Influence of Different Technique Factors on Image Quality for Chest Radiographs: Application of the Recent CEC Image Quality Criteria
- 2000
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Ingår i: Radiation Protection Dosimetry. - 1742-3406. ; 90:1-2, s. 203-206
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the first this work part of the EU-project, Trial I, was to evaluate and possibly improve the CEC image criteria for radiographic chest images. Chest images of healthy volunteers were acquired using different technique factors. The image criteria were used as a tool to discriminate between the different images. The technique factors were chosen so that the image quality would differ slightly. Four different technique parameters, each with two possible settings, used in clinical practice today, were used: tube voltage - 102 and 141 kV; screen/film speed - 160 and 320; maximum optical density in the parenchyma - 1.3 and 1.8; method for scatter reduction - air gap 30/390 and moving grid40/12. The results showed that the image criteria were able to separate between different technique groups. Some conclusions can be drawn from the results Optical density 1.8 was better than 1.3 independent of the other parameters. . Among the six combinations ranked best , four used tube voltage 141 kV and four used air gap technique for scatter reduction. No difference was seen for screen/film speed. No correlation was seen between the ranking of the systems and patient dose.
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| 2. |
- 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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| 3. |
- Lowe, Michael R., et al.
(författare)
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The length of the CTLA-4 microsatellite (AT)(N)-repeat affects the risk for type 1 diabetes
- 2000
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Ingår i: Autoimmunity. - : Informa UK Limited. - 0891-6934 .- 1607-842X. ; 32:3, s. 173-180
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Tidskriftsartikel (refereegranskat)abstract
- CTLA-4 is important to down-regulating T cell responses and has been implicated in type 1 (insulin dependent) diabetes mellitus in both linkage and association studies. The aim of our study was to relate the polymorphic (AT)(n) microsatellite in the 3' untranslated sequence of the CTLA-4 gene to diabetes risk. We studied 616 consecutively diagnosed 0-34 year-old Swedish patients and 502 matched controls by PCR-based genotyping to determine the length of the 3'-end (AT)(n)repeat region of the CTLA-4 gene and categorizing alleles as predominantly monomorphic short (S) or highly polymorphic (in length) long (L) alleles. The odds of type 1 diabetes of subjects with the L/L genotype was estimated to be 1.84 times that of subjects with the S/S genotype (95% CI 1.44-2.73, p=0.002). Further analysis of the long alleles, partitioned into intermediate (I) length and very long (VL) alleles, suggested that L alleles act recessively in conferring diabetes risk (p=0.0009). This study suggests that the 3'-end (AT)(n) repeat region of the CTLA-4 gene represents a recessive risk factor for type 1 diabetes.
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| 4. |
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| 5. |
- Sund, P., et al.
(författare)
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Comparison of two methods for evaluating image quality of chest radiographs
- 2000
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Ingår i: Proceedings of SPIE. - : SPIE. ; 3981, s. 251-258
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Konferensbidrag (refereegranskat)abstract
- A set of 15 analog chest images was digitized with a high performance scanner and manipulated in terms of noise and resolution to yield three sets of images; the original plus two with different noise and resolution properties. These sets were evaluated with Visual Grading Analysis (VGA) where the observer rates the visibility of certain normal anatomical structures (as described by the European Quality Criteria) compared to a reference image. One of the non-manipulated digitized images was used in an ROC-related method – the Free response Forced Error experiment. Simulated lesions of different contrast and size were randomly superimposed on 50 copies of this image. The images were then manipulated in the same way as the images used for VGA. All observations were done by a group of seven expert radiologists from six different European countries and all images were printed back to film before evaluation. The ranking of the image manipulations was the same for the two methods. Although a strong correlation cannot be predicted with only three sets of images, it is encouraging that the simpler VGA study in some cases might be used as a replacement for the more time- and effort-consuming ROC analysis.
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| 6. |
- Tingberg, Anders, et al.
(författare)
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Comparison of two methods for evaluation of the image quality of lumbar spine radiographs
- 2000
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Ingår i: Radiation Protection Dosimetry. - 1742-3406. ; 90:1, s. 165-168
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Tidskriftsartikel (refereegranskat)abstract
- Two methods for visual evaluation of image quality of clinical radiographs have been compared. In visual grading analysis (VGA) specified anatomical structures in an image are visually compared with the same structures in a reference image, and in a free-response forced error (FFE) experiment - an extension of conventional ROC (receiver operating characteristics) analysis - the objective is to correctly localise known lesions. The spatial resolution and noise of digitised clinical radiographs of the lumbar spine were altered by image processing, and pathological structures were added to the images for the FFE experiment. The images were printed to film and evaluated by seven European expert radiologists using VGA and FFE. The results of these two different methods showed a very good agreement. In conclusion, VGA methodology can be made as solid as the FFE experiment for evaluating image quality. The simplicity of VGA makes it very suitable for implementation in clinical practice.
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| 7. |
- Tingberg, Anders, et al.
(författare)
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Evaluation of lumbar spine images with added pathology
- 2000
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Ingår i: Proceedings of SPIE. - : SPIE. - 0819435988 ; 3981, s. 34-42
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Konferensbidrag (refereegranskat)abstract
- Optimisation of radiographic procedures require solid tools for evaluation of the image quality in order to ensure that it is sufficient to answer the clinical question at the lowest possible absorbed dose to the patient. Lumbar spine radiography is an examination giving a relatively high dose and good methods for evaluation of image quality as well as dose are needed. We have developed and used a method for the addition of artificial pathological structures into clinical images. The new images were evaluated in a study of detectability (free-response forced error experiment). The results from the study showed that the methodology can be used to detect differences in the screen-film systems used to produce the images, indicating that the method can be used in a study of image quality. The results of the study of detectability were compared with the outcome of a visual grading analysis based on the structures mentioned in the European Quality Criteria. The comparison indicated that a linear correlation exists between the two methods. This means that the simpler VGA can be used in the evaluation of clinical image quality.
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| 8. |
- Tingberg, Anders, et al.
(författare)
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What is worse: Decreased spatial resolution or increased noise?
- 2002
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Ingår i: Proceedings of SPIE. - : SPIE. - 9780819444318 ; 4686, s. 338-346
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Konferensbidrag (refereegranskat)abstract
- Purpose: To investigate the relative importance of spatial resolution and noise on the image quality of clinical radiographs. Methods: The spatial resolution and noise of fifteen digitised lumbar spine radiographs were altered with image processing. Three different MTF curves and three different Wiener spectra were combined into seven different combinations of spatial resolution and noise. These seven combinations were applied to the original data set, and the resulting images were printed on film. Seven expert radiologists evaluated the clinical image quality of the resulting images with visual grading analysis (VGA) of structures based on the European Image Criteria. Results: The results show that added noise is more deteriorating than reduced spatial resolution for the clinical image quality. For a given MTF and noise level, the worst was the one with increased noise followed by the one with both reduced MTF and added noise (mimicking a faster screen-film combination). Reduced MTF only gave the highest rating. Conclusions: It is more important to find methods for removing noise than to try to improve the MTF of a radiographic system. A noisy image can sometimes be improved by reducing the spatial resolution.
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