| 1. |
- Båth, Magnus, 1974, et al.
(författare)
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A conceptual optimisation strategy for radiography in a digital environment.
- 2005
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 230-5
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Tidskriftsartikel (refereegranskat)abstract
- Using a completely digital environment for the entire imaging process leads to new possibilities for optimisation of radiography since many restrictions of screen/film systems, such as the small dynamic range and the lack of possibilities for image processing, do not apply any longer. However, at the same time these new possibilities lead to a more complicated optimisation process, since more freedom is given to alter parameters. This paper focuses on describing an optimisation strategy that concentrates on taking advantage of the conceptual differences between digital systems and screen/film systems. The strategy can be summarised as: (a) always include the anatomical background during the optimisation, (b) perform all comparisons at a constant effective dose and (c) separate the image display stage from the image collection stage. A three-step process is proposed where the optimal setting of the technique parameters is determined at first, followed by an optimisation of the image processing. In the final step the optimal dose level-given the optimal settings of the image collection and image display stages-is determined.
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| 2. |
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| 3. |
- Båth, Magnus, 1974, et al.
(författare)
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Investigation of image components affecting the detection of lung nodules in digital chest radiography
- 2005
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Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE. - 1605-7422. ; 5749, s. 231-242
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this work was to investigate and quantify the effects of system noise, nodule location, anatomical noise and anatomical background on the detection of lung nodules in different regions of the chest x-ray. Simulated lung nodules of diameter 10 mm but with varying detail contrast were randomly positioned in four different kinds of images: 1) clinical images collected with a 200 speed CR system, 2) images containing only system noise (including quantum noise) at the same level as the clinical images, 3) clinical images with removed anatomical noise, 4) artificial images with similar power spectrum as the clinical images but random phase spectrum. An ROC study was conducted with 5 observers. The detail contrast needed to obtain an Az of 0.80, C0.8, was used as measure of detectability. Five different regions of the chest x-ray were investigated separately. The C0.8 of the system noise images ranged from only 2% (the hilar regions) to 20% (the lateral pulmonary regions) of those of the clinical images. Compared with the original clinical images, the C0.8 was 16% lower for the de-noised clinical images and 71% higher for the random phase images, respectively, averaged over all five regions. In conclusion, regarding the detection of lung nodules with a diameter of 10 mm, the system noise is of minor importance at clinically relevant dose levels. The removal of anatomical noise and other noise sources uncorrelated from image to image leads to somewhat better detection, but the major component disturbing the detection is the overlapping of recognizable structures, which are, however, the main aspect of an x-ray image.
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| 4. |
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| 5. |
- Båth, Magnus, 1974, et al.
(författare)
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Method of simulating dose reduction for digital radiographic systems.
- 2005
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 253-9
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Tidskriftsartikel (refereegranskat)abstract
- The optimisation of image quality vs. radiation dose is an important task in medical imaging. To obtain maximum validity of the optimisation, it must be based on clinical images. Images at different dose levels can then either be obtained by collecting patient images at the different dose levels sought to investigate-including additional exposures and permission from an ethical committee-or by manipulating images to simulate different dose levels. The aim of the present work was to develop a method of simulating dose reduction for digital radiographic systems. The method uses information about the detective quantum efficiency and noise power spectrum at the original and simulated dose levels to create an image containing filtered noise. When added to the original image this results in an image with noise which, in terms of frequency content, agrees with the noise present in an image collected at the simulated dose level. To increase the validity, the method takes local dose variations in the original image into account. The method was tested on a computed radiography system and was shown to produce images with noise behaviour similar to that of images actually collected at the simulated dose levels. The method can, therefore, be used to modify an image collected at one dose level so that it simulates an image of the same object collected at any lower dose level.
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| 6. |
- Båth, Magnus, 1974, et al.
(författare)
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Nodule detection in digital chest radiography: effect of anatomical noise.
- 2005
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 109-13
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Tidskriftsartikel (refereegranskat)abstract
- The image background resulting from imaged anatomy can be divided into those components that are meaningful to the observers, in the sense that they are recognised as separate structures, and those that are not. These latter components (reffered to as anatomical noise) can be removed using a method developed within the RADIUS group. The aim of the present study was to investigate whether the removal of the anatomical noise results in images where lung nodules with lower contrast can be detected. A receiver operating characteristic (ROC) study was therefore conducted using two types of images: clinical chest images and chest images in which the anatomical noise had been removed. Simulated designer nodules with a full-width-at-fifth-maximum of 10 mm but with varying contrast were added to the images. The contrast needed to obtain an area under the ROC curve of 0.80, C0.8, was used as a measure of detectability (a low value of C0.8 represents a high detectability). Five regions of the chest X ray were investigated and it was found that in all regions the removal of anatomical noise led to images with lower C0.8 than the original images. On average, C0.8 was 20% higher in the original images, ranging from 7% (the lateral pulmonary regions) to 41% (the upper mediastinal regions).
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| 7. |
- Båth, Magnus, 1974, et al.
(författare)
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Nodule detection in digital chest radiography: introduction to the RADIUS chest trial.
- 2005
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 85-91
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Tidskriftsartikel (refereegranskat)abstract
- Most digital radiographic systems of today have wide latitude and are hence able to provide images with a small constraint on dose level. This opens up for an unprejudiced dose optimisation. However, in order to succeed in the optimisation task, good knowledge of the imaging and detection processes is needed. As a part of the European-wide research project 'unification of physical and clinical requirements for medical X-ray imaging'-governed by the Radiological Imaging Unification Strategies (RADIUS) Group-a major image quality trial was conducted by members of the group. The RADIUS chest trial was focused on the detection of lung nodules in digital chest radiography with the aims of determining to what extent (1) the detection of a nodule is dependent on its location, (2) the system noise disturbs the detection of lung nodules, (3) the anatomical noise disturbs the detection of lung nodules and (4) the image background and anatomical background act as pure noise for the detection of lung nodules. The purpose of the present paper is to give an introduction to the trial and describe the framework and set-up of the investigation.
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| 8. |
- Båth, Magnus, 1974, et al.
(författare)
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Nodule detection in digital chest radiography: part of image background acting as pure noise.
- 2005
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 102-8
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Tidskriftsartikel (refereegranskat)abstract
- There are several factors that influence the radiologist's ability to detect a specific structure/lesion in a radiograph. Three factors that are commonly known to be of major importance are the signal itself, the system noise and the projected anatomy. The aim of this study was to determine to what extent the image background acts as pure noise for the detection of subtle lung nodules in five different regions of the chest. A receiver operating characteristic (ROC) study with five observers was conducted on two different sets of images, clinical chest X-ray images and images with a similar power spectrum as the clinical images but with a random phase spectrum, resulting in an image background containing pure noise. Simulated designer nodules with a full-width-at-fifth-maximum of 10 mm but with varying contrasts were added to the images. As a measure of the part of the image background that acts as pure noise, the ratio between the contrast needed to obtain an area under the ROC curve of 0.80 in the clinical images to that in the random-phase images was used. The ratio ranged from 0.40 (in the lateral pulmonary regions) to 0.83 (in the hilar regions) indicating that there was a large difference between different regions regarding to what extent the image background acted as pure noise; and that in the hilar regions the image background almost completely acted as pure noise for the detection of 10 mm nodules.
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| 9. |
- Båth, Magnus, 1974, et al.
(författare)
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VGC analysis: Application of the ROC methodology to visual grading tasks
- 2008
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Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE. - 1605-7422. ; 6917
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- To determine clinical image quality in radiography, visual grading of the reproduction of important anatomical landmarks is often used. The rating data from the observers in a visual grading study with multiple scale steps is ordinal, meaning that non-parametric rank-invariant statistical methods are required. However, many visual grading methods incorrectly use parametric statistical methods. This work describes how the methodology developed in receiver operating characteristics (ROC) analysis for characterising the difference in the observer's response to the signal and no-signal distributions can be applied to visual grading data for characterising the difference in perceived image quality between two systems. The method is termed visual grading characteristics (VGC) analysis. In a VGC study, the task of the observer is to rate her confidence about the fulfilment of image quality criteria. Using ROC software, the given ratings for the two systems are then used to determine the VGC curve, which describes the relationship between the proportions of fulfilled image criteria for the two compared systems for all possible decision thresholds. As a single measure of the difference in image quality between the two compared systems, the area under the VGC curve can be used.
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| 10. |
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| 11. |
- Båth, Magnus, 1974, et al.
(författare)
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Visual grading characteristics (VGC) analysis: a non-parametric rank-invariant statistical method for image quality evaluation.
- 2007
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Ingår i: The British journal of radiology. - : British Institute of Radiology. - 1748-880X .- 0007-1285. ; 80:951, s. 169-76
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Tidskriftsartikel (refereegranskat)abstract
- Visual grading of the reproduction of important anatomical structures is often used to determine clinical image quality in radiography. However, many visual grading methods incorrectly use statistical methods that require data belonging to an interval scale. The rating data from the observers in a visual grading study with multiple ratings is ordinal, meaning that non-parametric rank-invariant statistical methods are required. This paper describes such a method for determining the difference in image quality between two modalities called visual grading characteristics (VGC) analysis. In a VGC study, the task of the observer is to rate his confidence about the fulfilment of image quality criteria. The rating data for the two modalities are then analysed in a manner similar to that used in receiver operating characteristics (ROC) analysis. The resulting measure of image quality is the VGC curve, which--for all possible thresholds of the observer for a fulfilled criterion--describes the relationship between the proportions of fulfilled image criteria for the two compared modalities. The area under the VGC curve is proposed as a single measure of the difference in image quality between two compared modalities. It is also described how VGC analysis can be applied to data from an absolute visual grading analysis study.
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| 12. |
- Börjesson, Sara, et al.
(författare)
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A software tool for increased efficiency in observer performance studies in radiology.
- 2005
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 45-52
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Tidskriftsartikel (refereegranskat)abstract
- Observer performance studies are time-consuming tasks, both for the participating observers and for the scientists collecting and analysing the data. A possible way to optimise such studies is to perform them in a completely digital environment. A software tool-ViewDEX (Viewer for Digital Evaluation of X-ray images)-has been developed in Java, enabling it to function on almost any computer. ViewDEX is designed to handle several types of studies, such as visual grading analysis (VGA), image criteria scoring (ICS) and receiver operating characteristics (ROC). The results from each observer are saved in a log file, which can be exported for further analysis in, for example, a special software for analysing ROC results. By using ViewDEX for an ROC experiment, an evaluation rate of approximately 200 images per hour can be achieved, compared to approximately 25 images per hour using hard copy evaluation. The results are obtained within minutes of completion of the viewing. The risk of human errors in the process of data collection and analysis is also minimised. The viewer has been used in a major trial containing approximately 2700 images.
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| 13. |
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| 15. |
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| 16. |
- Erikson, Anders, et al.
(författare)
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Ten years' experience of enzyme infusion therapy of Norrbottnian (type 3) Gaucher disease.
- 2006
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Ingår i: Acta Paediatr. - 0803-5253. ; 95:3, s. 312-7
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Tidskriftsartikel (refereegranskat)abstract
- AIM: To study the long-term effects of enzyme replacement therapy on the neurological signs of chronic neuronopathic Gaucher disease and to evaluate some biochemical parameters for monitoring the treatment. METHODS: Eight patients from the Norrbottnian cohort were followed during 10 y of treatment. They were followed with regular clinical observations, biochemical tests and psychometric testing. RESULTS: After the start of treatment, their general well-being improved and was stable during the follow-up. In three of the patients there were some indications of slow neurological deterioration. The mean results of psychometric testing did not decrease. Glucosylceramide and chitotriosidase levels were useful in monitoring the treatment. The chemokine CCL18 also seems to be a useful parameter for future monitoring. CONCLUSIONS: Enzyme replacement therapy seems to slow down further neurological and mental deterioration in mild chronic neuronopathic (type 3) Gaucher disease.
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| 17. |
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| 18. |
- Gudjonsson, Sigurdur, et al.
(författare)
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Should All Patients with Non-Muscle-Invasive Bladder Cancer Receive Early Intravesical Chemotherapy after Transurethral Resection? The Results of a Prospective Randomised Multicentre Study.
- 2009
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Ingår i: European Urology. - : Elsevier BV. - 1873-7560 .- 0302-2838. ; 55, s. 773-780
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: To decrease recurrences in non-muscle-invasive bladder cancer (NMIBC), the European Association of Urology (EAU) guidelines recommend immediate, intravesical chemotherapy after transurethral resection (TUR) for all patients with Ta/T1 tumours. OBJECTIVE: To study the benefits of a single, early, intravesical instillation of epirubicin after TUR in patients with low- to intermediate-risk NMIBC. DESIGN, SETTING, AND PARTICIPANTS: In this prospective randomised multicentre trial, 305 patients with primary as well as recurrent low- to intermediate-risk (Ta/T1, G1/G2) tumours were enrolled between 1997 and 2004. Patients were randomly allocated to receive 80mg of epirubicin in 50ml of saline intravesically within 24h of TUR or no further treatment after TUR. MEASUREMENTS: The primary end point was time to first recurrence. RESULTS AND LIMITATIONS: A total of 219 patients remained for analysis after exclusions. The median follow-up time was 3.9 yr. During the study period, 62% (63 of 102) of the patients in the epirubicin group and 77% (90 of 117) in the control group experienced recurrence (p=0.016). In a multivariate model, the hazard ratio (HR) for recurrence was 0.56 (p=0.002) for early instillation of epirubicin versus no treatment. In a subgroup analysis, the treatment had a profound recurrence-reducing effect on patients with primary, solitary tumours, whereas it provided no benefits in patients with recurrent or multiple tumours. Furthermore, patients with a modified European Organisation for Research and Treatment of Cancer (EORTC) risk score of 0-2 with and without single instillation had recurrence rates of 41% and 69%, respectively (p=0.003), whereas the corresponding rates for those with a risk score of >/=3 were 81% and 85%, respectively (p=0.35). CONCLUSIONS: A single, early instillation of epirubicin after TUR for NMIBC reduces the likelihood of tumour recurrence; however, the benefit seems to be minimal in patients at intermediate or high risk of recurrence. Future trials will determine the value of early instillation in addition to serial instillations in NMIBC.
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| 19. |
- Gudjonsson, Sigurdur, et al.
(författare)
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The Value of the UroVysion((R)) Assay for Surveillance of Non-Muscle-Invasive Bladder Cancer.
- 2008
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Ingår i: European Urology. - : Elsevier BV. - 1873-7560 .- 0302-2838. ; 54:2, s. 402-408
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: Patients with non-muscle-invasive bladder cancer are traditionally followed by repeat cystoscopy and urine cytology. A fluorescence in situ hybridisation technique called UroVysion((R)) (UV) is now available for clinical diagnosis of urothelial cancer cells. The aim of the present study was to compare UV analysis with routine follow-up methods. METHODS: We studied an unselected cohort of patients undergoing cystoscopy follow-ups at two Swedish centres in 2004-2005. All patients were investigated by cystoscopy, cytology, and UV assay. The UV assay was evaluated with regards to sensitivity, specificity, and positive predictive value for tumour recurrence. RESULTS: In all, 159 cases were analysed. UV had a 30% overall sensitivity for the 27 biopsy-proven recurrences and 70% sensitivity for high-risk tumours (pT1 and carcinoma in situ [CIS]). The specificity of UV was 95%. UV detected all six CIS cases in the study and was predictive in two additional patients who developed CIS within 1 yr of inclusion. Cytology was positive in four of those eight CIS cases and atypical in the other four. CONCLUSIONS: The UV assay cannot replace cystoscopy for surveillance of patients with non-muscle-invasive bladder cancer, but it may be valuable as a supplement to traditional measures for detecting CIS. Before any conclusions can be drawn regarding the efficacy of novel markers of bladder cancer, they must be studied in bladder cancer patients undergoing endoscopic surveillance.
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| 20. |
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| 21. |
- Hansson, Jonny, et al.
(författare)
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An optimisation strategy in a digital environment applied to neonatal chest imaging.
- 2005
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 278-85
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to find the optimum tube voltage for neonatal chest imaging in computed radiography. The study was designed to take full advantage of the benefits of digital imaging, for example, by comparing the tube voltages at constant effective dose. A phantom study using a living rabbit was first conducted. Images were collected at tube voltages ranging from 40 to 90 kV(p). The reproduction of four structures (central vessels, peripheral vessels, carina and thoracic vertebrae) was rated by 10 radiologists. The reproduction of both central and peripheral vessels was relatively independent of tube voltage. The carina was better reproduced at higher tube voltages whereas the opposite was true for the thoracic vertebrae. Based on the higher importance of the reproduction of the carina it was decided that 90 kV(p) was the optimal tube voltage. To validate the result from the phantom study, a follow-up study was conducted in which images of neonates collected at the tube voltage regularly used at Sahlgrenska University Hospital (70 kV(p)) were compared with images collected at the tube voltage proposed by the phantom study. The follow-up study confirmed the results from the phantom study that the reproduction of the carina was better at 90 than at 70 kV(p). In conclusion, for neonatal chest imaging-given the same effective dose-90 kVp gives better reproduction of important structures than the regularly used 70 kV(p).
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| 22. |
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| 23. |
- Hansson, Magnus, et al.
(författare)
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Calcium-induced generation of reactive oxygen species in brain mitochondria is mediated by permeability transition.
- 2008
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Ingår i: Free Radical Biology & Medicine. - : Elsevier BV. - 0891-5849. ; 45, s. 284-294
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Tidskriftsartikel (refereegranskat)abstract
- Mitochondrial uptake of calcium in excitotoxicity is associated with subsequent increase in reactive oxygen species (ROS) generation and delayed cellular calcium deregulation in ischemic and neurodegenerative insults. The mechanisms linking mitochondrial calcium uptake and ROS production remain unknown but activation of the mitochondrial permeability transition (mPT) may be one such mechanism. In the present study, calcium increased ROS generation in isolated rodent brain and human liver mitochondria undergoing mPT despite an associated loss of membrane potential, NADH and respiration. Unspecific permeabilization of the inner mitochondrial membrane by alamethicin likewise increased ROS independently of calcium, and the ROS increase was further potentiated if NAD(H) was added to the system. Importantly, calcium per se did not induce a ROS increase unless mPT was triggered. Twenty-one cyclosporin A analogs were evaluated for inhibition of calcium-induced ROS and their efficacy clearly paralleled their potency of inhibiting mPT-mediated mitochondrial swelling. We conclude that while intact respiring mitochondria possess powerful antioxidant capability, mPT induces a dysregulated oxidative state with loss of GSH- and NADPH-dependent ROS detoxification. We propose that mPT is a significant cause of pathological ROS generation in excitotoxic cell death.
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| 24. |
- Hemdal, Bengt, et al.
(författare)
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Can the average glandular dose in routine digital mammography screening be reduced? A pilot study using revised image quality criteria.
- 2005
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 383-8
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Tidskriftsartikel (refereegranskat)abstract
- There is a need for tools that in a simple way can be used for the evaluation of image quality related to clinical requirements in mammography. The aim of this work was to adjust the present European image quality criteria to be relevant also for digital mammography images, and to use as simple and as few criteria as possible. A pilot evaluation of the new set of criteria was made with mammograms of 28 women from a General Electric Senographe 2000D full-field digital mammography system. One breast was exposed using the standard automatic exposure mode, the other using about half of that absorbed dose. Three experienced radiologists evaluated the images using visual grading analysis technique. The results indicate that the new quality criteria can be used for the evaluation of image quality related to clinical requirements in digital mammography in a simple way. The results also suggest that absorbed doses for the mammography system used may be substantially reduced.
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| 25. |
- Hemdal, Bengt, et al.
(författare)
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Clinical evaluation of a new set of image quality criteria for mammography.
- 2005
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 389-94
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Tidskriftsartikel (refereegranskat)abstract
- The European Commission (EC) quality criteria for screen-film mammography are used as a tool to assess image quality. A new set of criteria was developed and initially tested in a previous study. In the present study, these criteria are further evaluated using screen-film mammograms that have been digitised, manipulated to simulate different image quality levels and reprinted on film. Expert radiologists have evaluated these manipulated images using both the original (EC) and the new criteria. A comparison of three different simulated dose levels reveals that the new criteria yield a larger separation of image criteria scores than the old ones. These results indicate that the new set of image quality criteria has a higher discriminative power than the old set and thus seems to be more suitable for evaluation of image quality in mammography.
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