| 1. |
- Larsson, Joel, 1986, et al.
(författare)
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Assessment of clinical image quality in paediatric abdominal CT examinations – dependency on level of adaptive statistical iterative reconstruction (ASIR) and type of convolution kernel
- 2015
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Ingår i: Optimisation in X-ray and Molecular Imaging 2015 - the Fourth Malmö Conference on Medical Imaging, Gothenburg, Sweden, 28-30 May 2015.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Purpose: The purpose of this study was to investigate the effect of combinations of convolution kernel and level of Adaptive Statistical iterative Reconstruction (ASiR) on diagnostic quality and visualisation of anatomical structures for paediatric abdominal CT examinations. Materials and Methods: Thirty five patients (mean age 10 years-old, range; 2 to 15 years-old) undergoing routine abdominal CT on a 64 slice MDCT scanner (Discovery CT750 HD, GE Healthcare) were included in the study. Raw data was retrospectively reconstructed into 5 mm thick and interval 2.5 mm transaxial image stacks at levels of 30%, 50%, 70%, 90% and 100% ASiR, all in combination with three kernels; Soft, Standard and Detail. In a blinded randomized visual grading study, four paediatric radiologists with different experience rated a question of diagnostic quality and 6 questions related to anatomical structures, using a four point rating scale. Data were analysed in comparison with 30% ASiR with kernel Soft (the settings used clinically prior to the study) using a method for paired ordinal data that identifies and measures systematic shift in rating distributions. The shift is expressed as the Relative Position (RP). Results: A clear dependency on type of convolution kernel was seen for the relationship between ASiR level and image quality. For the Soft and Standard kernels, the optimal diagnostic quality was obtained at 70% ASiR. For the Detail kernel, the diagnostic quality increased with ASiR level, but at no ASiR level for this kernel a better diagnostic quality than at 30% ASiR with kernel Soft was obtained. The visibility of the extra hepatic part of the portal vein was best delineated at 70% ASiR with kernel Soft (RP -0.12; 95% CI -0.20 to -0.04). Conclusions: This study shows that for paediatric abdomen CT examinations the clinical image quality at a given ASiR level is dependent on the convolution kernel and that a more edge enhancing kernel can benefit from a higher ASiR level. For the acquisition settings used in the present work, the optimal combinations of ASiR level and convolution kernel was 70% ASiR with kernel Soft or Standard.
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| 2. |
- Larsson, Joel, 1986, et al.
(författare)
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Assessment of clinical image quality in paediatric abdominal CT examinations: dependency on the level of adaptive statistical iterative reconstruction (ASiR) and the type of convolution kernel
- 2016
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 169:1-4, s. 123-129
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study was to investigate the effect of different combinations of convolution kernel and the level of Adaptive Statistical iterative Reconstruction (ASiR™) on diagnostic image quality as well as visualisation of anatomical structures in paediatric abdominal computed tomography (CT) examinations. Thirty-five paediatric patients with abdominal pain with non-specified pathology undergoing abdominal CT were included in the study. Transaxial stacks of 5-mm-thick images were retrospectively reconstructed at various ASiR levels, in combination with three convolution kernels. Four paediatric radiologists rated the diagnostic image quality and the delineation of six anatomical structures in a blinded randomised visual grading study. Image quality at a given ASiR level was found to be dependent on the kernel, and a more edge-enhancing kernel benefitted from a higher ASiR level. An ASiR level of 70 % together with the Soft™ or Standard™ kernel was suggested to be the optimal combination for paediatric abdominal CT examinations.
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| 3. |
- Larsson, Joel, 1986, et al.
(författare)
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The effect of adaptive statistical iterative reconstruction (ASIR) on the assessment of diagnostic quality and visualisation of anatomical structures in paediatric head CT examinations
- 2015
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Ingår i: Optimisation in X-ray and Molecular Imaging 2015 - the Fourth Malmö Conference on Medical Imaging, Gothenburg, Sweden, 28-30 May 2015.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Purpose: The purpose of this study was to investigate the effect of different levels of Adaptive Statistical iterative Reconstruction (ASiR) on diagnostic quality and visualisation of anatomical structures for paediatric head CT examinations. Materials and Methods: Forty patients from infants to an age of 17 years-old undergoing routine head CT on a 64 slice MDCT scanner (Discovery CT750 HD, GE Healthcare) were included in the study and divided into age dependent sub groups (0-2, 3-5 and 6-17 years-old). Scanning raw data, acquired within tube current range 190 to 400 mA, was retrospectively reconstructed into 5 mm thick axial image stacks at levels of 0%, 20%, 30%, 40%, 50%, 60%, 70%, 80% and 100% ASiR with convolution kernel Soft. In a blinded randomized visual grading study, three paediatric radiologists with different experience rated a question of diagnostic quality (For what diagnostic situation is this image quality sufficient?) and 6 questions related to anatomical structures, using a four point rating scale. Data were analysed in comparison with 30 % ASiR with kernel Soft (the ASiR level and kernel used clinically prior to the study) using a method for paired ordinal data that identifies and measures systematic shift in rating distributions. Results: In all sub groups, 50%, 60% and 70% ASiR demonstrated a statistically significant negative Relative Position (RP) for diagnostic quality, indicating a higher diagnostic quality compared to 30% ASiR. All trends of the assessed anatomical structures, except the cerebrospinal fluid space around the brain, demonstrated enhancement in visibility with increased level of ASiR. The visibility of the cerebrospinal fluid space around the brain was degraded at ASiR levels above 60% ASiR. Diagnostic quality at 0% ASiR (100% filtered back projection) was significantly lower than 30% ASiR. Conclusion: This study shows that the commonly used 30% ASiR may not always be the optimal level of ASiR. The investigated effect of ASiR showed, in this study, that 60% ASiR was the optimal ASiR level for a paediatric head CT examinations at the tube current range 190 to 400 mA, when reconstructing 5 mm thick images with convolution kernel Soft.
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| 4. |
- Larsson, Joel, 1986, et al.
(författare)
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The effect of Adaptive Statistical iterative Reconstruction (ASiR) on the assessment of diagnostic quality and visualisation of anatomical structures in paediatric head CT examinations
- 2016
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 169:1-4, s. 115-122
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study was to investigate the effect of adaptive statistical iterative reconstruction (ASiR) on the visualisation of anatomical structures and diagnostic image quality in paediatric cerebral computed tomography (CT) examinations. Forty paediatric patients undergoing routine cerebral CT were included in the study. The raw data from CT scans were reconstructed into stacks of 5 mm thick axial images at various levels of ASiR. Three paediatric radiologists rated six questions related to the visualisation of anatomical structures and one question on diagnostic image quality, in a blinded randomised visual grading study. The evaluated anatomical structures demonstrated enhanced visibility with increasing level of ASiR, apart from the cerebrospinal fluid space around the brain. In this study, 60 % ASiR was found to be the optimal level of ASiR for paediatric cerebral CT examinations. This shows that the commonly used 30 % ASiR may not always be the optimal level.
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| 5. |
- Ledenius, Kerstin, 1979, et al.
(författare)
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A method to analyse observer disagreement in visual grading studies: example of assessed image quality in paediatric cerebral multidetector CT images.
- 2010
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Ingår i: The British journal of radiology. - : British Institute of Radiology. - 1748-880X .- 0007-1285. ; 83:991, s. 604-11
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Tidskriftsartikel (refereegranskat)abstract
- The purpose was to demonstrate a non-parametric statistical method that can identify and explain the components of observer disagreement in terms of systematic disagreement as well as additional individual variability, in visual grading studies. As an example, the method was applied to a study where the effect of reduced tube current on diagnostic image quality in paediatric cerebral multidetector CT (MDCT) images was investigated. Quantum noise, representing dose reductions equivalent to steps of 20 mA, was artificially added to the raw data of 25 retrospectively selected paediatric cerebral MDCT examinations. Three radiologists, blindly and randomly, assessed the resulting images from two different levels of the brain with regard to the reproduction of high- and low-contrast structures and overall image quality. Images from three patients were assessed twice for the analysis of intra-observer disagreement. The intra-observer disagreement in test-retest assessments could mainly be explained by a systematic change towards lower image quality the second time the image was reviewed. The inter-observer comparisons showed that the paediatric radiologist was more critical of the overall image quality, while the neuroradiologists were more critical of the reproduction of the basal ganglia. Differences between the radiologists regarding the extent to which they used the whole classification scale were also found. The statistical method used was able to identify and separately measure a presence of bias apart from additional individual variability within and between the radiologists which is, at the time of writing, not attainable by any other statistical approach suitable for paired, ordinal data.
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| 6. |
- Ledenius, Kerstin, 1979, et al.
(författare)
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Effect of tube current on diagnostic image quality in paediatric cerebral multidetector CT images.
- 2009
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Ingår i: The British journal of radiology. - : British Institute of Radiology. - 1748-880X .- 0007-1285. ; 82:976, s. 313-20
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to investigate the effect of tube current on diagnostic image quality in paediatric cerebral multidetector CT (MDCT) images in order to identify the minimum radiation dose required to reproduce acceptable levels of different diagnostic image qualities. Original digital scanning data (raw data) were selected retrospectively from routine MDCT brain examinations of 25 paediatric patients. All examinations had been performed using axial scanning on an eight-slice MDCT (LightSpeed Ultra, GE Healthcare). Their ages ranged from newborn to 15 years. Quantum noise was added artificially to the raw data representing dose reductions equivalent to steps of 20 mA. Patient identification information was removed. Three experienced radiologists blindly and randomly assessed the resulting images from two different levels of the brain with regard to reproduction of structures and overall image quality. Final data were evaluated using the non-parametric statistical approach of inter-scale concordance. The minimum value of tube current-time product (mAs) required to reproduce an image of sufficient diagnostic quality was established in relation to the age of the patient. The corresponding CT dose index values by volume (CTDI(vol) (mGy)) were also established. In conclusion, acceptable reproduction of low-contrast structures was possible at CTDI(vol) values down to 20 mGy (patients 1-5 years old). For acceptable reproduction of high-contrast structures, CTDI(vol) values down to 10 mGy were considered possible (patients 1-5 years old). The original image quality for patients under 6 months of age (15 mGy) was found to be inadequate for acceptable reproduction of low-contrast structures.
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| 7. |
- Ledenius, Kerstin, 1979, et al.
(författare)
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Evaluation Of Image-Enhanced Paediatric Computed Tomography Brain Examinations
- 2010
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 139:1-3, s. 287-292
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to evaluate the possibility of reducing the radiation dose to paediatric patients undergoing computed tomography (CT) brain examination by using image-enhancing software. Artificial noise was added to the raw data collected from 20 patients aged between 1 and 10 y to simulate tube current reductions of 20, 40 and 60 mA. All images were created in duplicate; one set of images remained unprocessed whereas the other was processed with image-enhancing software. Three paediatric radiologists assessed the image quality based on their ability to visualise the high- and low-contrast structures and their overall impression of the diagnostic value of the image. For patients aged 6-10 y, it was found that dose reductions from 27 mGy (CTDI(vol)) to 23 mGy (15 %) in the upper brain and from 32 to 28 mGy (13 %) in the lower brain were possible for standard diagnostic CT examinations when using the image-enhancing filter. For patients 1-5 y, the results for standard diagnostics in the upper brain were inconclusive, for the lower brain no dose reductions were found possible.
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| 8. |
- Ledenius, Kerstin, 1979
(författare)
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Optimization of paediatric CT examinations - An approach to minimize absorbed dose to patients with regard to image quality and observer variability
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The absorbed dose to paediatric patients is important bearing in mind the increased risk of radiation-induced cancer due to exposure to X-rays at young ages. Questions have also been raised of whether a CT examination of the paediatric brain might lead to a reduction in cognitive function. Considering the difference in anatomy and thus in X-ray attenuation, children have a special need in CT image quality and require separate scanning protocols and thus separate optimization from adults. The overall aim of the work described in this thesis was to find an optimization approach to minimize the absorbed dose to paediatric patients undergoing CT examinations, while maintaining the diagnostic image quality and taking into account observer variability. In a first study, the effect of reducing the tube current on the diagnostic image quality was evaluated for paediatric cerebral CT examinations using the non-parametric statistical method of inter-scale concordance. The observer variability was evaluated by means of Svensson’s method in a second study. The approaches in these two studies were then combined in a third study to optimize the noise index in abdominal paediatric CT examinations. The aim of the fourth study was to estimate the variability in the results when using inter-scale concordance. A post-processing 2D adaptive filter, claiming to enable reductions in radiation exposure, was investigated in the third study, and in a separate fifth study. Artificial noise was added to copies of raw data of paediatric CT examinations in order to simulate a reduction in radiation exposure without having to expose paediatric patients to further scans. When the adaptive filter was tested, all images were created in duplicate: one set being post-processed. All images, including the images duplicated for test-retest assessments were evaluated blindly and randomly by three (two in one study) observers using a software viewing station. The radiologists assessed the image quality visually by grading the reproduction of high- and low-contrast structures and overall image quality on a 4-point rating scale. For the cerebral CT examinations reductions in radiation exposure were possible for patients 1 to 10 years old. It was possible to further reduce the radiation exposure for shunt-treated patients. The original image quality for patients under 6 months of age was found to be inadequate. Noise index 11 was sufficient for a routine abdominal examination for patients aged 6 to 10 years, noise index 12 was considered sufficient for patients aged 11 to 15 years. The variability in results was less than 20 % between two cerebral studies regarding routine CT examinations. The post-processing filter enabled reductions in radiation exposure of approximately 15 % for some age groups. The approach used in this work enabled the inter-scale relations between radiation exposure and diagnostic image quality to be determined for paediatric cerebral and abdominal CT examinations. Observer variability was also evaluated and a minimum radiation exposure to paediatric patients was suggested. Applying the approach to post-processed images indicated a possible reduction in radiation exposure to paediatric patients.
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| 9. |
- Thilander-Klang, Anne, 1959, et al.
(författare)
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Evaluation of subjective assessment of the low-contrast visibility in constancy control of computed tomography
- 2010
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 139:1-3, s. 449-454
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of the present work was to investigate the reliability of subjective assessments of the low-contrast visibility in constancy control of computed tomography (CT). Axial CT images of a low-contrast phantom were acquired on an 8-slice multi-detector CT scanner at nine tube current settings ranging from 75 to 440 mA. Five medical physicists assessed the visibility of the low-contrast details in two sessions. In the first session, containing 54 images, the visibility was rated on an absolute scale by determining the number of visible details in each contrast group in each image. In the second session, 180 image pairs were presented to the observers with the task of determining if the two images had been acquired under identical conditions or not. In the absolute session, both the intra- and inter-observer variabilities were high. In the relative session, the variability was smaller, but an exposure difference of 50 % was needed for all observers to correctly identify a change in all cases. In conclusion, the present study indicates that subjective assessments of the low-contrast visibility in constancy control of CT are not reliable.
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| 10. |
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