| 1. |
- Aurumskjöld, Marie-Louise, et al.
(author)
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Evaluation of an iterative model-based reconstruction of pediatric abdominal CT with regard to image quality and radiation dose
- 2018
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In: Acta Radiologica. - : SAGE Publications. - 1600-0455 .- 0284-1851. ; 59:6, s. 740-747
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Journal article (peer-reviewed)abstract
- BackgroundIn pediatric patients, computed tomography (CT) is important in the medical chain of diagnosing and monitoring various diseases. Because children are more radiosensitive than adults, they require minimal radiation exposure. One way to achieve this goal is to implement new technical solutions, like iterative reconstruction.PurposeTo evaluate the potential of a new, iterative, model-based method for reconstructing (IMR) pediatric abdominal CT at a low radiation dose and determine whether it maintains or improves image quality, compared to the current reconstruction method.Material and MethodsForty pediatric patients underwent abdominal CT. Twenty patients were examined with the standard dose settings and 20 patients were examined with a 32% lower radiation dose. Images from the standard examination were reconstructed with a hybrid iterative reconstruction method (iDose4), and images from the low-dose examinations were reconstructed with both iDose4 and IMR. Image quality was evaluated subjectively by three observers, according to modified EU image quality criteria, and evaluated objectively based on the noise observed in liver images.ResultsVisual grading characteristics analyses showed no difference in image quality between the standard dose examination reconstructed with iDose4 and the low dose examination reconstructed with IMR. IMR showed lower image noise in the liver compared to iDose4 images. Inter- and intra-observer variance was low: the intraclass coefficient was 0.66 (95% confidence interval = 0.60–0.71) for the three observers.ConclusionIMR provided image quality equivalent or superior to the standard iDose4 method for evaluating pediatric abdominal CT, even with a 32% dose reduction.
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| 2. |
- Andersson, Henrik, et al.
(author)
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Comparison of image quality between a novel mobile CT scanner and current generation stationary CT scanners
- 2023
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In: Neuroradiology. - : Springer Science and Business Media LLC. - 0028-3940 .- 1432-1920. ; 65:3, s. 503-512
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Journal article (peer-reviewed)abstract
- Purpose: Point-of-care imaging with mobile CT scanners offers several advantages, provided that the image quality is satisfactory. Our aim was to compare image quality of a novel mobile CT to stationary scanners for patients in a neurosurgical intensive care unit (ICU). Methods: From November 2020 to April 2021, all patients above 18 years of age examined by a mobile CT scanner at a neurosurgical ICU were included if they also had a stationary head CT examination during the same hospitalization. Quantitative image quality parameters included attenuation and noise in six predefined regions of interest, as well as contrast-to-noise ratio between gray and white matter. Subjective image quality was rated on a 4-garde scale, by four radiologists blinded to scanner parameters. Results: Fifty patients were included in the final study population. Radiation dose and image attenuation values were similar for mobCT and stationary CTs. There was a small statistically significant difference in subjective quality rating between mobCT and stationary CT images. Two radiologists favored the stationary CT images, one was neutral, and one favored mobCT images. For overall image quality, 14% of mobCT images were rated grade 1 (poor image quality) compared to 8% for stationary CT images. Conclusion: Point-of-care brain CT imaging was successfully performed on clinical neurosurgical ICU patients with small reduction in image quality, predominantly affecting the posterior fossa, compared to high-end stationary CT scanners.
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| 3. |
- Aurumskjöld, Marie-Louise, et al.
(author)
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Improvements to image quality using hybrid and model-based iterative reconstructions: a phantom study.
- 2017
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In: Acta radiologica (Stockholm, Sweden : 1987). - : SAGE Publications. - 1600-0455 .- 0284-1851. ; 58:1, s. 53-61
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Journal article (peer-reviewed)abstract
- The number of computed tomography (CT) examinations is increasing and leading to an increase in total patient exposure. It is therefore important to optimize CT scan imaging conditions in order to reduce the radiation dose. The introduction of iterative reconstruction methods has enabled an improvement in image quality and a reduction in radiation dose.
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| 4. |
- Aurumskjöld, Marie-Louise, et al.
(author)
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MODEL-BASED ITERATIVE RECONSTRUCTION ENABLES THE EVALUATION OF THIN-SLICE COMPUTED TOMOGRAPHY IMAGES WITHOUT DEGRADING IMAGE QUALITY OR INCREASING RADIATION DOSE.
- 2016
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In: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 169:1-4, s. 100-106
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Journal article (peer-reviewed)abstract
- Computed tomography (CT) is one of the most important modalities in a radiological department. This technique not only produces images that enable radiological reports with high diagnostic confidence, but it may also provide an elevated radiation dose to the patient. The radiation dose can be reduced by using advanced image reconstruction algorithms. This study was performed on a Brilliance iCT, equipped with iDose(4) iterative reconstruction and an iterative model-based reconstruction (IMR) method. The purpose was to investigate the effect of reduced slice thickness combined with an IMR method on image quality compared with standard slice thickness with iDose(4) reconstruction. The results of objective and subjective image quality evaluations showed that a thinner slice combined with IMR can improve the image quality and reduce partial volume artefacts compared with the standard slice thickness with iDose(4). In conclusion, IMR enables reduction of the slice thickness while maintaining or even improving image quality versus iDose(4).
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| 5. |
- Fransson, Veronica, et al.
(author)
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Detection of Perfusion Deficits in Multiphase Computed Tomography Angiography—A Stroke Imaging Technique Based on Iodine Mapping on Spectral Computed Tomography: Initial Findings
- 2021
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In: Journal of Computer Assisted Tomography. - 1532-3145. ; 45:4, s. 618-624
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Journal article (peer-reviewed)abstract
- Objective: The purpose of this study was to explore a novel method forbrain tissue differentiation using quantitative analysis of multiphase computedtomography (CT) angiography (MP-CTA) on spectral CT, to assesswhether it can distinguish underperfused fromnormal tissue, using CT perfusion(CTP) as reference.Methods: Noncontrast CT and MP-CTA images from 10 patients wereanalyzed in vascular regions through measurements of Hounsfield unit (HU)at 120 kV, HU at 40 keV, and iodine density. Regions were categorizedas normal or ischemic according to CTP. Hounsfield unit and iodinedensity were compared regarding ability to separate normal and ischemictissue, the difference in maximum time derivative of the right overleft hemisphere ratio.Results: Iodine density had the highest maximum time derivatives andgenerated the largest mean separation between normal and ischemic tissue.Conclusions: The method can be used to categorize tissue as normal orunderperfused. Using iodine quantification seems to give a more distinctdifferentiation of perfusion defects compared with conventional HU.
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| 6. |
- Fransson, Veronica, et al.
(author)
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Image quality of spectral brain computed tomography angiography using halved dose of iodine contrast medium
- 2023
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In: Neuroradiology. - 0028-3940. ; 65:9, s. 1333-1342
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Journal article (peer-reviewed)abstract
- Purpose: Reduction in iodinated contrast medium (CM) dose is highly motivated. Our aim was to evaluate if a 50% reduction of CM, while preserving image quality, is possible in brain CT angiography (CTA) using virtual monoenergetic images (VMI) on spectral CT. As a secondary aim, we evaluated if VMI can salvage examinations with suboptimal CM timing. Methods: Consecutive patients older than 18 years without intracranial stenosis/occlusion were included. Three imaging protocols were used: group 1, full CM dose; group 2, 50% CM dose suboptimal timing; and group 3, 50% CM dose optimized timing. Attenuation, noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were measured in the internal carotid artery, M2 segment of the middle cerebral artery, and white matter for conventional images (CI) and VMI (40–200 keV). Qualitative image quality for CI and VMI (50 and 60 keV) was rated by 4 experienced reviewers. Results: Qualitatively and quantitatively, VMI (40–60 keV) improved image quality within each group. Significantly higher attenuation and CNR was found for group 3 VMI 40–50 keV, with unchanged SNR, compared to group 1 CI. Group 3 VMI 50 keV also received significantly higher rating scores than group 1 CI. Group 2 VMI (40–50 keV) had significantly higher CNR compared to group 3 CI, but the subjective image quality was similar. Conclusion: VMI of 50 keV with 50% CM dose increases qualitative and quantitative image quality over CI with full CM dose. Using VMI reduces non-diagnostic examinations and may salvage CTA examinations deemed non-diagnostic due to suboptimal timing.
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| 7. |
- Gunnarsson, Mikael, et al.
(author)
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Principles behind Computed Tomography (CT)
- 2022. - 1
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In: Handbook of Nuclear Medicine and Molecular Imaging for Physicists : Instrumentation and Imaging Procedures - Instrumentation and Imaging Procedures. - 9781138593268 - 9780429489556 ; 1
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Book chapter (peer-reviewed)abstract
- The use of Computed tomography (CT) for anatomical information in a combination with the SPECT system has in many ways added substantial information to many nuclear medicine imaging procedures. The information from the CT system can provide information on the location of lesions and can be used for attenuation correction. Modern SPECT/CT and PET/CT today have CT scanners that provide diagnostic quality. This chapter provides the principles behind the X-ray imaging and in particular CT. It describes scanner configurations and components for a typical CT system and how data are acquired. Also, a short description of dual-energy systems that provide additional information is included. Iterative reconstruction of image, and the definition of the Hounsfield unit is discussed together with how different factors affect the image quality. A part of the chapter also discusses CT dosimetry and how the absorbed doses can be measured, quantified, and possibly be reduced. A section also discusses different types of artefacts in the images caused by, for example, metals, respiratory movements, and beam hardening.
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| 8. |
- Mellander, Helena, et al.
(author)
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Metal artifact reduction by virtual monoenergetic reconstructions from spectral brain CT
- 2023
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In: European Journal of Radiology Open. - : Elsevier BV. - 2352-0477. ; 10, s. 1-6
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Journal article (peer-reviewed)abstract
- PURPOSE: Conventional computed tomography (CT) images are severely affected by metal artifacts in patients with intracranial coils. Monoenergetic images have been suggested to reduce metal artifacts.The aim of this study was to assess metal artifacts in virtual monoenergetic images (VMIs) reconstructed from spectral brain CT.METHODS: Thirty-two consecutive patients with intracranial coils examined by spectral non contrast brain CT (NCCT) at our center between November 2017 and April 2019 were included. Attenuation and standard deviations were measured in regions of interest (ROIs) at predefined areas in artifact-free and artifact-affected areas. Measurements were performed in conventional polyenergetic images (CIs) and the corresponding data for VMIs were retrieved through spectral diagrams for the each ROI. Subjective analysis was performed by visual grading of CIs and specific VMIs by two neuroradiologists, independently.RESULTS: In artefact-affected image areas distal from the metal objects, the attenuation values decreased with higher energy level VMIs. The same effect was not seen for artefact-affected image areas close to the metal.Subjective rating of the artefact severity was significantly better in VMIs at 50 keV for one of the two reviewers compared to the CIs. Overall image quality and tissue differentiation scores were significantly higher for both reviewers in VMIs at 60 and 70 keV compared to CIs.CONCLUSION: Our quantitative and qualitative image analysis shown that there is a small significant reduction of intracranial coils artifacts severity by all monoenergetic reconstructions from 50 to 200 keV with preserved or increased overall subjective image quality compared to conventional images.
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| 9. |
- Mellander, Helena, et al.
(author)
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Virtual monoenergetic images by spectral detector computed tomography may improve image quality and diagnostic ability for ischemic lesions in acute ischemic stroke
- 2023
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In: Acta Radiologica. - : SAGE Publications. - 0284-1851 .- 1600-0455. ; 64:4, s. 1631-1640
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Journal article (peer-reviewed)abstract
- Background: Acute ischemic lesions are challenging to detect by conventional computed tomography (CT). Virtual monoenergetic images may improve detection rates by increased tissue contrast. Purpose: To compare the ability to detect ischemic lesions of virtual monoenergetic with conventional images in patients with acute stroke. Material and Methods: We included consecutive patients at our center that underwent brain CT in a spectral scanner for suspicion of acute stroke, onset <12 h, with or without (negative controls) a confirmed cortical ischemic lesion in the initial scan or a follow-up CT or magnetic resonance imaging. Attenuation was measured in predefined areas in ischemic gray (guided by follow-up exams), normal gray, and white matter in conventional images and retrieved in spectral diagrams for the same locations in monoenergetic series at 40–200 keV. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. Visual assessment of diagnostic measures was performed by independent review by two neuroradiologists blinded to reconstruction details. Results: In total, 29 patients were included (January 2018 to July 2019). SNR was higher in virtual monoenergetic compared to conventional images, significantly at 60–150 keV. CNR between ischemic gray and normal white matter was higher in monoenergetic images at 40–70 keV compared to conventional images. Virtual monoenergetic images received higher scores in overall image quality. The sensitivity for diagnosing acute ischemia was 93% and 97%, respectively, for the reviewers, compared to 55% of the original report based on conventional images. Conclusion: Virtual monoenergetic reconstructions of spectral CIs may improve image quality and diagnostic ability in stroke assessment.
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