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| 2. |
- Abul-Kasim, Kasim, et al.
(author)
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Optimization of Radiation Exposure and Image Quality of the Cone-beam O-arm Intraoperative Imaging System in Spinal Surgery.
- 2012
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In: Journal of Spinal Disorders and Techniques. - 1539-2465. ; 25:1, s. 52-58
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Journal article (peer-reviewed)abstract
- STUDY DESIGN: Retrospective study. OBJECTIVES: To optimize the radiation doses and image quality for the cone-beam O-arm surgical imaging system in spinal surgery. SUMMARY OF BACKGROUND: Neurovascular compromise has been reported after screw misplacement during thoracic pedicle screw insertion. The use of O-arm with or without navigation system during spinal surgery has been shown to lower the rate of screw misplacement. The main drawback of such imaging surgical systems is the high radiation exposure. METHODS: Chest phantom and cadaveric pig spine were examined on the O-arm with different scan settings: 2 were recommended by the O-arm manufacturer (120 kV/320 mAs, and 120 kV/128 mAs), and 3 low-dose settings (80 kV/80 mAs, 80 kV/40 mAs, and 60 kV/40 mAs). The radiation doses were estimated by Monte Carlo calculations. Objective evaluation of image quality included interobserver agreement in the measurement of pedicular width in chest phantom and assessment of screw placement in cadaveric pig spine. RESULTS: The effective dose/cm for 120 kV/320 mAs scan was 13, 26, and 69 times higher than those delivered with 80 kV/80 mAs, 80 kV/40 mAs, and 60 kV/40 mAs scans, respectively. Images with 60 kV/40 mAs were unreliable. Images with 80 kV/80 mAs were considered reliable with good interobserver agreement when measuring the pedicular width (random error 0.38 mm and intraclass correlation coefficient 0.979) and almost perfect agreement when evaluating the screw placement (κ value 0.86). CONCLUSIONS: The radiation doses of the O-arm system can be reduced 5 to 13 times without negative impact on image quality with regard to information required for spinal surgery.
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| 3. |
- Aho Fält, Tobias, et al.
(author)
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Simulated Dose Reduction for Abdominal CT With Filtered Back Projection Technique: Effect on Liver Lesion Detection and Characterization
- 2019
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In: American Journal of Roentgenology: diagnostic imaging and related sciences. - 0361-803X. ; 212:1, s. 84-93
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Journal article (peer-reviewed)abstract
- OBJECTIVE. Previous studies have shown the possibility to reduce radiation dose in abdominal CT by 25–50% without negatively affecting detection of liver lesions. How radiation dose reduction affects characterization of liver metastases is not as well known. The objective of this study was to investigate how different levels of simulated dose reduction affect the detection and characterization of liver lesions, primarily hypovascular metastases. A secondary objective was to analyze the relationship between the lesion size and contrast-to-noise ratio (CNR) and the detection rate.MATERIALS AND METHODS. Thirty-nine patients (19 with metastases and 20 without) were retrospectively selected. The following radiation dose levels (DLs) were simulated: 100% (reference level), 75%, 50%, and 25%. Five readers were asked to mark liver lesions and rate the probability of malignancy on a 5-grade Likert scale. Noninferiority analysis using the jackknife free-response ROC (JAFROC) method was performed as well as direct comparison of detection rates and grades.RESULTS. JAFROC analysis showed noninferior detection and characterization of metastases at DL75 as compared with DL100. However, the number of benign lesions and false-positive localizations rated as “suspected malignancy” was significantly higher at DL75.CONCLUSION. Radiation dose can be reduced by 25% without negatively affecting diagnosis of hypovascular liver metastases. Characterization of benign lesions, however, is impaired at DL75, which may lead to unnecessary follow-up examinations. Finally, increased image noise seems to affect the detection of small lesions to a degree that cannot be explained solely by the reduction in CNR.
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| 6. |
- 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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| 7. |
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| 8. |
- 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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| 9. |
- 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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| 10. |
- Aurumskjöld, Marie-Louise, et al.
(author)
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Model based iterative reconstruction IMR gives possibility to evaluate thinner slice thicknesses than conventional iterative reconstruction iDose(4) - a phantom study
- 2015
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In: Medical Imaging 2015: Physics of Medical Imaging. - : SPIE. - 1996-756X .- 0277-786X. ; 9412, s. 94124-94124
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Conference paper (peer-reviewed)abstract
- Computed tomography (CT) is one of the most important modalities in a radiological department, which produces images with high diagnostic confidence, but in some cases contributes to a high radiation dose to the patient. The radiation dose can be reduced by the use of advanced image reconstruction algorithms. This study was done on a Philips Brilliance iCT with iterative reconstruction iDose(4) and model-based iterative reconstruction IMR. The purpose was to investigate the effect on the image quality with thin slice images reconstructed with IMR, compared to standard slice thickness reconstructed with iDose(4). Objective measurements of noise and contrast-to-noise ratio were performed using an image quality phantom, an anthropomorphic phantom and clinical cases. Subjective evaluations of low-contrast resolution were performed by observers using an image quality phantom. IMR gives strong noise reduction and enhanced low-contrast and thereby enable selection of thinner slice thickness. Objective evaluation of image noise shows that thin slices reconstructed with IMR provides lower noise than thicker slice images reconstructed with iDose(4). With IMR the slice thickness is of less importance for the noise. With thinner slices the partial volume artefacts becomes less pronounced. In conclusion, we have shown that IMR enables reduction of the slice thickness and at the same time maintain or even reduce the noise level compared to iDose(4) reconstruction with standard slice thickness. This will subsequently result in an improvement of image quality for images reconstructed with IMR.
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| 11. |
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| 12. |
- Bebbington, Natalie A., et al.
(author)
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A Nordic survey of CT doses in hybrid PET/CT and SPECT/CT examinations
- 2019
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In: EJNMMI Physics. - : Springer Science and Business Media LLC. - 2197-7364. ; 6:1
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Journal article (peer-reviewed)abstract
- Background: Computed tomography (CT) scans are routinely performed in positron emission tomography (PET) and single photon emission computed tomography (SPECT) examinations globally, yet few surveys have been conducted to gather national diagnostic reference level (NDRL) data for CT radiation doses in positron emission tomography/computed tomography (PET/CT) and single photon emission computed tomography/computed tomography (SPECT/CT). In this first Nordic-wide study of CT doses in hybrid imaging, Nordic NDRL CT doses are suggested for PET/CT and SPECT/CT examinations specific to the clinical purpose of CT, and the scope for optimisation is evaluated. Data on hybrid imaging CT exposures and clinical purpose of CT were gathered for 5 PET/CT and 8 SPECT/CT examinations via designed booklet. For each included dataset for a given facility and scanner type, the computed tomography dose index by volume (CTDIvol) and dose length product (DLP) was interpolated for a 75-kg person (referred to as CTDIvol,75kg and DLP75kg). Suggested NDRL (75th percentile) and achievable doses (50th percentile) were determined for CTDIvol,75kg and DLP75kg according to clinical purpose of CT. Differences in maximum and minimum doses (derived for a 75-kg patient) between facilities were also calculated for each examination and clinical purpose. Results: Data were processed from 83 scanners from 43 facilities. Data were sufficient to suggest Nordic NDRL CT doses for the following: PET/CT oncology (localisation/characterisation, 15 systems); infection/inflammation (localisation/characterisation, 13 systems); brain (attenuation correction (AC) only, 11 systems); cardiac PET/CT and SPECT/CT (AC only, 30 systems); SPECT/CT lung (localisation/characterisation, 12 systems); bone (localisation/characterisation, 30 systems); and parathyroid (localisation/characterisation, 13 systems). Great variations in dose were seen for all aforementioned examinations. Greatest differences in DLP75kg for each examination, specific to clinical purpose, were as follows: SPECT/CT lung AC only (27.4); PET/CT and SPECT/CT cardiac AC only (19.6); infection/inflammation AC only (18.1); PET/CT brain localisation/characterisation (16.8); SPECT/CT bone localisation/characterisation (10.0); PET/CT oncology AC only (9.0); and SPECT/CT parathyroid localisation/characterisation (7.8). Conclusions: Suggested Nordic NDRL CT doses are presented according to clinical purpose of CT for PET/CT oncology, infection/inflammation, brain, PET/CT and SPECT/CT cardiac, and SPECT/CT lung, bone, and parathyroid. The large variation in doses suggests great scope for optimisation in all 8 examinations.
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| 13. |
- Begano, Dino, et al.
(author)
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TO USE OR NOT USE PATIENT SHIELDING ON PREGNANT WOMEN UNDERGOING CT PULMONARY ANGIOGRAPHY : A PHANTOM STUDY
- 2020
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In: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 189:4, s. 458-465
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Journal article (peer-reviewed)abstract
- Pregnancy increases the risk of pulmonary embolism. Computed tomography pulmonary angiography (CTPA) is used for diagnosis. CT generates ionising radiation, and thus, abdominal shielding may be used. This phantom study investigated the effects of patient shielding and scan length reduction on the fetal and maternal ionising radiation dose from CTPA. The absorbed dose to the fetus was measured using thermoluminescent dosemeters. Estimated effective doses to the pregnant patient were based on the dose-length products. Shielding increased both the effective dose to the patient by 47% and the mean absorbed dose to the fetus (0.10 vs. 0.12 mGy; p < 0.001) compared with unshielded standard CTPA, as it affected the automatic exposure control. Shielded short CTPA marginally lowered only the mean fetal absorbed dose (0.03 vs. 0.02 mGy; p = 0.018). Shortening the scan reduced the fetal absorbed dose most effectively by 70% (0.10 vs. 0.03 mGy; p = 0.006), compared with the standard unshielded scan. Shielding modestly reduces fetal radiation dose but may compromise automatic exposure control, possibly increasing the maternal and fetal radiation dose. Shortening the scan is beneficial, assuming anatomical coverage is secured.
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| 14. |
- Box, Marcus
(author)
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New Venture, Survival, Growth : Continuance, Termination and Growth of Business Firms and Business Populations in Sweden During the 20th Century
- 2005
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Doctoral thesis (other academic/artistic)abstract
- This dissertation focuses on the formation, growth and discontinuance of business populations and firms in Sweden during the 20th century. It addresses some key issues in the domain of economic and social sciences, and in particular entrepreneurship and small business research: if and when firms grow, stagnate and decline, as well as how long firms survive and when they are likely to disband. Previous research has primarily analyzed these questions from a short time frame. Further, an individual or firm-oriented focus is commonly assumed. In that, alternative or complementary explanations to the growth and survival of firms may be disregarded. In contrast to much previous research, this dissertation assumes a micro-to-macro, longitudinal and demographic population approach. The period of investigation is over one hundred years. In addressing the growth and survival of firms, it takes into account the impact of firm-specific structural factors (such as firm age and size), generation (cohort) effects, as well as the influence of macroeconomic, exogenous factors. Further, the relationship between managerial/ownership succession and firm performance is also addressed. Both cross-sectional and longitudinal databases are employed in the dissertation. Its main empirical material consists of unique longitudinal data on new business firms, traced at the firm level from their birth to their termination. More specifically, seven birth cohorts – generations – of approximately 2,200 firms founded in 1899, 1909, 1912, 1921, 1930, 1942 and 1950 are included. The main findings show that ownership/management succession in firms had a quite weak correlation with firm performance and survival. At least at an aggregate level, and with some exceptions, it is debatable if the loss and replacement of owner-managers in small and in larger firms have any observable effects on firm performance. Furthermore, macroeconomic phenomena influence the conditions of individual firms as well as populations/aggregates of businesses. Both the growth and termination of firms and firm populations are found to be related to real economic (environmental) conditions; e.g. favorable macroeconomic conditions implied that firms grew in size. At the same time, under certain circumstances, the influence of structural variables (firm age and size) – as suggested in much previous research – is found to be of importance. As concerns firm growth, as well as firm termination, the economic environment and structural factors interact. These findings challenges individual or firm-level research that mainly focus on personal traits and behaviors in explaining firm success and failure. Other previous assumptions are also challenged when taking a longer time perspective into consideration. For decades, organization and business research have acknowledged a liability of newness and of size for business firms. While this might be true under some conditions, this liability of newness is falsified in the study: the termination behavior of some firm generations did not correspond with these assumptions. Thus, the perspectives and methodology applied in the dissertation complement earlier approaches in entrepreneurship and small business research.
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| 15. |
- Carlsson, Marcus, et al.
(author)
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A note on variable susceptibility, the herd-immunity threshold and modeling of infectious diseases
- 2023
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In: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 18
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Journal article (peer-reviewed)abstract
- The unfolding of the COVID-19 pandemic has been very difficult to predict using mathematical models for infectious diseases. While it has been demonstrated that variations in susceptibility have a damping effect on key quantities such as the incidence peak, the herd-immunity threshold and the final size of the pandemic, this complex phenomenon is almost impossible to measure or quantify, and it remains unclear how to incorporate it for modeling and prediction. In this work we show that, from a modeling perspective, variability in susceptibility on an individual level is equivalent with a fraction θ of the population having an “artificial” sterilizing immunity. We also derive novel formulas for the herd-immunity threshold and the final size of the pandemic, and show that these values are substantially lower than predicted by the classical formulas, in the presence of variable susceptibility. In the particular case of SARS-CoV-2, there is by now undoubtedly variable susceptibility due to waning immunity from both vaccines and previous infections, and our findings may be used to greatly simplify models. If such variations were also present prior to the first wave, as indicated by a number of studies, these findings can help explain why the magnitude of the initial waves of SARS-CoV-2 was relatively low, compared to what one may have expected based on standard models.
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| 16. |
- Carlsson, Marcus, et al.
(author)
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COVID-19 Modeling Outcome versus Reality in Sweden
- 2022
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In: Viruses. - : MDPI AG. - 1999-4915. ; 14:8
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Journal article (peer-reviewed)abstract
- It has been very difficult to predict the development of the COVID-19 pandemic based on mathematical models for the spread of infectious diseases, and due to major non-pharmacological interventions (NPIs), it is still unclear to what extent the models would have fit reality in a “do nothing” scenario. To shed light on this question, the case of Sweden during the time frame from autumn 2020 to spring 2021 is particularly interesting, since the NPIs were relatively minor and only marginally updated. We found that state of the art models are significantly overestimating the spread, unless we assume that social interactions significantly decrease continuously throughout the time frame, in a way that does not correlate well with Google-mobility data nor updates to the NPIs or public holidays. This leads to the question of whether modern SEIR-type mathematical models are unsuitable for modeling the spread of SARS-CoV-2 in the human population, or whether some particular feature of SARS-CoV-2 dampened the spread. We show that, by assuming a certain level of pre-immunity to SARS-CoV-2, we obtain an almost perfect data-fit, and discuss what factors could cause pre-immunity in the mathematical models. In this scenario, a form of herd-immunity under the given restrictions was reached twice (first against the Wuhan-strain and then against the alpha-strain), and the ultimate decline in cases was due to depletion of susceptibles rather than the vaccination campaign.
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| 17. |
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| 18. |
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| 19. |
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| 22. |
- Giussani, Augusto, et al.
(author)
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A Compartmental Model for Biokinetics and Dosimetry of 18F-Choline in Prostate Cancer Patients
- 2012
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In: Journal of Nuclear Medicine. - : Society of Nuclear Medicine. - 0161-5505 .- 2159-662X. ; 53:6, s. 985-993
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Journal article (peer-reviewed)abstract
- PET with F-18-choline (F-18-FCH) is used in the diagnosis of prostate cancer and its recurrences. In this work, biodistribution data from a recent study conducted at Skane University Hospital Malmo were used for the development of a biokinetic and dosimetric model. Methods: The biodistribution of F-18-FCH was followed for 10 patients using PET up to 4 h after administration. Activity concentrations in blood and urine samples were also determined. A compartmental model structure was developed, and values of the model parameters were obtained for each single patient and for a reference patient using a population kinetic approach. Radiation doses to the organs were determined using computational (voxel) phantoms for the determination of the S factors. Results: The model structure consists of a central exchange compartment (blood), 2 compartments each for the liver and kidneys, 1 for spleen, 1 for urinary bladder, and 1 generic compartment accounting for the remaining material. The model can successfully describe the individual patients' data. The parameters showing the greatest interindividual variations are the blood volume (the clearance process is rapid, and early blood data are not available for several patients) and the transfer out from liver (the physical half-life of F-18 is too short to follow this long-term process with the necessary accuracy). The organs receiving the highest doses are the kidneys (reference patient, 0.079 mGy/MBq; individual values, 0.033-0.105 mGy/MBq) and the liver (reference patient, 0.062 mGy/MBq; individual values, 0.036-0.082 mGy/MBq). The dose to the urinary bladder wall of the reference patient varies between 0.017 and 0.030 mGy/MBq, depending on the assumptions on bladder voiding. Conclusion: The model gives a satisfactory description of the biodistribution of F-18-FCH and realistic estimates of the radiation dose received by the patients.
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| 23. |
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| 25. |
- Haller, Paul M., et al.
(author)
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Biomarker-based prediction of fatal and non-fatal cardiovascular outcomes in individuals with diabetes mellitus
- 2023
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In: European Journal of Preventive Cardiology. - 2047-4873 .- 2047-4881. ; 30:12, s. 1218-1226
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Journal article (peer-reviewed)abstract
- AIMS: The role of biomarkers in predicting cardiovascular outcomes in high-risk individuals is not well established. We aimed to investigate benefits of adding biomarkers to cardiovascular risk assessment in individuals with and without diabetes. 'METHODS AND RESULTS: We used individual-level data of 95 292 individuals of the European population harmonized in the Biomarker for Cardiovascular Risk Assessment across Europe consortium and investigated the prognostic ability of high-sensitivity cardiac troponin I (hs-cTnI), N-terminal prohormone of brain natriuretic peptide (NT-proBNP), and high-sensitivity C-reactive protein (hs-CRP). Cox-regression models were used to determine adjusted hazard ratios of diabetes and log-transformed biomarkers for fatal and non-fatal cardiovascular events. Models were compared using the likelihood ratio test. Stratification by specific biomarker cut-offs was performed for crude time-to-event analysis using Kaplan-Meier plots. Overall, 6090 (6.4%) individuals had diabetes at baseline, median follow-up was 9.9 years. Adjusting for classical risk factors and biomarkers, diabetes [HR 2.11 (95% CI 1.92, 2.32)], and all biomarkers (HR per interquartile range hs-cTnI 1.08 [95% CI 1.04, 1.12]; NT-proBNP 1.44 [95% CI 1.37, 1.53]; hs-CRP 1.27 [95% CI 1.21, 1.33]) were independently associated with cardiovascular events. Specific cut-offs for each biomarker identified a high-risk group of individuals with diabetes losing a median of 15.5 years of life compared to diabetics without elevated biomarkers. Addition of biomarkers to the Cox-model significantly improved the prediction of outcomes (likelihood ratio test for nested models P < 0.001), accompanied by an increase in the c-index (increase to 0.81).CONCLUSION: Biomarkers improve cardiovascular risk prediction in individuals with and without diabetes and facilitate the identification of individuals with diabetes at highest risk for cardiovascular events.
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| 26. |
- Herrnsdorf, Lars, et al.
(author)
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A method to characterize the radiation output from a cone beam O-arm using a device for dose and dose profile scanning measurement
- 2013
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In: Medical Imaging 2013: Physics of Medical Imaging. - : SPIE. - 0277-786X .- 1996-756X. - 9780819494429 ; 8668, s. 86682-86682
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Conference paper (peer-reviewed)abstract
- The O-arm system is a mobile intraoperative imaging system that is comprised of fluoroscopy and cone beam CT. The configuration of the O-arm system with absence of patient table and a broad beam width (165 mm in isocenter) brings new practical and physical requirements on how to perform dose measurements. The purpose of this study was to describe a method that overcomes this and makes it possible to characterize the radiation output from the O-arm system. A holder with a clamp and a flexible ball joint that can orientate the radiation detector support and the Mover that can be adjusted to hold the dose detector in a horizontal position was used. Evaluation of the dose response for three different dose detectors of different active length (0.3, 23.1 and 100 mm) was made for three different beam qualities. Furthermore the dose profile free in air to control the possible heel effect and width of the x-ray field during rotation was measured and the dose rate waveform was analyzed. The FWHM of the dose profile was 162 mm The dose response of the three detectors is reported. The average dose response was lower for the detector with longer active length due to the influence of the dose profile shape. From dynamic measurement total exposure time, pulse width, and the number of pulses were verified. In conclusion, an external horizontal hanging holder with mover option helps to assist to make dose measurement easier and enables characterize the radiation output from the O-arm system.
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| 27. |
- Holmquist, Fredrik, et al.
(author)
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80-kV(p) hepatic CT to reduce contrast medium dose in azotemic patients: a feasibility study
- 2020
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In: Acta Radiologica. - : SAGE Publications. - 0284-1851 .- 1600-0455. ; 61:4, s. 441-449
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Journal article (peer-reviewed)abstract
- Background Low peak kilovoltage (kV(p)) computed tomography (CT) may be used to reduce contrast medium doses in patients at risk of contrast medium-induced acute kidney injury if image noise can be controlled by increasing X-ray tube loading (mAs). Purpose To evaluate objective and subjective image quality in 80-kV(p) CT with reduced contrast medium dose and compensated mAs for unchanged image noise in patients with estimated glomerular filtration rate Material and Methods 80-kV(p) CT with 300 mg I/kg in 40 patients (body mass index 18-32 kg/m(2), glomerular filtration rate <45 mL/min) and 120-kV(p) CT with 500 mg I/kg in 40 patients (body mass index = 17-30 kg/m(2), glomerular filtration rate >= 45 mL/min) was compared on mean hepatic attenuation, image noise, contrast medium enhancement, signal-to-noise ratio, contrast-to-noise ratio, effective radiation dose, and subjective image quality. Results There were no significant differences regarding median hepatic post-contrast attenuation, image noise, contrast medium enhancement, signal-to-noise ratio, contrast-to-noise ratio, or effective dose between the 80-kV(p) and 120-kV(p) cohorts: 114/110 HU; 14/14 HU; 57/53 HU; 8.0/7.4; 3.8/3.5; and 5.3/5.9 mSv, respectively. However, subjective image visual grading showed statistically significantly inferior scores for 80 kV(p) for six of eight items. After exclusion of seven inferior examinations not caused by the chosen kV(p) technique, only three items showed inferior scores for 80 kV(p). Only 5% of gradings regarding overall image quality were Conclusion Despite lower subjective image quality, objective data indicate that 80-kV(p) CT with reduced contrast medium doses and compensated mAs may have the potential to provide satisfactory diagnostic quality in patients with body mass index <30 kg/m(2), which could benefit patients at risk of contrast medium-induced acute kidney injury.
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| 28. |
- Holmquist, Fredrik, et al.
(author)
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Can iterative reconstruction algorithms replace tube loading compensation in low kVp hepatic CT? Subjective versus objective image quality
- 2020
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In: Acta Radiologica Open. - : SAGE Publications. - 2058-4601 .- 2058-4601. ; 9:3
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Journal article (peer-reviewed)abstract
- Background: Hepatic computed tomography (CT) with decreased peak kilovoltage (kVp) may be used to reduce contrast medium doses in patients at risk of contrast-induced acute kidney injury (CI-AKI); however, it increases image noise. To preserve image quality, noise has been controlled by X-ray tube loading (mAs) compensation (TLC), i.e. increased mAs. Another option to control image noise would be to use iterative reconstructions (IR) algorithms without TLC (No-TLC). It is unclear whether this may preserve image quality or only reduce image noise. Purpose: To evaluate image quality of 80 kVp hepatic CT with TLC and filtered back projection (FBP) compared with 80 kVp with No-TLC and IR algorithms (SAFIRE 3 and 5) in patients with eGFR <45 mL/min. Material and Methods: Forty patients (BMI 18-32 kg/m(2)) were examined with both protocols following injection of 300 mg I/kg. Hepatic attenuation, image noise, enhancement, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and subjective image quality were evaluated for each patient. Results: Comparing TLC/FBP with No-TLC/IR-S5, there were no significant differences regarding hepatic attenuation, image noise, enhancement, SNR and CNR: 114 vs. 115 HU, 14 vs. 14 HU, 55 vs. 57 HU, 8.0 vs. 8.4, and 3.8 vs. 4.0 in median, respectively. No-TLC/IR-S3 resulted in higher image noise and lower SNR and CNR than TLC/FBP. Subjective image quality scoring with visual grading showed statistically significantly inferior scores for IR-S5 images. Conclusion: CT of 80 kVp to reduce contrast medium dose in patients at risk of CI-AKI combined with IR algorithms with unchanged tube loading to control image noise does not provide sufficient diagnostic quality.
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| 29. |
- Johansson, Kristina, et al.
(author)
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Factor XII as a Risk Marker for Hemorrhagic Stroke : A Prospective Cohort Study
- 2017
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In: Cerebrovascular diseases extra. - : S. Karger. - 1664-5456. ; 7:1, s. 84-94
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Journal article (peer-reviewed)abstract
- BACKGROUND: Coagulation factor XII (FXII) is involved in pathological thrombus formation and is a suggested target of anticoagulants. It is unclear whether FXII levels are correlated with cardiovascular risk factors and whether they are associated with myocardial infarction or ischemic or hemorrhagic stroke. The aim of this study was to investigate the correlation between FXII and cardiovascular risk factors in the general population. We also aimed to study the associations between FXII levels and future myocardial infarction and ischemic and hemorrhagic stroke.METHODS: This prospective cohort study measured FXII levels in 1,852 randomly selected participants in a health survey performed in northern Sweden in 1994. Participants were followed until myocardial infarction, stroke, death, or until December 31, 2011.RESULTS: During the median follow-up of 17.9 years, 165 individuals were diagnosed with myocardial infarction, 108 with ischemic stroke, and 30 with hemorrhagic stroke. There were weak correlations between FXII and body mass index, cholesterol, and hypertension. There was no association between FXII and myocardial infarction or ischemic stroke, neither in univariable Cox regression analysis nor after adjustment for age, sex, smoking, body mass index, cholesterol, hypertension, and diabetes. In univariable Cox regression analysis, the hazard ratio for the association between FXII levels and hemorrhagic stroke was 1.42 per SD (95% confidence interval: 0.99-2.05). In the multivariable model, higher levels of FXII were associated with increased risk of hemorrhagic stroke (hazard ratio 1.51 per SD; 95% confidence interval: 1.03-2.21).CONCLUSION: We found an independent association between FXII levels and the risk of hemorrhagic stroke, but not between FXII levels and ischemic stroke or myocardial infarction.
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| 30. |
- Johansson, Kristina, et al.
(author)
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Phosphatidylethanol Levels, As a Marker of Alcohol Consumption, Are Associated With Risk of Intracerebral Hemorrhage
- 2020
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In: Stroke. - : Lippincott Williams & Wilkins. - 0039-2499 .- 1524-4628. ; 51:7, s. 2148-2152
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Journal article (peer-reviewed)abstract
- Background and Purpose: Previous observational studies have shown a moderately increased risk of intracerebral hemorrhage (ICH) with high self-reported alcohol consumption. However, self-reported data tend to underestimate alcohol consumption. Phosphatidylethanol is a specific biomarker reflecting alcohol intake during the last month and correlates with the amount of alcohol consumed. The present study aimed to investigate the association between phosphatidylethanol levels and the risk of future ICH.Methods: This population-based nested case-referent study was conducted within the Northern Sweden Health and Disease Cohort. At baseline, all participants underwent a health examination, including a questionnaire with questions about alcohol consumption. A blood sample was collected and stored at −80°C, and phosphatidylethanol 16:0/18:1 levels were measured in packed erythrocytes. Cases (n=97) were diagnosed with a first-ever ICH between 1985 and 2007. Two referents (n=180) were matched to each case.Results: The mean age at baseline was 55 years, 39% of participants were women, and the mean time from blood sampling to ICH was 7.3 years. Only phosphatidylethanol and hypertension remained independently associated with ICH in a multivariable model. Participants with phosphatidylethanol >0.30 μmol/L had an increased risk of ICH compared with those with phosphatidylethanol <0.01 μmol/L (odds ratio, 4.64 [95% CI, 1.49–14.40]).Conclusions: High blood concentrations of phosphatidylethanol were associated with an increased risk of future ICH. This association was independent of hypertension and other risk factors for ICH. Our findings suggest that phosphatidylethanol, as a marker of alcohol consumption, may be used as a risk marker of future ICH.
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| 31. |
- Kilpeläinen, Tuomas O, et al.
(author)
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Genome-wide meta-analysis uncovers novel loci influencing circulating leptin levels
- 2016
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 7
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Journal article (peer-reviewed)abstract
- Leptin is an adipocyte-secreted hormone, the circulating levels of which correlate closely with overall adiposity. Although rare mutations in the leptin (LEP) gene are well known to cause leptin deficiency and severe obesity, no common loci regulating circulating leptin levels have been uncovered. Therefore, we performed a genome-wide association study (GWAS) of circulating leptin levels from 32,161 individuals and followed up loci reaching P<10(-6) in 19,979 additional individuals. We identify five loci robustly associated (P<5 × 10(-8)) with leptin levels in/near LEP, SLC32A1, GCKR, CCNL1 and FTO. Although the association of the FTO obesity locus with leptin levels is abolished by adjustment for BMI, associations of the four other loci are independent of adiposity. The GCKR locus was found associated with multiple metabolic traits in previous GWAS and the CCNL1 locus with birth weight. Knockdown experiments in mouse adipose tissue explants show convincing evidence for adipogenin, a regulator of adipocyte differentiation, as the novel causal gene in the SLC32A1 locus influencing leptin levels. Our findings provide novel insights into the regulation of leptin production by adipose tissue and open new avenues for examining the influence of variation in leptin levels on adiposity and metabolic health.
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| 32. |
- King, Carina, et al.
(author)
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COVID-19—a very visible pandemic
- 2020
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In: The Lancet. - : Elsevier. - 0140-6736 .- 1474-547X. ; 396:10248, s. 15-15
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Journal article (peer-reviewed)
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| 33. |
- Krmar, R T, et al.
(author)
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Acute renal failure in dense deposit disease: complete recovery after combination therapy with immunosuppressant and plasma exchange.
- 2011
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In: Clinical Nephrology. - 0301-0430. ; 75:S1, s. 4-10
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Journal article (peer-reviewed)abstract
- We describe the clinical course of a female adolescent who was followed because of isolated microhematuria and hypocomplementemia before admission to hospital with a sudden onset of acute renal failure. At presentation, she exhibited complement consumption through the complement alternative pathway (AP) while other serologic tests were negative. Renal biopsy revealed dense deposit disease (DDD) with a crescentic pattern. Intravenous methylprednisolone, followed by plasma exchange (PE), and intravenous cyclophosphamide pulses were started shortly after admission. C3NeF and anti-factor H antibody tests were negative. Serum factor H and I levels were normal as well as factor H activity. Screening for mutation in the factor H gene revealed the H402 allele variant. Clinical remission, defined as normalization in renal function and in the activity levels of the complement AP, was noted at one month post-presentation and throughout the follow-up. A repeat renal biopsy showed the disappearance of crescent formation, whereas electron microscopy revealed no regression in dense transformation of the lamina densa. In summary, our patient was successfully treated with immunosuppressant and PE. The absence of known factors associated with DDD suggests that, in this particular case, other regulatory mechanisms of complement AP might have been involved in the disease process.
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| 34. |
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| 35. |
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| 36. |
- Leander, Peter, et al.
(author)
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Post-processing image filtration enabling dose reduction in standard abdominal CT
- 2010
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In: RADIATION PROTECTION DOSIMETRY. - : Oxford University Press. - 0144-8420 .- 1742-3406. ; 139:1-3, s. 180-185
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Journal article (peer-reviewed)abstract
- The collective effective radiation dose to the population is increasing due to a higher use of computerised tomography. SharpView AB, Linkoping, Sweden, has developed an adaptive non-linear post-processing image filtration that may enable the use of lower radiation doses. The present study assessed if a lower dose with image filtration had the same image quality as a higher dose without the filter applied. All imaging was performed on a Siemens Somatom Sensation 16 CT. The parameters used were 120 kV and 200 mAs (40 patients) and 130 mAs without and with image filtering (40 patients), respectively. All studies were quantitatively evaluated for noise and image quality was assessed by visual grading characteristics (VGC) analysis. After image filtration, the noise in the processed images was lowered and the image quality was improved as shown by the VGC analysis. However, images using the higher dose were still ranked as the best in five out of eight criteria as shown by the VGC analysis. Image filtration enhances CT images significantly and further studies will show if 130 mAs with image filtration may be sufficient for clinically general abdominal CT.
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| 37. |
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| 38. |
- Lehti, Leena, et al.
(author)
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Comparing Arterial- and Venous-Phase Acquisition for Optimization of Virtual Noncontrast Images From Dual-Energy Computed Tomography Angiography
- 2019
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In: Journal of Computer Assisted Tomography. - 1532-3145. ; 43:5, s. 770-774
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Journal article (peer-reviewed)abstract
- BACKGROUND: Follow-up with computed tomographic angiography is recommended after endovascular aneurysm repair, exposing patients to significant levels of radiation and iodine contrast medium. Dual-energy computed tomography allows virtual noncontrast (VNC) images to be reconstructed from contrast-enhanced images using a software algorithm. If the VNC images are a good-enough approximation of true noncontrast (TNC) images, a reduction in radiation dose can be ensured through omitting a TNC scan. PURPOSE: To compare image quality of VNC images reconstructed from arterial phase and venous phase dual-energy computed tomographic angiography to TNC images and to assess which one is more suitable to replace TNC images. METHODS: Sixty-three consecutive patients were examined using a dual-energy computed tomography as elective follow-up after endovascular aneurysm repair. The examination protocol included 1 unenhanced and 2 contrast-enhanced scans (80 kV/Sn140 kV) of the aorta. Virtual noncontrast data sets were reconstructed from the arterial (A-VNC) and venous (V-VNC) phase scans, respectively. Mean attenuation and image noise were measured for TNC, A-VNC, and V-VNC images within regions of interest at 2 levels in the aorta, the liver, retroperitoneal fat, and psoas muscle. Subjective image quality was assessed on a 4-point scale by 2 blinded readers. RESULTS: The differences between A-VNC and TNC, and between A-VNC and V-VNC, were substantial aorta at the level of diaphragm and aorta at the level of renal arteries. The difference between V-VNC and TNC was, on the other hand, very small and not statistically significant for the renal artery aorta. For liver, fat, and muscle tissue, there were significant differences between both A-VNC and V-VNC compared with TNC, but findings were similar between A-VNC and V-VNC. CONCLUSIONS: Virtual noncontrast images based on venous-phase scans appear to be a more accurate representation of TNC scans than VNC images based on arterial-phase scans.
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| 39. |
- Lehti, Leena, et al.
(author)
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Iterative metal artifact reduction in aortic CTA after Onyx®-embolization
- 2020
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In: European Journal of Radiology Open. - : Elsevier BV. - 2352-0477. ; 7
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Journal article (peer-reviewed)abstract
- Purpose: Onyx® embolization causes severe artifacts on subsequent CT-examinations, thereby seriously limiting the diagnostic quality. The purpose of this work was to compare the diagnostic quality of the tailored metal artifact reducing algorithms iMAR to standard reconstructions of CTA in patients treated with Onyx® embolization. Method: Twelve consecutive patients examined with Dual Energy CTA after Onyx® embolization were included. One standard image dataset without iMAR, and eight image datasets with different iMAR algorithms were reconstructed. Mean attenuation and noise were measured in the aorta or iliac arteries close to the Onyx® glue-cast and compared to the reference level in the diaphragmatic aorta. Mean attenuation and noise were also measured in the psoas muscle close to the Onyx®-glue and compared to the reference level in the psoas muscle at the level of the diaphragm. Subjective image quality and severity of artifacts was assessed by two experienced interventional radiologists blinded to reconstruction details. Results: All iMAR reconstructions had less distortion of the attenuation than the standard reconstructions and were also rated significantly better than the standard reconstructions by both interventional radiologists. Conclusion: The iMAR algorithms can significantly reduce metal artifacts and improve the diagnostic quality in CTA in patients treated with Onyx® embolization, in many cases restoring non-diagnostic examinations to acceptable diagnostic quality.
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| 40. |
- Lehti, Leena, et al.
(author)
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Reliability of virtual non-contrast computed tomography angiography: comparing it with the real deal
- 2018
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In: Acta Radiologica Open. - : SAGE Publications. - 2058-4601. ; 7, s. 1-6
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Journal article (peer-reviewed)abstract
- Background:Computed tomographic angiography (CTA) may require a non-contrast enhanced dataset for the diagnostic workup. By using dual-energy acquisition, it is possible to obtain a virtual non-contrast-enhanced (VNC) dataset, thereby possibly eliminating the non-contrast acquisition and reducing the radiation dose.Purpose:To compare image quality of VNC images reconstructed from arterial phase dual-energy CTA to true non-contrast (TNC) images, and to assess whether VNC images were of sufficient quality to replace TNC images.Material and methods:Thirty consecutive patients with suspected abdominal aortic aneurysm, aortic dissection, or subacute control after EVAR/TEVAR were examined with dual-energy CT (DECT). The examination protocol included a single-energy TNC, DECT arterial phase (80 kV/Sn140 kV), and single-energy in venous phase of the aorta. A VNC dataset was obtained from the DE acquisition from arterial phase scans. Mean attenuation and image noise were measured within regions of interest at three levels in the aorta in TNC and VNC images. Comparison of the TNC and VNC images for artefacts was made side-by-side. Subjective evaluation included overall image quality on a 4-grade scale, and quantitative analysis of algorithm-induced artefacts by two experienced readers.Results:For all cases, the aortic attenuation was significantly higher at VNC than at TNC. Image noise measured quantitatively was also significantly higher at VNC than at TNC. Subjective image quality was lower for VNC (mean = 3.1 for VNC, 3.7 = for TNC) but there were no cases rated non-diagnostic.Conclusion:VNC images based on arterial phase CTA have significantly higher mean attenuation and higher noise levels compared to TNC.
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| 41. |
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| 42. |
- Lodin-Sundström, Angelica, 1981-, et al.
(author)
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Splenic contraction is enhanced by exercise at simulated high altitude
- 2021
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In: European Journal of Applied Physiology. - : Springer Science and Business Media LLC. - 1439-6319 .- 1439-6327. ; 121:6, s. 1725-1732
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Journal article (peer-reviewed)abstract
- Purpose: Splenic contraction increases circulating hemoglobin (Hb) with advantages during hypoxia. As both hypoxia and exercise have been shown to be important separate triggers of splenic contraction we aimed to investigate if the spleen response to simulated high altitude (HA) is enhanced by superimposing exercise. Method: Fourteen healthy volunteers (seven females) performed the following protocol in a normobaric environment sitting on an ergometer cycle: 20 min rest in normoxia; 20 min rest while breathing hypoxic gas simulating an altitude of 3500 m; 10 min exercise at an individually set intensity while breathing the hypoxic gas; 20 min rest in hypoxia; and finally 20 min rest in normoxia. Spleen measurements were collected by ultrasonic imaging and venous Hb measured at the end of each intervention. Result: Mean ± SD baseline spleen volume during normoxic rest was 280 ± 107 mL, the volume was reduced by 22% during rest in hypoxia to 217 ± 92 mL (p < 0.001) and by 33% during exercise in hypoxia (189 mL; p < 0.001). Hb was 140.7 ± 7.0 g/L during normoxic rest and 141.3 ± 7.4 g/L during hypoxic rest (NS), but increased by 5.3% during hypoxic exercise (148.6 ± 6.3 g/L; p < 0.001). Spleen volume and Hb were stepwise changed back to baseline at cessation of exercise and return to normoxia. Conclusion: Splenic contraction is induced by hypoxia and further enhanced by superimposing exercise, and reduced when exercise ceases, in a step-wise manner, showing that the tonic but partial contraction observed in long-term field expeditions to HA may occur also in the short term. This “graded response” may be beneficial during acclimatization to HA, to cope with moderate chronic hypoxia during rest while allowing additional enhancement of oxygen carrying capacity to overcome short bouts of extreme hypoxia caused by exercise.
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| 43. |
- Löfgren Söderberg, Kajsa
(author)
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Interactions of Prion Proteins and PrP-derived Peptides in Scrapie infection
- 2010
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Doctoral thesis (other academic/artistic)abstract
- Prion diseases are fatal and incurable spongiform encephalopathies that occur amongst mammals. The central pathological event is the misfolding of the cellular prion protein (PrPC) into an amyloid, neurotoxic isoform called scrapie (PrPSc). PrPSc is the main, or sole, constituent of infectious prions. PrPSc resists cellular degradation and also induces misfolding of PrPC via a process called conversion. Conversion seems to be an endocytotic event implicating auxiliary cellular cofactors interacting with PrPC and/or PrPSc. The aim of this thesis is to decipher and modulate key events involved in prion conversion and cytopathology, by studying persistently scrapie infected murine neuronal cell cultures. This work shows that cell penetrating peptides derived from the prion protein (PrP-CPPs) can suppress cellular PrPSc levels. The PrP-CPPs assert these actions on two prion strains regardless of peptide configuration and do not inhibit any PrP-interaction with heparan sulfate (HS) proteoglycans (PG). A polybasic motif in the PrP-CPPs may interact with PrPSc, but the anti-prion effect is controlled by a signal peptide sequence. The PrP-CPPs represents a novel form of prion antagonizing compound. Prion-induced alterations in protein expression, cellular localization, activity and metabolism, designate putative mediators of disease or neuroprotective defence mechanisms. We report on interplay between the HSPG glypican-1 (Gpc-1) and scrapie-infection. Gpc-1 is aberrantly distributed in scrapie-infected cells and HS degradation by autocatalytic deaminative cleavage is elevated, suggestively in order to restrain PrPSc levels. Additionally, we demonstrate that scrapie-infection elevates the activity of Src family kinase members Src and Fyn, in part by affecting Src expression and Fyn membrane distribution. This causes an uncontrolled tyrosine phosphorylation which could contribute to neuronal loss in vivo.
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| 44. |
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| 45. |
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| 46. |
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| 47. |
- Magnussen, Christina, et al.
(author)
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Global effect of modifiable risk factors on cardiovascular disease and mortality
- 2023
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In: New England Journal of Medicine. - : Massachusetts Medical Society. - 0028-4793 .- 1533-4406. ; 389:14, s. 1273-1285
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Journal article (peer-reviewed)abstract
- Background: Five modifiable risk factors are associated with cardiovascular disease and death from any cause. Studies using individual-level data to evaluate the regional and sex-specific prevalence of the risk factors and their effect on these outcomes are lacking.Methods: We pooled and harmonized individual-level data from 112 cohort studies conducted in 34 countries and 8 geographic regions participating in the Global Cardiovascular Risk Consortium. We examined associations between the risk factors (body-mass index, systolic blood pressure, non-high-density lipoprotein cholesterol, current smoking, and diabetes) and incident cardiovascular disease and death from any cause using Cox regression analyses, stratified according to geographic region, age, and sex. Population-attributable fractions were estimated for the 10-year incidence of cardiovascular disease and 10-year all-cause mortality.Results: Among 1,518,028 participants (54.1% of whom were women) with a median age of 54.4 years, regional variations in the prevalence of the five modifiable risk factors were noted. Incident cardiovascular disease occurred in 80,596 participants during a median follow-up of 7.3 years (maximum, 47.3), and 177,369 participants died during a median follow-up of 8.7 years (maximum, 47.6). For all five risk factors combined, the aggregate global population-attributable fraction of the 10-year incidence of cardiovascular disease was 57.2% (95% confidence interval [CI], 52.4 to 62.1) among women and 52.6% (95% CI, 49.0 to 56.1) among men, and the corresponding values for 10-year all-cause mortality were 22.2% (95% CI, 16.8 to 27.5) and 19.1% (95% CI, 14.6 to 23.6).Conclusions: Harmonized individual-level data from a global cohort showed that 57.2% and 52.6% of cases of incident cardiovascular disease among women and men, respectively, and 22.2% and 19.1% of deaths from any cause among women and men, respectively, may be attributable to five modifiable risk factors. (Funded by the German Center for Cardiovascular Research (DZHK); ClinicalTrials.gov number, NCT05466825.)
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