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- Aurumskjöld, Marie-Louise, et al.
(författare)
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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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Ingår i: Acta Radiologica. - : SAGE Publications. - 1600-0455 .- 0284-1851. ; 59:6, s. 740-747
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Tidskriftsartikel (refereegranskat)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. |
- Carlström, Johan, et al.
(författare)
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Knotted non-Hermitian metals
- 2019
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Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 99:16
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Tidskriftsartikel (refereegranskat)abstract
- We report on the occurrence of knotted metallic band structures as stable topological phases in non-Hermitian (NH) systems. These knotted NH metals are characterized by open Fermi surfaces, known in mathematics as Seifert surfaces, that are bounded by knotted lines of exceptional points. Quite remarkably, and in contrast to the situation in Hermitian systems, no fine tuning or symmetries are required in order to stabilize these exotic phases of matter. By explicit construction, we derive microscopic tight-binding models hosting knotted NH metals with strictly short-ranged hopping, and investigate the stability of their topological properties against perturbations. Building up on recently developed experimental techniques for the realization of NH band structures, we discuss how the proposed models may be experimentally implemented in photonic systems.
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| 7. |
- Russell, David, et al.
(författare)
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Cardiovascular Events in Subgroups of Patients During Primary Treatment of Hypertension With Candesartan or Losartan
- 2011
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Ingår i: Journal of Clinical Hypertension. - : Wiley. - 1524-6175. ; 13:3, s. 189-197
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Tidskriftsartikel (refereegranskat)abstract
- Merging data from existing electronic patient records, and electronic hospital discharge and cause of death registers, is a fast and relatively inexpensive method for comparing different treatments with regard to clinical outcome. This study compared the effects of antihypertensive treatment with candesartan or losartan on cardiovascular disease (CVD) using Swedish registers. Patients without previous CVD who were prescribed candesartan (n=7329) or losartan (n=6771) for hypertension during 1999-2007 at 72 Swedish primary care centers were followed for up to 9 years. Both medications were given according to current recommendations, and there was no difference observed in achieved blood pressures. The authors have previously shown that candesartan lowered the risk of all CVD (primary composite end point) more so than losartan (adjusted hazard ratio, 0.86; 95% confidence interval, 0.77-0.96). Candesartan also had a significantly better effect with regards to reducing the development of heart failure, cardiac arrhythmias, and peripheral arterial disease. In the present analysis, the authors found that candesartan, compared with losartan, reduced the risk of all CVD, irrespective of sex, age, previous antihypertensive treatment, baseline blood pressure, and presence of diabetes. These clinical findings may reflect differences between candesartan and losartan in their binding characteristics to the angiotensin type 1 receptor.
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| 8. |
- Sayyad, Sharareh, et al.
(författare)
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Symmetry-protected exceptional and nodal points in non-Hermitian systems
- 2023
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Ingår i: SciPost Physics. - 2542-4653. ; 15:5
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Tidskriftsartikel (refereegranskat)abstract
- One of the unique features of non-Hermitian (NH) systems is the appearance of NH degeneracies known as exceptional points (EPs). The extensively studied defective EPs occur when the Hamiltonian becomes non-diagonalizable. Aside from this degeneracy, we show that NH systems may host two further types of non-defective degeneracies, namely, non-defective EPs and ordinary (Hermitian) nodal points. The non-defective EPs manifest themselves by i) the diagonalizability of the NH Hamiltonian at these points and ii) the non-diagonalizability of the Hamiltonian along certain intersections of these points, resulting in instabilities in the Jordan decomposition when approaching the points from certain directions. We demonstrate that certain discrete symmetries, namely parity-time, parity-particle-hole, and pseudo-Hermitian symmetry, guarantee the occurrence of both defective and non-defective EPs. We extend this list of symmetries by including the NH time-reversal symmetry in two-band systems. Two-band and four-band models exemplify our findings. Through an example, we further reveal that ordinary nodal points may coexist with defective EPs in NH models when the above symmetries are relaxed.
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| 9. |
- Sayyad, Sharareh, et al.
(författare)
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Symmetry-protected exceptional and nodal points in non-Hermitian systems
- 2023
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Ingår i: SciPost Physics. - : Stichting SciPost. - 2542-4653. ; 15:5
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Tidskriftsartikel (refereegranskat)abstract
- One of the unique features of non-Hermitian (NH) systems is the appearance of NH degeneracies known as exceptional points (EPs). The extensively studied defective EPs occur when the Hamiltonian becomes non-diagonalizable. Aside from this degeneracy, we show that NH systems may host two further types of non-defective degeneracies, namely, non-defective EPs and ordinary (Hermitian) nodal points. The non-defective EPs manifest themselves by i) the diagonalizability of the NH Hamiltonian at these points and ii) the non-diagonalizability of the Hamiltonian along certain intersections of these points, resulting in instabilities in the Jordan decomposition when approaching the points from certain directions. We demonstrate that certain discrete symmetries, namely parity-time, parity-particle-hole, and pseudo-Hermitian symmetry, guarantee the occurrence of both defective and non-defective EPs. We extend this list of symmetries by including the NH time-reversal symmetry in two-band systems. Two-band and four-band models exemplify our findings. Through an example, we further reveal that ordinary nodal points may coexist with defective EPs in NH models when the above symmetries are relaxed.
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| 10. |
- Stålhammar, Marcus, 1994-, et al.
(författare)
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Classification of exceptional nodal topologies protected by PT symmetry
- 2021
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Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 104:20
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Tidskriftsartikel (refereegranskat)abstract
- Exceptional degeneracies, at which both eigenvalues and eigenvectors coalesce, and parity-time (PT) symmetry, reflecting balanced gain and loss in photonic systems, are paramount concepts in non-Hermitian systems. We here complete the topological classification of exceptional nodal degeneracies protected by PT symmetry in up to three dimensions and provide simple example models whose exceptional nodal topologies include previously overlooked possibilities such as second-order knotted surfaces of arbitrary genus, third-order knots, and fourth-order points.
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