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- Wang, Chunliang, 1980-, et al.
(författare)
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Can segmented 3D images be used for stenosis evaluation in coronary CT angiography?
- 2012
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Ingår i: Acta Radiologica. - : Sage Publications. - 0284-1851 .- 1600-0455. ; 53:8, s. 845-851
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Tidskriftsartikel (refereegranskat)abstract
- Background: Thanks to the development of computed tomography (CT) scanners and computer software, accurate coronary artery segmentation can be achieved with minimum user interaction. However, the question remains whether we can use these segmented images for reliable diagnosis. Purpose: To retrospectively evaluate the diagnostic accuracy of coronary CT angiography (CCTA) using segmented 3D data for the detection of significant stenosis. Material and Methods: CCTA data-sets from 30 patients were acquired with a 64-slice CT scanner and segmented using the region growing (RG) method and the "virtual contrast injection" (VC) method. Three types of images of each patient were reviewed by different reviewers for the presence of stenosis with diameter reduction of 50% or more. The evaluation was performed on four main arteries of each patient (120 arteries in total). For the original series, the reviewer was allowed to use all the 2D and 3D visualization tools available (conventional method). For the segmented results from RG and VC, only maximum intensity projection was used. Evaluation results were compared with catheter angiography (CA) for each artery in a blinded fashion. Results: Overall, 34 arteries with significant stenosis were identified by CA. The percentage of evaluable arteries, accuracy and negative predictive value for detecting stenosis were, respectively, 86%, 74%, and 93% for the conventional method, 83%, 71%, and 92% for VC, and 64%, 56%, and 93% for RG. Accuracy was significantly lower for the RG method than for the other two methods (P < 0.01), whereas there was no significant difference in accuracy between the VC method and the conventional method (P = 0.22). Conclusion: The diagnostic accuracy for the RG-segmented 3D data is lower than those with access to 2D images, whereas the VC method shows diagnostic accuracy similar to the conventional method.
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- Andersson, Malin, et al.
(författare)
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How to measure renal artery stenosis - a retrospective comparison of morphological measurement approaches in relation to hemodynamic significance
- 2015
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Ingår i: BMC Medical Imaging. - : BioMed Central. - 1471-2342 .- 1471-2342. ; 15
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Tidskriftsartikel (refereegranskat)abstract
- Background: Although it is well known that renal artery stenosis may cause renovascular hypertension, it is unclear how the degree of stenosis should best be measured in morphological images. The aim of this study was to determine which morphological measures from Computed Tomography Angiography (CTA) and Magnetic Resonance Angiography (MRA) are best in predicting whether a renal artery stenosis is hemodynamically significant or not. Methods: Forty-seven patients with hypertension and a clinical suspicion of renovascular hypertension were examined with CTA, MRA, captopril-enhanced renography (CER) and captopril test (Ctest). CTA and MRA images of the renal arteries were analyzed by two readers using interactive vessel segmentation software. The measures included minimum diameter, minimum area, diameter reduction and area reduction. In addition, two radiologists visually judged the diameter reduction without automated segmentation. The results were then compared using limits of agreement and intra-class correlation, and correlated with the results from CER combined with Ctest (which were used as standard of reference) using receiver operating characteristics (ROC) analysis. Results: A total of 68 kidneys had all three investigations (CTA, MRA and CER + Ctest), where 11 kidneys (16.2 %) got a positive result on the CER + Ctest. The greatest area under ROC curve (AUROC) was found for the area reduction on MRA, with a value of 0.91 (95 % confidence interval 0.82-0.99), excluding accessory renal arteries. As comparison, the AUROC for the radiologists' visual assessments on CTA and MRA were 0.90 (0.82-0.98) and 0.91 (0.83-0.99) respectively. None of the differences were statistically significant. Conclusions: No significant differences were found between the morphological measures in their ability to predict hemodynamically significant stenosis, but a tendency of MRA having higher AUROC than CTA. There was no significant difference between measurements made by the radiologists and measurements made with fuzzy connectedness segmentation. Further studies are required to definitely identify the optimal measurement approach.
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- Begovic, Ermina, et al.
(författare)
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Experimental modelling of local structure responses for high-speed planing craft in waves
- 2020
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Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 216
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Tidskriftsartikel (refereegranskat)abstract
- The modelling of planing craft dynamics in waves and related fluid-structure interaction is a hard challenge due to the highly nonlinear, transient and stochastic nature of the whole process. This paper explores the prospectives of detailed experimental modelling of the local structure responses for high-speed planing craft in waves. A novel experimental setup is presented where a well-defined model structure is integrated into the hull bottom of a typical planing craft model. The model is instrumented for measuring strains in the model structure, related slamming pressures, craft rigid body motions and accelerations. The experimental setup is thoroughly described and motivated and crucial aspects of the setup are verified through testing in idealized static loading conditions and by modal analysis. The capabilities of the experimental setup are demonstrated through systematic experiments in regular waves. The most indicative results are presented and discussed in relation to corresponding results from time-domain simulations The presented experimental modelling approach is concluded to enable uniquely detailed studies of the complete slamming related fluid-structure interaction process and provides a good tool for further research and development towards establishment of first principles-based methods for hydrodynamic and structure design of high-speed planing craft.
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- Beye, Martin, et al.
(författare)
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Chemical Bond Activation Observed with an X-ray Laser
- 2016
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185 .- 1948-7185. ; 7:18, s. 3647-3651
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Tidskriftsartikel (refereegranskat)abstract
- The concept of bonding and antibonding orbitals is fundamental in chemistry. The population of those orbitals and the energetic difference between the two reflect the strength of the bonding interaction. Weakening the bond is expected to reduce this energetic splitting, but the transient character of bond-activation has so far prohibited direct experimental access. Here we apply time-resolved soft X-ray spectroscopy at a free electron laser to directly observe the decreased bonding antibonding splitting following bond-activation using an ultrashort optical laser pulse.
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- Dumas, Randy K., et al.
(författare)
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Spin-Wave-Mode Coexistence on the Nanoscale : A Consequence of the Oersted-Field-Induced Asymmetric Energy Landscape
- 2013
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 110:25, s. 257202-
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Tidskriftsartikel (refereegranskat)abstract
- It has been argued that if multiple spin wave modes are competing for the same centrally located energy source, as in a nanocontact spin torque oscillator, that only one mode should survive in the steady state. Here, the experimental conditions necessary for mode coexistence are explored. Mode coexistence is facilitated by the local field asymmetries induced by the spatially inhomogeneous Oersted field, which leads to a physical separation of the modes, and is further promoted by spin wave localization at reduced applied field angles. Finally, both simulation and experiment reveal a low frequency signal consistent with the intermodulation of two coexistent modes.
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- Eklund, Anders, et al.
(författare)
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Dependence of the colored frequency noise in spin torque oscillators on current and magnetic field
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 104:9, s. 092405-
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Tidskriftsartikel (refereegranskat)abstract
- The nano-scale spin torque oscillator (STO) is a compelling device for on-chip, highly tunable microwave frequency signal generation. Currently, one of the most important challenges for the STO is to increase its longer-time frequency stability by decreasing the 1/f frequency noise, but its high level makes even its measurement impossible using the phase noise mode of spectrum analyzers. Here, we present a custom made time-domain measurement system with 150MHz measurement bandwidth making possible the investigation of the variation of the 1/f as well as the white frequency noise in a STO over a large set of operating points covering 18-25GHz. The 1/f level is found to be highly dependent on the oscillation amplitude-frequency non-linearity and the vicinity of unexcited oscillation modes. These findings elucidate the need for a quantitative theoretical treatment of the low-frequency, colored frequency noise in STOs. Based on the results, we suggest that the 1/f frequency noise possibly can be decreased by improving the microstructural quality of the metallic thin films.
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| 10. |
- Eklund, Anders J., et al.
(författare)
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Triple mode-jumping in a spin torque oscillator
- 2013
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Ingår i: 2013 22nd International Conference on Noise and Fluctuations, ICNF 2013. - New York : IEEE conference proceedings. - 9781479906680 ; , s. 6578965-
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Konferensbidrag (refereegranskat)abstract
- In a nano-contact Co/Cu/NiFe spin torque oscillator, mode-jumping between up to three frequencies within 22.5-24.0 GHz is electrically observed in the time domain. The measurements reveal toggling between two states with differing oscillation amplitude, of which the low-amplitude state is further divided into two rapidly alternating modes. Analysis of the mode dwell time statistics and the total time spent in each mode is carried out, and it is found that in both aspects the balance between the modes is greatly altered with the DC drive current.
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