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| 3. |
- Johnell, Matilda, et al.
(författare)
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Coagulation, fibrinolysis and cell activation in patients and shed mediastinal blood during coronary artery bypass grafting using a new heparin-coated surface
- 2002
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Ingår i: Journal of Thoracic and Cardiovascular Surgery. - : Elsevier BV. - 0022-5223 .- 1097-685X. ; 124:2, s. 321-332
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: Heparin coating of the cardiopulmonary bypass circuit is shown to improve the biocompatibility of the surface. We have studied a new heparin surface, the Corline Heparin Surface, applied to a complete set of an extracorporeal device used during coronary artery bypass grafting in terms of activation of inflammation, coagulation, and fibrinolysis in patients and in shed mediastinal blood. METHODS: Sixty patients scheduled for coronary artery bypass grafting were randomized to one of 3 groups with heparin-coated devices receiving either a standard, high, or low dose of systemic heparin or to an uncoated but otherwise identical circuit receiving a standard dose of systemic heparin. Samples were drawn before, during, and after the operation from the pericardial cavity and in shed mediastinal blood. No autotransfusion of shed mediastinal blood was performed. RESULTS: The Corline Heparin Surface significantly reduced the activation of coagulation, fibrinolysis, platelets, and inflammation compared with that seen with the uncoated surface in combination with a standard dose of systemic heparin during cardiac surgery with cardiopulmonary bypass. Both a decrease and an increase of systemic heparin in combination with the coated heparin surface resulted in higher activation of these processes. A significantly higher expression of all studied parameters was found in the shed mediastinal blood compared with in systemic blood at the same time. CONCLUSIONS: The Corline Heparin Surface used in cardiopulmonary bypass proved to be more biocompatible than an uncoated surface when using a standard systemic heparin dose. The low dose of systemic heparin might not be sufficient to maintain the antithrombotic activity, and the high dose resulted in direct cell activation rather than a further anti-inflammatory and anticoagulatory effect.
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- Larsson, David, et al.
(författare)
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An ex-vivo setup for characterization of atherosclerotic plaque using shear wave elastography and micro-computed tomography
- 2016
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Ingår i: IEEE International Ultrasonics Symposium, IUS. - : IEEE conference proceedings. - 9781467398978
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Konferensbidrag (refereegranskat)abstract
- Quantification of the mechanical properties of atherosclerotic plaque has shown to be important in assessing carotid artery plaque vulnerability. For such, shear wave elastography (SWE) has been applied on both in-vitro and in-vivo setups. The aim of this study was to build an ex-vivo setup for combined evaluation of plaque characteristics using SWE and micro-computed tomography (μCT). As a proof-of-concept of the constructed experimental setup, a single human carotid plaque specimen was extracted during carotid endarterectomy. The plaque was imaged in the μCT system, and subsequently imaged using SWE. For the SWE measurement, group and phase velocity was extracted from the obtained in-phase/quadrature data, with its spatial distribution being compared to anatomical features visible in the μCT images. The results indicated wave velocity changes at boundaries identified in the μCT, with group velocity data slightly increasing when entering a calcified nodule. Additionally, μCT images seemed to provide good contrast between several plaque constituens using the defined imaging settings. Overall, the study represents a proof-of-concept for detailed ex-vivo plaque analysis using combined SWE and μCT, with obtained wave speed and shear modulus values falling within observed values for atherosclerotic plaque tissue. With an experimental setup defined, future studies on carotid plaque behaviour both in SWE and μCT is enabled, where a large-scale plaque study could be performed to investigate the ability of SWE to differentiate between different plaque types.
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- Larsson, David, et al.
(författare)
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Estimation of left ventricular blood flow parameters : Clinical application of patient-specific CFD simulations from 4D echocardiography
- 2017
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Ingår i: Medical Imaging 2017. - : SPIE - International Society for Optical Engineering. - 9781510607231
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Konferensbidrag (refereegranskat)abstract
- Echocardiography is the most commonly used image modality in cardiology, assessing several aspects of cardiac viability. The importance of cardiac hemodynamics and 4D blood flow motion has recently been highlighted, however such assessment is still difficult using routine echo-imaging. Instead, combining imaging with computational fluid dynamics (CFD)-simulations has proven valuable, but only a few models have been applied clinically. In the following, patient-specific CFD-simulations from transthoracic dobutamin stress echocardiography have been used to analyze the left ventricular 4D blood flow in three subjects: two with normal and one with reduced left ventricular function. At each stress level, 4D-images were acquired using a GE Vivid E9 (4VD, 1.7MHz/3.3MHz) and velocity fields simulated using a presented pathway involving endocardial segmentation, valve position identification, and solution of the incompressible Navier-Stokes equation. Flow components defined as direct flow, delayed ejection flow, retained inflow, and residual volume were calculated by particle tracing using 4th-order Runge-Kutta integration. Additionally, systolic and diastolic average velocity fields were generated. Results indicated no major changes in average velocity fields for any of the subjects. For the two subjects with normal left ventricular function, increased direct flow, decreased delayed ejection flow, constant retained inflow, and a considerable drop in residual volume was seen at increasing stress. Contrary, for the subject with reduced left ventricular function, the delayed ejection flow increased whilst the retained inflow decreased at increasing stress levels. This feasibility study represents one of the first clinical applications of an echo-based patient-specific CFD-model at elevated stress levels, and highlights the potential of using echo-based models to capture highly transient flow events, as well as the ability of using simulation tools to study clinically complex phenomena. With larger patient studies planned for the future, and with the possibility of adding more anatomical features into the model framework, the current work demonstrates the potential of patient-specific CFD-models as a tool for quantifying 4D blood flow in the heart.
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- Larsson, David, et al.
(författare)
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Multimodal validation of patient-specific intraventricular flow simulations from 4D echocardiography
- 2016
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Ingår i: 2016 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS). - : IEEE conference proceedings. - 9781467398978
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Konferensbidrag (refereegranskat)abstract
- The combination of refined medical imaging techniques and computational fluid dynamics (CFD) models has enabled the study of complex flow behavior on a highly regional level. Recently, we have developed a platform for patient-specific CFD modelling of blood flow in the left ventricle (LV), with input data and required boundary conditions acquired from 4D echocardiography. The platform robustness has been evaluated with respect to input variable variations, but for any clinical implementation model flow validation is essential. Therefore, the aim of this study is to evaluate the accuracy of the patient-specific CFD model against multimodal image-based flow measurements. For the validation, 4D echocardiography was acquired from two healthy subjects, from which LV velocity fields were simulated. In-vivo flows from the same two subjects were then acquired by pulsed wave (PW) Doppler imaging over both LV-valves, and by cine phase-contract magnetic resonance imaging (PC-MRI) at eight defined anatomical planes in the LV. By fusing PC-MRI and the ultrasound acquisitions using a three-chamber alignment algorithm, simulated and measured flows were quantitatively compared. General flow pattern correspondence was observed, with a mean error of 1.4 cm/s and root mean square deviation of 5.7 cm/s for all measured PC-MRI LV-planes. For the PW-Doppler comparison, a mean error of 3.6 cm/s was reported. Overall, the following work represents a validation of the proposed patient-specific CFD platform, and the agreement with clinical data highlight the potential for future clinical use of the models.
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| 7. |
- Larsson, David, et al.
(författare)
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Patient-specific flow simulation of the left ventricle from 4D echocardiography - feasibility and robustness evaluation
- 2015
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Ingår i: 2015 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS). - : IEEE. - 9781479981823
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Konferensbidrag (refereegranskat)abstract
- In recent years, computational fluid dynamics (CFD) simulations on in-silico models of the heart have provided a valuable insight into cardiac hemodynamic behaviour. However, so far most models have been either based on simplified geometries or on imaging acquisitions with relatively low temporal resolution. It has been suggested that models based entirely on subject-specific ultrasonic images should be used to capture transient flow changes. Therefore, the aim of this study is to present a pathway from routine 4D echocardiography to a patient-specific flow simulation of the left ventricle (LV), evaluating the model robustness and clinical feasibility. The created pathway consisted of initial LV segmentation and mitral/aortic valve positioning, being subsequently used as input for the CFD simulations (based on solving the Navier-Stokes equation using an Arbitrary Lagrangian-Eulerian approach). The output consisted of 4D blood flow velocities and relative pressures in the entire LV. On five subjects, the model robustness was evaluated with regards to variations in singular boundary conditions. The clinical feasibility of the output was compared to clinical PW Doppler measurements and, as a proof-of-concept, synthetic contrast enhanced ultrasound images were simulated on the flow field using the COLE-method. Results indicated a relatively robust model, with variations in regional flow of approximately 5.1/6.2% and 9.7/7.0% for healthy and pathological subject respectively (end diastole/end systole). Furthermore, showing similar behaviour to clinical Doppler measurements the technique serves as a promising tool for future clinical investigations. Additionally, the ability of simulating synthetic ultrasound images further underlines the applicability of the pathway, being potentially useful in studies on improved echocardiographic image analysis.
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| 8. |
- Larsson, David, et al.
(författare)
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Patient-Specific Left Ventricular Flow Simulations From Transthoracic Echocardiography : Robustness Evaluation and Validation Against Ultrasound Doppler and Magnetic Resonance Imaging
- 2017
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Ingår i: IEEE Transactions on Medical Imaging. - : Institute of Electrical and Electronics Engineers (IEEE). - 0278-0062 .- 1558-254X. ; 36:11, s. 2261-2275
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Tidskriftsartikel (refereegranskat)abstract
- The combination of medical imaging with computational fluid dynamics (CFD) has enabled the study of 3D blood flow on a patient-specificlevel. However, with models based on gated high-resolution data, the study of transient flows, and any model implementation into routine cardiac care, is challenging. The present paper presents a novel pathway for patient-specific CFD modelling of the left ventricle (LV), using 4D transthoracic echocardiography (TTE) as input modality. To evaluate the clinical usability, two sub-studies were performed. First, a robustness evaluation was performed where repeated models with alternating input variables were generated for 6 subjects and changes in simulated output quantified. Second, a validation study was carried out where the pathway accuracy was evaluated against pulsed-wave Doppler (100 subjects), and 2D through-plane phase-contrast magnetic resonance imaging measurements over 7 intraventricular planes (6 subjects). The robustness evaluation indicated a model deviation of <12%, with highest regional and temporal deviations at apical segments and at peak systole, respectively. The validation study showed an error of < 11% (velocities < 10 cm/s) for all subjects, with no significant regional or temporal differences observed. With the patient-specific pathway shown to provide robust output with high accuracy, and with the pathway dependent only on 4DTTE, the method has a high potential to be used within future clinical studies on 3D intraventricular flowpatterns. To this, future model developments in the form of e.g. anatomically accurate LV valves may further enhance the clinical value of the simulations.
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| 9. |
- Larsson, Malin, 1983-, et al.
(författare)
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A new ultrasound-based approach to visualize target specific polymeric contrast agent
- 2011
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Ingår i: 2011 IEEE International Ultrasonics Symposium (IUS). - : IEEE. - 9781457712524 ; , s. 1626-1629
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Konferensbidrag (refereegranskat)abstract
- There are advantages of using a polymeric shelled contrast agent (CA) during ultrasound imaging instead of lipid shelled CA, e.g. particles can be attached to the surface, which enables an introduction of antibodies to the surface making the CA target specific. For this application it is essential to have a sensitive imaging technique suitable for polymeric CA. However, previously presented results have indicated difficulties in visualizing polymeric CA with commercially available contrast algorithms. Therefore a new subtraction algorithm (SA), was developed that define the difference between contrast and reference images. The aim of this study was to evaluate the response from a polymeric CA, when using the SA and compare it with existing contrast algorithms. Moreover, the possibility to detect a thin layer of CA was tested using the SA.Ultrasound short-axis images of a tissue-mimicking vessel phantom with a pulsating flow were obtained using a GE Vivid7 system (M12L) and a Philips iE33 system (S5-1). Repeated (n=91) contrast to tissue ratios (CTR) calculated at various mechanical index (MI) using the contrast algorithms pulse inversion (PI), power modulation (PM) and SA at a concentration of 105microbubbles/ml.The developed SA showed improvements in CTR compared to existing contrast algorithms. The CTRs were -0.99 dB ± 0.67 (MI 0.2), 9.46 dB ± 0.77 (MI 0.4) and 2.98 dB ± 0.60 (MI 0.8) with PI, 8.17 dB ± 1.15 (MI 0.2), 15.60 dB ± 1.29 (MI0.4) and 11.60 dB ± 0.73 (MI 0.8) with PM and 14.97 dB ± 3.97 (MI 0.2), 20.89 dB ± 3.54 (MI 0.4) and 21.93 dB ± 4.37 (MI 0.8) with the SA. In addition to this, the layer detection, when using the SA was successful.
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