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  • 1. Kremer, F.
    et al.
    Rabayah, M.
    Choi, H.F.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    D'hooge, Jan
    Spatial compounding for 2D strain estimation in the mouse heart: a pilot study2010Conference paper (Refereed)
    Abstract [en]

    Estimating cardiac strain in the mouse in the lateral direction usingspeckle tracking with adapted clinical equipment was shown to be challenging dueto the fast heart rate and the large speckle size relative to the wallthickness. Compounding axial motion estimates acquired from different insonationangles can potentially improve lateral strain estimates. Therefore, the aim ofthis study was to test the feasibility of this methodology in the murine heartbased on simulated data sets. A 3D kinematic model of a murine left ventriclewas simulated and filled randomly with scatterers. Ultrasound short-axis images(10mm 6mm) were obtained by assuming a linear array transducer. Beam steeringwas simulated at 3 different angles (22, 0, 22). Axial motion was estimated ineach data set by 1D cross-correlation. A dynamic programming approach wasintegrated in the motion estimation algorithm to avoid discontinuities. Axialcomponents were combined to reconstruct the in-plane motion vector. The 2Ddisplacement fields were subsequently accumulated over the whole cycle. Theprocedure was repeated for 10 different distributions of scatterers to acquire10 different RF data sets (5 for parameter tuning and 5 for comparing themethods). Radial and circumferential RMS strain errors calculated from theaccumulated motion fields were compared with those obtained with 2D speckletracking. Spatial compounding yielded significantly better radial (RMSE: 0.07370.0078 vs. 0.112 0.0094) as well as circumferential strain (RMSE: 0.102 0.0097vs. 0.281 0.054).

  • 2.
    Larsson, Daniel
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Roy, J.
    Gasser, T. Christian
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Urban, M. W.
    Colarieti-Tosti, Massimiliano
    KTH, School of Technology and Health (STH), Medical Engineering.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    An ex-vivo setup for characterization of atherosclerotic plaque using shear wave elastography and micro-computed tomography2016In: IEEE International Ultrasonics Symposium, IUS, IEEE conference proceedings, 2016Conference paper (Refereed)
    Abstract [en]

    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. © 2016 IEEE.

  • 3.
    Larsson, David
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Spuhler, Jeannette H.
    KTH, School of Computer Science and Communication (CSC), High Performance Computing and Visualization (HPCViz).
    Nordenfur, Tim
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Hoffman, Johan
    KTH, School of Computer Science and Communication (CSC), High Performance Computing and Visualization (HPCViz).
    Colarieti-Tosti, Massimiliano
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Gao, Hang
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Patient-specific flow simulation of the left ventricle from 4D echocardiography - feasibility and robustness evaluation2015In: 2015 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS), IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    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.

  • 4.
    Larsson, David
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Spuhler, Jeannette H.
    Petersson, Sven
    Nordenfur, Tim
    Hoffman, Johan
    KTH, School of Computer Science and Communication (CSC), High Performance Computing and Visualization (HPCViz).
    Colarieti-Tosti, Massimiliano
    Winter, Reidar
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Multimodal validation of patient-specific intraventricular flow simulations from 4D echocardiography2016In: 2016 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS), IEEE conference proceedings, 2016Conference paper (Refereed)
    Abstract [en]

    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.

  • 5.
    Larsson, David
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Insitutet, Sweden.
    Spühler, Jeannette
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Günyeli, E.
    Weinkauf, Tino
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Hoffman, Johan
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Colarieti-Tosti, Massimiliano
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Institutet, Sweden.
    Winter, R.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Institutet, Sweden.
    Estimation of left ventricular blood flow parameters: Clinical application of patient-specific CFD simulations from 4D echocardiography2017In: Medical Imaging 2017: Ultrasonic Imaging and Tomography, SPIE - International Society for Optical Engineering, 2017, Vol. 10139, article id 101390LConference paper (Refereed)
    Abstract [en]

    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.

  • 6.
    Larsson, Malin
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    Caidahl, Kenneth
    Karolinska Institutet.
    Winter, Reidar
    KTH, School of Technology and Health (STH), Medical Engineering.
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical sensors, signals and systems (MSSS).
    A new ultrasound-based approach to visualize target specific polymeric contrast agent2011In: 2011 IEEE International Ultrasonics Symposium (IUS), IEEE , 2011, p. 1626-1629Conference paper (Refereed)
    Abstract [en]

    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.

  • 7.
    Larsson, Malin
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    Caidahl, Kenneth
    Winter, Reidar
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    A novel technique to visualize target specific polymeric contrast agents2011Conference paper (Other academic)
  • 8.
    Larsson, Matilda
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Claus, P.
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    D'Hooge, J.
    Ultrasound-based 2D Strain Estimation of the Carotid Artery: an in-silico feasibility study2009In: Ultrasonics Symposium (IUS), 2009 IEEE International, IEEE , 2009, , p. 4p. 5441992-Conference paper (Refereed)
    Abstract [en]

    Ultrasound based estimation of arterial wall properties is commonly used to assess vessel wall stiffness in studies of vascular diseases. Recently, it was shown that the longitudinal motion of the vessel during systole can be measured using speckle tracking. However, the assessment of longitudinal strain in the vessel wall has to be further investigated. The aim of this study was to test the feasibility of simultaneous assessment of radial and longitudinal strain in the carotid artery using computer simulations. A kinematic cylindrical model of the carotid artery with realistic dimensions was constructed. The model was deformed radially according to temporal distention measured in-vivo while longitudinal deformation was the result of conservation of volume. Moreover, longitudinal motion was superimposed based on profiles obtained in-vivo. Ultrasound long axis images were simulated using a generalized convolution model (COLE) with realistic image properties. Four models with different scatterer distributions were built. For each of them, longitudinal and radial motion were estimated using normalized cross-correlation with spline interpolation to detect sub-sample motion. Radial and longitudinal strains, obtained by linear regression were compared with the ground truth from the model. The maximal systolic radial strain was estimated to be -12.77 ± 0.4% (ground truth -13.89%) while longitudinal strain was 5.21 ± 0.67% (ground truth 5.3%). This study shows the feasibility of simultaneously measuring radial and longitudinal strain in the carotid artery by making use of currently available hardware.

  • 9.
    Larsson, Matilda
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Kremer, F.
    Claus, P.
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    D'hooge, Jan
    A novel measure to express tracking quality in ultrasound block matching2010In: Proceedings - IEEE Ultrasonics Symposium, 2010, p. 1636-1639Conference paper (Refereed)
    Abstract [en]

    Speckle de-correlation is a major problem in block matching based ultrasound methodologies as it limits the accuracy of the tracking result. It would be of benefit to have a quantitative measure expressing the local tracking quality as it would allow discarding unreliable motion estimates. We hypothesized that kernels showing sufficient gray scale pattern would more reliably track than kernels with more homogenous gray scale distributions. The aim of this study was to test this hypothesis in-silico. Ultrasound B-mode sequences were simulated from a kinematic model of the carotid artery. Two-dimensional motion was estimated using block matching with the normalized cross-correlation function as similarity measure. For each kernel, two measures of tracking quality were stored: the normalized cross-correlation coefficient (Ccc) and a measure of the amount of edges inside the kernel detected using a canny filter and counted on a pixel-by-pixel basis. As such, a quality measure (Cedge) between 0 (no edges) and 1 (nothing but edges) was obtained. Axial and lateral strains were subsequently obtained by linear regression in regions of interest (ROIs) with best/worst mean tracking quality scores. The root-mean-squared-error (RMSE) was significantly lower in regions with low Ccc (worst ROI) compared to ROIs with high Ccc. However, more edges in the kernel did indeed result in better overall tracking (lower RMSE). Thus, the proposed edge-detection method showed to be a better tracking quality measure than the commonly used Ccc.

  • 10.
    Larsson, Matilda
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Kremer, F.
    Heyde, B.
    Brodin, Lars Åke
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    D'hooge, J.
    Ultrasound-based speckle tracking for 3D Strain estimation of the Arterial wall - An experimental validation study in a tissue mimicking phantom2011Conference paper (Refereed)
    Abstract [en]

    Arterial stiffness is an important risk factor for cardiovascular disease. As such, ultrasound-based methods have been proposed to assess arterial strain as a measure of stiffness. The aim of the current study was to validate our recently proposed speckle tracking (ST) algorithm to estimate the in-plane wall strain tensor in an experimental setup. Three polyvinyl alcohol phantoms mimicking the carotid artery were constructed with different mechanical properties (2, 3 and 4 freeze-thaw cycles). The phantoms were connected to a pump, programmed to generate carotid flow profiles at peak flows of 7, 14, 21, 28 and 35 ml/s. Long and short-axis ultrasound images were obtained using a Vivid7 Dimension system. Radial, longitudinal and circumferential strains were estimated using the ST algorithm (kernel size: 2.7λx2λ, normalized cross-correlation; spline inter-polation for subsample motion estimation; 40% window overlap). Sonomicrometry was used to acquire reference values of strain in the phantoms. Good agreement was found between the estimated radial, longitudinal and circumferential strain and the acquired reference strain. The correlation between estimated mean peak strain values and reference peak strain values was r = 0.92 (p < 0.001) for radial strain, r = 0.72 (p = 0.006) for longitudinal strain and r = 0.91 (p < 0.001) for circumferential strain.

  • 11.
    Larsson, Matilda
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Kremer, F.
    Heyde, B.
    Widman, Erik
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    D'Hooge, J.
    Carotid strain estimation using an ultrasound-based speckle tracking algorithm2012In: 2012 IEEE International Ultrasonics Symposium (IUS), IEEE , 2012, p. 1394-1397Conference paper (Refereed)
    Abstract [en]

    Carotid strain imaging using ultrasound-based speckle tracking has showed potential in risk stratification of cardiovascular diseases. However, assessing strain in the artery wall and in atherosclerotic plaques is challenging because of small dimensions and low deformations in relation to the applied ultrasound wavelength. High-resolution ultrasound has potential to improve the speckle tracking performance by increasing spatial resolution. The aim of this study was to compare carotid strain estimation by speckle tracking using standard clinical ultrasound and high-resolution ultrasound in an experimental setup. Ultrasound long-axis images were obtained using a standard clinical ultrasound system (Vivid7) and a high-resolution ultrasound system (Vevo2100) in dynamic phantoms mimicking the carotid artery. Speckle tracking was performed to estimate radial and longitudinal strain whereas sonomicrometry was used as reference. The results showed a significant better performance for speckle tracking applied on images from the high-resolution system compared to the standard clinical system.

  • 12.
    Larsson, Matilda
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Kremer, F.
    Kuznetsova, T.
    Lind, Britta
    KTH, School of Technology and Health (STH), Medical Engineering.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering.
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    D'hooge, J.
    In-vivo assessment of radial and longitudinal strain in the carotid artery using speckle tracking2010In: 2010 IEEE International Ultrasonics Symposium Proceedings, IEEE , 2010, p. 1328-1331Conference paper (Refereed)
    Abstract [en]

    Ultrasound-based algorithms are commonly used to assess mechanical properties of arterial walls in studies of arterial stiffness and atherosclerosis. Speckle tracking based techniques used for estimation of myocardial strain can be applied on vessels to estimate strain of the arterial wall. Previous elastography studies in vessels have mainly focused on radial strain measurements, whereas the longitudinal strain has been more or less ignored. However, recently we showed the feasibility of speckle tracking to assess longitudinal strain of the carotid artery in-silico. The aim of this study was to test this methodology in-vivo. Ultrasound images were obtained in seven healthy subjects with no known cardiovascular disease (39 ± 14 years old) and in seven patients with coronary artery disease (CAD), (69 ± 4 years old). Speckle tracking was performed on the envelope detected data using our previous developed algorithm. Radial and longitudinal strains were estimated throughout two cardiac cycles in a region of interest (ROI) positioned in the posterior vessel wall. The mean peak systolic radial and longitudinal strain values from the two heart cycles were compared between the groups using a student's t-test. The mean peak radial strain was -39.1 ± 15.1% for the healthy group and -20.4 ± 7.5% for the diseased group (p = 0.01), whereas the mean peak longitudinal strain was 4.8 ± 1.1% and 3.2 ± 1.6% (p = 0.05) for the healthy and diseased group, respectively. Both peak radial and longitudinal strain values were thus significantly reduced in the CAD patient group. This study shows the feasibility to estimate radial and longitudinal strain in-vivo using speckle tracking and indicates that the method can detect differences between groups of healthy and diseased (CAD) subjects.

  • 13.
    Larsson, Matilda
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Verbrugghe, Peter
    KU Leuven.
    Smoljkić, Marija
    KU Leuven.
    Heyde, Brecht
    KU Leuven.
    Famaey, Nele
    KU Leuven.
    Herijgers, Paul
    KU Leuven.
    D'hooge, Jan
    KU Leuven.
    Assessment of longitudinal strain in the Carotid artery wall using ultrasound-based Speckle tracking - validation in a sheep model2013In: Proceedings of the IEEE International Ultrasonics symposium, 2013, 2013Conference paper (Other academic)
    Abstract [en]

    Assessment of strain in the longitudinal direction of the arterial wall has been suggested to improve the evaluation of arterial stiffness and atherosclerosis. Recently, we showed the feasibility of ultrasound speckle tracking to assess carotid longitudinal strain in-silico and in-vitro. However, validation in the more challenging in-vivo setting is still lacking. The aim of this study was to validate longitudinal strain assessment in the common carotid artery (CCA) in an animal setup. The left CCAs of five sheep were exposed during Isoflurane anesthesia and sonomicrometry crystals were sutured onto the artery wall to obtain reference longitudinal strain. Ultrasound long-axis images were recorded at baseline and hypertension (Phenylephrine) and an in-house speckle tracking algorithm was applied to estimate longitudinal strain. The estimated strain curves varied cyclically throughout the cardiac cycles, showing a lengthening of the arterial segment in systole. A significant correlation between peak systolic estimated and reference strain was found (r=0.95, p < 0.001). The results indicate the feasibility of arterial longitudinal strain assessment in-vivo using ultrasound speckle tracking.

  • 14.
    Nordenfur, Tim
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Babic, Aleksandar
    Bulatovic, Ivana
    Giesecke, Anders
    Gunyeli, Elif
    Ripsweden, Jonaz
    Samset, Eigil
    Winter, Reidar
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Algorithm Comparison for Cardiac Image Fusion of Coronary Computed Tomography Angiography and 3D Echocardiography2015In: 2015 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS), IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    Treatment decision for coronary artery disease (CAD) is based on both morphological and functional information. Image fusion of coronary computed tomography angiography (CCTA) and three-dimensional echocardiography (3DE) could combine morphology and function into a single image to facilitate diagnosis. Three semi-automatic feature-based algorithms for CCTA/3DE registration were implemented and applied on CAD patients. Algorithms were verified and compared using landmarks manually identified by a cardiologist. All algorithms were found feasible for CCTA/3DE fusion.

  • 15. Ughi, G. J.
    et al.
    Adriaenssens, T.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering. Katholieke Universiteit Leuven, Belgium.
    Dubois, C.
    Sinnaeve, P.
    Coosemans, M.
    Desmet, W.
    D'Hooghe, J.
    Automatic three-dimensional registration of intra-vascular optical coherence tomography images for the clinical evaluation of stent implantation over time2012In: Progress in Biomedical Optics and Imaging - Proceedings of SPIE, SPIE - International Society for Optical Engineering, 2012, Vol. 8213, p. 82132K-Conference paper (Refereed)
  • 16. Ughi, Giovanni
    et al.
    Adriaenssens, T.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    Dubois, C.
    Sinnaeve, P.
    Coosemans, M.
    Desmet, W.
    D'hooge, Jan
    Automated three-dimensional registration of intra-vascular optical coherence tomography images for the clinical evaluation of stent implantation over time2012Conference paper (Refereed)
  • 17.
    Widman, Erik
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Caidahl, K.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    In vivo radial and longitudinal carotid artery plaque strain estimation via ultrasound-based speckle tracking2014In: 2014 IEEE International Ultrasonics Symposium (IUS), IEEE Computer Society, 2014, p. 523-526Conference paper (Refereed)
    Abstract [en]

    Our objective was to assess strain in common carotid artery (CCA) plaques using a previously validated speckle tracking algorithm. Radial and longitudinal strain was measured in 7 patients (77 ± 6 years) with carotid atherosclerosis and was compared with a quantitative visual assessment grading of plaques on the Gray-Weale scale by two experienced physicians. A greater pulse-pressure adjusted radial and longitudinal strain was found in echolucent plaques compared to echogenic plaques. This study shows the feasibility of ultrasound speckle tracking strain estimation in plaques and indicates the possibility to characterize plaques using speckle tracking strain in vivo.

  • 18.
    Widman, Erik
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Caidahl, Kenneth
    Karolinska Institutet.
    Heyde, Brecht
    KU Leuven.
    D’hooge, Jan
    KU Leuven.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Speckle tracking strain estimation of a carotid artery plaque phantom - Validation via sonomicrometry2013In: 2013 IEEE International Ultrasonics Symposium (IUS), IEEE conference proceedings, 2013, , p. 4p. 1757-1760Conference paper (Refereed)
    Abstract [en]

    Current clinical ultrasound-based methods for plaque characterization are limited to visual assessment of plaque echogenicity creating demand for quantitative diagnostic tools. Our objective was to validate radial and longitudinal speckle tracking (ST) strain in phantom plaques via sonomicrometry (sono), and to compare the peak plaque and arterial wall strain. Four carotid artery gel-phantoms with a soft wall inclusion, mimicking a vulnerable plaque, were constructed. The phantoms were connected to a programmable pump simulating a carotid flow. Cineloops were acquired using a GE Vivid E9 where radial and longitudinal strain were calculated using a normalized cross-correlation ST algorithm. The region of interest was adjusted according to the plaque size. Sonomicrometry was used as a reference measurement. The correlation between estimated mean peak strain and the reference peak strain was r = 0.96 (p < 0.001) radially and r = 0.75 (p ≤ 0.005) longitudinally. The soft plaque exhibited 35.1% (SD 16.9%) greater radial (p < 0.001) and 88.6% (SD 72.0%) greater longitudinal (p < 0.001) peak strain than the arterial wall when measured with speckle tracking. It was possible to estimate plaque strain by ST and to distinguish a soft plaque from the vessel wall via strain measurements.

  • 19.
    Widman, Erik
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Inst, Sweden.
    Maksuti, Elira
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Carrascal, Carolina Amador
    Urban, Matthew W.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Inst, Sweden.
    Evaluating Arterial and Plaque Elasticity with Shear Wave Elastography in an ex vivo Porcine Model2015In: 2015 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS), IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    Our objective was to use shear wave elastography (SWE) to characterize the mechanical properties of an arterial wall with a simulated calcified plaque in an ex vivo setup. A small porcine aorta was used as a model for a human carotid artery and attached to a fixture while pressurized with a water column. The stiffness of the arterial wall and a simulated plaque were estimated using SWE. The mean arterial wall and plaque shear modulus varied from 42 +/- 0 kPa to 100 +/- 1 kPa and 81 +/- 2 kPa to 174 +/- 2 kPa respectively over a pressure range of 20-120 mmHg. The results show the ability of SWE to characterize the mechanical properties of an arterial wall with a simulated plaque and take steps toward an in vivo implementation for quantitative plaque assessment.

  • 20.
    Widman, Erik
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Maksuti, Elira
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Larsson, David
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Urban, M.
    Caidahl, K.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Feasibility of shear wave elastography for plaque characterization2014In: IEEE International Ultrasonics Symposium, IUS, 2014, p. 1818-1821Conference paper (Refereed)
    Abstract [en]

    Determining plaque vulnerability is critical when selecting the most suitable treatment for patients with atherosclerotic plaque in the common carotid artery and quantitative characterization methods are needed. In this study, shear wave elastography (SWE) was used to characterize soft plaque mimicking inclusions in three atherosclerotic arterial phantoms by using phase velocity analysis in a static environment. The results were validated with axial tensile mechanical testing (MT). SWE measured a mean shear modulus of 5.8 ± 0.3 kPa and 25.0 ± 1.2 kPa versus 3.0 kPa and 30.0 kPa measured by mechanical testing in the soft plaques and phantom walls respectively. The results show good agreement between MT and SWE for both the plaque and phantom wall.

  • 21.
    Widman, Erik
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Maksuti, Elira
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Caidahl, K.
    D'Hooge, J.
    Shear wave elastography for characterization of carotid artery plaques-A feasibility study in an experimental setup2012In: 2012 IEEE International Ultrasonics Symposium (IUS), IEEE , 2012, p. 6562400-Conference paper (Refereed)
    Abstract [en]

    Characterization of vulnerable plaques in the carotid artery is critical for the prevention of ischemic stroke. However, ultrasound-based methods for plaque characterization used in the clinics today are limited to visual assessment and evaluation of plaque echogenicity. Shear Wave Elastography (SWE) is a new tissue characterization technique based on radiation force-induced shear wave propagation with potential use in plaque vulnerability assessment. The purpose of this study was to develop an experimental setup to test the feasibility of SWE for carotid plaque characterization. A carotid artery phantom with a soft inclusion in the wall, mimicking a vulnerable plaque, was constructed (10% polyvinyl alcohol (PVA), 3% graphite) by exposing the vessel and plaque to three and one freeze-thaw cycles (6h freeze, 6h thaw) respectively. An Aixplorer SWE system (Supersonic Imagine) was used to measure the shear wave speed (cT) in the vessel wall and plaque. The Young's modulus (E) was then calculated via the Moens-Korteweg (M-K) equation. For comparison, eight cylinders (d = 4 cm, h = 4 cm) were constructed for mechanical testing from the same PVA batch, of which four were exposed to three freeze-thaw cycles (mimicking the vessel wall) and four to one freeze-thaw cycle (mimicking the plaque). The Young's moduli for the cylinders were obtained via a displacement controlled mechanical compression test (Instron 5567) by applying 5% strain. The mean shear wave speed was 2.6 (±0.7) m/s in the vessel wall, 1.8 (±0.7) m/s in the plaque, resulting in Evessel = 11.5 (±0.5) kPa, Eplaque = 4.3 (±0.5) kPa. The compression tests resulted in E = 64.2 (±11.1) kPa in the hard cylinder and E = 9.7 (±3.1) kPa in the soft cylinder. The results showed that it was possible to distinguish between the arterial wall and the plaque. The disagreement between mechanical testing and SWE can be explained by the fact that the shear wave does not propagate monochromatically in cylindrical geometry. To achieve a better calculation of the elastic modulus, the frequency dependency of the shear wave velocity must be considered.

  • 22. Zahnd, G.
    et al.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    Gao, H.
    Serusclat, A.
    Vray, D.
    D'Hooge, J.
    A novel method to generete synthetic ultrasound data of the carotid artery based on in vivo observation as a tool to validate algorithm accuracy2012In: 2012 IEEE International Ultrasonics Symposium (IUS), 2012, p. 1674-1677Conference paper (Refereed)
    Abstract [en]

    Ultrasound imaging represents a well designed modality to estimate the motion of biological tissues in vivo, from which relevant clinical information can be assessed. However, the lack of ground truth constitutes a challenging issue when it comes to evaluate the accuracy of computerized methods. Indeed, quantification of the reliability of experimental results often involves manual or visual human operations, which may introduce subjectivity and variability. Nonetheless, numerical simulation of the imaged tissues allow a comparison with a known reference. For this purpose, we propose in this work a realistic kinematic multi-layer model of the common carotid artery. A set of 10 models was generated by randomly positioning scatterers, on which intensity, specular reflection, and bi-dimensional motion over the duration of one cardiac cycle were applied. Two computerized methods, namely a block-matching method and a segmentation method, were also applied on our model using identical parameter settings as those used for in vivo clinical data, in the objective to assess their accuracy. The tracking errors were 42 ± 40 μm and 12 ± 10 μm in the longitudinal and radial directions, respectively. The segmentation errors were 28±18 μm for the lumen diameter, and 15±10 μm for the intima-media thickness. We conclude from these results that our model can constitute a reliable method to quantify the accuracy of computerized algorithms.

1 - 22 of 22
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