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  • 1. Bassan, Gioia
    et al.
    Larsson, David
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Nordenfur, Tim
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    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.
    Acquisition of multiple mode shear wave propagation in transversely isotropic medium using dualprobe setup2015Conference paper (Refereed)
  • 2.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering.
    New ultrasonographic approaches to monitoring cardiac and vascular function2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Atherosclerotic cardiovascular disease is the leading cause of death worldwide. To decrease mortality and morbidity in cardiovascular disease, the development of accurate, non-invasive methods for early diagnosis of atherosclerotic cardiac and vascular engagement is of considerable clinical interest. Cardiovascular ultrasound imaging is today the cornerstone in the routine evaluation of cardiovascular function and recent development has resulted in two new techniques, tissue velocity imaging (TVI) and speckle tracking, which allow objective quantification of cardiovascular function. TVI and speckle tracking are the basis for three new approaches to cardiac and vascular monitoring presented in this thesis: wave intensity wall analysis (WIWA), two-dimensional strain imaging in the common carotid artery, and the state diagram of the heart.

     

    WIWA uses longitudinal and radial strain rate as input for calculations of wave intensity in the arterial wall. In this thesis, WIWA was validated against a commercially available wave intensity system, showing that speckle tracking-derived strain variables can be useful in wave intensity analysis. WIWA was further tested in patients with end stage renal disease and documented high mortality in cardiovascular disease. The latter study evaluated the effects of a single session of hemodialysis using WIWA and TVI variables and showed improved systolic function after hemodialysis. The results also indicated that preload-adjusted early systolic wave intensity obtained by the WIWA system may contribute in the assessment of left ventricular contractility in this patient category. Two-dimensional strain imaging in the common carotid artery is a new approach showing great potential to detect age-dependent differences in mechanical properties of the common carotid artery. Among the measured strain variables, global circumferential strain had the best discriminating performance and appeared to be superior to conventional measures of arterial stiffness such as elastic modulus and β stiffness index. The state diagram is a visualisation tool that provides a quantitative overview of the temporal interrelationship of mechanical events in the left and right ventricles. Case examples and a small clinical study showed that state diagrams clearly visualize cardiac function and can be useful in the detection of non ST-elevation myocardial infarction (NSTEMI).

     

    Even though WIWA, two-dimensional strain imaging in the common carotid artery and the state diagram show potential to be useful in the evaluation of cardiovascular function, there still remains a considerable amount of work to be done before they can be used in the daily clinical practice.

  • 3.
    Bjällmark, Anna
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Gustafsson, U
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    Waldenström, A
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    A system to quantify and visualize ventricular rotation pattern of the heart2009Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    Different modalities have been used to describe the rotational motion of the ventricles of the heart and studies have indicated LV twist to be an additional integral component in LV function. So far, only amplitudes and timings of rotation have been reported, whereas no method is available to fully describe the rotation pattern of the ventricles. The object of the present application is to achieve a system that presents a novel way to quantify and visualize the ventricular rotation pattern of the heart. We present a novel method that assesses and describes the rotation pattern by calculating the rotation axis of the ventricle. Non- invasive image acquisition is required to collect rotation values from different positions of the myocardium. Thereafter, a kinematic model of a ventricle is constructed to determine the rotation planes at different levels of the heart. The motion of the rotation planes are visualized by plotting the normal vectors of the planes over time, i.e. the rotation axis of the planes. This new method is different to all other methods used today for assessing cardiac function, as it does not describe the amplitude of a motion but the relationship in motion between different parts within a ventricle. Preliminary results indicate that the rotation axis is more sensitive to changes in the rotation pattern than conventional measurements of ventricular rotation. This new method could be used for early detection of cardiac diseases and for selection of patients for and optimization of cardiac resynchronization therapy.

  • 4.
    Bjällmark, Anna
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    Nowak, Jacek
    Lind, Britta
    KTH, School of Technology and Health (STH), Medical Engineering.
    Hayashi, Shirley
    Mazza do Nascimento, Marcelo
    Riella, Miquel
    Seeberger, Astrid
    Effects of hemodialysis on the cardiovascular system: Quantitative analysis using wave intensity wall analysis and tissue velocity imaging2010In: Heart and Vessels, ISSN 0910-8327, E-ISSN 1615-2573Article in journal (Refereed)
    Abstract [en]

    Cardiovascular disease is the leading cause of death in patients with end stage renal disease (ESRD). The aim of this study was to investigate the changes in cardiovascular function induced by a single session of hemodialysis (HD) by the analysis of cardiovascular dynamics using wave intensity wall analysis (WIWA) and of systolic and diastolic myocardial function using tissue velocity imaging (TVI). Grey-scale cine loops of the left common carotid artery, conventional echocardiography and TVI images of the left ventricle were acquired before and after HD in 45 patients (17 women, mean age 54) with ESRD. The WIWA indexes, W1 preload-adjusted W1, W2 and preload-adjusted W2, and the TVI variables, isovolumic contraction velocity (IVCV), isovolumic contraction time (IVCT), peak systolic velocity (PSV), displacement, isovolumic relaxation velocity (IVRV), isovolumic relaxation time (IVRT), peak early diastolic velocity (E’) and peak late diastolic velocity (A’), were compared before and after HD. The WIWA measurements showed significant increases in W1 (p < 0.05) and preload-adjusted W1 (p < 0.01) after HD. W2 was significantly decreased (p < 0.05) after HD, whereas the change in preload-adjusted W2 was not significant. Systolic velocities, IVCV (p < 0.001) and PSV (p < 0.01), were increased after HD, whereas the AV-plane displacement were decreased (p < 0.01). For the measured diastolic variables, E’ was significantly decreased (p < 0.01) and IVRT was significantly prolonged (p < 0.05), after HD. A few correlations were found between WIWA and TVI variables. The WIWA and TVI measurements indicate that a single session of HD improves systolic function. The load dependency of the diastolic variables seems to be more pronounced than for the systolic variables. Preload-adjusted wave intensity indexes may contribute in the assessment of true LV contractility and relaxation.

  • 5.
    Bjällmark, Anna
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    Lind, Britta
    KTH, School of Technology and Health (STH), Medical Engineering.
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    Winter, Reidar
    Westholm, Carl
    Jacobsen, Per
    Velocity tracking - a novel method for quantitative analysis of longitudinal myocardial function2007In: Journal of the American Society of Echocardiography, ISSN 0894-7317, E-ISSN 1097-6795, Vol. 20, no 7, p. 847-856Article in journal (Refereed)
    Abstract [en]

    Doppler tissue imaging is a method for quantitative analysis of longitudinal myocardial velocity. Commercially available ultrasound systems can only present velocity information using a color Dopplerbased overlapping continuous color scale. The analysis is time-consuming and does not allow for simultaneous analysis in different projections. We have developed a new method, velocity tracking, using a stepwise color coding of the regional longitudinal myocardial velocity. The velocity data from 3 apical projections are presented as static and dynamic bull's-eye plots to give a 3-dimensional understanding of the function of the left ventricle. The static bull's-eye plot can display peak systolic velocity, late diastofic tissue velocity, or the sum of peak systolic velocity and early diastolic tissue velocity. Conversely, the dynamic bull's-eye plot displays how the myocardial velocities change over one heart cycle. Velocity tracking allows for a fast, simple, and hituitive visual analysis of the regional longitudinal contraction pattern of the left ventricle with a great potential to identify characteristic pathologic patterns.

  • 6.
    Bjällmark, Anna
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    Shahgaldi, Kambiz
    Lind, Britta
    KTH, School of Technology and Health (STH).
    Winter, Reidar
    Brodin, Lars-Ake
    KTH, School of Technology and Health (STH), Medical Engineering.
    Differences in myocardial velocities during supine and upright exercise stress echocardiography in healthy adults2009In: Clinical Physiology and Functional Imaging, ISSN 1475-0961, E-ISSN 1475-097X, Vol. 29, no 3, p. 216-223Article in journal (Refereed)
    Abstract [en]

    Tissue Velocity Imaging (TVI) is a method for quantitative analysis of longitudinal myocardial velocities, which can be used during exercise and pharmacological stress echocardiography. It is of interest to evaluate cardiac response to different types of stress tests and the differences between upright and supine bicycle exercise tests have not been fully investigated. Therefore, the aim of this study was to compare cardiac response during supine and upright exercise stress tests. Twenty young healthy individuals underwent supine and upright stress test. The initial workload was set to 30 W and was increased every minute by a further 30 W until physical exhaustion. Tissue Doppler data from the left ventricle were acquired at the end of every workload level using a GE Vivid7 Dimension system (> 200 frames s(-1)). In the off-line processing, isovolumic contraction velocity (IVCV), peak systolic velocity (PSV), isovolumic relaxation velocity (IVRV), peak early diastolic velocity (E') and peak late diastolic velocity (A') were identified at every workload level. No significant difference between the tests was found in PSV. On the contrary, E' was shown to be significantly higher (P < 0.001) during supine exercise than during upright exercise and IVRV was significantly lower (P < 0.001) during supine exercise compared to upright exercise. Upright and supine exercise stress echocardiography give a comparable increase in measured systolic velocities and significant differences in early diastolic velocities.

  • 7.
    Bjällmark, Anna
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Lind, Britta
    KTH, School of Technology and Health (STH), Medical Engineering.
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    Peolsson, Michael
    KTH, School of Technology and Health (STH).
    Shahgaldi, Kambiz
    KTH, School of Technology and Health (STH), Medical Engineering.
    Nowak, Jacek
    Ultrasonographic strain imaging is superior to conventional non-invasive measures of vascular stiffness in the detection of age-dependent differences in the mechanical properties of the common carotid artery2010In: European Journal of Echocardiography, ISSN 1525-2167, E-ISSN 1532-2114, Vol. 11, no 7, p. 630-636Article in journal (Refereed)
    Abstract [en]

    Aims: Elastic properties of large arteries have been shown to deteriorate with age and in the presence of atherosclerotic vascular disease. In this study, the performance of ultrasonographic strain measurements was compared to conventional measures of vascular stiffness in the detection of age-dependent differences in the elastic properties of the common carotid artery.

    Methods and results: In 10 younger (25-28 years, 4 women) and 10 older (50-59 years, 4 women) healthy individuals, global and regional circumferential and radial strain variables were measured in the short-axis view of the right common carotid artery using ultrasonographic two-dimensional (2D) strain imaging with recently introduced speckle tracking technique. Conventional elasticity variables, elastic modulus (Ep) and β stiffness index, were calculated using M-mode sonography and non-invasive blood pressure measurements. Global and regional circumferential systolic strain and strain rate values were significantly higher (p < 0.001, p < 0.01 for regional late systolic strain rate) in the younger individuals, whereas the values of conventional elasticity variables in the same group were lower (p < 0.05). Among all strain and conventional elasticity variables, principal component analysis and its regression extension identified only circumferential systolic strain variables as contributing significantly to the observed discrimination between the younger and older age groups.

    Conclusion: Ultrasonographic 2D-strain imaging is a sensitive method for the assessment of elastic properties in the common carotid artery, being in this respect superior to conventional measures of vascular elasticity. The method has potential to become a valuable non-invasive tool in the detection of early atherosclerotic vascular changes.

  • 8.
    Brodin, Lars-Åke
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Elmqvist, H
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    Global and local detection of blood vessel elasticity2006Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    The present invention is a non-invasive analysis system for detection of global and local blood vessel elasticity. The analysis system comprises two subsystems where subsystem 1 is data collecting unit and subsystem 2 is an analysis unit. The data collecting unit comprises one or many non-invasive image generating systems, or the data collecting system makes the registration possible of movement parameters that quantifies the dynamics of the blood vessel wall in longitudinal and radial directions. Subsystem 2 performs Wave Intensity Analysis which is an analysis method using co-related parts of the circulation system by measuring the intensity change (dl) of the blood vessel during a heart cycle. The intensity change is calculated as the product of the pressure derivate and the flow velocity derivate. In subsystem 2 the changes of pressure and flow are approximated by the deformation velocity or velocity of the radial and longitudinal direction, respectively. By calculating time constants and amplitudes of the intensity change graph a measure is obtained of the local and global elasticity of the blood vessel and atherosclerotic constrictions of arterial vessels may then be identified at an early stage.

  • 9.
    Broomé, Michael
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Frenckner, Björn
    Broman, Mikaeö
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Recirculation during veno-venous extra-corporeal membrane oxygenation: a simulation study2015In: International Journal of Artificial Organs, ISSN 0391-3988, E-ISSN 1724-6040, Vol. 38, no 1, p. 23-30Article in journal (Refereed)
    Abstract [en]

    PURPOSE:

    Veno-venous ECMO is indicated in reversible life-threatening respiratory failure without life-threatening circulatory failure. Recirculation of oxygenated blood in the ECMO circuit decreases efficiency of patient oxygen delivery but is difficult to measure. We seek to identify and quantify some of the factors responsible for recirculation in a simulation model and compare with clinical data.

    METHODS:

    A closed-loop real-time simulation model of the cardiovascular system has been developed. ECMO is simulated with a fixed flow pump 0 to 5 l/min with various cannulation sites - 1) right atrium to inferior vena cava, 2) inferior vena cava to right atrium, and 3) superior+inferior vena cava to right atrium. Simulations are compared to data from a retrospective cohort of 11 consecutive adult veno-venous ECMO patients in our department.

    RESULTS:

    Recirculation increases with increasing ECMO-flow, decreases with increasing cardiac output, and is highly dependent on choice of cannulation sites. A more peripheral drainage site decreases recirculation substantially.

    CONCLUSIONS:

    Simulations suggest that recirculation is a significant clinical problem in veno-venous ECMO in agreement with clinical data. Due to the difficulties in measuring recirculation and interpretation of the venous oxygen saturation in the ECMO drainage blood, flow settings and cannula positioning should rather be optimized with help of arterial oxygenation parameters. Simulation may be useful in quantification and understanding of recirculation in VV-ECMO.

  • 10.
    Broomé, Michael
    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.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Frenckner, Björn
    Janerot-Sjöberg, Birgitta
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Closed-loop real-time simulation model of hemodynamics and oxygen transport in the cardiovascular system2013In: Biomedical engineering online, ISSN 1475-925X, E-ISSN 1475-925X, Vol. 12, no 1, p. 69-Article in journal (Refereed)
    Abstract [en]

    Background: Computer technology enables realistic simulation of cardiovascular physiology. The increasing number of clinical surgical and medical treatment options imposes a need for better understanding of patient-specific pathology and outcome prediction. Methods: A distributed lumped parameter real-time closed-loop model with 26 vascular segments, cardiac modelling with time-varying elastance functions and gradually opening and closing valves, the pericardium, intrathoracic pressure, the atrial and ventricular septum, various pathological states and including oxygen transport has been developed. Results: Model output is pressure, volume, flow and oxygen saturation from every cardiac and vascular compartment. The model produces relevant clinical output and validation of quantitative data in normal physiology and qualitative directions in simulation of pathological states show good agreement with published data. Conclusion: The results show that it is possible to build a clinically relevant real-time computer simulation model of the normal adult cardiovascular system. It is suggested that understanding qualitative interaction between physiological parameters in health and disease may be improved by using the model, although further model development and validation is needed for quantitative patient-specific outcome prediction.

  • 11. Broomé, Michael
    et al.
    Maksuti, Elira
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Waldenström, Anders
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Simulation of arterial hypertension and progressive arteriosclerosis with a 0-D multipurpose cardiovascular model2013In: CMBE13: 3rd International Conference on Computational & Mathematical Biomedical Engineering, 2013, p. 433-436Conference paper (Refereed)
    Abstract [en]

    The effects of systemic vascular resistance and progressive stiffening/arteriosclerosis inthe vascular tree on arterial blood pressure is explored in a 0D cardiovascular simulationmodel. Pulse pressure is both sensitive and specific for increases in stiffness and meanarterial pressure both sensitive and specific for changes in vascular resistance.

  • 12. Falkmer, Marita
    et al.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    Falkmer, Torbjorn
    Recognition of facially expressed emotions and visual search strategies in adults with Asperger syndrome2011In: RES AUTISM SPECTR DISORD, ISSN 1750-9467, Vol. 5, no 1, p. 210-217Article in journal (Refereed)
    Abstract [en]

    Can the disadvantages persons with Asperger syndrome frequently experience with reading facially expressed emotions be attributed to a different visual perception, affecting their scanning patterns? Visual search strategies, particularly regarding the importance of information from the eye area, and the ability to recognise facially expressed emotions were compared between 24 adults with Asperger syndrome and their matched controls. While wearing a head mounted eye tracker, the participants viewed 12 pairs of photos of faces. The first photo in each pair was cut up into puzzle pieces. Six of the 12 puzzle pieced photos had the eyes bisected. The second photo showed a happy, an angry and a surprised face of the same person as in the puzzle pieced photo. Differences in visual search strategies between the groups were established. Adults with Asperger syndrome had greater difficulties recognizing these basic emotions than controls. The distortion of the eye area affected the ability to identify emotions even more negatively for participants with Asperger syndrome.

  • 13. Falkmer, Marita
    et al.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    Falkmer, Torbjörn
    The influences of static and interactive dynamic facial stimuli on visual strategies in persons with Asperger syndrome2011In: Research in Autism Spectrum Disorders, ISSN 1750-9467, Vol. 5, no 2, p. 935-940Article in journal (Refereed)
    Abstract [en]

    Several studies, using eye tracking methodology, suggest that different visual strategies in persons with autism spectrum conditions, compared with controls, are applied when viewing facial stimuli. Most eye tracking studies are, however, made in laboratory settings with either static (photos) or non-interactive dynamic stimuli, such as video clips. Whether or not these results are transferable to a "real world" dialogue situation remains unclear. In order to examine the consistency of visual strategies across conditions, a comparison of two static conditions and an interactive dynamic "real world" condition, in 15 adults with Asperger syndrome and 15 matched controls, was made using an eye tracker. The static stimuli consisted of colour photos of faces, while a dialogue between the participants and the test leader created the interactive dynamic condition. A within-group comparison showed that people with AS, and their matched controls, displayed a high degree of stability in visual strategies when viewing faces, regardless of the facial stimuli being static or real, as in the interactive dynamic condition. The consistency in visual strategies within the participants suggests that results from studies with static facial stimuli provide important information on individual visual strategies that may be generalized to "real world" situations.

  • 14. Falkmer, Marita
    et al.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering.
    Falkmer, Torbjörn
    The importance of the eye area in face identification abilities and visual search strategies in persons with Asperger syndrome2010In: Research in Autism Spectrum Disorders, ISSN 1750-9467, Vol. 4, no 4, p. 724-730Article in journal (Refereed)
    Abstract [en]

    Partly claimed to explain social difficulties observed in people with Asperger syndrome, face identification and visual search strategies become important. Previous research findings are, however, disparate. In order to explore face identification abilities and visual search strategies, with special focus on the importance of the eye area, 24 adults with Asperger syndrome and matched controls viewed puzzle pieced photos of faces, in order to identify them as one of three intact photos of persons. Every second puzzle pieced photo had the eyes distorted. Fixation patterns were measured by an eye tracker. Adults with Asperger syndrome had greater difficulties in identifying faces than controls. However, the entire face identification superiority in controls was found in the condition when the eyes were distorted supporting that adults with Aspergers syndrome do use the eye region to a great extent in face identification. The visual search strategies in controls were more effective and relied on the use of the 'face information triangle', i.e. the two eyes and the mouth, while adults with Asperger syndrome had more fixations on other parts of the face, both when obtaining information and during the identification part, suggesting a less effective use of the 'face information triangle'.

  • 15. Falkmer, Torbjern
    et al.
    Dahlman, Joakim
    Dukic, Tania
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    Fixation identification in centroid versus start-point modes using eye-tracking data2008In: Perceptual and Motor Skills, ISSN 0031-5125, E-ISSN 1558-688X, Vol. 106, no 3, p. 710-724Article in journal (Refereed)
    Abstract [en]

    Fixation-identification algorithms, needed for analyses of eye movements, may typically be separated into three categories, viz. (i) velocity-based algorithms, (ii) area-based algorithms, and (iii) dispersion-based algorithms. Dispersion-based algorithms are commonly used but this application introduces some difficulties, one being optimization. Basically, there are two modes to reach this goal of optimization, viz., the start-point mode and the centroid mode. The aim of the present study was to compare and evaluate these two dispersion-based algorithms. Manual inspections were made of 1,400 fixations in each mode. Odds ratios showed that by using the centroid mode for fixation detection, a valid fixation is 2.86 times more likely to be identified than by using the start-point mode. Moreover, the algorithm based on centroid mode dispersion showed a good interpretation speed, accuracy, robustness, and ease of implementation, as well as adequate parameter settings.

  • 16.
    Hayashi, Shirley Yumi
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering. Karolinska University Hospital Huddinge, Stockholm, Sweden .
    Nowak, Jacek
    Lindholm, Bengt
    do Nascimento, Marcelo Mazza
    Lind, Britta
    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.
    Pachaly, Maria Aparecida
    Seeberger, Astrid
    Riella, Miguel C.
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    Left ventricular mechanical dyssynchrony in patients with different stages of chronic kidney disease and the effects of hemodialysis2013In: Hemodialysis International, ISSN 1492-7535, E-ISSN 1542-4758, Vol. 17, no 3, p. 346-358Article in journal (Refereed)
    Abstract [en]

    Left ventricular (LV) dyssynchrony is a known cause of mortality in patients with heart failure and may possibly play a similar role in patients with chronic kidney disease (CKD) in whom sudden death is one of the most common and as yet not fully explained cause of death. LV synchronicity and its relationship with increased volume load and various biomarkers was analyzed in 145 patients including 53 patients with CKD stages 3 and 4 and in 92 CKD stage 5 patients undergoing hemodialysis (HD) or peritoneal dialysis (PD) using color tissue Doppler imaging and tissue synchronization imaging. The HD patients were evaluated both before and after a single HD session. LV dyssynchrony was defined as a regional difference in time to peak systolic myocardial velocity, between 12 LV segments>105milliseconds. LV dyssynchrony was present in 54% of the patients with no difference between CKD 3 and 4 (58%), HD (48%), and PD (51%). LV dyssynchrony was independently associated with LV mass index and increased estimation of LV end-diastolic pressure. A single HD session resulted in significant changes in LV synchronicity variableswith improvement in 50% of the patientsespecially in patients with higher myocardial systolic velocities and lower LV mass index. Abnormalities in LV synchronicity are highly prevalent in CKD patients already prior to dialysis treatment and are associated with LV hypertrophy, LV dysfunction and load conditions, underlining the importance of volume status for LV synchronicity in CKD patients.

  • 17.
    Härmark, Johan
    et al.
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Structural Biotechnology.
    Larsson, Malin K.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Razuvajev, Anton
    Koeck, Philip JB
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Structural Biotechnology.
    Paradossi, Gaio
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Caidahl, Kenneth
    Hebert, Hans
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Structural Biotechnology.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Investigation of the elimination process of a multimodal polymer-shelled contrast agent in rats using ultrasound and transmission electron microscopy2015In: Biomedical Spectroscopy and Imaging, ISSN 2212-8794, Vol. 4, no 1, p. 81-93Article in journal (Refereed)
    Abstract [en]

    BACKGROUND: A novel polymer-shelled contrast agent (CA) with multimodal imaging and target specific potential was developed recently and tested for its acoustical properties using different in-vitro setups.

    OBJECTIVE: The aim of this study was to investigate the elimination of three types of the novel polymer-shelled CA, one unmodified and two shell modified versions, in rats.

    METHODS: The blood elimination time was estimated by measuring the image intensity, from ultrasound images of the common carotid artery, over time after a bolus injection of the three types of the novel CA. The commercially available CA SonoVue was used as a reference. The subcellular localization of the three CAs was investigated using transmission electron microscopy.

    RESULTS: The ultrasound measurements indicated a blood half-life of 17–85 s for the different types of the novel CA, which was significant longer than the blood half-life time for SonoVue. Additionally, CAs were exclusively found in the circulatory system, either taken up by, or found in the vicinity of macrophages.

    CONCLUSIONS: Compared to the commercially available CA SonoVue, the blood circulation times for the three types of the novel polymer-shelled CA were prolonged. Moreover, macrophages were suggested to be responsible for the elimination of the CA.

  • 18.
    Josefsson, Leila
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Larsson, Malin K.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Institute, Sweden.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Analysis of polyvinyl alcohol microbubbles in human blood plasma using capillary electrophoresis2016In: Journal of Separation Science, ISSN 1615-9306, E-ISSN 1615-9314, Vol. 39, no 8, p. 1551-1558Article in journal (Refereed)
    Abstract [en]

    Recently, a new type of ultrasound contrast agent that consists of air-filled microbubbles stabilized with a shell of polyvinyl alcohol was developed. When superparamagnetic nanoparticles of iron oxide are incorporated in the polymer shell, a multimodal contrast agent can be obtained. The biodistribution and elimination pathways of the polyvinyl alcohol microbubbles are essential to investigate, which is limited with today's techniques. The aim of the present study was, therefore, to develop a method for qualitative and quantitative analysis of microbubbles in biological samples using capillary electrophoresis with ultraviolet detection. The analysis parameters were optimized to a wavelength at 260 nm and pH of the background electrolyte ranging between 11.9 and 12. Studies with high-intensity ultrasonication degraded microbubbles in water showed that degraded products and intact microbubbles could be distinguished, thus it was possible to quantify the intact microbubbles solely. Analysis of human blood plasma spiked with either plain microbubbles or microbubbles with nanoparticles demonstrated that it is possible to separate them from biological components like proteins in these kinds of samples.

  • 19.
    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.

  • 20.
    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)
  • 21.
    Larsson, Malin
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Da Silva, Cristina
    Department of Cardiology, Karolinska Institutet, Karolinska University Hospital.
    Gunyeli, Elif
    Department of Cardiology, Karolinska Institutet, Karolinska University Hospital.
    Akebat Bin Ilami, Ali
    Department of Cardiology, Karolinska Institutet, Karolinska University Hospital.
    Szummer, Karolina
    Department of Cardiology, Karolinska Institutet, Karolinska University Hospital.
    Winter, Reidar
    Department of Cardiology, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    The potential clinical value of contrast-enhanced echocardiography beyond current recommendationsManuscript (preprint) (Other academic)
  • 22.
    Larsson, Malin K.
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Da Silva, Cristina
    Gunyeli, Elif
    Bin Ilami, Ali Akebat
    Szummer, Karolina
    Winter, Reidar
    KTH, School of Technology and Health (STH), Medical Engineering. Karolinska University Hospital, Sweden.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering. Karolinska Institutet, Sweden.
    The potential clinical value of contrast-enhanced echocardiography beyond current recommendations2016In: Cardiovascular Ultrasound, ISSN 1476-7120, E-ISSN 1476-7120, Vol. 14, article id 2Article in journal (Refereed)
    Abstract [en]

    Background: Contrast agents are used in resting echocardiography to opacify the left ventricular (LV) cavity and to improve LV endocardial border delineation in patients with suboptimal image quality. If a wider use of contrast-enhanced echocardiography would be adopted instead of the current selective approach, diagnoses such as myocardial ischemia and LV structural abnormalities could potentially be detected earlier. The aim was therefore to retrospectively investigate if contrast- enhanced echocardiography beyond the current recommendations for contrast agent usage affects assessment of wall motion abnormalities, ejection fraction (EF) and detection of LV structural abnormalities. A secondary aim was to evaluate the user dependency during image analysis. Methods: Experienced readers (n = 4) evaluated wall motion score index (WMSI) and measured EF on greyscale and contrast-enhanced images from 192 patients without indications for contrast-enhanced echocardiography. Additionally, screening for LV structural abnormalities was performed. Repeated measurements were performed in 20 patients by the experienced as well as by inexperienced (n = 2) readers. Results: Contrast analysis resulted in significantly higher WMSI compared to greyscale analysis (p < 0.003). Of the 83 patients, classified as healthy by greyscale analysis, 55 % were re-classified with motion abnormalities by contrast analysis. No significant difference in EF classification (>= 55 %, 45-54 %, 30-44 %, < 30 %) was observed. LV structural abnormalities, such as increased trabeculation (n = 21), apical aneurysm (n = 4), hypertrophy (n = 1) and thrombus (n = 1) were detected during contrast analysis. Intra- and interobserver variability for experienced readers as well as the variability between inexperienced and experienced readers decreased for WMSI and EF after contrast analysis. Conclusions: Contrast-enhanced echocardiography beyond current recommendations for contrast agent usage increased the number of detected wall motion and LV structural abnormalities. Moreover, contrast- enhanced echocardiography increased reproducibility for assessment of WMSI and EF.

  • 23.
    Larsson, Malin K.
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Nowak, Greg
    Paradossi, Gaio
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Janerot Sjöberg, Birgitta
    KTH, School of Technology and Health (STH), Medical Engineering.
    Caidahl, Kenneth
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Endocardial border delineation capability of a novel multimodal polymer-shelled contrast agent2014In: Cardiovascular Ultrasound, ISSN 1476-7120, E-ISSN 1476-7120, Vol. 12, p. 24-Article in journal (Refereed)
    Abstract [en]

    Background: A novel polymer-shelled contrast agent (CA) with multimodal and target-specific potential was developed recently. To determine its ultrasonic diagnostic features, we evaluated the endocardial border delineation as visualized in a porcine model and the concomitant effect on physiological variables. Methods: Three doses of the novel polymer-shelled CA (1.5 ml, 3 ml, and 5 ml [5 x 10(8) microbubbles (MBs)/ml]) and the commercially available CA SonoVue (1.5 ml [2-5 x 10(8) MBs/ml]) were used. Visual evaluations of ultrasound images of the left ventricle were independently performed by three observers who graded each segment in a 6-segment model as either 0 = not visible, 1 = weakly visible, or 2 = visible. Moreover, the duration of clinically useful contrast enhancement and the left ventricular opacification were determined. During anesthesia, oxygen saturation, heart rate, and arterial pressure were sampled every minute and the effect of injection of CA on these physiological variables was evaluated. Results: The highest dose of the polymer-shelled CA gave results comparable to SonoVue. Thus, no significant difference in the overall segment score distribution (2-47-95 vs. 1-39-104), time for clinically sufficient contrast enhancement (20-40 s for both) and left ventricular overall opacification was found. In contrast, when comparing the endocardial border delineation capacity for different regions SonoVue showed significantly higher segment scores for base and mid, except for the mid region when injecting 1.5 ml of the polymer-shelled CA. Neither high nor low doses of the polymer-shelled CA significantly affected the investigated physiological variables. Conclusions: This study demonstrated that the novel polymer-shelled CA can be used in contrast-enhanced diagnostic imaging without influence on major physiological variables.

  • 24.
    Larsson, Malin
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    Oddo, Letizia
    Margheritelli, Silvia
    Paradossi, Gaio
    Nowak, Jacek
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    Caidahl, Kenneth
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering.
    Visualization of multimodal polymer-shelled contrast agents using ultrasound contrast sequences: an experimental study in a tissue mimicking flow phantom2013In: Cardiovascular Ultrasound, ISSN 1476-7120, E-ISSN 1476-7120, Vol. 11, p. 33-Article in journal (Refereed)
    Abstract [en]

    Background: A multimodal polymer-shelled contrast agent (CA) with target specific potential was recently developed and tested for its acoustic properties in a single element transducer setup. Since the developed polymeric CA has different chemical composition than the commercially available CAs, there is an interest to study its acoustic response when using clinical ultrasound systems. The aim of this study was therefore to investigate the acoustic response by studying the visualization capability and shadowing effect of three polymer-shelled CAs when using optimized sequences for contrast imaging. Methods: The acoustic response of three types of the multimodal CA was evaluated in a tissue mimicking flow phantom setup by measuring contrast to tissue ratio (CTR) and acoustic shadowing using five image sequences optimized for contrast imaging. The measurements were performed over a mechanical index (MI) range of 0.2-1.2 at three CA concentrations (10(6), 10(5), 10(4) microbubbles/ml). Results: The CTR-values were found to vary with the applied contrast sequence, MI and CA. The highest CTR-values were obtained when a contrast sequence optimized for higher MI imaging was used. At a CA concentration of 106 microbubbles/ml, acoustic shadowing was observed for all contrast sequences and CAs. Conclusions: The CAs showed the potential to enhance ultrasound images generated by available contrast sequences. A CA concentration of 106 MBs/ml implies a non-linear relation between MB concentration and image intensity.

  • 25.
    Larsson, Matilda
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering.
    Lind, Britta
    KTH, School of Technology and Health (STH), Medical Engineering.
    Balzano, Rita
    KTH, School of Technology and Health (STH), Medical Engineering.
    Peolsson, Michael
    KTH, School of Technology and Health (STH).
    Winter, Reidar
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    Wave intensity wall analysis: a novel noninvasive method to measure wave inntensity2009In: Heart and Vessels, ISSN 0910-8327, E-ISSN 1615-2573, Vol. 24, p. 357-365Article in journal (Refereed)
    Abstract [en]

    Wave intensity analysis is a concept providing information about the interaction of the heart and the vascular system. Originally, the technique was invasive. Since then new noninvasive methods have been developed. A recently developed ultrasound technique to estimate tissue motion and deformation is speckle-tracking echocardiography. Speckle tracking-based techniques allow for accurate measurement of movement and deformation variables in the arterial wall in both the radial and the longitudinal direction. The aim of this study was to test if speckle tracking-derived deformation data could be used as input for wave intensity calculations. The new concept was to approximate changes of flow and pressure by deformation changes of the arterial wall in longitudinal and radial directions. Flow changes (dU/dt) were approximated by strain rate (sr, 1/s) of the arterial wall in the longitudinal direction, whereas pressure changes (dP/dt) were approximated by sign reversed strain rate (1/s) in the arterial wall in the radial direction. To validate the new concept, a comparison between the newly developed Wave Intensity Wall Analysis (WIWA) algorithm and a commonly used and validated wave intensity system (SSD-5500, Aloka, Tokyo, Japan) was performed. The studied population consisted of ten healthy individuals (three women, seven men) and ten patients (all men) with coronary artery disease. The present validation study indicates that the mechanical properties of the arterial wall, as measured by a speckle tracking-based technique are a possible input for wave intensity calculations. The study demonstrates good visual agreement between the two systems and the time interval between the two positive peaks (W1-W2) measured by the Aloka system and the WIWA system correlated for the total group (r = 0.595, P < 0.001). The correlation for the diseased subgroup was r = 0.797, P < 0.001 and for the healthy subgroup no significant correlation was found (P > 0.05). The results of the study indicate that the mechanical properties of the arterial wall could be used as input for wave intensity calculations. The WIWA concept is a promising new method that potentially provides several advantages over earlier wave intensity methods, but it still has limitations and needs further refinement and larger studies to find the optimal clinical use.

  • 26.
    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.

  • 27.
    Maksuti, Elira
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Institute, Sweden .
    Broomé, Michael
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Institute, Sweden .
    Modelling the heart with the atrioventricular plane as a piston unit2015In: Medical Engineering and Physics, ISSN 1350-4533, E-ISSN 1873-4030, Vol. 37, no 1, p. 87-92Article in journal (Refereed)
    Abstract [en]

    Medical imaging and clinical studies have proven that the heart pumps by means of minor outer volume changes and back-and-forth longitudinal movements in the atrioventricular (AV) region. The magnitude of AV-plane displacement has also shown to be a reliable index for diagnosis of heart failure. Despite this, AV-plane displacement is usually omitted from cardiovascular modelling. We present a lumped-parameter cardiac model in which the heart is described as a displacement pump with the AV plane functioning as a piston unit (AV piston). This unit is constructed of different upper and lower areas analogous with the difference in the atrial and ventricular cross-sections. The model output reproduces normal physiology, with a left ventricular pressure in the range of 8-130 mmHg, an atrial pressure of approximatly 9 mmHg, and an arterial pressure change between 75 mmHg and 130 mmHg. In addition, the model reproduces the direction of the main systolic and diastolic movements of the AV piston with realistic velocity magnitude (similar to 10 cm/s). Moreover, changes in the simulated systolic ventricular-contraction force influence diastolic filling, emphasizing the coupling between cardiac systolic and diastolic functions. The agreement between the simulation and normal physiology highlights the importance of myocardial longitudinal movements and of atrioventricular interactions in cardiac pumping.

  • 28.
    Maksuti, Elira
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Johnson, Jonas
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Broomé, Michael
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Institutet Department of Physiology and Pharmacology.
    Physical modeling of the heart with the atrioventricular plane as a piston unit2013Conference paper (Other academic)
    Abstract [en]

    Cardiac models do not often take the atrioventricular (AV) interactioninto account, even though medicalimaging and clinical studies have shown that the heart pumps with minorouter volume changes throughout the cardiac cycle and with backand forthlongitudinal movements in the AVregion. We present a novel cardiac model based on physical modeling of the heart withthe AV-plane asa piston unit. Model simulationsgeneratedrealistic outputsforpressures and flows as well asAV-piston velocity, emphasizing the relevance of myocardial longitudinal movements in cardiac function

  • 29.
    Maksuti, Elira
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Institutet, Sweden.
    Widman, Erik
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Institutet, Sweden.
    Larsson, David
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Urban, Matthew W.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Institutet, Sweden.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Institutet, Sweden.
    ARTERIAL STIFFNESS ESTIMATION BY SHEAR WAVE ELASTOGRAPHY: VALIDATION IN PHANTOMS WITH MECHANICAL TESTING2016In: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 42, no 1, p. 308-321Article in journal (Refereed)
    Abstract [en]

    Arterial stiffness is an independent risk factor found to correlate with a wide range of cardiovascular diseases. It has been suggested that shear wave elastography (SWE) can be used to quantitatively measure local arterial shear modulus, but an accuracy assessment of the technique for arterial applications has not yet been performed. In this study, the influence of confined geometry on shear modulus estimation, by both group and phase velocity analysis, was assessed, and the accuracy of SWE in comparison with mechanical testing was measured in nine pressurized arterial phantoms. The results indicated that group velocity with an infinite medium assumption estimated shear modulus values incorrectly in comparison with mechanical testing in arterial phantoms (6.7 +/- 0.0 kPa from group velocity and 30.5 +/- 0.4 kPa from mechanical testing). To the contrary, SWE measurements based on phase velocity analysis (30.6 +/- 3.2 kPa) were in good agreement with mechanical testing, with a relative error between the two techniques of 8.8 +/- 6.0% in the shear modulus range evaluated (40-100 kPa). SWE by phase velocity analysis was validated to accurately measure stiffness in arterial phantoms.

  • 30.
    Mårtensson, Mattias
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering.
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    Evaluation of tissue Doppler-based velocity and deformation imaging: a phantom study of ultrasound systems.2011In: European Journal of Echocardiography, ISSN 1525-2167, E-ISSN 1532-2114, Vol. 12, no 6, p. 467-476Article in journal (Refereed)
    Abstract [en]

    AIMS: The objective of this study was to test the accuracy and diagnostic interchangeability of tissue Doppler-based displacement, velocity, strain, and strain rate measurements in commercially used ultrasound (US) systems. METHODS AND RESULTS: Using an in-house made phantom, four different US scanner models were evaluated. Two different scanners of the same model were tested, and one scanner acquisition was tested twice with two generations of the same workstation giving six test results in total. The scanners were in active clinical use and are subject to regular maintenance checks. There were three displacement and four velocity results that stood out from the rest and could be regarded as accurate and interchangeable. Among the deformation measurements, three acceptable strain results were found while there were no acceptable strain rate results. Furthermore, the study showed that measurements from scanners of the same model, same acquisition post-processed on different workstations and repeated measurements from the same scanner, can yield disparate results. CONCLUSION: Measurements that are accurate and of interchangeable use can be found for displacement and velocity measurements, but are less likely to be found for strain and strain rate measurements. It is strongly recommended that the ability of each individual US scanner to measure displacement, velocity, strain, and strain rate is evaluated before it is introduced into clinical practice, and it must always be evaluated together with the workstation the scanner is intended to be used in conjunction with.

  • 31.
    Nordenfur, Tim
    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.
    Widman, Erik
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    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.
    A Comparison of Shear Wave Elastography Pushing Sequences2013Conference paper (Refereed)
  • 32. Westholm, Carl
    et al.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    Jacobsen, Per
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    Winter, Reidar
    Velocity tracking, a new and user independent method for detecting regional function of the left ventricle2009In: Clinical Physiology and Functional Imaging, ISSN 1475-0961, E-ISSN 1475-097X, Vol. 29, no 1, p. 24-31Article in journal (Refereed)
    Abstract [en]

    The use of two-dimensional echocardiography (2D echo) for detection of ischaemia is limited due to high user dependency. Longitudinal motion is sensitive for ischaemia and usable for quantitative measurement of longitudinal myocardial function but time consuming. Velocity tracking (VeT) is a new method that gives an easy three-dimensional understanding of both systolic and diastolic regional motion, using colour coded bull's eye presentation of longitudinal velocity, derived from colour coded tissue Doppler. The aim of this study was to test the accuracy of VeT in detecting ischaemia in non-ST-segment elevation myocardial infarction (NSTEMI) patients bedside. Twenty patients with NSTEMI and 10 controls were included. Echocardiography was performed within 24 h of symptoms and prior to coronary angiography. Bull's eye plots presenting the peak systolic velocity (PSV) and the sum of PSV and the E-wave-velocity (PSV+E) were created using our developed software. VeT was compared to expert wall motion scoring (WMS) and bedside echo. We used the clinical conclusion based on ECG, angiography and clinical picture as 'gold standard'. Sensitivity for ischaemia with VeT (PSV+E) was 85% and specificity 60%. The corresponding sensitivities for expert WMS were 75% (specificity 40%). For regional analysis VeT and WMS showed comparable results with correct regional outcome in 11/20 of patients both superior to bedside echo. Velocity tracking is a promising technique that provides an easily understandable three-dimensional bull's eye plot for assessment of regional left ventricular longitudinal velocity with great potential for detection of regional dysfunction and myocardial ischaemia.

  • 33.
    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.

  • 34.
    Widman, Erik
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Department of Molecular Medicine and Surgery, Karolinska Institutet, Solna, Sweden .
    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 W
    Bjallmark, 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. Department of Molecular Medicine and Surgery, Karolinska Institutet, Solna, Sweden .
    Shear wave elastography plaque characterization with mechanical testing validation: a phantom study.2015In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 60, no 8, p. 3151-3174Article in journal (Refereed)
    Abstract [en]

    Determining plaque vulnerability is critical when selecting the most suitable treatment for patients with atherosclerotic plaque. Currently, clinical non-invasive ultrasound-based methods for plaque characterization are limited to visual assessment of plaque morphology and new quantitative methods are needed. In this study, shear wave elastography (SWE) was used to characterize hard and soft plaque mimicking inclusions in six common carotid artery phantoms by using phase velocity analysis in static and dynamic environments. The results were validated with mechanical tensile testing. In the static environment, SWE measured a mean shear modulus of 5.8±0.3kPa and 106.2±17.2kPa versus 3.3±0.5kPa and 98.3±3.4kPa measured by mechanical testing in the soft and hard plaques respectively. Furthermore, it was possible to measure the plaques' shear moduli throughout a simulated cardiac cycle. The results show good agreement between SWE and mechanical testing and indicate the possibility for in vivo arterial plaque characterization using SWE.

  • 35.
    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.

  • 36.
    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.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    Bjällmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering.
    Nordenfur, Tim
    KTH, School of Technology and Health (STH), Medical Engineering.
    Caidahl, Kenneth
    D’hooge, Jan
    SHEAR WAVE ELASTOGRAPHY OF THE ARTERIAL WALL – WHERE WE ARE TODAY2013Conference paper (Refereed)
    Abstract [en]
    1. 1.  Introduction

    Shear Wave Elastography (SWE) is a recently developed noninvasive method for elastography assessment using ultrasound. The technique consists of sending an acoustic radiation force (pushing sequence) into the tissue that in turn generates an orthogonal low frequency propagating shear wave. The shear wave propagation is measured real time by high speed B-mode imaging. From the B-mode images, the shear wave is tracked via normalized cross-correlation and the speed is calculated, which is used to generate an elasticity map of the tissue’s shear modulus. To date, the technique has mostly been used in large homogeneous tissues such as breast and liver where it successfully detects lesions and tumors that are easily missed with normal B-mode ultrasound [1]. SWE could potentially be applied in vascular applications to assess elasticity of the arterial wall to characterize the stiffness as an early indicator of cardiac disease. Furthermore, SWE could aid in the characterization of plaques in the carotid artery, which is critical for the prevention of ischemic stroke

    1. 2.  Methods and Results

    An initial study was performed using an Aixplorer SWE system (Supersonic Imagine, France) to measure the shear modulus in a polyvinyl alcohol phantom (PVA) vessel with a plaque inclusion (Figure 1). It was possible to distinguish the softer inclusion mean shear wave speed (2.1 m/s) from the arterial wall (3.5 m/s) on the SWE colour-map, but the Young’s Modulus calculation of the arterial wall (E=19.8 kPa) did not match the measured Young’s Modulus (E=53.1 kPa) from comparative mechanical testing.

    We have begun implementing various pushing sequences (single unfocused push, single focused push, line push, comb push) on a programmable ultrasound machine (Verasonics, USA) using a linear transducer (Philips L7-4) in a homogeneous PVA phantom. An algorithm for one dimensional cross-correlation tracking and shear wave speed estimation has been developed and initially tested in an experimental setup

    1. 3.  Discussion

    According to our initial results, it is possible that SWE could be applied in vascular applications. However, the initial mechanical testing vs. SWE comparison indicated that further development to the post processing is needed before applying it on the carotid artery, which is a heterogeneous tissue with other wave propagation properties than e.g. breast tissue. The carotid artery has a difficult geometry to study for several reasons. The intima-media complex is very thin (< 1mm), and the vessel wall is not stationary. Furthermore, the cylindrical shape of the artery produces complex wave reflections within the arterial wall, which result in a polychromatic propagation of the shear wave. A few studies have applied techniques based on SWE to the arterial wall with promising results and a pilot study demonstrating the feasibility of the technique in-vivo has been published [2]. Still, a considerable effort is needed to validate and optimize the technique for the clinical vascular setting.

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