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  • 51.
    Maksuti, Elira
    et al.
    KTH, Medicinsk avbildning.
    Johnson, Jonas
    KTH, Medicinsk avbildning.
    Bjällmark, Anna
    KTH, Medicinsk avbildning.
    Broomé, Michael
    KTH, Medicinsk avbildning.
    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

  • 52.
    Maksuti, Elira
    et al.
    KTH, Medicinsk bildteknik.
    Widman, Erik
    KTH, Medicinsk bildteknik.
    Larsson, David
    KTH, Medicinsk bildteknik.
    Urban, Matthew W.
    Larsson, Matilda
    KTH, Medicinsk bildteknik.
    Bjällmark, Anna
    KTH, Medicinsk bildteknik.
    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.

  • 53. Manouras, A
    et al.
    Bjällmark, Anna
    Winter, R
    Brodin, L-Å
    Color coded tissue Doppler is more accurate and less sensitive to filtering and gain settings compared to spectral tissue Doppler: A comparison of two commonly used tissue doppler techniques in the clinical setting2007Conference paper (Other academic)
  • 54.
    Mårtensson, Mattias
    et al.
    KTH, Medicinsk bildteknik.
    Bjällmark, Anna
    KTH, Medicinsk teknik.
    Brodin, Lars-Åke
    KTH, Medicinsk teknik.
    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.

  • 55.
    Nordenfur, Tim
    et al.
    KTH, Medicinsk bildteknik.
    Maksuti, Elira
    KTH, Medicinsk bildteknik.
    Widman, Erik
    KTH, Medicinsk bildteknik.
    Bjällmark, Anna
    KTH, Medicinsk bildteknik.
    Larsson, Matilda
    KTH, Medicinsk bildteknik.
    A Comparison of Shear Wave Elastography Pushing Sequences2013Conference paper (Refereed)
  • 56.
    Westholm, C
    et al.
    Karolinska University Hospital, Stockholm, Sweden.
    Bjällmark, Anna
    Karolinska University Hospital, Stockholm, Sweden.
    Larsson, M
    Karolinska University Hospital, Stockholm, Sweden.
    Winter, R
    Karolinska University Hospital, Stockholm, Sweden.
    Jacobsen, P
    Karolinska University Hospital, Stockholm, Sweden.
    Nygren, M
    Karolinska University Hospital, Stockholm, Sweden.
    Brodin, L-Å
    Karolinska University Hospital, Stockholm, Sweden.
    Velocity tracking: a new user independent method for bedside detection of myocardial ischemia2007In: European Journal of Echocardiography, ISSN 1525-2167, E-ISSN 1532-2114, Vol. 7, no suppl_1, p. S37-, article id 292Article in journal (Refereed)
  • 57. Westholm, Carl
    et al.
    Bjällmark, Anna
    KTH, Medicinsk teknik.
    Larsson, Matilda
    KTH, Medicinsk teknik.
    Jacobsen, Per
    Brodin, Lars-Åke
    KTH, Medicinsk teknik.
    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.

  • 58. Widman, E
    et al.
    Maksuti, E
    Larsson, M
    Bjällmark, Anna
    Caidahl, K
    D'hooge, J
    An experimental validation study for plaque characterization using shear wave elastography2012Conference paper (Other academic)
  • 59.
    Widman, Erik
    et al.
    KTH, Medicinsk bildteknik.
    Maksuti, Elira
    KTH, Medicinsk bildteknik.
    Larsson, David
    KTH, Medicinsk bildteknik.
    Urban, M.
    Caidahl, K.
    KTH, Medicinsk teknik.
    Bjällmark, Anna
    KTH, Medicinsk bildteknik.
    Larsson, Matilda
    KTH, Medicinsk bildteknik.
    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.

  • 60.
    Widman, Erik
    et al.
    KTH, Medicinsk bildteknik.
    Maksuti, Elira
    KTH, Medicinsk bildteknik.
    Larsson, David
    KTH, Medicinsk bildteknik.
    Urban, M W
    Bjällmark, Anna
    KTH, Medicinsk bildteknik.
    Larsson, Matilda
    KTH, Medicinsk bildteknik.
    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.

  • 61.
    Widman, Erik
    et al.
    KTH, Medicinsk avbildning.
    Maksuti, Elira
    KTH, Medicinsk avbildning.
    Larsson, Matilda
    KTH, Medicinsk avbildning.
    Bjällmark, Anna
    KTH, Medicinsk avbildning.
    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.

  • 62.
    Widman, Erik
    et al.
    KTH, Medicinsk avbildning.
    Maksuti, Elira
    KTH, Medicinsk teknik.
    Larsson, Matilda
    KTH, Medicinsk teknik.
    Bjällmark, Anna
    KTH, Medicinsk teknik.
    Nordenfur, Tim
    KTH, Medicinsk teknik.
    Caidahl, Kenneth
    D’hooge, Jan
    Shear wave elastography of the arterial wall: Where are we today2013Conference paper (Refereed)
    Abstract [en]

    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

    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.</p><p>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

    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 (&lt; 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.

  • 63. Yumi Hayashi, S
    et al.
    Mazza do Nascimento, M
    B. L. B,
    Riella, M
    Larsson, M
    Bjällmark, Anna
    Seeberger, A
    Nowak, J
    Lindholm, B
    Brodin, L-Å
    The prevalence of intraventricular dyssynchrony, detected by tissue synchronization imaging, in hemodialysis, peritoneal dialysis and chronic kidney disease stages 3 and 4.2009Conference paper (Other academic)
  • 64. Yumi Hayashi, S
    et al.
    Mazza do Nascimento, M
    Lind, B
    Riella, M
    Larsson, M
    Bjällmark, Anna
    Seeberger, A
    Nowak, J
    Lindholm, B
    Brodin, L-Å
    Improvement of left ventricular synchronicity, assessed by tissue synchronization imaging, after a single hemodialysis session in chronic hemodialysis patients.2009Conference paper (Other academic)
  • 65. Yumi Hayashi, S
    et al.
    Mazza do Nascimento, M
    Lind, B
    Riella, M
    Larsson, M
    Bjällmark, Anna
    Seeberger, A
    Nowak, J
    Lindholm, B
    Brodin, L-Å
    The prevalence of right ventricular dysfunction and the acute effect of HD on right ventricular function in CKD2009Conference paper (Other academic)
12 51 - 65 of 65
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  • en-US
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