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  • 1.
    Broomé, Michael
    et al.
    KTH, Medicinsk avbildning.
    Maksuti, Elira
    KTH, Medicinsk avbildning.
    Bjällmark, Anna
    KTH, Medicinsk avbildning.
    Frenckner, Björn
    Janerot-Sjöberg, Birgitta
    KTH, Medicinsk avbildning.
    Closed-loop real-time simulation model of hemodynamics and oxygen transport in the cardiovascular system2013Ingår i: Biomedical engineering online, ISSN 1475-925X, E-ISSN 1475-925X, Vol. 12, nr 1, s. 69-Artikel i tidskrift (Refereegranskat)
    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.

  • 2. Broomé, Michael
    et al.
    Maksuti, Elira
    KTH, Medicinsk avbildning.
    Waldenström, Anders
    Bjällmark, Anna
    KTH, Medicinsk avbildning.
    Simulation of arterial hypertension and progressive arteriosclerosis with a 0-D multipurpose cardiovascular model2013Ingår i: CMBE13: 3rd International Conference on Computational & Mathematical Biomedical Engineering, 2013, s. 433-436Konferensbidrag (Refereegranskat)
    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.

  • 3.
    Maksuti, Elira
    et al.
    KTH, Medicinsk bildteknik.
    Bjällmark, Anna
    KTH, Medicinsk bildteknik.
    Broomé, Michael
    KTH, Medicinsk bildteknik.
    Modelling the heart with the atrioventricular plane as a piston unit2015Ingår i: Medical Engineering and Physics, ISSN 1350-4533, E-ISSN 1873-4030, Vol. 37, nr 1, s. 87-92Artikel i tidskrift (Refereegranskat)
    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.

  • 4.
    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 unit2013Konferensbidrag (Övrigt vetenskapligt)
    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

  • 5.
    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 testing2016Ingår i: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 42, nr 1, s. 308-321Artikel i tidskrift (Refereegranskat)
    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.

  • 6.
    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 Sequences2013Konferensbidrag (Refereegranskat)
  • 7.
    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 characterization2014Ingår i: IEEE International Ultrasonics Symposium, IUS, 2014, s. 1818-1821Konferensbidrag (Refereegranskat)
    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.

  • 8.
    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.2015Ingår i: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 60, nr 8, s. 3151-3174Artikel i tidskrift (Refereegranskat)
    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.

  • 9.
    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 setup2012Ingår i: 2012 IEEE International Ultrasonics Symposium (IUS), IEEE , 2012, s. 6562400-Konferensbidrag (Refereegranskat)
    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.

  • 10.
    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 today2013Konferensbidrag (Refereegranskat)
    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.

1 - 10 av 10
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