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  • 1. Brandberg, J
    et al.
    Janerot-Sjöberg, B
    Hälsouniversitetet, Linköping University.
    Ask, P
    Increased accuracy of echocardiographic measurement of flow using automated spherical integration of multiple plane velocity vectors.1999In: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 25, no 2, p. 249-57Article in journal (Refereed)
    Abstract [en]

    The calculation of blood flow in the heart by surface integration of velocity vectors (SIVV) using Doppler ultrasound is independent of the angle. Flow is normally calculated from velocity in a spherical thick shell with its center located at the ultrasound transducer. In a numerical simulation, we have shown that the ratio between minor and major axes of an elliptic flow area substantially influences the accuracy of the estimation of flow in a single scan plane. The accuracy of flow measurements by SIVV can be improved by calculating the mean of the values from more than one scan plane. We have produced an automated computer program that includes an antialiasing procedure. We confirmed an improvement of flow measurements in a pulsatile hydraulic flow model, the 95% confidence interval for single estimations being reduced from 20% to 10% (p < 0.05) using the newly developed software. We think that the SIVV method has important implications for clinical transthoracic echocardiography.

  • 2.
    Grishenkov, Dmitry
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Pecorari, Claudio
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Brismar, Torkel B.
    Paradossi, Gaio
    Characterization of acoustic properties of PVA-shelled ultrasound contrast agents: linear properties (Part I)2009In: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 35, no 7, p. 1127-1138Article in journal (Refereed)
    Abstract [en]

    This work examines the linear acoustic behavior of ultrasound contrast agents made of three types of poly (vinyl alcohol) (PVA) shelled microbubbles manufactured at different pH and temperature conditions. Back-scattered power, attenuation coefficient and phase velocity of ultrasonic waves propagating through suspensions of PVA contrast agents were measured at temperature values ranging between 24 degrees C and 37 degrees C in a frequency range from 3 MHz to 13 MHz. Enhancement of the backscattered power higher than 20 dB and displaying a weak dependence on temperature was observed. Attenuation and phase velocity, on the other hand, showed higher sensitivity to temperature variations. A modified version of the Church model, which accounts for the dispersion of the dynamic modulus of the PVA shells, was developed to simultaneously fit the attenuation and phase velocity data at 24 degrees C. The frequency dependence of the storage modulus was found to be that of semiflexible polymeric networks. On the other hand, the frequency dependence of the dynamic loss modulus suggests that additional mechanisms, which may be related to the finite dimensions of the shell and/or to its inhomogeneity, may play a significant role in the dissipation of the acoustic energy. For the microbubbles of interest, this model predicts frequency dependent resonance frequency higher than 100 MHz.

  • 3.
    Grishenkov, Dmitry
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Pecorari, Claudio
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Brismar, Torkel B.
    Paradossi, Gaio
    Characterization of acoustic properties of PVA-shelled ultrasound contrast agents: ultrasound-induced fracture (Part II)2009In: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 35, no 7, p. 1139-1147Article in journal (Refereed)
    Abstract [en]

    Knowledge of the magnitude of the peak negative pressure, P-thr, at which ultrasound contrast agents fracture is relevant for using these microbubbles both as devices for contrast enhancement purposes, as well as carriers of drugs to be delivered locally. In the second part of this communication, the acoustic properties of three types of microbubbles stabilized by poly (vinyl alcohol) (PVA) shells are further investigated. In particular, the dependence of P-thr on system parameters such as the number of cycles, frequency and exposure is examined. The effects of temperature, blood and, wherever data are available, of the dimension of the microbubbles on P-thr are also considered. The large shelf thickness notwithstanding, the results of this investigation show that at room temperature, PVA contrast agents fracture at negative peak pressure values within the recommended safety limit. Furthermore, P-thr decreases with increasing temperature, radius of the microbubbles and number of cycles of the incident wave. Fatigue seems to be a physical mechanism playing a dominant role in the fracture process. The effect of blood on P-thr varies according to condition under which the microbubbles have been synthesized, although stiffening of the shell is observed in most cases. In conclusion, these results suggest that PVA-shelled microbubbles may offer a potentially viable system to be employed for both imaging and therapeutic purposes.

  • 4.
    Hultström, Jessica
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Manneberg, Otto
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Dopf, Katja
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Hertz, Hans M.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Wiklund, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Proliferation and viability of adherent cells manipulated by standing-wave ultrasound in a microfluidic chip2007In: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 33, p. 145-151Article in journal (Refereed)
    Abstract [en]

    Ultrasonic-standing-wave (USW) technology has potential to become a standard method for gentle and contactless cell handling in microfluidic chips. We investigate the viability of adherent cells exposed to USWs by studying the proliferation rate of recultured cells following ultrasonic trapping and aggregation of low cell numbers in a microfluidic chip. The cells form 2-D aggregates inside the chip and the aggregates are held against a continuous flow of cell culture medium perpendicular to the propagation direction of the standing wave. No deviations in the doubling time from expected values (24 to 48 h) were observed for COS-7 cells held in the trap at acoustic pressure amplitudes up to 0.85 MPa and for times ranging between 30 and 75 min. Thus, the results demonstrate the potential of ultrasonic standing waves as a tool for gentle manipulation of low cell numbers in microfluidic systems.

  • 5.
    Kothapalli, Veeravenkata S.
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Oddo, Letizia
    Paradossi, Gaio
    Brodin, Lars- Åke
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Grishenkov, Dmitry
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Inst, Sweden.
    Assessment of the Viscoelastic and Oscillation Properties of a Nano-engineered Multimodality Contrast Agent2014In: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 40, no 10, p. 2476-2487Article in journal (Refereed)
    Abstract [en]

    Combinations of microbubbles (MBs) and superparamagnetic iron oxide nanoparticles (SPIONs) are used to fabricate dual contrast agents for ultrasound and MRI. This study examines the viscoelastic and oscillation characteristics of two MB types that are manufactured with SPIONs and either anchored chemically on the surface (MBs-chem) or physically embedded (MBs-phys) into a polymer shell. A linearized Church model was employed to simultaneously fit attenuation coefficients and phase velocity spectra that were acquired experimentally. The model predicted lower viscoelastic modulus values, undamped resonance frequencies and total damping ratios for MBs-chem. MBs-chem had a resonance frequency of approximately 13 MHz and a damping ratio of approximately 0.9; thus, MBs-chem can potentially be used as a conventional ultrasound contrast agent with the combined functionality of MRI detection. In contrast, MBs-phys had a resonance frequency and damping of 28 MHz and 1.2, respectively, and requires further modification of clinically available contrast pulse sequences to be visualized.

  • 6.
    Lindberg, Frida
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Öhberg, Fredrik
    Granåsen, Gabriel
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    Grönlund, Christer
    Pennation angle dependency in skeletal muscle tissue doppler strain in dynamic contractions2011In: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 37, no 7, p. 1151-1160Article in journal (Refereed)
    Abstract [en]

    Tissue velocity imaging (TVI) is a Doppler based ultrasound technique that can be used to study regional deformation in skeletal muscle tissue. The aim of this study was to develop a biomechanical model to describe the TVI strain's dependency on the pennation angle. We demonstrate its impact as the subsequent strain measurement error using dynamic elbow contractions from the medial and the lateral part of biceps brachii at two different loadings; 5% and 25% of maximum voluntary contraction (MVC). The estimated pennation angles were on average about 4 degrees in extended position and increased to a maximal of 13 degrees in flexed elbow position. The corresponding relative angular error spread from around 7% up to around 40%. To accurately apply TVI on skeletal muscles, the error due to angle changes should be compensated for. As a suggestion, this could be done according to the presented model.

  • 7.
    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.

  • 8. Ressner, Marcus
    et al.
    Jansson, Tomas
    Cedefamn, Jonny
    Ask, Per
    Janerot-Sjöberg, Birgitta
    Department of Medicine and Health, Linköping University, Linköping, Sweden.
    Contrast biases the autocorrelation phase shift estimation in Doppler tissue imaging2009In: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 35, no 3, p. 447-457Article in journal (Refereed)
    Abstract [en]

    Quantitative assessment of regional myocardial function at rest and during stress with Doppler tissue imaging (DTI) plays an important role in daily routine echocardiography. However, reliable visual analysis is largely dependent on image quality and adequate border delineation, which still remains a challenge in a significant number of patients. In this respect, an ultrasound contrast agent (UCA) is often used to improve visualization in patients with suboptimal image quality. The knowledge of how DTI measurements will be affected by UCA present in the tissue is therefore of significant importance for an accurate interpretation of local myocardial motion. The aim of this paper was to investigate how signal contribution from UCA and nonlinear wave propagation influence the performance of the autocorrelation phase shift estimator used for DTI applications. Our results are based on model experiments with a clinical 2-D grayscale scanner and computational simulations of the DTI velocity estimator for synthetically-derived pulses, simulated bubble echoes and experimentally-sampled RF data of transmitted pulses and backscattered contrast echoes. The results show that destruction of UCA present in the tissue will give rise to an apparent bidirectional velocity bias of individual velocity estimates, but that spatial averaging of individual velocity measurements within a region-of-interest will result in a negative bias (away from the transducer) of the estimated mean or mean peak velocity. The UCA destruction will also have a significant impact on the measured integrated mean velocity over time, i.e., displacement. To achieve improved visualization with UCA during DTI-examinations, we either recommend that it is performed at low acoustic powers, mechanical index <or=0.3, thereby minimizing the effects from bubble rupture, or that each Doppler pulse package is preceded by a destruction burst similar to "Flash imaging" to clear the target area of contrast microbubbles.

  • 9. Storaa, C.
    et al.
    Lind, Britta
    Department of Clinical Physiology, Karolinska Univ. Hospital Huddinge.
    Brodin, Lars-Åke
    Department of Clinical Physiology, Karolinska Univ. Hospital Huddinge.
    Distribution of left ventricular longitudinal peak systolic strain and impact of low frame rate2004In: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 30, no 8, p. 1049-1055Article in journal (Refereed)
    Abstract [en]

    The myocardium has complex 3-D motion that is frequently described using ultrasound (US) Doppler techniques that are limited to recording velocities in one dimension only. Studies using 3-D tagged magnetic resonance show that the myocardium has strain components with varying angles throughout the myocardium. Despite this, there seems to be a belief that the left ventricular longitudinal strain distribution should be homogeneous. When measuring myocardial strain, there are several parameters for the clinician to decide on, one of them being recording frame rate. The current study aims to further investigate the alleged homogeneity of the longitudinal myocardial strain distribution and to discover the impact that the frame rate has on these measurements. Myocardial strain was measured in 43 healthy individuals at different frame rates. Analysis of variance results clearly demonstrate that the strain is not uniformly distributed over the wall; there seems to be an increasing strain from apex toward the base. However, subjects exist with different distributions; thus, it is not possible to conclude that certain strain patterns are normal. Reduced frame rate had a highly significant impact on the measured strain results and it is seen that, at low frame rates, the strain values were reduced. (E-mail: Camilia.Storaa@labmed.ki.se)

  • 10.
    Widman, Erik
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Caidahl, Kenneth
    Karolinska Institutet, Stockholm, Sweden.
    Heyde, Brecht
    Department of Cardiovascular Sciences, KU Leuven.
    D'hooge, Jan
    Department of Cardiovascular Sciences, KU Leuven.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Department of Cardiovascular Sciences, KU Leuven, Leuven, Belgium.
    Ultrasound speckle tracking strain estimation of in vivo carotid artery plaque with in vitro sonomicrometry validation2015In: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 41, no 1, p. 77-88Article in journal (Refereed)
    Abstract [en]

    Our objective was to validate a previously developed speckle tracking (ST) algorithm to assess strain in common carotid artery plaques. Radial and longitudinal strain was measured in common carotid artery gel phantoms with a plaque-mimicking inclusion using an in-house ST algorithm and sonomicrometry. Moreover, plaque strain by ST for seven patients (77 ± 6 y) with carotid atherosclerosis was compared with a quantitative visual assessment by two experienced physicians. In vitro, good correlation existed between ST and sonomicrometry peak strains, both radially (r = 0.96, p < 0.001) and longitudinally (r = 0.75, p < 0.01). In vivo, greater pulse pressure-adjusted radial and longitudinal strains were found in echolucent plaques than in echogenic plaques. This illustrates the feasibility of ultrasound ST strain estimation in plaques and the possibility of characterizing plaques using ST strain in vivo.

  • 11.
    Widman, Erik
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Institutet, Sweden.
    Maksuti, Elira
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Institutet, Sweden.
    Amador, Carolina
    Urban, Matthew W.
    Caidahl, Kenneth
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Institutet, Sweden.
    Shear Wave Elastography Quantifies Stiffness in Ex Vivo Porcine Artery with Stiffened Arterial Region2016In: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 42, no 10, p. 2423-2435Article in journal (Refereed)
    Abstract [en]

    Five small porcine aortas were used as a human carotid artery model, and their stiffness was estimatedusing shear wave elastography (SWE) in the arterial wall and a stiffened artery region mimicking a stiff plaque. Tooptimize the SWE settings, shear wave bandwidth was measured with respect to acoustic radiation force pushlength and number of compounded angles used for motion detection with plane wave imaging. The mean arterialwall and simulated plaque shear moduli varied from 41 ± 5 to 97 ± 10 kPa and from 86 ± 13 to 174 ± 35 kPa, respectively,over the pressure range 20–120 mmHg. The results revealed that a minimum bandwidth of approximately1500 Hz is necessary for consistent shear modulus estimates, and a high pulse repetition frequency using no imagecompounding is more important than a lower pulse repetition frequency with better image quality when estimatingarterial wall and plaque stiffness using SWE.

  • 12. Wågström, Elle
    et al.
    Johnson, Jonas
    KTH, School of Technology and Health (STH), Medical Engineering.
    Ferm-Widlund, Kjerstin
    Elmstedt, Nina
    KTH, School of Technology and Health (STH), Medical Engineering.
    Liuba, Karina
    Lind, Britta
    KTH, School of Technology and Health (STH), Medical Engineering.
    Brodin, Lars-Åke
    KTH, School of Technology and Health (STH), Medical Engineering.
    Lundbäck, Stig
    Westgren, Magnus
    The cardiac state diagram as a novel approach for the evaluation of pre- and post-ejection phases of the cardiac cycle in asphyxiated fetal lambs2013In: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 39, no 9, p. 1682-1687Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to investigate myocardial wall motion using echocardiography and color-coded tissue velocity imaging and to generate a cardiac state diagram for evaluation of the duration of the pre- and post-ejection phases in asphyxiated fetal lambs. Six near-term lambs were partly exteriorized and brought to cardiac arrest through asphyxia. Echocardiography measurements were recorded simultaneously with arterial blood sampling for lactate and blood gases. All fetal lambs exhibited prolongation of the pre- and post-ejection phases at the time when the most pronounced changes in lactate concentration and pH occurred. The mean change in duration of the pre- and post-ejection phases for all fetal lambs was 36 +/- 7 ms (p < 0.002) and 77 +/- 17 ms (p < 0.019), respectively, and the percentage change was 50% (p < 0.001) and 38% (p < 0.049), respectively. As asphyxia progressed in fetal lambs, the duration of the pre- and post-ejection phases increased. The cardiac state diagram has the potential to be a comprehensible tool for detecting fetal asphyxia.

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