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Publications (10 of 16) Show all publications
Marlevi, D., Maksuti, E., Urban, M. W., Winter, R. & Larsson, M. (2018). Plaque characterization using shear wave elastography-evaluation of differentiability and accuracy using a combined ex vivo and in vitro setup. Physics in Medicine and Biology, 63(23), Article ID 235008.
Open this publication in new window or tab >>Plaque characterization using shear wave elastography-evaluation of differentiability and accuracy using a combined ex vivo and in vitro setup
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2018 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 63, no 23, article id 235008Article in journal (Refereed) Published
Abstract [en]

Ultrasound elastography has shown potential for improved plaque risk stratification. However, no clear consensus exists on what output metric to use, or what imaging parameters would render optimal plaque differentiation. For this reason we developed a combined ex vivo and in vitro setup, in which the ability to differentiate phantom plaques of varying stiffness was evaluated as a function of plaque geometry, push location, imaging plane, and analysed wave speed metric. The results indicate that group velocity or phase velocity >= 1 kHz showed the highest ability to significantly differentiate plaques of different stiffness, successfully classifying a majority of the 24 analysed plaque geometries, respectively. The ability to differentiate plaques was also better in the longitudinal views than in the transverse view. Group velocity as well as phase velocities <1 kHz showed a systematic underestimation of plaque stiffness, stemming from the confined plaque geometries, however, despite this group velocity analysis showed lowest deviation in estimated plaque stiffness (0.1 m s(-1) compared to 0.2 m s(-1) for phase velocity analysis). SWE results were also invariant to SWE push location, albeit apparent differences in signal-to-noise ratio (SNR) and generated plaque particle velocity. With that, the study has reinforced the potential of SWE for successful plaque differentiation; however the results also highlight the importance of choosing optimal imaging settings and using an appropriate wave speed metric when attempting to differentiate different plaque groups.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2018
Keywords
shear wave elastography, elastography, ultrasound, atherosclerosis, plaque characterization
National Category
Medical Biotechnology
Identifiers
urn:nbn:se:kth:diva-239984 (URN)10.1088/1361-6560/aaec2b (DOI)000451049000003 ()30468683 (PubMedID)2-s2.0-85057084601 (Scopus ID)
Note

QC 20181211

Available from: 2018-12-11 Created: 2018-12-11 Last updated: 2019-08-21Bibliographically approved
Maksuti, E., Carlsson, M., Arheden, H., Kovacs, S. J., Broome, M. & Ugander, M. (2017). Hydraulic forces contribute to left ventricular diastolic filling. Scientific Reports, 7, Article ID 43505.
Open this publication in new window or tab >>Hydraulic forces contribute to left ventricular diastolic filling
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2017 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 43505Article in journal (Refereed) Published
Abstract [en]

Myocardial active relaxation and restoring forces are known determinants of left ventricular (LV) diastolic function. We hypothesize the existence of an additional mechanism involved in LV filling, namely, a hydraulic force contributing to the longitudinal motion of the atrioventricular (AV) plane. A prerequisite for the presence of a net hydraulic force during diastole is that the atrial short-axis area (ASA) is smaller than the ventricular short-axis area (VSA). We aimed (a) to illustrate this mechanism in an analogous physical model, (b) to measure the ASA and VSA throughout the cardiac cycle in healthy volunteers using cardiovascular magnetic resonance imaging, and (c) to calculate the magnitude of the hydraulic force. The physical model illustrated that the anatomical difference between ASA and VSA provides the basis for generating a hydraulic force during diastole. In volunteers, VSA was greater than ASA during 75-100% of diastole. The hydraulic force was estimated to be 10-60% of the peak driving force of LV filling (1-3 N vs 5-10 N). Hydraulic forces are a consequence of left heart anatomy and aid LV diastolic filling. These findings suggest that the relationship between ASA and VSA, and the associated hydraulic force, should be considered when characterizing diastolic function and dysfunction.

Place, publisher, year, edition, pages
Nature Publishing Group, 2017
National Category
Physiology
Identifiers
urn:nbn:se:kth:diva-205472 (URN)10.1038/srep43505 (DOI)000396283100001 ()28256604 (PubMedID)2-s2.0-85014668174 (Scopus ID)
Note

QC 20170511

Available from: 2017-05-11 Created: 2017-05-11 Last updated: 2018-01-13Bibliographically approved
Maksuti, E., Bini, F., Fiorentini, S., Blasi, G., Urban, M. W., Marinozzi, F. & Larsson, M. (2017). Influence of wall thickness and diameter on arterial shear wave elastography: a phantom and finite element study.. Physics in Medicine and Biology, 62(7), 2694-2718
Open this publication in new window or tab >>Influence of wall thickness and diameter on arterial shear wave elastography: a phantom and finite element study.
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2017 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 62, no 7, p. 2694-2718Article in journal (Refereed) Published
Abstract [en]

Quantitative, non-invasive and local measurements of arterial mechanical properties could be highly beneficial for early diagnosis of cardiovascular disease and follow up of treatment. Arterial shear wave elastography (SWE) and wave velocity dispersion analysis have previously been applied to measure arterial stiffness. Arterial wall thickness (h) and inner diameter (D) vary with age and pathology and may influence the shear wave propagation. Nevertheless, the effect of arterial geometry in SWE has not yet been systematically investigated. In this study the influence of geometry on the estimated mechanical properties of plates (h  =  0.5-3 mm) and hollow cylinders (h  =  1, 2 and 3 mm, D  =  6 mm) was assessed by experiments in phantoms and by finite element method simulations. In addition, simulations in hollow cylinders with wall thickness difficult to achieve in phantoms were performed (h  =  0.5-1.3 mm, D  =  5-8 mm). The phase velocity curves obtained from experiments and simulations were compared in the frequency range 200-1000 Hz and showed good agreement (R (2)  =  0.80  ±  0.07 for plates and R (2)  =  0.82  ±  0.04 for hollow cylinders). Wall thickness had a larger effect than diameter on the dispersion curves, which did not have major effects above 400 Hz. An underestimation of 0.1-0.2 mm in wall thickness introduces an error 4-9 kPa in hollow cylinders with shear modulus of 21-26 kPa. Therefore, wall thickness should correctly be measured in arterial SWE applications for accurate mechanical properties estimation.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2017
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-205227 (URN)10.1088/1361-6560/aa591d (DOI)000425859000004 ()28081009 (PubMedID)2-s2.0-85015751378 (Scopus ID)
Note

QC 20170419

Available from: 2017-04-10 Created: 2017-04-10 Last updated: 2018-03-09Bibliographically approved
Maksuti, E., Larsson, D., Urban, M. W., Caidahl, K. & Larsson, M. (2017). Strain and strain rate generated by shear wave elastography in an ex vivo porcine aorta. In: 2017 IEEE International Ultrasonics Symposium (IUS): . Paper presented at 2017 IEEE International Ultrasonics Symposium, IUS 2017, Washington, United States, 6 September 2017 through 9 September 2017. IEEE Computer Society, Article ID 8091581.
Open this publication in new window or tab >>Strain and strain rate generated by shear wave elastography in an ex vivo porcine aorta
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2017 (English)In: 2017 IEEE International Ultrasonics Symposium (IUS), IEEE Computer Society, 2017, article id 8091581Conference paper (Refereed)
Abstract [en]

In order to generate trackable shear waves in soft tissues, transmitted pulses in shear wave elastography (SWE) are longer than conventional clinical ultrasound pulses. Nevertheless, they typically obey mechanical and thermal regulatory limits. In arterial applications, specific safety concerns may arise, as acoustic radiation (ARF)-induced stresses and strain rates could potentially affect the arterial wall. The aim of this study was to assess ARF-induced strain and strain rates in ex vivo arteries. A porcine aorta (diameters 8.5 mm, wall thickness 1.2 mm) was pressurized by a saline-filled water column at 60 and 120 mmHg. A Verasonics V1 system and a L7-4 transducer were used to generate the ARF in the middle of the anterior wall (F-number = 1, push length = [100, 200, 300] μs) and to perform plane-wave imaging (10 kHz). Cumulative axial displacement was estimated using 2D auto-correlation. The axial strain rate was calculated as the time-derivative of the axial strain, obtained by spatial linear regression of the displacement inside the anterior wall. The ex vivo peak strain and strain rate were compared with peak strain and strain rate values induced by the blood pressure changes in two healthy individuals and two patients with coronary artery disease at rest and measured by a dedicated in house speckle tracking algorithm. ARF-induced ex vivo peak strains were in the range 0.3-1% and strain rates in the range 6-23 s-1. Peak values were more affected by longer push duration than pressurization level. In vivo physiological peak strain was 33% and strain rate was 2 s-1. ARF-induced strain rates in vivo are likely to be lower than those assessed in this ex vivo setup due to ultrasound attenuation and the effect of surrounding tissue. Therefore, the results of the performed study suggest that SWE could be used in a safe manner for arterial applications even though specific effects of high strain rates are to be explored.

Place, publisher, year, edition, pages
IEEE Computer Society, 2017
Series
IEEE International Ultrasonics Symposium, IUS, ISSN 1948-5719
Keywords
Acoustic radiation force, Artery, Safety, Shear wave elastography, Strain, Strain rate
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:kth:diva-220744 (URN)10.1109/ULTSYM.2017.8091581 (DOI)000416948400025 ()2-s2.0-85039434244 (Scopus ID)9781538633830 (ISBN)
Conference
2017 IEEE International Ultrasonics Symposium, IUS 2017, Washington, United States, 6 September 2017 through 9 September 2017
Funder
Swedish Research Council, 2015-04237
Note

QC 20180105

Available from: 2018-01-05 Created: 2018-01-05 Last updated: 2018-01-12Bibliographically approved
Maksuti, E., Larsson, D., Urban, M. W., Caidahl, K. & Larsson, M. (2017). Strain and strain rate generated by shear wave elastography in ex vivo porcine aortas. In: IEEE International Ultrasonics Symposium, IUS: . Paper presented at 2017 IEEE International Ultrasonics Symposium, IUS 2017, 6 September 2017 through 9 September 2017. IEEE Computer Society
Open this publication in new window or tab >>Strain and strain rate generated by shear wave elastography in ex vivo porcine aortas
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2017 (English)In: IEEE International Ultrasonics Symposium, IUS, IEEE Computer Society , 2017Conference paper, Published paper (Refereed)
Abstract [en]

In shear wave elastography (SWE), acoustic radiation forces (ARF) are employed to generate shear waves within the tissue. Although the transmitted pulses are longer than those in conventional clinical ultrasound, they typically obey the mechanical and thermal regulatory limits. In arterial applications, specific safety concerns may arise, as ARF-induced stresses and strain rates could potentially affect the arterial wall. A previous simulation study (Doherty et al., J Biomech, 2013 Jan; 46(1):83-90) showed that stresses imposed by the ARF used in SWE are orders of magnitude lower than those caused by blood pressure. ARF-induced strain rates have not been investigated yet, therefore the aim of this study was to assess such strain rates in an ex vivo setup.

Place, publisher, year, edition, pages
IEEE Computer Society, 2017
National Category
Medical Equipment Engineering
Identifiers
urn:nbn:se:kth:diva-227077 (URN)10.1109/ULTSYM.2017.8092757 (DOI)2-s2.0-85039461127 (Scopus ID)9781538633830 (ISBN)
Conference
2017 IEEE International Ultrasonics Symposium, IUS 2017, 6 September 2017 through 9 September 2017
Note

QC 20180518

Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2018-05-18Bibliographically approved
Maksuti, E., Widman, E., Larsson, D., Urban, M. W., Larsson, M. & Bjällmark, A. (2016). ARTERIAL STIFFNESS ESTIMATION BY SHEAR WAVE ELASTOGRAPHY: VALIDATION IN PHANTOMS WITH MECHANICAL TESTING. Ultrasound in Medicine and Biology, 42(1), 308-321
Open this publication in new window or tab >>ARTERIAL STIFFNESS ESTIMATION BY SHEAR WAVE ELASTOGRAPHY: VALIDATION IN PHANTOMS WITH MECHANICAL TESTING
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2016 (English)In: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 42, no 1, p. 308-321Article in journal (Refereed) Published
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.

Keywords
Accuracy, Arterial phantom, Arterial stiffness, Group velocity, Lamb waves, Mechanical testing, Phase velocity, Poly(vinyl alcohol), Shear modulus, Shear wave elastography
National Category
Medical Image Processing
Identifiers
urn:nbn:se:kth:diva-181377 (URN)10.1016/j.ultrasmedbio.2015.08.012 (DOI)000367733800032 ()26454623 (PubMedID)2-s2.0-84957007046 (Scopus ID)
Funder
VINNOVA, 2011-01365Swedish Research Council, 2012-2795
Note

QC 20160203

Available from: 2016-02-03 Created: 2016-02-01 Last updated: 2019-08-21Bibliographically approved
Widman, E., Maksuti, E., Carrascal, C. A., Urban, M. W. & Larsson, M. (2015). Evaluating Arterial and Plaque Elasticity with Shear Wave Elastography in an ex vivo Porcine Model. In: 2015 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS): . Paper presented at IEEE International Ultrasonics Symposium (IUS), OCT 21-24, 2015, Taipei, TAIWAN. IEEE
Open this publication in new window or tab >>Evaluating Arterial and Plaque Elasticity with Shear Wave Elastography in an ex vivo Porcine Model
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2015 (English)In: 2015 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS), IEEE , 2015Conference paper, Published paper (Refereed)
Abstract [en]

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

Place, publisher, year, edition, pages
IEEE, 2015
Series
IEEE International Ultrasonics Symposium, ISSN 1948-5719
Keywords
Carotid Artery, Phase Velocity, Plaque Characterization, Shear Wave Elastography, Ultrasound
National Category
Medical Engineering
Identifiers
urn:nbn:se:kth:diva-180170 (URN)10.1109/ULTSYM.2015.0120 (DOI)000366045700426 ()2-s2.0-84962018816 (Scopus ID)978-1-4799-8182-3 (ISBN)
Conference
IEEE International Ultrasonics Symposium (IUS), OCT 21-24, 2015, Taipei, TAIWAN
Note

QC 20160112

Available from: 2016-01-12 Created: 2016-01-07 Last updated: 2016-01-12Bibliographically approved
Maksuti, E., Bjällmark, A. & Broomé, M. (2015). Modelling the heart with the atrioventricular plane as a piston unit. Medical Engineering and Physics, 37(1), 87-92
Open this publication in new window or tab >>Modelling the heart with the atrioventricular plane as a piston unit
2015 (English)In: Medical Engineering and Physics, ISSN 1350-4533, E-ISSN 1873-4030, Vol. 37, no 1, p. 87-92Article in journal (Refereed) Published
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.

Keywords
Atrioventricular interaction, Cardiac function, Cardiac pumping, Longitudinal function, Cardiac model, Bond graphs
National Category
Biomedical Laboratory Science/Technology
Identifiers
urn:nbn:se:kth:diva-161634 (URN)10.1016/j.medengphy.2014.11.002 (DOI)000349585100011 ()25466260 (PubMedID)2-s2.0-84920913473 (Scopus ID)
Note

QC 20150324

Available from: 2015-03-24 Created: 2015-03-13 Last updated: 2017-12-04Bibliographically approved
Widman, E., Maksuti, E., Larsson, D., Urban, M. W., Bjallmark, A. & Larsson, M. (2015). Shear wave elastography plaque characterization with mechanical testing validation: a phantom study.. Physics in Medicine and Biology, 60(8), 3151-3174
Open this publication in new window or tab >>Shear wave elastography plaque characterization with mechanical testing validation: a phantom study.
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2015 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 60, no 8, p. 3151-3174Article in journal (Refereed) Published
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.

National Category
Medical Image Processing
Identifiers
urn:nbn:se:kth:diva-164418 (URN)10.1088/0031-9155/60/8/3151 (DOI)000352525200013 ()25803520 (PubMedID)2-s2.0-84927602186 (Scopus ID)
Funder
Swedish Research CouncilVINNOVA, 2011-01365
Note

QC 20150518

Available from: 2015-04-27 Created: 2015-04-17 Last updated: 2017-08-15Bibliographically approved
Widman, E., Maksuti, E., Larsson, D., Urban, M., Caidahl, K., Bjällmark, A. & Larsson, M. (2014). Feasibility of shear wave elastography for plaque characterization. In: IEEE International Ultrasonics Symposium, IUS: . Paper presented at 2014 IEEE International Ultrasonics Symposium, IUS 2014, 3 September 2014 through 6 September 2014 (pp. 1818-1821).
Open this publication in new window or tab >>Feasibility of shear wave elastography for plaque characterization
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2014 (English)In: IEEE International Ultrasonics Symposium, IUS, 2014, p. 1818-1821Conference paper, Published 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.

Series
IEEE International Ultrasonics Symposium, IUS, ISSN 1948-5719 ; 6932274
Keywords
Carotid Artery, Mechanical Testing, Phase Velocity, Plaque Characterization, Shear Wave Elastography
National Category
Medical Engineering
Identifiers
urn:nbn:se:kth:diva-167518 (URN)10.1109/ULTSYM.2014.0451 (DOI)000352792500449 ()2-s2.0-84910072590 (Scopus ID)9781479970490 (ISBN)
Conference
2014 IEEE International Ultrasonics Symposium, IUS 2014, 3 September 2014 through 6 September 2014
Note

QC 20150611

Available from: 2015-06-11 Created: 2015-05-22 Last updated: 2016-12-05Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-9654-447X

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