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ARTERIAL STIFFNESS ESTIMATION BY SHEAR WAVE ELASTOGRAPHY: VALIDATION IN PHANTOMS WITH MECHANICAL TESTING
KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Institutet, Sweden.ORCID iD: 0000-0002-9654-447X
KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Institutet, Sweden.ORCID iD: 0000-0002-2487-7400
KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.ORCID iD: 0000-0003-1002-2070
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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
Resource type
Text
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.

Place, publisher, year, edition, pages
2016. Vol. 42, no 1, p. 308-321
Keywords [en]
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: urn:nbn:se:kth:diva-181377DOI: 10.1016/j.ultrasmedbio.2015.08.012ISI: 000367733800032PubMedID: 26454623Scopus ID: 2-s2.0-84957007046OAI: oai:DiVA.org:kth-181377DiVA, id: diva2:900298
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
In thesis
1. Imaging and modeling the cardiovascular system
Open this publication in new window or tab >>Imaging and modeling the cardiovascular system
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Understanding cardiac pumping function is crucial to guiding diagnosis, predicting outcomes of interventions, and designing medical devices that interact with the cardiovascular system.  Computer simulations of hemodynamics can show how the complex cardiovascular system is influenced by changes in single or multiple parameters and can be used to test clinical hypotheses. In addition, methods for the quantification of important markers such as elevated arterial stiffness would help reduce the morbidity and mortality related to cardiovascular disease.

The general aim of this thesis work was to improve understanding of cardiovascular physiology and develop new methods for assisting clinicians during diagnosis and follow-up of treatment in cardiovascular disease. Both computer simulations and medical imaging were used to reach this goal.

In the first study, a cardiac model based on piston-like motions of the atrioventricular plane was developed. In the second study, the presence of the anatomical basis needed to generate hydraulic forces during diastole was assessed in heathy volunteers. In the third study, a previously validated lumped-parameter model was used to quantify the contribution of arterial and cardiac changes to blood pressure during aging. In the fourth study, in-house software that measures arterial stiffness by ultrasound shear wave elastography (SWE) was developed and validated against mechanical testing.

The studies showed that longitudinal movements of the atrioventricular plane can well explain cardiac pumping and that the macroscopic geometry of the heart enables the generation of hydraulic forces that aid ventricular filling. Additionally, simulations showed that structural changes in both the heart and the arterial system contribute to the progression of blood pressure with age. Finally, the SWE technique was validated to accurately measure stiffness in arterial phantoms.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2016. p. 96
Series
TRITA-STH ; 2016:9
Keywords
Cardiac pumping, diastolic function, hemodynamics, modeling, simulation, arterial stiffness, ultrasound, shear wave elastography.
National Category
Other Medical Engineering
Research subject
Medical Technology
Identifiers
urn:nbn:se:kth:diva-196538 (URN)978-91-7729-192-3 (ISBN)
Public defence
2016-12-09, T2, Hälsovägen 11C, Huddinge, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2012-2800, 2012-2795VINNOVA, 2011-01365
Note

QC 20161115

Available from: 2016-11-15 Created: 2016-11-15 Last updated: 2016-11-15Bibliographically approved
2. Non-invasive imaging for improved cardiovascular diagnostics: Shear wave elastography, relative pressure estimation, and tomographic reconstruction
Open this publication in new window or tab >>Non-invasive imaging for improved cardiovascular diagnostics: Shear wave elastography, relative pressure estimation, and tomographic reconstruction
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Throughout the last century, medical imaging has come to revolutionise the way we diagnose disease, and is today an indispensable part of virtually any clinical practice. In cardiovascular care imaging is extensively utilised, and the development of novel techniques promises refined diagnostic abilities: ultrasound elastography allows for constitutive tissue assessment, 4D flow magnetic resonance imaging (MRI) enables full-field flow mapping, and micro-Computed Tomography (CT) permits high-resolution imaging at pre-clinical level. However, following the complex nature of cardiovascular disease, refined methods are still very much needed to accurately utilise these techniques and to effectively isolate disease developments.

The aim of this thesis has been to develop such methods for refined cardiovascular image diagnostics. In total eight studies conducted over three separate focus areas have been included: four on vascular shear wave elastography (SWE), three on non-invasive cardiovascular relative pressure estimations, and one on tomographic reconstruction for pre-clinical imaging.

In Study I-IV, the accuracy and feasibility of vascular SWE was evaluated, with particular focus on refined carotid plaque characterisation. With confined arterial or plaque tissue restricting acoustic wave propagation, analysis of group and phase velocity was performed with SWE output validated against reference mechanical testing and imaging. The results indicate that geometrical confinement has a significant impact on SWE accuracy, however that a combined group and phase velocity approach can be utilised to identify vulnerable carotid plaque lesions in-vivo.

In Study V-VII, a non-invasive method for the interrogation of relative pressure from imaged cardiovascular flow was developed. Using the concept of virtual work-energy, the method was applied to accurately assess relative pressures throughout complex, turbulence-inducing, branching vasculatures. The method was also applied on a dilated cardiomyopathy cohort, indicating arterial hemodynamic changes in cardiac disease.

Lastly, in Study VIII a method for multigrid image reconstruction of tomographic data was developed, utilising domain splitting and operator masking to accurately reconstruct high-resolution regions-of-interests at a fraction of the computational cost of conventional full-resolution methods.

Together, the eight studies have incorporated a range of different imaging modalities, developed methods for both constitutive and hemodynamic cardiovascular assessment, and utilised refined pre-clinical imaging, all with the same purpose: to refine current state cardiovascular imaging and to improve our ability to non-invasively assess cardiovascular disease. With promising results reached, the studies lay the foundation for continued clinical investigations, advancing the presented methods and maturing their usage for an improved future cardiovascular care.

Abstract [sv]

Medicinsk avbildning utgör idag en central del av modern klinisk diagnostik, och bildgivande diagnostikverktyg har kommit att i grunden förändra sättet på vilket dagligt kliniskt arbete utförs. Medicinsk bildteknik används också i stor utsträckning inom hjärt-kärldiagnostik, och i takt med att nya tekniker utvecklas kan förfinad information inhämtas: ultraljudsbaserad elastografi möjliggör avbildning av vävnaders mekaniska egenskaper, fyrdimensionella blodflödesmönster kan kartläggas genom 4D flödes-magnetresonanstomografi (MRI), och mikro-Datortomografi (mikro-CT) möjliggör preklinisk avbildning i mikrometerupplösning. För att kunna dra nytta av dessa teknikers potential i ett kliniskt sammanhang behövs dock förfinade och validerade analysverktyg, särskilt med tanke på hjärt-kärlsjukdomars komplexa och multifaktoriella natur.

Syftet med följande avhandling har varit att utveckla sådana metoder för förbättrad hjärt-kärlavbildning. Avhandlingen innehåller totalt åtta delarbeten fördelat över tre fokusområden: fyra inom vaskulär skjuvvågselastografi (SWE), tre inom icke-invasiv tryckfallsmätning, och en inom pre-klinisk tomografisk bildrekonstruktion.

I studie I-IV utvärderades vaskulär SWE, med särskilt fokus på teknikens potential för förfinad karaktärisering av karotisplack. I alla studier undersöktes SWE grupp- och fashastighet, med estimerade hastigheter och styvheter validerade mot mekanisk referensmätning eller kompletterande avbildning. Resultaten visar hur spatialt avgränsade kärl eller plack har en tydlig inverkan på SWE:s noggrannhet, men indikerar även hur rupturbenägna plack kan identifieras genom en kombination av grupp- och fashastighetsanalys.

I studie V-VII utvecklades en ny metod för icke-invasiv tryckfallsmätning baserad uteslutande på uppmätt 4D-flödesdata. Genom en komplett flödesmekanisk beskrivning i kombination med ett virtuellt flödesfält kan exakta och robusta tryckfallsmätningar genomföras genom komplexa, turbulensinducerande, och kliniskt relevant kardiovaskulära strukturer. Metoden användes också för att analysera en klinisk kohort med dilaterad kardiomyopati, där tydliga förändringar i arteriellt blodtrycksbeteende detekterades.

I studie VIII utvecklades en metod för multidimensionell bildrekonstruktion av tomografisk mikro-CT-data. Genom domän- och operatorseparering visar resultaten hur högupplöst rekonstruktion av en subdomän kan uppnås till en bråkdel av den totala tids- eller minnesåtgången som annars fordras för en fullupplöst bildrekonstruktion.

Tillsammans har de åtta delstudierna använt ett antal olika avbildningsmodaliteter, applicerat både vävnadsbaserat och hemodynamisk utvärdering av hjärt-kärlsystemet, och slutligen inkluderat preklinisk avbildning, allt för att uppnå samma mål: att förbättra klinisk hjärt-kärlavbildning och ge en fördjupad förståelse av olika hjärt-kärlsjukdomars kliniska manifestation genom icke-invasiv avbildning. Avhandlingen utgör också grunden för fortsatta vetenskapliga studier, där de utvärderade metoderna kan komma att förfinas ytterligare som del av en mer omfattande klinisk implementering.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. p. 192
Series
TRITA-CBH-FOU ; 2019: 38
Keywords
Medical imaging, Cardiovascular disease, Atherosclerosis, Hemodynamics, Ultrasound, Shear Wave Elastography (SWE), Magnetic Resonance Imaging (MRI), 4D flow MRI, Relative Pressure, Virtual Work-Energy, micro-Computed Tomography (micro-CT), Tomographic reconstruction, Pre-clinical imaging, Medicinsk avbildning, Hjärt-kärlsjukdomar, Ateroskleros, Hemodynamik, Ultraljud, Skjuvvågselastografi (SWE), Magnetresonanstomografi (MRI), 4D flödes-MRI, Tryckfall, Virtuellt flöde, mikro-Datortomografi (mikro-CT), Tomografisk rekonstruktion, Preklinisk avbildning
National Category
Medical Engineering Medical Image Processing
Research subject
Medical Technology
Identifiers
urn:nbn:se:kth:diva-256321 (URN)978-91-7873-251-7 (ISBN)
Public defence
2019-09-20, T2, Hälsovägen 11C, Huddinge, 09:00 (English)
Opponent
Supervisors
Note

Karolinska Institutet-KTH joint degree doctoral thesis in in medical technology and medical sciences

Available from: 2019-08-23 Created: 2019-08-21 Last updated: 2019-08-23Bibliographically approved

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Maksuti, EliraWidman, ErikLarsson, DavidLarsson, Matilda

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