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Measurement and Analysis of Intracardiac Blood Flow and Vortex Ring Formation

Töger, Johannes LU (2014) In Doctoral theses in mathematical sciences
Abstract (Swedish)
Popular Abstract in Swedish

Ökad förståelse för hjärtats pumpfunktion är av stort intresse för att kunna förbättra diagnostik, behandling och prognoser för hjärtsjuka patienter. Blodflöde i hjärtat är direkt kopplat till hjärtats form och rörelse och kan därför vara en viktig markör för hjärtats funktion. Därför var målet med denna avhandling att utveckla och förbättra mätningar av blodflöde med hjälp av magnetisk resonanstomografi (MR, eller magnetkamera) i hjärtat. Speciellt behandlas tredimensionella, tidsupplösta flödesmätningar, även kallat 4D-flöde. Avhandlingen behandlar tre områden: mätningarnas noggrannhet, virvelbildning och visualisering.



Mätningarnas noggrannhet jämfördes med så kallat... (More)
Popular Abstract in Swedish

Ökad förståelse för hjärtats pumpfunktion är av stort intresse för att kunna förbättra diagnostik, behandling och prognoser för hjärtsjuka patienter. Blodflöde i hjärtat är direkt kopplat till hjärtats form och rörelse och kan därför vara en viktig markör för hjärtats funktion. Därför var målet med denna avhandling att utveckla och förbättra mätningar av blodflöde med hjälp av magnetisk resonanstomografi (MR, eller magnetkamera) i hjärtat. Speciellt behandlas tredimensionella, tidsupplösta flödesmätningar, även kallat 4D-flöde. Avhandlingen behandlar tre områden: mätningarnas noggrannhet, virvelbildning och visualisering.



Mätningarnas noggrannhet jämfördes med så kallat 2D-flöde, som ger en mer begränsad, men exaktare mätning. Resultaten visar att starkare magnetfält ger bättre flödesmätningar än ett svagare magnetfält.

En snabbare variant på 4D-flödessekvensen ger inte tillräckligt bra mätningar för kliniskt utvärdering av hjärtats funktion, medan en något längre bildinsamling ger fullgod kvalitet. Dessutom utvecklades en ny uppställning för att validera 4D-flödesmätningar jämfört med mer exakta lasermetoder. Med hjälp av den nya uppställningen visas att 4D-flöde visar rätt hastighet i medel, men att topphastigheter underskattas med 8-25%. Vidare visades att 4D-flöde kan mäta volymen på virvlar i blodflödet, men att det fortfarande är svårt att mäta hur blodet blandar sig i virveln.



En ny metod för att mäta virvelbildning under hjärtats fyllnadsfas, kallad Lagrangian Coherent Structures, utvecklades. Mätningar av virvelbildning under hjärtats fyllnadsfas utfördes i friska frivilliga och patienter med hjärtsvikt. I friska personer fyllde virveln ut c:a 50\% av blodvolymen, men bara 20\% hos patienterna. Detta kan betyda att blodet blandar sig mindre effektivt hos patienterna, vilket kan leda till en ökad risk för blodproppar.



Slutligen undersöktes visualisering av blodflöde, det vill säga hur flödesmätningarna kan presenteras i bildform för tolkning av läkare och forskare. En ny metod, Volume Tracking, utvecklades för att följa hur blodvolymer rör sig genom hjärtat. Dessutom jämfördes visualiseringar med tidigare standardmetoder mellan två olika snabba 4D-flödessekvenser. Ingen skillnad i kvaliteten på visualiseringarna kunde mätas, vilket betyder att den snabbare sekvensen kan användas om målet med undersökningen enbart är att visualisera flödet och därmed ge en kortare undersökning för patienten. (Less)
Abstract
Increased understanding of the pumping mechanics of the heart are of great importance to develop diagnostics, treatment and prognostics for cardiovascular diseases. Blood flow in the heart is connected to its anatomy and function, and may therefore be a sensitive marker of cardiac health and disease. Therefore, the aim of this thesis is to develop and validate methods for quantification and visualization of intracardiac blood flow measurements using 4D phase contrast magnetic resonance velocity mapping (4D PC-MR). The thesis, which is based on five papers, aims to 1) validate measurement accuracy, 2) investigate vortex ring formation in the left ventricle (LV), and 3) evaluate and improve visualization of flow.



For aim... (More)
Increased understanding of the pumping mechanics of the heart are of great importance to develop diagnostics, treatment and prognostics for cardiovascular diseases. Blood flow in the heart is connected to its anatomy and function, and may therefore be a sensitive marker of cardiac health and disease. Therefore, the aim of this thesis is to develop and validate methods for quantification and visualization of intracardiac blood flow measurements using 4D phase contrast magnetic resonance velocity mapping (4D PC-MR). The thesis, which is based on five papers, aims to 1) validate measurement accuracy, 2) investigate vortex ring formation in the left ventricle (LV), and 3) evaluate and improve visualization of flow.



For aim 1), 4D PC-MR stroke volume (SV) measurements in the aorta and main pulmonary artery were validated against 2D PC-MR at 1.5T and 3T, using two different 4D PC-MR sequences, one accelerated using SENSE and the other using k-t BLAST (Paper I). SENSE measurements showed good accuracy and measurements at 3T compared favorably to 1.5T. The k-t BLAST measurements showed a too high bias to be used for SV quantification.



Furthermore, a phantom setup for validation of 4D PC-MR against independent measurements by particle imaging velocimetry (PIV) and planar laser-induced flourescence (PLIF) was developed and constructed (Paper II). The developed flow phantom showed excellent stability (R^2 =0.96, bias -0.06 +- unit 0.70 cm/s), making it suitable for validation of 4D PC-MR measurements. Validation of 4D PC-MR velocities against PIV show good agreement for mean velocities, but 4D PC-MR underestimates peak velocities by 8-25%. Vortex ring volume (VV) measurements with 4D PC-MR showed good agreement with PLIF. However, vortex ring mixing ratio (MXR) showed poor agreement. Due to possible differences between the phantom setup and in vivo vortex ring formation, further studies are needed to determine if MXR can be measured under in vivo flow conditions.



For aim 2), a new method for quantification of vortex ring formation in the left ventricle using Lagrangian Coherent Structures was developed and implemented in software (Paper IV). Vortex ring volume was quantified in 15 healthy volunteers and 15 patients with heart failure. The vortex ring occupied 51 +- 7% of the LV blood volume in healthy volunteers, but only 26+-5% in the patients (p<0.001). This suggests that a larger volume of blood is static in the LV of the patients, with an associated increase in the risk of thrombus formation (Papers IV and V).



The vortex ring mixing ratio (MXR), defined as the amount of blood pulled into the vortex ring due to its rotation divided by the total volume of the vortex ring, was also quantified in healthy volunteers and heart failure patients (Paper V). MXR was higher in the patients compared to the volunteers (33+-7% vs 19+-7%, p<0.001).



For aim 3), a new method for visualization of 4D PC-MR blood flow measurements was developed and implemented in software. The new method, called Volume Tracking (Paper III), allows visualization of the motion of a blood volume through the heart. Volume Tracking gives incremental information about the blood flow compared to earlier used methods, e.g. by revealing a complex blood flow pattern in the right ventricle (RV) when compared to the LV. Additionally, the quality of particle tracing visualizations in 4D PC-MR accelerated using SENSE or k-t BLAST was evaluated (Paper I). No difference could be measured, showing that the higher acceleration, and therefore shorter scan duration, in k-t BLAST measurements can be used when the main goal is to visualize, and not quantify, blood flow. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Pedrizzetti, Gianni, University of Trieste, Italy
organization
publishing date
type
Thesis
publication status
published
subject
keywords
blood flow, dynamical systems, magnetic resonance imaging, heart failure, vortex ring formation
in
Doctoral theses in mathematical sciences
pages
184 pages
defense location
Lecture hall MH:C, Centre for Mathematical Sciences, Sölvegatan 18, Lund University Faculty of Engineering
defense date
2014-10-17 09:00
ISSN
1404-0034
ISBN
978-91-7623-072-5
978-91-7623-073-2
language
English
LU publication?
yes
id
c20f75d0-20a0-4db6-9e93-f7da5717a6a0 (old id 4648004)
date added to LUP
2014-09-25 10:41:41
date last changed
2016-09-19 08:45:00
@misc{c20f75d0-20a0-4db6-9e93-f7da5717a6a0,
  abstract     = {Increased understanding of the pumping mechanics of the heart are of great importance to develop diagnostics, treatment and prognostics for cardiovascular diseases. Blood flow in the heart is connected to its anatomy and function, and may therefore be a sensitive marker of cardiac health and disease. Therefore, the aim of this thesis is to develop and validate methods for quantification and visualization of intracardiac blood flow measurements using 4D phase contrast magnetic resonance velocity mapping (4D PC-MR). The thesis, which is based on five papers, aims to 1) validate measurement accuracy, 2) investigate vortex ring formation in the left ventricle (LV), and 3) evaluate and improve visualization of flow.<br/><br>
<br/><br>
For aim 1), 4D PC-MR stroke volume (SV) measurements in the aorta and main pulmonary artery were validated against 2D PC-MR at 1.5T and 3T, using two different 4D PC-MR sequences, one accelerated using SENSE and the other using k-t BLAST (Paper I). SENSE measurements showed good accuracy and measurements at 3T compared favorably to 1.5T. The k-t BLAST measurements showed a too high bias to be used for SV quantification.<br/><br>
<br/><br>
Furthermore, a phantom setup for validation of 4D PC-MR against independent measurements by particle imaging velocimetry (PIV) and planar laser-induced flourescence (PLIF) was developed and constructed (Paper II). The developed flow phantom showed excellent stability (R^2 =0.96, bias -0.06 +- unit 0.70 cm/s), making it suitable for validation of 4D PC-MR measurements. Validation of 4D PC-MR velocities against PIV show good agreement for mean velocities, but 4D PC-MR underestimates peak velocities by 8-25%. Vortex ring volume (VV) measurements with 4D PC-MR showed good agreement with PLIF. However, vortex ring mixing ratio (MXR) showed poor agreement. Due to possible differences between the phantom setup and in vivo vortex ring formation, further studies are needed to determine if MXR can be measured under in vivo flow conditions.<br/><br>
<br/><br>
For aim 2), a new method for quantification of vortex ring formation in the left ventricle using Lagrangian Coherent Structures was developed and implemented in software (Paper IV). Vortex ring volume was quantified in 15 healthy volunteers and 15 patients with heart failure. The vortex ring occupied 51 +- 7% of the LV blood volume in healthy volunteers, but only 26+-5% in the patients (p&lt;0.001). This suggests that a larger volume of blood is static in the LV of the patients, with an associated increase in the risk of thrombus formation (Papers IV and V).<br/><br>
<br/><br>
The vortex ring mixing ratio (MXR), defined as the amount of blood pulled into the vortex ring due to its rotation divided by the total volume of the vortex ring, was also quantified in healthy volunteers and heart failure patients (Paper V). MXR was higher in the patients compared to the volunteers (33+-7% vs 19+-7%, p&lt;0.001).<br/><br>
<br/><br>
For aim 3), a new method for visualization of 4D PC-MR blood flow measurements was developed and implemented in software. The new method, called Volume Tracking (Paper III), allows visualization of the motion of a blood volume through the heart. Volume Tracking gives incremental information about the blood flow compared to earlier used methods, e.g. by revealing a complex blood flow pattern in the right ventricle (RV) when compared to the LV. Additionally, the quality of particle tracing visualizations in 4D PC-MR accelerated using SENSE or k-t BLAST was evaluated (Paper I). No difference could be measured, showing that the higher acceleration, and therefore shorter scan duration, in k-t BLAST measurements can be used when the main goal is to visualize, and not quantify, blood flow.},
  author       = {Töger, Johannes},
  isbn         = {978-91-7623-072-5},
  issn         = {1404-0034},
  keyword      = {blood flow,dynamical systems,magnetic resonance imaging,heart failure,vortex ring formation},
  language     = {eng},
  pages        = {184},
  series       = {Doctoral theses in mathematical sciences},
  title        = {Measurement and Analysis of Intracardiac Blood Flow and Vortex Ring Formation},
  year         = {2014},
}