Volumetric MRI measurements of velocity and flow - Accuracy, visualisation and technical improvements
(2014)- Abstract
- In the last two decades, phase-contrast magnetic resonance imaging (PC-MRI) has evolved from two-dimensional velocity and flow
measurements to volumetric, time-resolved depictions of velocity fields (4D PC). The acquisition of time-resolved velocity fields allows
flow visualisations that might provide better understanding of the dynamics of the cardiac system. Because 4D PC is increasingly being
used to quantify certain physiological parameters and derive others, the need for validation and sufficient accuracy is increasing.
Additionally, because 4D PC is a time-consuming technique, strategies for reducing the acquisition time are being developed and are
crucial for 4D PC to realise its clinical... (More) - In the last two decades, phase-contrast magnetic resonance imaging (PC-MRI) has evolved from two-dimensional velocity and flow
measurements to volumetric, time-resolved depictions of velocity fields (4D PC). The acquisition of time-resolved velocity fields allows
flow visualisations that might provide better understanding of the dynamics of the cardiac system. Because 4D PC is increasingly being
used to quantify certain physiological parameters and derive others, the need for validation and sufficient accuracy is increasing.
Additionally, because 4D PC is a time-consuming technique, strategies for reducing the acquisition time are being developed and are
crucial for 4D PC to realise its clinical potential. The aims of the papers in this thesis were the following: 1) To validate a conventional
4D PC sequence with two commonly used acquisition acceleration strategies in a phantom setup, especially with respect to the
visualisation accuracy (Paper I). Furthermore, two common background phase correction strategies were compared. The results of this
study showed that background phase correction is important for accurate flow visualisations and quantitative flow measurement. 2)
develop and evaluate a 4D PC sequence with a spiral readout scheme and short echo time (TE) for the depiction of high velocities in
restricted geometries, and to investigate its properties compared to those of standard approaches (Paper II). The results of this study
showed that short-TE sequences with spiral readouts accurately quantified the maximum velocities, and demonstrated the feasibility of
using volumetric sequences for complete coverage of the stenotic region. 3) To develop and investigate a 4D PC sequence with variable
velocity encoding (4D vPC) throughout the cardiac cycle in an effort to reduce the noise and improve visualisations of time-varying
flow patterns (Paper III). The conclusion drawn from this study was that variable velocity encoding provided lower noise levels in the
diastolic parts of the cardiac cycle and improved flow visualisations. 4) To evaluate the previously constructed 4D vPC sequence with
respect to wall shear stress (WSS) measurements in the aorta (Paper IV). The measured WSS agreed with the corresponding
measurements performed with conventional 4D PC in both the systole and diastole. Furthermore, a smoother WSS distribution could
be observed in the 4D vPC datasets. (Less) - Abstract (Swedish)
- Popular Abstract in Swedish
Magnetresonanstomografi med faskontrast (PC-MRI) är en icke-invasiv metod
för att mäta hastigheter och blodflöden i kroppens större blodkärl, och är ett
viktigt verktyg för att diagnosticera och avbilda onormala fysiologiska förlopp.
Under de senaste två årtiondena har PC-MRI utvecklats från
hastighetsmätningar i enskilda riktningar och snitt till avbildning av kompletta
tidsupplösta hastighetsfält över större volymer (här benämnt 4D PC). Med hjälp
av 4D PC kan dynamiska blodflöden mätas, avbildas och visualiseras, vilket
avsevärt underlättar förståelsen för hjärt-kärlsystemets funktion. Fastän 4D PC
har börjat bli kliniskt... (More) - Popular Abstract in Swedish
Magnetresonanstomografi med faskontrast (PC-MRI) är en icke-invasiv metod
för att mäta hastigheter och blodflöden i kroppens större blodkärl, och är ett
viktigt verktyg för att diagnosticera och avbilda onormala fysiologiska förlopp.
Under de senaste två årtiondena har PC-MRI utvecklats från
hastighetsmätningar i enskilda riktningar och snitt till avbildning av kompletta
tidsupplösta hastighetsfält över större volymer (här benämnt 4D PC). Med hjälp
av 4D PC kan dynamiska blodflöden mätas, avbildas och visualiseras, vilket
avsevärt underlättar förståelsen för hjärt-kärlsystemets funktion. Fastän 4D PC
har börjat bli kliniskt användbart återstår arbete med att validera och optimera
4D PC tekniken. Arbetena i denna avhandling har därför haft följande syften:
I arbete I validerades en konventionell 4D PC sekvens med avseende på hur
noggrant hastigheter mäts, och två olika faskorrektionsmetoder för att korrigera
bakgrundsfel utvärderades. Vidare jämfördes avvikelsen i pathlines (en vanlig
visualiseringsteknik där spår av virtuella partiklar genom hastighetsfältet
beräknas) före och efter att vardera faskorrektionsmetod hade applicerats.
Resultaten visade att bakgrundskorrigering är nödvändig för att få tillförlitliga
visualiseringar och blodflödesmätningar.
I arbete II presenteras en 4D PC sekvens med spiralutläsning, utvecklad för att
kunna mäta höga hastigheter. I kärlförträngningar bildas områden där blodets
hastighet är onormalt hög. Att kunna mäta höga hastigheter med PC-MRI är
svårt och fodrar kunskap om den exakta positionen av förträngningen. Den
föreslagna sekvensen utvärderades i en modell av kärlförträngning och resultaten
jämfördes med simulerade flödesfält (CFD). Maximala hastigheter uppmätta
med den föreslagna 4D-spiralsekvensen överensstämde med CFD-beräknade
maxhastigheter. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/4437171
- author
- Nilsson, Anders LU
- supervisor
- opponent
-
- Professor Kozerke, Sebastian, ETH Zürich, Switzerland
- organization
- publishing date
- 2014
- type
- Thesis
- publication status
- published
- subject
- keywords
- MRI, 4D flow, phase contrast MRI, velocity mapping
- pages
- 170 pages
- publisher
- Department of Medical Radiation Physics, Clinical Sciences, Lund, Lund University
- defense location
- Lecture hall 3, Blocket, Skåne University Hospital
- defense date
- 2014-06-05 13:00:00
- ISBN
- 978-91-7623-014-5
- language
- English
- LU publication?
- yes
- id
- 274557c2-fcd9-425f-9aaa-acd18c277926 (old id 4437171)
- date added to LUP
- 2016-04-04 11:03:02
- date last changed
- 2018-11-21 21:02:21
@phdthesis{274557c2-fcd9-425f-9aaa-acd18c277926, abstract = {{In the last two decades, phase-contrast magnetic resonance imaging (PC-MRI) has evolved from two-dimensional velocity and flow<br/><br> measurements to volumetric, time-resolved depictions of velocity fields (4D PC). The acquisition of time-resolved velocity fields allows<br/><br> flow visualisations that might provide better understanding of the dynamics of the cardiac system. Because 4D PC is increasingly being<br/><br> used to quantify certain physiological parameters and derive others, the need for validation and sufficient accuracy is increasing.<br/><br> Additionally, because 4D PC is a time-consuming technique, strategies for reducing the acquisition time are being developed and are<br/><br> crucial for 4D PC to realise its clinical potential. The aims of the papers in this thesis were the following: 1) To validate a conventional<br/><br> 4D PC sequence with two commonly used acquisition acceleration strategies in a phantom setup, especially with respect to the<br/><br> visualisation accuracy (Paper I). Furthermore, two common background phase correction strategies were compared. The results of this<br/><br> study showed that background phase correction is important for accurate flow visualisations and quantitative flow measurement. 2)<br/><br> develop and evaluate a 4D PC sequence with a spiral readout scheme and short echo time (TE) for the depiction of high velocities in<br/><br> restricted geometries, and to investigate its properties compared to those of standard approaches (Paper II). The results of this study<br/><br> showed that short-TE sequences with spiral readouts accurately quantified the maximum velocities, and demonstrated the feasibility of<br/><br> using volumetric sequences for complete coverage of the stenotic region. 3) To develop and investigate a 4D PC sequence with variable<br/><br> velocity encoding (4D vPC) throughout the cardiac cycle in an effort to reduce the noise and improve visualisations of time-varying<br/><br> flow patterns (Paper III). The conclusion drawn from this study was that variable velocity encoding provided lower noise levels in the<br/><br> diastolic parts of the cardiac cycle and improved flow visualisations. 4) To evaluate the previously constructed 4D vPC sequence with<br/><br> respect to wall shear stress (WSS) measurements in the aorta (Paper IV). The measured WSS agreed with the corresponding<br/><br> measurements performed with conventional 4D PC in both the systole and diastole. Furthermore, a smoother WSS distribution could<br/><br> be observed in the 4D vPC datasets.}}, author = {{Nilsson, Anders}}, isbn = {{978-91-7623-014-5}}, keywords = {{MRI; 4D flow; phase contrast MRI; velocity mapping}}, language = {{eng}}, publisher = {{Department of Medical Radiation Physics, Clinical Sciences, Lund, Lund University}}, school = {{Lund University}}, title = {{Volumetric MRI measurements of velocity and flow - Accuracy, visualisation and technical improvements}}, year = {{2014}}, }