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Volumetric MRI measurements of velocity and flow - Accuracy, visualisation and technical improvements

Nilsson, Anders LU (2014)
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)
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)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Kozerke, Sebastian, ETH Zürich, Switzerland
organization
publishing date
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
ISBN
978-91-7623-014-5
language
English
LU publication?
yes
id
274557c2-fcd9-425f-9aaa-acd18c277926 (old id 4437171)
date added to LUP
2014-05-15 10:54:12
date last changed
2016-09-19 08:45:08
@misc{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},
  keyword      = {MRI,4D flow,phase contrast MRI,velocity mapping},
  language     = {eng},
  pages        = {170},
  publisher    = {ARRAY(0xb1b2760)},
  title        = {Volumetric MRI measurements of velocity and flow - Accuracy, visualisation and technical improvements},
  year         = {2014},
}