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Title Three-dimensional T1 quantification techniques for assessment of cartilage quality using dGEMRIC
Author/s Carl Siversson
Department/s Medical Radiation Physics, Malmö
Full-text Available as PDF
Defence date 2011-09-09
Defence time 09:15
Defence place Jubileumsaulan (entrance 59) at Skåne University Hospital in Malmö
Opponent Professor, Ph.D. Pottumarthi V. Prasad
Publication/Series Lund University, Faculty of Medicine Doctoral Dissertation Series
Publishing year 2011
Volume 2011:74
Pages 101
Document type Dissertation
Language English
Publisher Medical Radiation Physics
Popular science abstract Swedish Artros är en av de vanligaste kroniska sjukdomarna och en av de främsta orsakerna till funktionshinder för människor världen över. Artros angriper ofta knä- och höftlederna och bryter ner det brosk som finns där. För den som drabbats av artros tar förloppet ofta många år, med successivt ökande smärtor och rörelsesvårigheter. Ofta upptäcks dessutom inte sjukdomen förrän i ett sent stadie, när processen inte längre går att förhindra. I många fall är den enda utvägen att den skadade leden, efter en tids sjukdom, opereras bort och ersätts med en protes.
Under de senaste åren har vår forskargrupp, tillsammans med andra grupper, utvecklat en metod för att upptäcka artros i ett så tidigt skede att sjukdomsförloppet förhoppningsvis kan fördröjas med många år. Metoden benämns dGEMRIC (delayed gadolinium-enhanced MRI of cartilage) och bygger på att man ger patienten ett ofarligt kontrastmedel som tas upp av brosket i en mängd som beror av artrosgraden. Genom att med en magnetkamera därefter mäta den så kallade T1 parametern i brosket, kan koncentrationen av kontrastmedel i brosket bestämmas och därmed graden av artros uppskattas.
En nackdel med dGEMRIC metoden hittills har varit att man med magnetkamerorna bara har kunnat mäta T1 i tvådimensionella snittbilder genom brosket, vilket har inneburit att det har varit svårt att få en uppfattning om artrosgraden i hela leden. Det är detta problem som denna avhandling syftar till att lösa, genom att ta fram nya tredimensionella volumetriska T1-mätningsmetoder som gör att magnetkameran kan undersöka allt brosk i leden samtidigt.
Som en del i detta arbete har egna pulssekvenser till magnetkamerorna utvecklats samt analysverktyg tagits fram som genom matematiska algoritmer beräknar broskkvaliteten utifrån magnetkamerabilderna. För att utvärdera de nya mätmetoderna har flera studier genomförts, både på friska och artrossjuka personer. Resultaten visar att de nya tredimensionella metoderna fungerar, vilket kommer att göra det möjligt att följa sjukdomen på sätt som tidigare inte varit möjligt.
Analys- och visualiseringsmetoderna kommer nu att vidareutvecklas samt paketeras så att de blir enkla att använda. Bland annat håller ett datorprogram på att tas fram där man enkelt kan se hur kvaliteten på brosket varierar på olika ställen i leden. Framförallt riktar sig detta till läkare, men det ska också kunna användas för att utvärdera funktionen hos framtida artrosläkemedel. Därigenom är förhoppningen att detta kommer att bli ett viktigt verktyg inom brosk- och leddiagnostik.
Abstract English Osteoarthritis (OA) is a common chronic disease and one of the major global causes for functional disabilities. The disease is characterized by loss and degradation of cartilage, commonly affecting the knees and hips. Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) is a previously presented method for identification of early OA using magnetic resonance imaging (MRI). By quantifying the T1 parameter in the cartilage after distribution of a contrast agent, a measure of the glycosaminoglycan (GAG) content is retrieved, which in turn is known to be decreased at early stages of OA.
In this thesis a series of three-dimensional (3D) T1 quantification methods have been developed and evaluated for use in dGEMRIC. Traditionally, such sequences have not been widely adopted for this purpose and in this work it has been shown that the main obstacles are related to B1 variations within the volume.
As part of the work a 3D Look-Locker (3D-LL) T1 quantification pulse sequence have been created. In addition, new methods were developed for correction of B1 inhomogeneities and slab profile flip angle variations in the 3D-LL data. From in vivo and phantom measurements the methods were shown to be reliable, with T1 results that agreed very well to gold standard two-dimensional inversion recovery (2D-IR).
A 3D variable flip angle (3D-VFA) T1 quantification sequence in combination with a B1 mapping sequence was also investigated. The results with and without B1 correction was studied in vivo and in phantoms. It was concluded that 3D-VFA should always be used with B1 correction, especially at higher field strengths
In addition, two dedicated clinical studies were set up, to both verify the usability of the developed methods and to explore new dGEMRIC applications. In one of these studies, the repeatability of successive dGEMRIC measurements for each of the T1 quantification methods was investigated for a group of subjects at risk of developing OA. 2D-IR and 3D-LL performed equally well, while 3D-VFA (without B1 correction) was inferior. Repeatability was shown to be similar to previously reported results in healthy subjects.
The other of these studies was a time-response study, using 3D-LL, to explore the feasibility of performing dGEMRIC in the meniscus. It was concluded that the temporal contrast uptake in the meniscus follows that of the articular cartilage and that differences can be seen between vascular and avascular parts of the meniscus.
The overall conclusion of this work is that 3D T1 quantification in dGEMRIC is feasible and should allow for both new and improved means of diagnostics.
Subject Medicine and Health Sciences
Keywords T1, B1, MRI, 3D, correction, dGEMRIC, cartilage, Look-Locker, Variable Flip Angle
ISBN/ISSN/Other ISSN: 1652-8220
ISBN: 978-91-86871-24-6
Supervisor Jonas Svensson
Supervisor Sören Mattsson
Supervisor Leif Dahlberg
Additional info Please note that the reproduction licenses from the publishers of the papers that are included in the thesis file are uploaded as separate documents.
Other relation Reproduction license for Paper 1
Description: This is the authorization from the publisher of Paper I (which is included in the thesis document), allowing the paper to be used both in printed and electronic versions of my thesis.
Restriction: Restricted Access (Alternative Location)
Other relation Reproduction license for Paper 2
Description: This is the authorization from the publisher of Paper II (which is included in the thesis document), allowing the paper to be used both in printed and electronic versions of my thesis.
Restriction: Restricted Access (Alternative Location)
Part of Local Flip Angle Correction for Improved Volume T1-Quantification in Three-Dimensional dGEMRIC Using the Look-Locker Technique
Part of Repeatability of T1-quantification in dGEMRIC for three different acquisition techniques: two-dimensional inversion recovery, three-dimensional look locker, and three-dimensional variable flip angle.

 

 

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