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Functional studies on magnetic resonance
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Resumo(s)
Background: Magnetic Resonance Imaging (MRI) is an imaging technique used
primarily to produce high quality structural and functional images of the human body.
Functional MRI techniques, among which are included the Arterial Spin Labeling (ASL)
and the Blood Oxygenation Level-Dependent (BOLD), are used to measure brain
activity. Several studies have shown that ASL holds several advantages when compared
with BOLD, namely the fact of being more reproducible and perfusion quantitative.
Purpose: The main aim of this work is to obtain perfusion quantification of the human
brain within several of its territories and to compare the results obtained using two
different ASL protocols. Secondarily this study aimed to validate an ASL protocol to be
used in clinical exams – Protocol #2 by comparing the values obtained for all the
regions considered with the ones present in literature.
Methods: The methodology used in this study was applied to fifteen adult volunteers.
Two ASL protocols were used in a single functional imaging session. Subjects were
asked to perform a motor finger tapping task with their right hand while being scanned.
Images were acquired on a 3 Tesla equipment – Magnetom Verio MRI System from
SIEMENS in Hospital da Luz. For the definition of the regions to study the Talairach
anatomical atlas was used and the brain was segmented considering five different
segmentation levels.
Results: Perfusion quantification studies have demonstrated that ASL allows a correct
calculation of Cerebral Blood Flow (CBF), especially when compared to other studies
which used other invasive perfusion measuring techniques. The perfusion values
obtained for several regions considered are in agreement with the ones available in
literature.
Conclusions: ASL protocols are now becoming commercially available and have been
demonstrating coherent results with other techniques already established. The current
study presents one of the first detailed perfusion studies using this technique to
evaluate several structures of the brain. The adequacy of Protocol 2 for functional
studies was also proved considering the stimulus used.
Descrição
Dissertation submitted in Faculdade de Ciências e Tecnologia of Universidade Nova de Lisboa for the degree of Master in Biomedical Engineering
Palavras-chave
Functional magnetic resonance imaging (fMRI) Cerebral blood flow (CBF)