Author(s): Pimentel, Marco André Figueiredo
Date: 2009
Persistent ID: http://hdl.handle.net/10362/10570
Origin: Repositório Institucional da UNL
Subject(s): fMRI (functional magnetic resonance imaging); ASL (arterial spin labeling); BOLD (blood oxygen level dependent); CBF (cerebral blood perfusion)
Dissertation submitted in Faculdade de Ciências e Tecnologia of Universidade Nova de Lisboa for the degree of Master of Biomedical Engineering
Background: The new clinically available arterial spin labelling (ASL) sequences present some advantages relatively to the commonly used blood oxygenation level dependent (BOLD) method for functional brain studies using magnetic resonance imaging (MRI), namely the fact of being potentially quantitative and more reproducible. Purpose: The main aim of this work was to evaluate the functional use of a commercial ASL sequence implemented on a 3 Tesla MRI system (Siemens, Verio) in the Imaging Department of Hospital da Luz. The first aim was to obtain a functional validation of this technique by comparison with the BOLD contrast, using a number of different approaches. The second aim was to accomplish perfusion quantification, by resolving some important quantification issues. Materials and Methods: Fifteen adult volunteers participated in a single functional imaging session using three different protocols: one using BOLD and two using ASL. The subjects performed a motor finger tapping task and the data analysis was performed using Siemens Neuro3D and FSL (FMRIB’s Software Library). The location and variability of the activated areas were analysed in MNI (Montereal Neurological Institute) standard space. Results: Topographic agreement between the activated regions obtained by BOLD and ASL was found. However, the results show that inter-subject variability and distance to the hand motor cortex were smaller when measured with ASL as compared with BOLD fMRI. Quantitative studies revealed that ASL allows the calculation of cerebral blood flow (CBF), both at baseline and upon functional activation. Conclusion: The results suggest that the functional imaging protocols using ASL produce comparable results to a conventional BOLD protocol, with the additional advantages of reduced inter-subject variability, better spatial specificity and quantification possibilities.
