Investigating the BOLD haemodynamic response

Blockley, Nicholas Paul (2007) Investigating the BOLD haemodynamic response. PhD thesis, University of Nottingham.

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Abstract

In this thesis the underlying mechanisms behind the phenomenon known as

the BOLD response were investigated.

Functional imaging of the brain relies on the oxygenation level of blood, therefore the relaxation properties of blood were measured at different oxygenations. The relaxation properties of blood are also modified by introduction of a paramagnetic contrast agent and are dependent on the static magnetic field of the MRI system. These dependencies were also characterised. This led to the discovery that the transverse relaxation rate is non-linearly related to contrast agent concentration. This result was confirmed by performing a Monte-Carlo simulation.

A measurement of total cerebral blood volume (CBV) change, during neural activity, was performed at high temporal resolution (TR = 300 ms). This was achieved by infusing a contrast agent, whilst a visual stimulus was presented to the volunteer. This technique also provided an interesting and novel method to test models of the BOLD response. The temporal characteristics of the BOLD response were differentially effected by the contrast agent, reflecting the dependency of each feature on blood volume change. This allowed a qualitative understanding of the volume contribution to each of these characteristics to be gathered.

Two models of the BOLD haemodynamic response were constructed to describe the contrast agent infusion experiment. Each model was developed from several existing models of the BOLD response, with the aim of comparing empirical and biomechanical model elements. As part of this work an existing model of BOLD signal change was extended to include the arterial and venous vasculature. Both models were separately fitted to the experimental total CBV and BOLD signal data. The results of fitting the data show that existing haemodynamic models cannot fully describe the measured results.

Item Type:Thesis (PhD)
Supervisors:Gowland, Penny
Francis, Susan
Uncontrolled Keywords:MRI, fMRI, BOLD, blood oxygenation level dependent, balloon model, relaxometry, blood, 7T
Faculties/Schools:UK Campuses > Faculty of Science > School of Physics and Astronomy
ID Code:473
Deposited By:Nicholas Paul Blockley
Deposited On:30 Jun 2008
Last Modified:06 Feb 2009 14:43

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