Abstract
Cerebral perfusion, or cerebral blood flow, CBF, is a physiological variable thatmeasures the amount of blood delivered to brain tissue per unit time. In neonates, CBF assumes an important role as alterations in CBF are linked to many instances of brain injury, particularly following preterm or complicated births.
CBF can be measured using a number of techniques, most of which rely on ionising radiation and require the administration of exogenous substances. This renders them unsuitable for studying CBF in healthy neonates and for repeated studies. In this thesis, Magnetic Resonance Imaging (MRI) techniques capable of measuring CBF non-invasively are optimised for the neonatal population.
The longitudinal relaxation time constant, T1, of blood is an important parameter
in many MRI techniques, such as perfusion quantification using Arterial Spin
Labelling (ASL). In most applications, ex-vivo literature values are used for blood
T1. A novel method to measure blood T1 in vivo in a very short time is presented. It is found that blood T1 values in neonates are very variable and strongly correlated to the haematocrit. This method can be used to improve CBF quantification using ASL in neonates.
A robust method used to measure mean CBF is also presented. Firstly, the mean
flow to the brain in the arteries of the neck was measured using an optimised
phase-contrast angiography protocol. This was then divided by the brain volume,
computed from an anatomical MR image, to yield mean CBF. This method was
applied to a small cohort of infants, where the relationship between CBF and
postmenstrual age was investigated. Arterial Spin Labelling was also used in both adults and neonates. In adults, CBF values were compared to those obtained using the PCA method. Techniques to estimate the parameters needed in the ASL model for CBF quantification were also explored. Finally, ASL data acquired in neonates is presented and further improvements to CBF measurements using ASL in this age group are discussed.
| Date of Award | 2011 |
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| Original language | English |