Punwani, Shonit; (1997) The use of quantitative magnetic resonance imaging in perinatal brain injury. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The clinical signs and symptoms of hypoxic-ischaemic encephalopathy in human neonates are usually masked by the treatment administered to them. Hence a greater reliance on non-invasive monitoring techniques is required to aid prognosis. This thesis presents results of quantitative MRI techniques that are currently under development in order to study perinatally asphyxiated infants. Quantitative ADC and T2 measurements were made in a piglet model of perinatal hypoxic ischaemic brain injury The global directionally averaged ADC (ADCav) falls during the 48 hour period of monitoring following the transient hypoxic-ischaemic insult. There is also a gradual rise in T2 values during the 48 hour period. 31P MRS shows a decrease in [PCr]/[Pi] ratio during this same period. An early significant (p < 0.05) drop in global ADCav occurs at four hours post hypoxia-ischaemia. Additionally, a parasagittal pattern of cerebral injury is discernible in ADCav maps. A strong relationship between changes in ADCav and [PCr]/[Pi] is demonstrated (r = 0.95). The quantitative relationship between R2* and deoxyhaemoglobin was investigated using the piglet model. R2* is found to correlate strongly with absolute deoxyhaemoglobin concentration ([dHb]) as measured by near infra red spectroscopy (r = 0.95). It is hoped that quantitation of R2* can provide a non-invasive regional measure of cerebral deoxyhaemoglobin concentration in the perinatally asphyxiated infant. However, R2' may provide a more sensitive measure of [dHb]. Hence an imaging sequence was developed allowing the acquisition of both T2 and T2* weighted images from the same NMR signal, enabling these parameters to be rapidly quantified in future studies. The pulse sequence utilises spin coherence generated by a stimulated echo experiment. The sequence makes it possible to investigate the line broadening component, T2' of T2*-weighted signal, as this component is believed to be a more specific measure of cerebral tissue changes.

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