Quantitative diffusion weighted imaging : techniques and applications to perinatal asphyxia
This thesis describes the results of a study to investigate early cerebral changes in a piglet model of perinatal asphyxia using quantitative diffusion-weighted imaging (DWI) and subsequent work to develop a robust DWI technique to enable similar studies to be performed in neonates. 31Phophorus magnetic resonance spectroscopy and quantitative diffusion and T2 imaging of the cerebrum were performed in a piglet model of perinatal asphyxia. A significant decline in the ratio of phosphocreatine to inorganic phosphate concentrations ([PCr]/[Pi]) was observed during the 48 hours following the transient hypoxicischaemic (H-I) insult. The global directionally averaged apparent diffusion coefficient (ADCav) also declined significantly during the same period and a strong correlation between the [PCr]/[Pi] and ADCav was found. Strong regional and temporal variations in the cerebral response were observed following the H-I insult. In the basal ganglia and parasagittal cortex, significant decline in ADCs was seen approximately 8 hours after the H-I insult. In the thalamus, internal capsule, periventricular white matter and medial cortex, significant ADCs decline was not observed until 32 hours following the H-I insult. A significant T2 increase was observed in the internal capsule but not in the other regions of interest. To enable clinical DWI to be performed in neonates a novel `reacquisition' technique that overcomes the problem of motion artefact in DWI is presented. The reacquisition technique involves the automatic detection and reacquisition of motion-corrupted data in real-time. Computer simulations were used to demonstrate that motion-corrupted data may be detected accurately and reacquired in a time efficient manner. The reacquisition technique was implemented on a Bruker AVANCE scanner in combination with a spinecho 2DFT DWI sequence and an interleaved EPI DWI sequence. The effectiveness of the technique was demonstrated with both a computer-controlled motion phantom and neonates from an ongoing study of perinatal asphyxia.