Pericontusional Ischaemia Following Head Injury: Imaging Correlates

It has been well established that ischaemia can result in secondary injury to the brain following trauma. While such ischaemia has been imaged, it has been difficult demonstrate its physiological significance. The aim of this research was to use diffusion weighted magnetic resonance imaging (DWI) to characterise the patterns of cytotoxic and vasogenic oedema early after head injury and correlate changes with regional physiology, imaged using lsO positron emission tomography (,sO-PET). Data from methodological developments carried out in the course o f this research are presented. These include the testing of MR compatibility o f infusion pumps, optimisation of image processing routines, assessment of the validity of commonly used MR measures of tissue injury in the context of head injury, and an assessment of the test-retest reproducibility o f DWI. Early DWI imaging in 30 patients with significant head injury (range 8 134 hours) revealed a characteristic contusional morphology, with a haemorrhagic core and concentric rings o f vasogenic and cytotoxic oedema. In the regions studied, the integrated volume o f pericontusional oedema was over three times the volume of the central core. An analysis across patients, although confounded by interindividual variation, suggested that this pericontusional oedema increased in size with time from injury. Correlation with electron microscopy suggested microvascular ischaemia as a mechanism for these changes The physiological correlates of the ADC changes described above were investigated in a subset of nine patients with lsO-PET. The contusion core showed significant reductions in cerebral blood flow (CBF), oxygen extraction fraction (OEF) and cerebral oxygen metabolism (CMR02), while the region of vasogenic oedema only showed significantly reductions in CMR02. Other studies explored the use of dynamic DWI to assess the impact of hyperventilation on ADC changes around contusions. The implications of these findings are discussed and further research directions explored.