[Background] Hypoxic-ischemic encephalopathy (HIE), results from birth asphyxia in perinatal period and from cardiopulmonary arrest with heart diseases or near-drowning in childhood. Disturbed cerebral blood flow (CBF) is the primary cause in HIE. Nevertheless, temporal profiles of hemodynamics in association with cerebral brain damage are not well understood, which is due mostly to technical difficulties in obtaining data in both clinical and animal studies. Recently we have developed a non-invasive hybrid MR/PET imaging system for small animals.
[Objectives] 1) To clarify temporal profiles of brain injury and hemodynamics in immature rats with HIE by using the MR/PET imaging. 2) To analyze associations between parameters, especially between early indicators of brain injury and the later morphological damage.
[Methods] Postnatal day 21 rats were subjected to unilateral common carotid artery ligation followed by transient hypoxic insult. Nine rats were sequentially evaluated with the MR/¹⁵O-PET imaging; 2-3h, 24h, 48h, 7, and 42 days after the HI insult. The brains were removed and evaluated morphologically/histologically at 42 days after the HI. We set regions of interest in the cortices, and analyzed the ipsilateral/contralateral ratios of each parameter.
[Results] At immediately after the HI, the ratio of mean CBF was the only parameter distinctively altered, i.e. decreased. At 24h after the HI, the ratio of mean T₂-weighted signal (T2WS) increased, and that of mean apparent diffusion coefficient (ADC) decreased, while the ratio of CBF returned to normal. At 48h after the HI, the ratio of fractional anisotropy and that of cerebral metabolic rate of oxygen (CMRO₂) decreased. T2WS and ADC at 24h and 48h, and CMRO₂ at 48h after the HI significantly correlated with the later brain damage.
[Conclusion] Our MR/PET imaging revealed temporal changes in brain injury and hemodynamics in immature rats with HI. T2WS, ADC, and CMRO₂ at subacute phase after the HI were predictive of the later brain damage.