 The main purpose of this study is to explore whether xenon is neuroprotective in humans. In addition, the purpose is to explore the underlying mechanisms for the possible synergistic neuroprotective interaction of xenon and hypothermia in patients suffering cerebral ischemia post cardiac arrest, by undertaking brain imaging to evaluate their effects on cerebral hypoxia, neuronal loss and mitochondrial dysfunction. In addition, the investigators aim to correlate these findings with neurological outcome to determine surrogate markers of favourable clinical outcome at six months. 