- Poster presentation
Blood flow and oxygen extraction fraction in regions of oedema following head injury
Critical Care volume 8, Article number: P311 (2004)
Cerebral blood flow (CBF) is reduced around areas of contused brain after head injury . However, since the cerebral metabolism is also reduced this may represent appropriate flow-metabolism coupling, rather than ischaemia. Matching of CBF to metabolism is quantified as the oxygen extraction fraction (OEF). We performed magnetic resonance imaging (MRI) and Oxygen 15 positron emission tomography (O-PET) to quantify CBF and OEF in regions of pericontusional oedema after head injury.
After local ethical approval, five patients with severe head injury underwent structural MRI and O-PET, in the first week after injury. The two studies were performed in immediate succession, with every effort made to maintain stable physiology. The fluid attenuation inversion recovery (FLAIR) MRI sequence provides cerebrospinal fluid-nulled, T2-weighted MRI images, on which oedema is hyperintense. The FLAIR images were coregistered and voxel resized to O-PET-derived maps of CBF and OEF, using a published methodology . Each patient's coregistered FLAIR image was inspected for the largest and most apparent region of pericontusional oedema. These regions were then manually outlined and applied to PET maps, and CBF and OEF in these regions of oedema were calculated. Results were compared with unit reference data obtained from healthy volunteers .
Normal values of CBF and OEF obtained from volunteer datasets for mixed grey-white regions were 35 ± 5 ml/100 g/min and 45 ± 5%, respectively. While pericontusional regions showed a significantly lower CBF (20.5 ± 8.3 ml/100 g/min), we observed a wide range of values both across subjects and within individual lesions (14.7–35 and 5.1–52.3 ml/100 g/min, respectively). However, mean OEF values were low (35.4 ± 2.1%), with a much smaller range of values across patients (31.8–37.5%) and individual image voxels (24.9–41.8%). The 95% confidence intervals for the population mean pericontusional CBF and OEF were 10.2 and 30.8 ml/100 g/min and 32.8 and 38.1%, respectively.
The wide range of CBF values should make clinicians wary of predicting the viability of tissue in regions of pericontusional oedema. The values are all above the threshold, of 8.4 ml/100 g/min , for irreversible ischemia from the stroke literature. Thresholds for irreversible ischemia after head injury are unknown. The upper 95% confidence interval for the OEF is only 38% and the maximum OEF in any voxel was 42%, suggesting that the reduction in CBF may be appropriate to the metabolic demands of the tissue.
Steiner LA, Czosnyka M: Should we measure cerebral blood flow in head-injured patients? Br J Neurosurg 2002, 16: 429-439. 10.1080/0268869021000030221
Hawkes DJ, Hill DL: Medical imaging at Guy's Hospital, King's College London. IEEE Trans Med Imaging 2003, 22: 1033-1041. 10.1109/TMI.2003.815866
Coles JP, et al.: Defining ischemic burden after traumatic brain injury using 15O PET imaging of cerebral physiology. J Cerebral Blood Flow Metab 2004, 24: 191-202. 10.1097/01.WCB.0000100045.07481.DE
Marchal G, Benali K, Iglesias S, Viader F, Derlon J-M, Baron J-C: Voxel-based mapping of irreversible ischaemic damage with PET in acute stroke. Brain 1999, 122: 2387-2400. 10.1093/brain/122.12.2387
Rights and permissions
About this article
Cite this article
Bradley, P., Harding, S., Coles, J. et al. Blood flow and oxygen extraction fraction in regions of oedema following head injury. Crit Care 8 (Suppl 1), P311 (2004). https://doi.org/10.1186/cc2778
- Cerebral Blood Flow
- Head Injury
- Severe Head Injury
- Magnetic Resonance Imaging Sequence
- Flair Image