1. ¹The Division of Anaesthesia, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK
2. ²The Wolfson Brain Imaging Centre, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK
3. ³Department of Neurosurgery, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK
4. ⁴Medical Research Council Biostatistics Unit, Institute of Public Health, Forvie Site, Addenbrooke's Hospital, Cambridge, UK

Correspondence: Dr JP Coles, The Division of Anaesthesia, University of Cambridge, Box 93, Addenbrooke's Hospital, Hills Road, Cambridge, CB2 2QQ, UK. E-mail: jpc44@wbic.cam.ac.uk

Received 21 January 2005; Revised 12 April 2005; Accepted 31 May 2005; Published online 29 June 2005.

Abstract

Oxygen-15 positron emission tomography (¹⁵O PET) can provide important data regarding patients with head injury. We provide reference data on intersubject variability and reproducibility of cerebral blood flow (CBF), cerebral blood volume (CBV), cerebral metabolism (CMRO₂) and oxygen extraction fraction (OEF) in patients and healthy controls, and explored alternative ways of assessing reproducibility within the context of a single PET study. In addition, we used independent measurements of CBF and CMRO₂ to investigate the effect of mathematical correlation on the relationship between flow and metabolism. In patients, intersubject coefficients of variation (CoV) for CBF, CMRO₂ and OEF were larger than in controls (32.9%2.2%, 23.2%2.0% and 22.5%3.4% versus 13.5%1.4%, 12.8%1.1% and 7.3%1.2%), while CoV for CBV were lower (15.2%2.1% versus 22.5%2.8%) (P<0.001). The CoV for the test–retest reproducibility of CBF, CBV, CMRO₂ and OEF in patients were 2.1%1.5%, 3.8%3.0%, 3.7%3.0% and 4.6%3.5%, respectively. These were much lower than the intersubject CoV figures, and were similar to alternative measures of reproducibility obtained by fractionating data from a single study. The physiological relationship between flow and metabolism was preserved even when mathematically independent measures were used for analysis. These data provide a context for the design and interpretation of interventional PET studies. While ideally each centre should develop its own bank of such data, the figures provided will allow initial generic approximations of sample size for such studies.