Day-to-Day Test-Retest Variability of CBF, CMRO2, and OEF Measurements Using Dynamic 15O PET Studies

We assessed test-retest variability of cerebral blood flow (CBF), cerebral blood volume (CBV), cerebral metabolic rate of oxygen (CMRO2), and oxygen extraction fraction (OEF) measurements derived from dynamic O-15 positron emission tomography (PET) scans. In seven healthy volunteers, complete test-retest O-15 PET studies were obtained; test-retest variability and left-to-right ratios of CBF, CBV, OEF, and CMRO2 in arterial flow territories were calculated. Whole-brain test-retest coefficients of variation for CBF, CBV, CMRO2, and OEF were 8.8%, 13.8%, 5.3%, and 9.3%, respectively. Test-retest variability of CBV left-to-right ratios was < 7.4% across all territories. Corresponding values for CBF, CMRO2, and OEF were better, i.e., < 4.5%, < 4.0%, and < 1.4%, respectively. The test-retest variability of CMRO2 measurements derived from dynamic O-15 PET scans is comparable to within-session test-retest variability derived from steady-state O-15 PET scans. Excellent regional test-retest variability was observed for CBF, CMRO2, and OEF. Variability of absolute CBF and OEF measurements is probably affected by physiological day-to-day variability of CBF.