PET measurements of CBF, OEF, and CMRO2 without arterial sampling in hyperacute ischemic stroke: Method and error analysis
- 190 Downloads
A method for relative measurement of cerebral blood flow (CBF), oxygen extraction fraction (OEF), and metabolic rate of oxygen (CMRO2) using positron emission tomography (PET) without arterial sampling in patients with hyperacute ischemic stroke was presented.
The method requires two PET scans, one for H2 15O injection and one for15O2 inhalation, and calculates regional CBF, CMRO2, and OEF relative to those at the reference brain region by means of table-lookup method. In this study, we calculated “relative lookup-tables” which relate relative CBF to relative H2 15O count, relative CMRO2 to relative15O2 count, and relative OEF to relative15O2/H2 15O count. Two assumptions were applied to the lookup-table calculation: 1) In the reference region, CBF and OEF were assumed to be 50.0 ml/min/100ml and 0.40, respectively, 2) Cerebral blood volume (CBV) was assumed to be constant at 4.0 ml/100ml over the whole brain. Simulation studies were done to estimate the error of the present method derived from the assumptions.
For relative CBF measurements, 20% variation in reference CBF gave about ±10% error for measured relative CBF at maximum. Changes in CBV caused relatively large errors in measured OEF and CMRO2 when relative CBF and OEF decreased. Errors for measured relative OEF caused by 50% variation in CBV were within ±8% at 0.8 of relative CBF and ±12% at 0.4 of relative CBF when relative OEF was greater than 1.0.
CBV effects caused larger errors in estimated OEF and CMRO2 in the region of the ischemie core with decreasing relative CBF and/or OEF but only slight errors in the region of “misery perfusion” with relative OEF values greater than 1.0. The present method makes PET measurements simpler than with the conventional method and increases understanding of the cerebral circulation and oxygen metabolism in patients with hyperacute stroke of several hours after onset.
Key wordsPET relative measurement cerebral blood flow oxygen metabolism hyperacute stroke
- 14.Kanno I, Lammertsma AA, Heather JD, Gibbs JM, Rhodes CG, Clark JC, et al. Measurement of cerebral blood flow using bolus inhalation of C15O2 and positron emission tomography: Description of the method and its comparison with the C15O2 continuous inhalation method.J Cereb Blood Flow Metab 1984; 4: 224–234.PubMedGoogle Scholar
- 15.Kety SS. The theory and applications of the exchange of inert gas at the lungs and tissues.Pliarmacol Rev 1951; 3: 1–41.Google Scholar
- 17.Iida H, Miura S, Kanno I, Ogawa T, Uemura K. A new PET camera for noninvasi ve quantitation of physiological functional parametric images: Headtome-V-Dual. In: Myers R, Cunningham V, Bailey D, Jones T, eds.Quantification of Brain Function Using PET. San Diego, CA; Academic Press, 1996:57–61.Google Scholar
- 23.Lammertsma AA, Wise RJS, Heather JD, Gibbs JM, Leenders KL, Frackowiak RSJ, et al. Correction for the presence of intravascular oxygen-15 in steady-state technique for measuring regional oxygen extraction ratio in the brain: 2. Results in normal subjects and brain tumour and stroke patients.J Cereb Blood Flow Metab 1983; 3: 425–431.PubMedGoogle Scholar