Estimation of Cerebral Oxygen Utilization Rate by Single-Bolus 15O2 Inhalation and Dynamic Positron Emission Tomography

Abstract

This study shows that regional CMRO₂ can be estimated by means of nonlinear regression using dynamic positron emission tomographic data acquired during 1 min following single-bolus inhalation of ¹⁵O₂. The feasibility of simultaneous estimation of CBF, cerebral blood volume (CBV), oxygen extraction ratio (OER), and CMRO₂ was assessed by simulations using the model of Mintun et al. Four oxygen metabolic measurements, each consisting of a CBF, CBV, and ¹⁵O₂ bolus study, were carried out on three volunteers. Regional values for CBF, CBV, OER, and CMRO₂ were derived in two ways: from the fits of the time-activity curves of the dynamic ¹⁵O₂ bolus study alone [CMRO₂(fit)] and from the three separate studies [CMRO₂ (control)]. For the 56 regions of interest analyzed, using a fit interval of 60 s, CMRO₂(fit) was 93.4 ± 7.8% of CMRO₂(control) (mean ± SD) with a correlation coefficient of r = 0.95. CMRO₂(control) ranged from 87 to 290 μmol/min/100 g. Individual simultaneous estimates of CBF, CBV, and OER were not reliable. Finally, we found that the validity of the model was limited in practice to the first minute after tracer inhalation.