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BACKGROUND: A method has been developed to measure the regional myocardial metabolic rate of oxygen consumption (rMMRO2) and oxygen extraction fraction (rOEF) quantitatively and noninvasively in humans by use of 15O2 inhalation and positron emission tomography. This article describes the theory, an error analysis of the technique, and procedures of the method used in a human feasibility study. METHODS AND RESULTS: Inhaled 15O2 is transported to peripheral tissues, where it is converted to 15O-labeled water of metabolism, which exchanges with the relatively large extravascular tissue space. Quantification of this buildup of radioactivity allows the calculation of rMMRO2 and rOEF. However, a correction for the spillover of the pulmonary gas radioactivity signal into myocardial regions is required and has been made by use of a gas volume distribution estimated from the transmission scan. This was validated by comparative measurements using the inert gas 11CCH4 in four greyhounds. Spillover of the cardiac chamber radioactivity has been corrected for with an inhaled 13OCO (blood volume) scan. The underestimation of myocardial radioactivity due to wall motion and thickness has been corrected for by use of values of tissue fraction obtained from the flow measurement 15OKCO2 scan). Values of rOEF were similar (within 4%) whether obtained from gas volume measurements determined from the transmission or [11CCH4 scan data. 15O2 scan information from six healthy volunteers showed a clear distribution of myocardial radioactivity after the vascular and pulmonary gas 15O background was subtracted. Subsequent compartmental analysis resulted in values for rOEF and rMMRO2 of 0.60 +/- 0.11 and 0.10 +/- 0.03 mL.min-1.g-1 in the human myocardium at rest. CONCLUSIONS: The results of this study are in good agreement with established values. This is the first known approach to allow the direct quantitative determination of rOEF and oxygen metabolism to be made noninvasively on a regional basis.
Iida et al. (Thu,) studied this question.