Noninvasive quantification of regional myocardial metabolic rate for oxygen by use of O-15(2) inhalation and positron emission tomography - Theory, error analysis, and application in humans

Background A method has been developed to measure the regional myocardial metabolic rate of oxygen consumption (rMMRO(2)) and oxygen extraction fraction (rOEF) quantitatively and noninvasively in humans by use of O-15(2) 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 O-15(2) is transported to peripheral tissues, where it is converted to O-15-labeled water of metabolism. which exchanges with the relatively large extravascular tissue space. Quantification of this buildup of radioactivity allows the calculation of rMMRO(2) 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 [C-11]CH4 in four greyhounds. Spillover of the cardiac chamber radioactivity has been corrected for with an inhaled [O-15]CO (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 Bow measurement [O-15](CO2 scan). Values of rOEF were similar (within 4%) whether obtained from gas volume measurements determined from the transmission or [C-11]CH4 scan data, O-15(2) scan information from six healthy volunteers showed a clear distribution of myocardial radioactivity after the vascular and pulmonary gas O-15 background was subtracted. Subsequent compartmental analysis Insulted in values for rOEF and rMMRO(2) 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.