Development of injectable O-15 oxygen and its application for estimation of OEF

Abstract

In the basic research on cerebral perfusion disorders, a new method for measurement of oxygen extraction fraction (OEF) and cerebral metabolic rate for oxygen (CMRO 2) has been desired. Although the O-15-labeled gas inhalation method is performed in clinical studies, application of the inhalation method to small animals requires too many intensive procedures. Therefore, this study investigated a new method of assessing OEF in small animals using intravenously injectable oxygen (injectable 15O-O 2). Additionally, it was compared with the inhalation method, using a monkey for further validation. Using injectable 15O-O 2, 72 MBq/ml of radioactivity was obtained after 15O-O 2 gas circulation into an artificial lung. OEF with injectable 15O-O 2 was calculated using the same equation as that applied to the bolus inhalation method. The OEF value obtained by injectable 15O-O 2 was well in accordance with that evaluated by the arterial-venous difference of oxygen concentration. Furthermore, the OEF and CMRO 2 images obtained with two methods using a monkey brain showed a similar distribution. These results indicate that this method is useful for the estimation of OEF and CMRO 2 in small animals using an animal positron emission tomography system and may accelerate the basic research of cerebral perfusion diseases.