Development of injectable O-15 oxygen and estimation of OEF in a transient ischemia–reperfusion rat model

In the basic research about 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 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 15 O-O 2 ). Moreover, OEF after transient ischemia–reperfusion was estimated to validate the usefulness of the method. Injectable 15 O-O 2 , 72 MBq/ml of radioactivity, was obtained after 15 O-O 2 gas circulation into the artificial lung. OEF after injection of injectable 15 O-O 2 was calculated using the same equation as that applied to the bolus inhalation method. OEF value obtained by injectable 15 O-O 2 was well in accordance with that evaluated by arterial-venous difference of oxygen concentration. Furthermore, misery perfusion was depicted in the lesioned hemisphere after transient ischemia–reperfusion. These results indicated that this method is useful for the estimation of OEF and CMRO 2 in small animals using an animal positron emission tomography (PET) system and may accelerate the basic research of cerebral perfusion diseases.