Objectives: In this study our aim was to compare possibleeffects of two different oxygen concentrations (100%vs. 50%) on hyperintense signal abnormality (HSA) in pediatricpatients undergoing cranial magnetic resonanceimaging (MRI) under sevoflurane anesthesia.Materials and methods: Thirty pediatric patients undergoingcranial MRI were studied. Sevoflurane was usedfor induction and maintenance of anesthesia with an MRcompatibleanesthesia machine. Patients, whose airwaypatency was maintained with laryngeal mask, were dividedrandomly in two groups. 100% oxygen and 50% oxygen/50% nitrous oxide was used for maintenance of anesthesiain Group I and II, respectively. FLAIR sequenceimages were analyzed by a radiologist who was unawareof the groups and were evaluated for HSA in 11 differentbrain regions in cerebrospinal fluid neighborhood. Athree-point scale was used for evaluation.Results: HSA was seen in all study patients at least inone brain region. However, no significant difference wasobtained between two groups in almost all brain regions(p>0.05).Conclusions: Use of oxygen in pediatric patients undergoingcranial MRI under sevoflurane anesthesia caused alow grade HSA. However, concentration of oxygen had nosignificant effect on the severity of HSA. J Clin Exp Invest2012; 3(4): 477-482Key words: Anesthesia, pediatric, brain, magnetic resonanceimaging, cerebrospinal fluid, oxygen