Cerebrospinal fluid signal intensity increase on FLAIR MR images in patients under general anesthesia: The role of supplemental O-2

PURPOSE: To determine whether increased cerebrospinal fluid (CSF) signal in tensity is seen on fluid-attenuated inversion recovery (FLAIR) magnetic res onance (MR) images in patients under general anesthesia and to investigate the cause of these changes. MATERIALS AND METHODS: MR images from nine examinations performed in eight patients under general anesthesia were reviewed retrospectively. In phantom experiments, T1 measurements obtained with several inhaled anesthetic agen ts and propofol dissolved in saline were compared with those obtained with either 100% O-2 or room air. To confirm phantom experiment results, a healt hy volunteer underwent sequential FLAIR imaging while breathing high-flow 1 00% O-2. RESULTS: Of the nine examinations performed with patients under general ane sthesia, eight had resultant images that showed increased CSF signal intens ity within the basal cisterns and sulci over the cerebral convexities. Anes thetic phantom measurements showed T1 shortening only when the agent was ad ministered with high concentrations of oxygen. In the healthy volunteer, im ages obtained before and during administration of 100% O-2 demonstrated inc reased CSF signal intensity after O-2 administration; this was identical to the changes observed in patients under anesthesia. CONCLUSION: The paramagnetic effects of supplemental O-2 administration res ult in shortened CSF T1. Radiologists should be aware of this phenomenon to avoid attributing increased CSF signal intensity on FLAIR images to abnorm al CSF properties such as hemorrhage or elevated protein content.