Proper fraction of inspired oxygen for reduction of oxygen-induced canine cerebrospinal fluid hyperintensity on fluid attenuation inversion recovery sequence using low-field magnetic resonance imaging.

Oxygen-induced cerebrospinal fluid (CSF) hyperintensity artifact is inevitable in fluid attenuation inversion recovery (FLAIR) magnetic resonance (MR) images of anesthetized animals. This experimental study aimed to confirm the occurrence of this artifact on low-field magnetic resonance imaging (MRI), and to determine the fraction of inspired oxygen (FiO) that is safe and does not induce this artifact in canine brain MRI. Six healthy dogs underwent brain FLAIR MR scans under general anesthesia with 21%, 30%, 50%, 70%, and 100% FiO. The signal intensity (SI) ratio was calculated as the SI of CSF spaces divided by that of normalizing regions. The SI ratios of 21% FiO images were significantly different from those of 100% FiO images, indicating the presence of artifacts on 100% FiO images. The SI ratios of 30% FiO images were not significantly different from those of 21% FiO images for any of CSF spaces. However, they were significantly different from those of 100% FiO images in the cerebral sulci, third ventricle, interpeduncular cistern, mesencephalic aqueduct, and subarachnoid space at the level of the first cervical vertebra (P<0.05). All dogs had normal partial pressure of arterial oxygen (PaO) during inhalation of 30% FiO, while two dogs had low PaO during inhalation of 21% FiO. Our findings support the hypothesis that high FiO induces CSF hyperintensity artifact on low-field FLAIR MR images in dogs. FiO of 30% is appropriate for obtaining brain FLAIR MR images with fewer artifacts in dogs.