Visualization of intravenously administered contrast material in the CSF on fluid-attenuated inversion-recovery MR images: An in vitro and animal-model investigation

BACKGROUND AND PURPOSE: The FLAIR (fluid-attenuated inversion-recovery) pul se sequence has been shown to be sensitive to abnormalities of the subarach noid space, Our clinical experience led us to investigate whether intraveno usly injected contrast material can affect the appearance of the subarachno id space on FLAIR MR images. METHODS: After noting unexplained high signal in the subarachnoid space on FLAIR images in a patient, we studied two dogs with sequential FLAIR MR ima ging after IV administration of contrast material. A third dog was studied with a 6-hour delayed FLAIR sequence after triple-dose (0.3 mmol/kg) IV con trast administration. CSF was obtained from two animals for measurement of gadolinium concentration. A phantom was developed to determine the lowest c oncentration at which the effects of gadolinium were evident on FLAIR image s in vitro. RESULTS: In all three animals, the appearance of the CSF in the ventricles or subarachnoid space was modified after administration of IV contrast. Thi s was most evident on delayed images. The CSF samples showed a gadolinium c oncentration of 0.007 mmol/L in the dog who received the 0.1 mmol/kg dose a nd 0.02 mmol/L in the dog who received a triple dose. In our in vitro phant om experiments, gadolinium effects were evident on FLAIR images at a concen tration four times lower than those on T1-weighted images. CONCLUSION: IV contrast material can cross into the CSF in sufficient conce ntration to alter the appearance of the subarachnoid space on FLAIR images in normal dogs. Although we encountered two patients with CNS disease in wh om enhancement of the CSF was seen on postcontrast FLAIR images, additional investigation is needled in humans to determine whether enhancement may oc cur at triple dose in healthy subjects.