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

Abstract

Background and purpose: The FLAIR (fluid-attenuated inversion-recovery) pulse sequence has been shown to be sensitive to abnormalities of the subarachnoid space. Our clinical experience led us to investigate whether intravenously injected contrast material can affect the appearance of the subarachnoid 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 imaging after i.v. administration of contrast material. A third dog was studied with a 6-hour delayed FLAIR sequence after triple-dose (0.3 mmol/kg) i.v. contrast administration. CSF was obtained from two animals for measurement of gadolinium concentration. A phantom was developed to determine the lowest concentration at which the effects of gadolinium were evident on FLAIR images in vitro.

Results: In all three animals, the appearance of the CSF in the ventricles or subarachnoid space was modified after administration of i.v. contrast. This was most evident on delayed images. The CSF samples showed a gadolinium concentration of 0.007 mmol/L in the dog who received the 0.1 mmol/kg dose and 0.02 mmol/L in the dog who received a triple dose. In our in vitro phantom experiments, gadolinium effects were evident on FLAIR images at a concentration four times lower than those on T1-weighted images.

Conclusion: I.v. contrast material can cross into the CSF in sufficient concentration to alter the appearance of the subarachnoid space on FLAIR images in normal dogs. Although we encountered two patients with CNS disease in whom enhancement of the CSF was seen on postcontrast FLAIR images, additional investigation is needed in humans to determine whether enhancement may occur at triple dose in healthy subjects.

fig. 1. A–E, Axial contrast-enhanced FLAIR images (A) (TR/TE_eff/excitations = 10,002/158.8/1, TI = 2200; 5-mm-thick sections) show linear increased signal in several sulci over both convexities. Corresponding T1-weighted images (B) show no analogous abnormality. Coronal FLAIR image (C) (10,002/158.8/1, TI = 2200) obtained 6 hours after the axial image shows hyperintense CSF in sulci over both hemispheres (arrows). An unenhanced CT scan (D) was normal. Follow-up FLAIR image 2 days later (E) was also normal

fig. 2. A and B, Noncontrast FLAIR image (A) shows the expected dark cortical sulci over the frontal convexity. Contrast-enhanced FLAIR image (B) 15 minutes after injection of a triple dose of contrast material shows high signal in multiple sulci, most consistent with contrast effects

fig. 3. A and B, Sagittal FLAIR image (A) (10,007/189, TI = 2200; 5-mm-thick sections) in dog 2 immediately after injection of contrast agent (0.1 mmol/kg) reveals the expected low signal intensity of CSF in the fourth ventricle (arrow). Sagittal FLAIR image 30 minutes after contrast administration (B) shows that the CSF in the fourth ventricle is now isointense with surrounding brain (arrow)

fig. 4. A–C, Sagittal T1-weighted image (A) (550/15/1) obtained 6 hours after IV contrast administration (0.3 mmol/kg) shows the expected low-signal CSF in the cingulate sulcus (arrow). Sagittal FLAIR image (B), also obtained 6 hours after triple-dose contrast injection, shows abnormal high signal in the premedullary cistern (black arrow) as well as the cingulate sulcus (white arrow). The abnormal CSF signal on the coronal FLAIR image (C) is striking in the occipital sulci (arrows)

fig. 5. A and B, Images of the phantom obtained with FLAIR (10,000/154, TI = 1630) (A) and T1-weighted (400/16/1) (B) techniques. The lower tubes contain increasing dilutions of gadodiamide. There are more bright tubes in the lower two rows (lowest concentrations of contrast material) on the FLAIR image than on the T1-weighted image.

fig. 6. Graph shows the effect of varying the concentrations of contrast material (range, 0.000001 to 0.5 mM) on the mean FLAIR and T1 signal intensity in the test tube phantom. The error bars represent +ISD and the data are from two separate experiments.