Imaging of acute subarachnoid hemorrhage with a fluid-attenuated inversionrecovery sequence in an animal model: Comparison with non-contrast-enhanced CT

BACKGROUND AND PURPOSE: Fluid-attenuated inversion recovery (FLAIR) MR imag ing sequences have been previously described in the evaluation of acute sub arachnoid hemorrhage (SAH) in human subjects and have demonstrated good sen sitivity. The purpose of this study was to evaluate a FLAIR sequence in an animal model of SAH and to compare the results with those obtained with non -contrast-enhanced CT. METHODS: SAH was experimentally induced in 18 New Zealand rabbits by inject ing autologous arterial blood into the subarachnoid space of the foramen ma gnum. Nine animals had high-volume (1-2 mL) injections, and nine animals ha d low-volume (0.2-0.5 mL) injections. Four control animals were injected wi th 0.5 mL of saline. The animals were imaged with a FLAIR sequence and stan dard CT 2-5 hours after injection. Gross pathologic evaluation of seven of the animals was performed. Four blinded readers independently evaluated the CT and FLAIR images for SAH and graded the probability of SAH on a scale o f 1 to 5 (1 = no hemorrhage, 5 = definite hemorrhage). RESULTS: Overall, the sensitivity of FLAIR was 89%, and the sensitivity of CT was 39% (P < .01). In animals with a high volume of SAH, the sensitivity of FLAIR was 100%, and the sensitivity of CT was 56%. In animals with a lo w volume of SAH, the sensitivity of FLAIR was 78%, and the sensitivity of C T was 22%. The specificity of FLAIR in animals without SAH was 100%, and th e specificity of CT was 100%. The average reader score for FLAIR was 3.8, a nd that for CT was 2.2 (P < .001). Reader scores for FLAIR were higher than those for CT in 94% (P < .01) of animals with SAH and in 25% of animals wi thout SAH (P > .05). Seven animals underwent gross pathologic examination, and all had blood in the subarachnoid space around the brain stem. CONCLUSION. FLAIR was more sensitive than CT in the evaluation of acute SAH in this model, especially when a high volume of SAH was present. This stud y provides a model for further experimentation with MR imaging in the evalu ation of SAH. These findings are consistent with those of current clinical literature, which show FLAIR to be an accurate MR sequence in the diagnosis of SAH.