Purpose: Three-dimensional fluid-attenuated inversion recovery (3D-FLAIR) imaging after intratympanic gadolinium injection is useful for pathophysiologic and morphologic analysis of the inner ear. However, statistical analysis of differences in inner ear signal intensity among 3D-FLAIR and other sequences has not been reported. We evaluated the signal intensity of cochlear fluid on each of 3D-FLAIR, 3D-T₁-weighted imaging (T₁WI), and 3D-constructive interference in the steady state (CISS) to clarify the differences in contrast effect among these 3 sequences using intratympanic gadolinium injection.
Methods: Twenty-one patients underwent 3D-FLAIR, 3D-T₁WI, and 3D-CISS imaging at 3 tesla 24 hours after intratympanic injection of gadolinium. We determined regions of interest of the cochleae (C) and medulla oblongata (M) on each image, evaluated the signal intensity ratio between C and M (CM ratio), and determined the ratio of cochlear signal intensity of the injected side to that of the non-injected side (contrast value).
Results: The CM ratio of the injected side (3.00±1.31, range, 0.53 to 4.88, on 3D-FLAIR; 0.83±0.30, range, 0.36 to 1.58 on 3D-T₁WI) was significantly higher than that of the non-injected side (0.52±0.14, range, 0.30 to 0.76 on 3D-FLAIR; 0.49±0.11, range, 0.30 to 0.71 on 3D-T₁WI) on 3D-FLAIR and 3D-T₁WI (P<0.001), although no significant difference was observed on 3D-CISS (10.03±2.19, range, 5.19 to 14.98, on the injected side; 9.52±1.63 range, 7.48 to 13.48, on the non-injected side) (P=0.11). The mean contrast value on 3D-FLAIR (5.93±2.57, range, 1.22 to 11.05) was significantly higher than that on 3D-T₁WI (1.73±0.60, range, 0.98 to 3.09) (P<0.001).
Conclusion: The 3D-FLAIR sequence is the most sensitive for observing alteration in inner ear fluid signal after intratympanic gadolinium injection. Our results warrant use of 3D-FLAIR as a sensitive imaging technique to clarify the pathological and morphological mechanisms of disorders of the inner ear.