Pitfalls of Using T2-contrast Enhancement Techniques in 3D-FLAIR to Detect Endolymphatic Hydrops

Abstract

Purpose: To determine whether T2-contrast enhancement techniques can be used to diagnose endolymphatic hydrops, we compared fluid signal artifacts with and without T2-contrast enhancement techniques in 3D fluid-attenuated inversion recovery (3D-FLAIR).

Methods: We prepared a custom-made phantom consisting of eight tubes half-filled with saline. Images were obtained using four 3D-FLAIR: without T2-contrast enhancement (Normal), with non-selective T2-inversion recovery (T2-IR), and two with non-selective T2 preparation IR (T2-prep). Scans were performed with and without rice covering the phantom to simulate minimal and severe B0-inhomogeneity conditions. The average signal intensity (SI) values of eight saline tubes were compared between the four sequences and between each other. Comparisons were performed for all measurement slices and the central 10 slices. The images using T2-contrast enhancement technique were obtained from a volunteer and a patient suspected of Meniere's disease.

Results: The Normal sequence SI for all slices was significantly lower than that for the other sequences, with smaller standard deviation (SD) and no outliers. Several outliers were detected in the other sequences. The SDs and outliers were larger without rice than with rice. When the central 10 slices with rice, the T2-IR had a significantly higher SI with more outliers compared with the Normal sequence. The T2-prep had no outliers and SIs that were comparable to those of the Normal sequence. However, without rice, the T2-IR and T2-prep sequences had significantly higher SIs with outliers and larger SDs compared to the Normal sequence. In the corresponding images, the Normal sequence achieved excellent fluid suppression, whereas the T2-IR and T2-prep sequences showed high-signal artifacts. Imperfect fluid suppressions were observed in the volunteer image and the endolymphatic hydrops on the post-gadolinium image differed in size and shape in the non-injected T2-IR in the patient image.

Conclusion: T2-contrast enhancement techniques should be used with caution in 3D-FLAIR for diagnosing endolymphatic hydrops.

Keywords: T2-preparation pulse; endolymphatic hydrops; fluid-attenuated inversion recovery; magnetic resonance imaging.

Fig. 1

Schematic diagram of the custom-made phantom. Polyvinyl alcohol was prepared to ensure signals during acquisition, whereas control saline was prepared to determine the inversion time. Eight test tubes with saline were prepared to evaluate fluid signal suppression. Gadolinium in two test tubes was used to simulate the gadolinium concentration in the perilymph at 4 h after administration. Eye drops in two test tubes were used to confirm the effects of the T2-contrast enhancement techniques. The surrounding area was filled with or without rice.

Fig. 2

The phantom images using the four sequences (a) with and (b) without rice. The images show MIP, sagittal-MPR, and center slice of the fluid. (a) T2-IR shows band high-signals at the air-fluid interface in all tubes (narrow arrows), and several spot high-signals at the center slice (arrowhead). T2-prep dramatically reduced band high-signals (not completely removed) and completely removed spot high-signals. (b) T2-IR exhibited band high-signals and poor suppressions (dotted arrows). T2-prep showed banding-like artifacts (wide arrow). MIP, maximum intensity projection; MPR, multiplanar reconstruction; T2-IR, T2-inversion recovery; T2-prep, T2 preparation inversion recovery.

Fig. 3

Box plots comparing the average signal intensity of all saline tubes with the four sequences. All measurement slices (a) with and (b) without rice, and the central 10 slices (c) with and (d) without rice. T2-IR, T2-inversion recovery; T2-prep, T2 preparation inversion recovery.

Fig. 4

Box plots comparing the average signal intensity between the eight saline tubes. All measurement slices (a) with and (c) without rice, and the central 10 slices (b) with and (d) without rice. T2-IR, T2-inversion recovery; T2-prep, T2 preparation inversion recovery.

Fig. 5

Box plots comparing the average signal intensity using the four sequences in diluted gadolinium and eye drop tubes. T2-IR, non-selective T2-inversion recovery; T2-prep, non-selective T2 preparation inversion recovery.

Fig. 6

A 41-year-old man with right Meniere’s disease. (a) On the right ear, the HYDROPS image showed significant endolymphatic hydrops in both the cochlea and vestibule (enlarged endolymphatic space shows as black signals). However, T2-IR without gadolinium showed a low signal area that differed in shape and size from the endolymphatic hydrops observed in the HYDROPS image (arrows). Moreover, the low signal area of the cochlea in the HYDROPS image was not observed in the T2-IR image (arrowhead). (b) The left ear showed no abnormalities in the HYDROPS image, indicating that the shape of the endolymph is completely different from that of the right ear. Nevertheless, the left and right endolymph-like structures were similar in the T2-IR image without gadolinium (arrows). 3D-FLAIR, 3D fluid-attenuated inversion recovery; HYDROPS, hybrid of reversed image of positive endolymph signal and native image of positive perilymph signal; T2-IR, T2-inversion recovery.

Fig. 7

A 42-year-old healthy man without any symptoms of dizziness. The top row shows the whole view obtained using MR cisternography, Normal (TI of 2250 ms), T2-IR (TI of 2350 ms), and T2-prep with 200 ms (TI of 2100 ms). The middle and bottom rows are enlarged views of the right and left ears, respectively. The T2-IR showed residual fluid signals, whereas the T2-prep improved these poor suppressions (dotted arrows). However, fluid suppression in the inner ear is still insufficient even with T2-prep. Moreover, the shapes of the endolymph-like structures in the images obtained using both techniques were relatively different (arrows). 3D-FLAIR, 3D fluid-attenuated inversion recovery; T2-IR, T2-inversion recovery; T2-prep, non-selective T2 preparation inversion recovery; TI, inversion time.