this method is intensively used as a clinical research method [89–91]. To establish the normal range of endolymph ratio, healthy volunteers were scanned after intratympanic [70, 73] and intravenous [92] GdC applications. Figure 4 demonstrates the visualization of endolymphatic hydrops with different MRI protocols. Figure 5 demonstrates a combined use of intratympanic GdC in right side and intravenous GdC in the a patient with Meniere’s disease with affected right side to allow comparison between both ears and contrasting of GdC in both inner ears.
Fig. 4. A 72-year-old man with the clinical suspection of left Meniere’s disease. Images are obtained 4 hours after IV-SD-GBCM. Conceptual diagram for the image generation of HYDROPS-Mi2 and HYDROPS2-Mi2. Upper row images indicate the generation of HYDROPS-Mi2. HYDROPS image, which is the subtraction of positive endolymphatic image (not shown) from positive perilymphatic image (heavily T2-weighted 3D-FLAIR, not shown) is multiplied by T2-weighed MR cisternography. Note that black areas (arrows) represent endolymphatic space in labyrinth and white areas represent perilymphatic space on HYDROPS-Mi2. Contrast between endo- and perilymphatic space is very strong, while the back ground signal is quite uniform on HYDROPS-Mi2. Lower row images indicate the generation of HYDROPS2-Mi2. HYDROPS2 image, which is the subtraction T2-weighed MR cisternography from positive perilymphatic image (heavily T2-weighted 3D-FLAIR, not shown) is multiplied by T2-weighed MR cisternography. Note that black areas (arrows) represent endolymphatic space in labyrinth and white areas represent perilymphatic space on HYDROPS2-Mi2 similar to HYDROPS-Mi2. Contrast between endo- and perilymphatic space is very strong, while the back ground signal is quite uniform on HYDROPS2-Mi2 similar to HYDROPS-Mi2. With permission of Jpn J Radiol [58].
The measurement of endolymph volume ratio following 3D-real inversion recovery images obtained 24 h after intratympanic GdC using machine learning and automated local thresholding segmentation algorithms has been reported with highly reproducible results and a highly significant correlation between hearing loss and cochlear endolymphatic hydrops [93]. Semi-automated volume ratio measurement of endolymph from images obtained 4 h after single dose intravenous GdC using short (8 min) and long (18 min) acquisition times [57] has been recommended. The correlation of the volume ratio between the long and short acquisition time images was high, ranging from 0.77 (endolymphatic hydrops in the cochlea) to 0.99 (endolymphatic hydrops in the vestibule); the Pearson’s correlation coefficients were all statistically significant (p < 0.001). Later they demonstrated that 3-Inversion-recovery turbo spin echo with real reconstruction (3D-real IR) showed higher contrast between the non-enhanced endolymph and the surrounding bone [94] (Fig. 6). Regular contrast 3D-FLAIR cannot readily visualize cochlear hydrops after single dose IV-Gd, especially in apical turn. Recently, Naganawa et al. [85, 95] developed the positive endolymph image method, which visualizes endolymph as both a bright signal and subtraction image (HYDROPS images, HYbriD of reversed image of positive endolymph signal and native image of positive perilymph signal images) and allowed more easily interpretable images. In our experience, using heavily T2-weighted 3D-FLAIR positive perilymph image and positive endolymph image and subtracted images (HYDROPS technique) are useful to compensate for the lower concentration of Gd by IV. A further developed technique for generating improved HYDROPS (i-HYDROPS) images allows for a higher contrast to noise ratio per unit time compared to conventional HYDROPS imaging; this is accomplished by elongating the repetition time and increasing the refocusing flip angle [96]. In the study, the size of the endolymphatic space was comparable in both i-HYDROPS and 3D-real IR images. The 3D-real IR does not require post-processing for subtraction and might be more robust towards slight compositional alterations in endolymph than i-HYDROPS imaging based on magnitude reconstruction, and the scan time for 3D real IR images was 10 min.
Fig. 5. A 42-year-old man with a clinical diagnosis of definite Ménière’s disease of the right ear. Images were obtained 24 h after IT-Gd in the right ear and 4 h after IV-SD-GBCM. The right ear shows the combined IT + IV effect while the left ear shows only the IV-Gd effect. Note that only on the IT + IV side is the conventional 3D-FLAIR and 3D-real IR sufficient to show enhancement of the perilymph in order to distinguish the endolymphatic space; however, heavily T2-weighted 3D-FLAIR and HYDROPS2 allows the differentiation between the perilymphatic and endolymphatic space in both the IV side and IT + IV side. Significant endolymphatic hydrops (arrows) is seen in both the cochlea and vestibule on the right side, but no endolymphatic hydrops is observed in the left cochlea. Absence of endolymphatic hydrops in the left vestibule is confirmed in lower-level slices (not shown). With permission of Jpn J Radiol [58].
Fig. 6. 3D Real reconstruction inversion recovery MRI of the right ear illustrates high signal-to-noise ratio and severe cochleovestibular endolmyphatic hydrops in a patient with Ménière’s disease 24 hours after intratympanic GdC application (Magnevist 1:8 diluted). Section thickness 0.3 mm. Siemens Verio scanner, 32-channel head coil. Endolymph appears black, perilymph appears white, temporal bone appears grey. The sections are positioned from left to right and from top to bottom so that they move through the inner ear in a caudal-to-cranial direction. The cochlea displays endolymphatic hydrops in all three turns. The vestibulum displays severe endolymphatic hydrops, with only a weak perilymph signal at its outer borders. The horizontal semicircular canal is completely visualized by its perilymph signal. (With kind permission of Prof. B. Ertl-Wagner, Institute of Clinical Radiology, University of Munich).
Figure 4 (after intravenous injection of GdC) and Fig. 5 (after intratympanic injection plus intravenous injection of GdC) demonstrates the inner ear fluid compartments, anatomical structures and endolymphatic hydrops. Nakashima et al. [59], Pyykko et al. [71], and Fiorino et al. [97] demonstrated, with MRI, that endolymphatic hydrops was present in all living patients with definite MD, which is different from the reports by Shi et al. [98] in which endolymphatic hydrops was absent in some definite MD. Recently, it has been demonstrated that endolymphatic hydrops can affect the cochlear and vestibular compartments differently and cause different complaints [71]. However, the association between clinical symptoms and endolymphatic hydrops in individual patients is not yet clarified, as hearing can be relatively
