Introduction

Endolymphatic hydrops (EH) is recognized worldwide as a histopathological change in Meniere's disease[1]. Currently, EH can be visualized directly using MRI after intratympanic (IT-method) or intravenous administration of gadodiamide (IV-method). However, there are some limitations to the use of the IT-method in patients with diseases such as external ear malformation and tympanic membrane perforations. In contrast, as a widely used method in clinical contrast-enhanced MRI examination in humans, IV administration is less invasive. We performed a comprehensive comparison between the IT-method and IV-method in the present study.

Materials and methods

From May 2016 to December 2017, 152 Meniere’s disease patients were enrolled in this study. For the IT-method, the patients underwent MRI examination 24 hours after the injection of gadolinium diluted eight-fold with saline. As for the IV-method, the patients underwent MRI scan 4 hours after IV injection of gadolinium with double dose (0.4 mL/kg body weight, [i.e., 0.2 mmol/kg body weight]). All scans were performed with a 3T MRI scanner (MAGNETOM Verio, Siemens Healthcare, Erlangen, Germany) using a 4-channel phased array ear coil（Shanghai Chenguang Medical Technologies Co., Ltd.). 3D real inversion-recovery (3D real IR) and T2 SPACE MRI were performed among all the patients. The 3D real IR protocol for the IT-method were as follows: slice thickness, 0.6 mm; TR/TE, 6000/181 ms; TI, 1730 ms; number of averages, 1; FA, 180ﾟ; matrix, 768x768; FOV, 160x100 mm2; and TA, 15 minutes 20 seconds. The TI of 3D real IR sequence of IV-method was 1850 ms, and other parameters were as same as IT-method’s. The signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and detection rate of endolymphatic hydrops of cochleae or vestibules were compared between the images acquired by the 3D real IR sequences using IT-method and IV-method, respectively. Image analysis was performed on a PACS workstation (Fig. 3). All images were rated according to a scale ranging from 1 (unacceptable image quality) to 5 (image with high-level anatomic detail). The statistical analyses were performed using the SPSS 20.0 (version 20.0, IBM, Armonk, NY, USA). P values<0.05 were considered statistic significant. Independent-samples t tests, Wilcoxon's rank sum test and x2 test was used in this study.

Results

The quantitative and qualitative data analysis of the IT-method and IV-method is show in Fig 1 and Fig 2. IV-method by the 3D real IR sequence can clearly distinguish endolymph, perilymph, bone, and air like IT-method (Figs. 4 and 5). The SNRROI and CNRs of the IT-method were higher than those of the IV-method.

Discussion

In general, 3D FLAIR and 3D real IR sequences are widely used for the visualization of endolymphatic hydrops. However，it is difficult to determine the boundary between the endolymph and surrounding bone by using FLAIR sequence. While in the images obtained by 3D real IR sequences, the endolymphatic space (negative value) can be distinguished between the perilymphatic space (positive value) and bone (near zero). Many studies[2-4] have examined the application of 3D real IR sequences with the IT-method, but relatively few studies have used 3D real IR sequences with the IV-method, this may be due to the poor sensitivity of 3D real IR sequences to low dose contrast agents. Our study achieved great improvement in image quality for both IT-method and IV-method by setting appropriate TI values and applying a 4-channel phased array ear coil. Due to the sufficient concentration of gadolinium in the perilymphatic space, the SNR and CNR of the 3D real IR sequences obtained using the IT-method were higher than those of for IV-method. However, this has little effect on the assessment of endolymphatic hydrops in images obtained after IV administration compared to the evaluation of images obtained after IT administration. The clear separation between the endolymphatic space and the perilymphatic space can be achieved by the IV-method and IT-method individually. No statistically significant difference of image quality was found between the two methods. In addition, no significant difference was observed in the detection rate of endolymphatic hydrops between the two methods. The limitation of this study is that the two samples used for comparisons between the IT-method and IV-method were identical because the same patient could not receive two injections. And the double dosed contrast agent used in this study is still within safe limits. The IV-method can be used as an alternative to the IT-method in clinical applications to some extent.

Acknowledgements

This study is supported by Shanghai Shenkang Hospital Development Center (SHDC22015036).

References

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