Abstract
In-vivo non-invasive verification of endolymphatic hydrops (ELH) by means of intravenous delayed gadolinium (Gd) enhanced magnetic resonance imaging of the inner ear (iMRI) is rapidly developing into a standard clinical tool to investigate peripheral vestibulo-cochlear syndromes. In this context, methodological comparative studies providing standardization and comparability between labs seem even more important, but so far very few are available. One hundred eight participants [75 patients with Meniere's disease (MD; 55.2 ± 14.9 years) and 33 vestibular healthy controls (HC; 46.4 ± 15.6 years)] were examined. The aim was to understand (i) how variations in acquisition protocols influence endolymphatic space (ELS) MR-signals; (ii) how ELS quantification methods correlate to each other or clinical data; and finally, (iii) how ELS extent influences MR-signals. Diagnostics included neuro-otological assessment, video-oculography during caloric stimulation, head-impulse test, audiometry, and iMRI. Data analysis provided semi-quantitative (SQ) visual grading and automatic algorithmic quantitative segmentation of ELS area [2D, mm2] and volume [3D, mm3] using deep learning-based segmentation and volumetric local thresholding. Within the range of 0.1–0.2 mmol/kg Gd dosage and a 4 h ± 30 min time delay, SQ grading and 2D- or 3D-quantifications were independent of signal intensity (SI) and signal-to-noise ratio (SNR; FWE corrected, p < 0.05). The ELS quantification methods used were highly reproducible across raters or thresholds and correlated strongly (0.3–0.8). However, 3D-quantifications showed the least variability. Asymmetry indices and normalized ELH proved the most useful for predicting quantitative clinical data. ELH size influenced SI (cochlear basal turn p < 0.001), but not SNR. SI could not predict the presence of ELH. In conclusion, (1) Gd dosage of 0.1–0.2 mmol/kg after 4 h ± 30 min time delay suffices for ELS quantification. (2) A consensus is needed on a clinical SQ grading classification including a standardized level of evaluation reconstructed to anatomical fixpoints. (3) 3D-quantification methods of the ELS are best suited for correlations with clinical variables and should include both ears and ELS values reported relative or normalized to size. (4) The presence of ELH increases signal intensity in the basal cochlear turn weakly, but cannot predict the presence of ELH.
Highlights
In-vivo non-invasive verification of endolymphatic hydrops (ELH) by means of delayed gadolinium (Gd) enhanced magnetic resonance imaging of the inner ear is rapidly developing into a standard clinical tool to investigate episodic vertigo [1,2,3]
The medians of the cochlear ELS ratio (ER) [%] data were (7.9%, 5.3%) for the Menière’s disease (MD) group and (6.3%, 6.3%) for the healthy control (HC) group. This methodological study with 108 participants (75 MD, 33 HC) focused on comparability and parametrization of different endolymphatic space (ELS) quantification methods (SQ grading of three raters, 2D- or 3D-quantification of three cutoffs) used in intravenous gadolinium-enhanced magnetic resonance imaging (iMRI) and their (i) interrelations with subtle variations in data acquisition protocols; (ii) correlations to each other, clinical symptoms, or neurophysiological testing; and (iii) the influence of ELH on signal quality
The results were as follows: (i) Within the range of 0.1–0.2 mmol/kg Gd dosage and a 3 h 41 min to 5 h 19 min time delay, SQ gradings, and 2D- or 3D-quantifications were independent of signal intensity (SI) and signal-to-noise ratio (SNR), but they were found to be significantly related to Gd dosage and time delay themselves. (ii) The ELS quantification methods used were highly reproducible across raters (SQ gradings) or thresholds (2Dand 3D-quantification), 3D-quantifications showed least variability in comparison to 2D-quantifications and SQ gradings
Summary
In-vivo non-invasive verification of endolymphatic hydrops (ELH) by means of delayed gadolinium (Gd) enhanced magnetic resonance imaging of the inner ear (iMRI) is rapidly developing into a standard clinical tool to investigate episodic vertigo [1,2,3]. This is due to iMRI allowing pre-mortem detection of ELH for the first time [4, 5], demonstrating that ELH is not pathognomonic to Menière’s disease (MD) [6,7,8], but rather a concomitant that can be found in various etiologies of episodic vertigo [9,10,11,12,13]. A variety of cochlear and vestibular ELH quantification conventions have been suggested, including ELS semi-quantitative visual grading [19,20,21,22,23,24,25], manual measurement [26,27,28], semi-automatic [29, 30], and automatic algorithmic area ratio (AR), and volumetric segmentation [31, 32]
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