A Novel Trans-Impedance Matrix (TIM) Abnormality Pattern in Cochlear Implants.

Abstract

In our clinical setting, we have identified a novel pattern of Trans-Impedance Matrix (TIM) measurement that we call 'scatter', a measure characterised by a loss of definition in the heat and line maps. Objective: the aim of this study was to describe the basic characteristics of the anomaly pattern. The secondary purpose is to evaluate correlations between the "scatter" pattern and normal TIM by considering different parameters. Methods: the experimental sample, therefore, consisted of 565 patients (81.1% of people with a checked TIM at follow-up; M: 279, F: 286 and mean age: 27 years (sd 26). The scatter pattern was found in 55 devices (9.7%). We classified this pattern as severe (20 devices) or mild (35 devices) according to the visual extent of the abnormality. We considered the visual extension of the pattern, device lifetime, type of internal part of the CI, and auditory performance (speech audiometry in quiet at 65 dB and in noise-Ita Matrix Sentence Test). We also analysed two quantitive parameters: Shannon entropy and exponential decay. Results: a difference was found in these two quantitative parameters between the severe scatter, mild scatter, and normal TIM groups (p-value < 0.0001). The severe scatter group seems to be related to the type of device (CI24RE and CI512) and long device life (average 133 months); it did not show differences in audiology performances compared to the other groups. Conclusions: this result gives a numerical validation to the more subjective visual inspection approach. The scatter pattern is a novel, previously undescribed abnormality of TIM. It can vary from moderate to severe. A numerical basis to validate the inspection approach is described here.