Reducing Artifacts in Intracochlear Pressure Measurements to Study Sound Transmission by Bone Conduction Stimulation in Humans

Abstract

Hypothesis: Intracochlear pressure (ICP) measurements during bone conduction (BC) stimulation may be affected by motion of the pressure sensor relative to the cochlear promontory bone, demonstrating the need to cement the sensor firmly to the cochlear bone. Background: ICP is a promising measurement tool for investigating the cochlear drive in BC transmission, but its use is not yet standardized. Previous ICP studies have reported artificially increased pressure due to motion of the sensor relative to the temporal bone. The artifact can be reduced by firmly cementing the sensor to the bone, but this is destructive for the sensor. Previous studies used a custom-made sensor; the use of commercially available sensors, however, is more generic, but also more challenging to combine with the cement. Therefore, the goals of the current study are: firstly, to evaluate a non-destructive cementing method suitable for a commercially available sensor, and secondly, to investigate ICP measurements during BC stimulation in more detail. Methods: To study the effect of sensor cementing, three fixation conditions were investigated on six fresh-frozen temporal bones: 1) alginate, 2) alginate and dental composite, 3) alginate and dental composite, released from micromanipulators. Pressures in scala tympani and vestibuli were measured simultaneously, while velocity measurements were performed on the cochlear promontory and sensor. The ratio between sensor and promontory bone velocity was computed to quantify the relative motion. Results: For air conduction stimulation, results were in line with those from previous ICP studies, indicating that baseline measurements were valid and could be used to interpret the results obtained with BC stimulation. Results showed that cementing the sensors and releasing them from the micromanipulators is crucial for valid ICP measurements. When the sensors were only sealed with alginate, the pressure was overestimated, especially at low and mid-frequencies. When the sensors were cemented and held in the micromanipulators, the pressure was underestimated. Compared with the scala tympani measurements, ICP measurements showed a lower scala vestibuli pressure below 1 kHz, and a higher pressure above 1 kHz. Conclusion: Dental composite is effective as a cement to attach commercially available sensors to the cochlear promontory bone. When sensors are firmly attached, valid ICP measurements can be obtained with BC stimulation.

The Impact of Location and Device Coupling on the Performance of the Osia System Actuator

“…In general, the technique of intracochlear pressure measurements that is followed in this work has been documented by Borgers et al The technique outlined in this work has been based on prior work by other authors [ 12 , 13 , 21 ]. Similar to Borgers et al [ 23 ], the middle ear was submerged in saline again before dental cement was applied on the bone surrounding the cochleostomy to fix the sensors in place. After cementing each sensor, it was removed from the micromanipulators.…”

“…Valuable insights regarding nonlinearity [ 16 ], the correlation between scala vestibuli pressure and ear canal pressure [ 17 ], the contribution of the two scalar pressures on the pressure difference [ 15 ], the exploration of sensor technologies [ 18 – 20 ], and the definition of proper experimental procedures [ 12 , 21 ] were obtained during this period. Only recently, researchers have started looking into using the technique for bone conduction stimulation as well [ 22 , 23 ], as measurement results indicate that vibrational artifacts can be limited with proper sensor fixation.…”

“…This is done by measuring the vibrational response of the cochlear promontory at lower and clinically more relevant stimulation levels compared to a prior study using this device [ 6 ]. As an additional measure of performance, intracochlear pressure (ICP) measurements will be performed, as they are hypothesized to be an accurate measure for investigating cochlear transmission with BC stimulation [ 22 , 23 ]. As a secondary goal, the incidence of bone undergrowth under the implanted actuator is considered a simulation model to investigate any degrading effects on efficiency due to device-bone interference.…”

Objective preclinical measures for bone conduction implants

“…In contrast with live patients who can provide subjective feedback to evaluate the hearing sensation, tests in cadaveric specimens require objective measures. Currently, three measures are commonly employed: intracochlear pressure ( Greene et al, 2015 ; Borgers et al, 2019 ; Mattingly et al, 2020 ; Fierens et al, 2022 ; Putzeys et al, 2022 ), promontory velocity ( Stenfelt and Goode, 2005 ; Rosowski et al, 2007 ; Dobrev et al, 2016 , 2020 , 2023 ; Roosli et al, 2016 ; Rigato et al, 2019 ; Ghoncheh et al, 2021 ; Prodanovic and Stenfelt, 2021 ), and ear canal pressure ( Mertens et al, 2014 ; Nie et al, 2022 ).…”

A Miniature, Fiber-Optic Vibrometer for Measuring Unintended Acoustic Output of Active Hearing Implants during Magnetic Resonance Imaging

“…Measurement of unintended acoustic output requires a technique that is able to measure sub-nanometer movements [ 22 ] in the audible frequency range using a technique that does not suffer from electromagnetic interference. In otology, the output of acoustic implants or other acoustic energy sources is often quantified by measuring the vibration amplitude of certain anatomical structures using laser Doppler vibrometry (LDV) [ 23 ] or by measuring the complex pressure difference in the cochlear scalae using miniature fiber-optic pressure sensors [ 24 , 25 , 26 ]. Applying these techniques during MRI would, however, be challenging as the techniques would also be sensitive to the high ambient sound pressures present during scanning.…”