Round window stimulation with the floating mass transducer at constant pretension

Influence of the Coupling on the Hearing Outcome After Implantation of an Active Middle Ear Implant: Comparison of the Transmission Behavior in Temporal Bone Experiments With Clinical Data

OBJECTIVES

The active middle ear implant, Vibrant Soundbridge (VSB), can be implanted with a variety of couplers. Hearing outcome after implantation has been investigated in both temporal bone (TB) experiments and patient studies, but the relationship between experimental and clinical data is still weak in the literature. Therefore, experimental data from TB experiments should be compared with patient data in a retrospective study, in which the floating mass transducer is used with couplers of the third generation. Actuator coupling structures included the long (LP coupler) and short (SP coupler) incus process, the stapes head (Clip coupler), and the round window membrane (RW soft coupler).

METHODS

In the TB experiments, the sound transmission after vibroplasty on the above-mentioned actuator coupling structures was determined in 32 specimens by means of laser Doppler vibrometry on the stapes footplate. Data of 69 patients were analyzed. The main target audiometric parameters were the postoperative aided word recognition score (WRS) in the free field at 65 dB SPL (WRS 65 dB in %), the preoperative and postoperative pure-tone average (PTA4, including the frequencies 0.5, 1, 2, and 4 kHz) of the bone conduction hearing threshold (PTA4BC), the aided postoperative air conduction hearing threshold in the free field (PTA4FF) and the direct threshold (Vibrogram) at least 6 months postoperatively. The coupling efficiency of the actuator (Vibrogram-PTA4BC) as well as the effective hearing gain (PTA4FF-PTA4BC) was compared between the couplers.

RESULTS

The analysis in the main speech range (0.5-4 kHz) indicated that in the TB experiments, the LP coupler tends to have the best coupling quality at low frequencies (500-1000 Hz). This was up to 15 dB above the worst actuator (RW soft coupler). However, the results missed the significance level ( p > 0.05). In the high frequencies (2000-4000 Hz), the Clip coupler showed the best coupling quality. This was 15 dB above the worst actuator (SP coupler). However, the results missed the significance level ( p > 0.05), too. The postoperative WRS at 65 dB SPL and the postoperative PTA4FF were independent of the actuator coupling structure. The PTA4BC was stable at 6 months postoperatively. For the PTA4 of the coupling efficiency, there were no significant differences between the actuator coupling structures (LP 8.9 dB ± 12.9; SP 9.5 ± 6.5 dB; Clip 5.2 ± 10.5 dB; RW 12.7 ± 11.0 dB). However, the tendential inferiority of the RW soft coupler with regard to transmission in the low-frequency range and the tendential superiority of the Clip coupler in the high-frequency range that have already been displayed experimentally could be confirmed in the clinical results. However, the clinical results missed the significance level, too ( p > 0.05).

CONCLUSIONS

In vivo, there are no significant differences in the postoperative outcome stratified according to coupling the target structure. The differences known from the experimental setting were repressed by individual biasing factors. However, to ensure sufficient postoperative speech intelligibility, the frequency-specific transmission behavior of the couplers should be taken into account when setting the indication for VSB implantation.

The Hannover Coupler V2: Audiological outcomes of a round window coupler for the Vibrant Soundbridge

Introduction

The Hannover Coupler version 2 (HC2) was designed to (1) adapt the coupler geometry to the round window (RW) niche (2) to stabilize the floating mass transducer, and (3) to control static coupling forces to the RW. First audiological outcomes with a custom-made HC2 are reported here.

Material and Methods

Ten patients were enrolled in our site-initiated, prospective study. To assess audiological outcomes up to 6 months, preoperative and postoperative hearing thresholds, word recognition score (WRS) at 65 dB SPL and the speech recognition threshold in quiet and noise were performed. The effective gain (EG) and the coupling efficiency were calculated.

Results

One revision surgery had to be performed during the study period and a significant, but clinically not relevant bone conduction thresholds change was observed at 4 and 6 kHz at 6-month follow-up. At 6 months, the median WRS (n = 10) improved significantly from 0% to 80%. The median speech reception threshold in noise improved significantly from 11.6 to -2.4 dB SNR, and in quiet significantly from 79.6 to 44.4 dB SPL. The average EG of -1.3 dB indicated a closure of the air bone gap. The determined average coupling efficiency of 23.3 dB was within the acceptance range suggested by the manufacturer.

Conclusion

For patients with mixed hearing loss and multiple ear surgeries, the HC2 provided good and stable speech recognition results exceeding published results of RW coupling without a coupler or coupling with the RW soft coupler.

Comparative study of efficiency and characteristics of FMT and DRT installed in human cadavers for round-window stimulation

Acoustic hearing aids generate amplified sound in the ear canal, and they are the standard of care for patients with mild to moderate sensorineural hearing loss. However, because of their limited frequency bandwidth, gain, and feedback, there is substantial room for improvement. Active middle ear implants, which directly vibrate the middle ear and cochlea, are an alternative approach to conventional acoustic hearing aids. They provide an opportunity to improve sound quality and speech understanding with amplification rehabilitation. For floating-mass type and direct-rod type (DRT) middle ear transducers, a differential floating-mass transducer (DFMT) and a tri-coil bellows transducer (TCBT), respectively, were fabricated to measure the output characteristics in four human temporal bones. Both were fabricated to have similar output forces per unit input and were placed in four human temporal bones to measure their output performances. The TCBT resulted in higher output than did the DFMT throughout the audible frequency range, and the output was more prominent at lower frequency ranges. In this study, we showed that DRT was a more effective method for round window stimulation. Because of its frequency characteristics and vibration efficiency, this implantation method can be utilized as a driving solution for middle ear implants.

Evaluation of a New Material From an Allogenic Collagen Scaffold as a Suitable Coupling Option for Round Window Vibroplasty

INTRODUCTION

In round window vibroplasty the most efficient coupling technique for contact of the floating mass transducer (FMT) to the round window membrane (RWM) is yet to be determined. Various materials placed between the FMT and the RWM have been proposed to enable better stimulation of the cochlea. Collagenous scaffolds derived from decellularized extracellular cartilage matrices as a commercially available biomaterial are already used for other applications in ear surgery. We aimed to examine the coupling properties of collagen scaffolds compared with commonly used other materials (round window soft coupler, porcine perichondrium, and cartilage) as interponate between the FMT and the RWM in vibroplasty.

METHODS

A well-established in vitro temporal bone model was used. Volume velocities were measured with collagen scaffold compared with different interponates (round window soft coupler, porcine perichondrium, and cartilage) at 800, 1000, 1250, 1600, 2000, 2500, 3150, and 4000 Hz levels.

RESULTS

Statistical analysis revealed no superiority of commonly used materials compared with collagen scaffolds at all tested volume velocities (p > 0.05).

DISCUSSION

We could demonstrate that collagenous scaffolds of decellularized extracellular cartilage matrices have similar vibrational properties as conventional coupling materials of the FMT to the RWM in vibroplasty. Therefore, as a commercially available new material they display a suitable coupling option for round window vibroplasty.

The design of a lumped parameter model considering the stimulus path of round window

BACKGROUND:

Sound normally enters the ear canal, passes through the middle ear, and stimulates the cochlea through the oval window. Alternatively, the cochlea can be stimulated in a reverse manner, namely round window stimulation. The reverse stimulation is not well understood, partly because in classic lumped-parameter models the path of reverse drive during the round window stimulation is usually not considered.

OBJECTIVE:

The study goal is to gain a better understanding of the hearing mechanism during round window stimulation.

METHODS:

A piezo actuator was coupled to the oval and round window of the guinea pigs. The auditory brainstem response produced by the forward and reverse stimulation at four frequencies was recorded.

RESULTS:

The results show that the input voltage of the actuator required at the hearing threshold in the round window drive was higher than that in the oval window drive. In order to understand the data, we designed a lumped-parameter cochlear model that can simulate both forward and reverse drive. The model-predicted results were consistent with the experimental results.

CONCLUSIONS:

The response of the auditory system to stimulus of oval window and round window was quantified through animal experimentation, and guinea pigs were used as experimental animals. When the same stimulus was applied to the oval window and round window of the cochlea, the ABR signals were compared. A lumped parameter model was designed to incorporate the sound transmission paths in both oval and round window stimulation. The simulated results are consistent with those of animal experiments. This model will be useful in understanding the inner-ear response in round window.

[Laser Doppler vibrometric measurements on human temporal bones]

Laser Doppler vibrometric (LDV) measurements on human temporal bones represent the standard method for predicting the performance of active middle ear implants (AMEI) and are used as preclinical tests in the development, approval process, and indication expansion of AMEI. The quality of the coupling of the floating mass transducer to the mobile structures of the middle ear is decisive for the performance of the implant and patients' hearing perception. The cochlea can be stimulated via the oval window (forward stimulation) or the round window (reverse stimulation). For forward stimulation, the ASTM standard F2504-05 defines a method to ensure physiologically normal properties of the temporal bones used in the experiments. For reverse stimulation, which depends even more critically on the quality of the temporal bone, a comparable standard method is lacking. Appropriate preparation and storage of the human petrous bone as well as suitable LDV test setups with respect to calibration and reproducibility of measuring positions and angles provide results that allow a comparison of different types of coupling and also correlate well with clinical data.

Evaluation of Coupling Efficiency in Round Window Vibroplasty With a New Handheld Probe

HYPOTHESIS

A handheld measuring probe was developed that analyzes the vibration characteristics of the stapes footplate after backward stimulation of the cochlea in round window vibroplasty. In temporal bone experiments, the measuring accuracy of the probe was tested.

BACKGROUND

In round window vibroplasty, the effectiveness of the transmitted vibrations into the inner ear is provided with limited visual and tactile information. Currently, there is no objective measuring tool available.

METHODS

In five unfixed temporal bones, a floating mass transducer was coupled to the round window membrane. During the excitation with different voltage levels (0, 5, 25, 100, 300 mV root mean square) corresponding to 0, 80, 94, 106, and 116 dB equivalent ear canal sound pressure respectively, the deflections of the footplate were recorded in parallel by laser Doppler vibrometry and the measuring probe.

RESULTS

The probe allowed for differentiation of the coupling efficiency. The measured footplate vibrations from the excitation levels of 106 dB (and 116 dB) were statistically significant compared with the testing without excitation. The footplate deflections determined in parallel by laser Doppler vibrometry showed comparable results.

CONCLUSION

In principal, the newly developed measuring probe allows for measuring the quality of retrograde cochlear excitation in a round window vibroplasty by detecting footplate vibrations. Further developments are directed for its application in clinical, intraoperative procedures.

Case Report of a New Coupler for Round Window Application of an Active Middle Ear Implant

OBJECTIVES

To evaluate feasibility, surgical handling, audiological outcome, and coupling efficiency of a new coupler (custom-made device) for an active middle ear implant.

PATIENT

Revision surgery after implantation of an active middle ear implant in a 66-year-old male patient with mixed hearing loss.

INTERVENTION

Prosthetic hearing rehabilitation with a new coupler for round window application.

MAIN OUTCOME AND RESULTS

The patient obtained good speech perception in quiet (word recognition scores 80%; Freiburg monosyllables) and noise (-3.3 dB SNR; Oldenburg Sentence Test). The effective gain with the Hannover coupler improved at frequencies > 0.5 kHz compared with the values reported for other round window (RW)-coupling modalities.

CONCLUSION

The coupler provides a feasible option for the RW application of the middle ear implant actuator. The spring concept of the coupler needs to be improved to further standardize RW-coupling and improve coupling efficiency at low frequencies (0.5 kHz).

Influence of ossicular chain malformation on the performance of round-window stimulation: A finite element approach

As a novel application of implantable middle ear hearing device, round-window stimulation is widely used to treat hearing loss with middle ear disease, such as ossicular chain malformation. To evaluate the influence of ossicular chain malformations on the efficiency of the round-window stimulation, a human ear finite element model, which incorporates cochlear asymmetric structure, was constructed. Five groups of comparison with experimental data confirmed the model’s validity. Based on this model, we investigated the influence of three categories of ossicular chain malformations, that is, incudostapedial disconnection, incus and malleus fixation, and fixation of the stapes. These malformations’ effects were evaluated by comparing the equivalent sound pressures derived from the basilar membrane displacement. Results show that the studied ossicular chain malformations mainly affected the round-window simulation’s performance at low frequencies. In contrast to the fixation of the ossicles, which mainly deteriorates round-window simulation’s low-frequency performance, incudostapedial disconnection increases this performance, especially in the absence of incus process and stapes superstructure. Among the studied ossicular chain malformations, the stapes fixation has a much more severe impact on the round-window stimulation’s efficiency. Thus, the influence of the patients’ ossicular chain malformations should be considered in the design of the round-window stimulation’s actuator. The low-frequency output of the round-window simulation’s actuator should be enhanced, especially for treating the patients with stapes fixation.

Sensor-actuator component for a Floating Mass Transducer-based fully implantable hearing aid

We propose a novel system based on the Floating Mass Transducer (FMT) to be used as the active component of a fully implantable, Vibrant Soundbridge-like middle ear implant. The new system replaces the external microphone used in the currently available design with an implantable piezoelectric sensor that is inserted into the incudostapedial joint and picks up the vibrations transmitted to the long process of the incus. The FMT is coupled to the round window of the cochlea. We characterize the system by measuring the gain in intracochlear sound pressure using laser Doppler vibrometry at a surgically installed "third window" into the cochlea of six temporal bones. Closed-loop feedback oscillations limit the system's available output. We show that using an adaptive control algorithm, a mean functional gain of up to 40 dB is achieved, which is similar to Soundbridge functional gain. The concept matches the FMT's one-point fixation philosophy and offers several advantages over other designs, namely an easy and time-efficient surgery, reversibility of implantation, and natural hearing for the prospective patient.

Vibroplasty combined with tympanic membrane reconstruction in middle ear ventilation disorders

Although the Vibrant Soundbridge is one of the most frequently used active middle ear implants, data regarding how middle ear ventilation disorders may affect the transmission behavior of its floating mass transducer are still insufficient. Studies involving coupling the floating mass transducer to the stapes head are particularly lacking. This temporal bone study evaluated the influence of simulated middle ear ventilation disorders on the middle ear transfer function in the reconstructed middle ear. The middle ear transfer function was measured using Laser Doppler Vibrometry after vibroplasty onto the stapes head, with or without tympanic membrane reconstruction. Middle ear ventilation disorders were simulated through changes in static pressure via the external ear channel with a maximum pressure of +3 kPa. Slice thickness of tympanic membrane reconstruction material was measured using micro-CT. When the reconstructed ossicular chain and the reconstructed tympanic membrane were mechanically excited by the floating mass transducer under conditions of ambient static pressure, the transmission behavior was found to be independent of the type of tissue used. Increase in static pressure up to +3 kPa caused maximum low frequency transmission loss of 15 dB when elastic grafts were used and 5 dB when stiff tissue was inserted. At high frequencies, measured loss of up to 5 dB was relatively independent of the tissue stiffness. Increase in static pressure led to displacement of the tissues towards the vestibulum and caused stiffening, especially of the annular ligament. Stiffening-induced transmission losses were mainly found at low frequencies and could not be compensated by the floating mass transducer in this range. Above 1300 Hz, the continuous force spectrum of the actuator sufficiently protected against loss of amplitude. To minimize postoperative transmission loss due to persisting ventilation disorders, choosing a very stiff tympanic membrane reconstruction material seems to be appropriate.

Numerical Study and Optimization of a Novel Piezoelectric Transducer for a Round-Window Stimulating Type Middle-Ear Implant

Round window (RW) stimulation is a new application of middle ear implants for treating hearing loss, especially for those with middle ear disease. However, most reports on it are based on the use of the floating mass transducer (FMT), which was not originally designed for round window stimulation. The mismatch of the FMT's diameter and the round window membrane's diameter and the uncontrollable preload of the transducer, leads to a high variability in its clinical outcomes. Accordingly, a new piezoelectric transducer for the round-window-stimulating-type middle ear implant is proposed in this paper. The transducer consists of a piezoelectric stack, a flextensional amplifier, a coupling rod, a salver, a plate, a titanium housing and a supporting spring. Based on a constructed coupling finite element model of the human ear and the transducer, the influences of the transducer design parameters on its performance were analyzed. The optimal structure of the supporting spring, which determines the transducer's resonance frequency, was ascertained. The results demonstrate that our designed transducer generates better output than the FMT, especially at low frequency. Besides this, the power consumption of the transducer was significantly decreased compared with a recently reported RW-stimulating piezoelectric transducer.

The Hannover Coupler: Controlled Static Prestress in Round Window Stimulation With the Floating Mass Transducer

INTRODUCTION

Stimulation of the cochlear round window (RW) with the floating mass transducer (FMT) still suffers from large variation in clinical outcomes. Beside the geometric mismatch between RW and FMT diameter that is a known limiting factor in achieving optimal coupling between actuator and RW membrane, the applied static force between FMT and RW is usually undefined. In this study, the feasibility and efficacy of a specially designed FMT coupler permitting application of static preloads to the RW membrane to optimize FMT-RW coupling was investigated.

METHODS

Experiments were performed in fresh human cadaveric temporal bones. The "Hannover Coupler" FMT-prosthesis has a spherical tip (d=0.5 mm) at the front end and a spring at the prosthesis back that enables the application of static preloads and mobility of the FMT at the same time. Stapes footplate (SFP) displacements in response to acoustic stimulation of the tympanic membrane and to RW stimulation by the FMT were measured by a Laser-Doppler vibrometer.

RESULTS

Average SFP displacement responses of ASTM standard F2504-05 compliant temporal bones to RW stimulation by the "Hannover Coupler" were dependent on the applied force (∼0-100 mN) and increased by up to 25 dB at frequencies ≥ 1 kHz. When averaged at speech relevant frequencies (0.5, 1, 2, 4 kHz) SFP displacements showed a global maximum at RW preloads of ∼4 mN.

CONCLUSION

The coupling between FMT and RW membrane was improved by the application of static RW preloads as indicated by increased SFP amplitudes to RW stimulation.

Influence of backside loading on the floating mass transducer: An in vitro experimental study

HYPOTHESIS

The vibration of the floating mass transducer (FMT) of a single active middle-ear implant (AMEI) is distinctly influenced by the properties of the material coupled to its back side.

BACKGROUND

In round window vibroplasty, the FMT needs to be padded against the surrounding bone opposite from the round window membrane. This represents one factor influencing its performance as a round window driver. Therefore, we examined the effects of different materials linked to the back side of an FMT on its vibration range.

METHODS

The back side of an FMT was glued to a silicone cylinder 1.0 mm in diameter and 1.0 mm - 1.5 mm in length and of 40A, 50A or 70A Shore hardness; to cartilage of equivalent size; or to a round window soft coupler (RWSC), all firmly fixed on a steel plate. The vibrations were determined by a laser Doppler vibrometer (LDV) measuring the velocity of the centre point on the front side of the FMT.

RESULTS

The materials on the back side of the FMT significantly influenced the vibration range of the FMT. The RWSC and silicone of 40A Shore hardness allowed for the highest detected velocities, while cartilage led to a distinct reduction similarly to 70A silicone.

CONCLUSION

The coupling on the back side of an FMT distinctly affects its vibration range. In this regard, the RWSC and silicone of 40A Shore hardness yield the least impairment of vibration. Thus, the RWSC may be a feasible option in round window vibroplasty when additionally connected to the FMT opposite from the round window membrane.

A comparative study of MED-EL FMT attachment to the long process of the incus in intact middle ears and its attachment to disarticulated stapes head

The Vibrant Soundbridge^© (VSB) active middle-ear implant provides an effective treatment for mild-to-severe sensorineural hearing loss in the case of normal middle ear anatomy and mixed hearing loss in middle ear malformation. The VSB floating mass transducer (FMT), with proper couplers, can be installed on various structures of the ossicular chain, e.g., the short and long process of the incus, the stapes head, and the stapes footplate. A long process (LP) coupler is most commonly used for FMT attachment to the long process of the incus with intact ossicular chain, while CliP and Bell couplers are two standardized and reliable methods for FMT attachment to the stapes head with missing incus and malleus. However, the difference and relationship of the vibration properties among these three FMT couplers remain unclear. In the present study, the stapes footplate velocity responses of the LP, CliP, and Bell couplers have been investigated in eight fresh temporal bones (TBs) to evaluate the vibration properties of these three couplers. Normal and reconstructed middle ear transfer functions (METFs) were determined from laser Doppler vibrometer (LDV) measurements. A mastoidectomy and a posterior tympanotomy were performed to expose the ossicular chain. The METFs of the normal middle ear and middle ear with LP-FMT-coupler were compared under acoustic stimulation, thus the mass effect of the FMT with LP coupler was evaluated. Additional comparisons were made between the stapes footplate vibrations of the LP-FMT-coupler (with the intact ossicular chain at the long process of the incus), CliP-FMT-coupler and Bell-FMT-coupler on the stapes head (after incus and malleus removed) under active electromechanical stimulation. After the installation of CliP-FMT-coupler and Bell-FMT-coupler to the middle ear, the average velocity amplitude of the stapes footplate, comparing to the LP-FMT-coupler, was about 15 dB higher between 1 and 6 kHz, and 10 dB lower at about 0.5 kHz. Quantitatively, there was no significant difference between the CliP-FMT-coupler and Bell-FMT-coupler. According to our study, installation of CliP-FMT-coupler or Bell-FMT-coupler on the stapes head provides considerable improvement of the middle ear mechanical and functional responses, comparing with the LP-FMT-coupler in the temporal bone experiments. Moreover, the installation of the Bell-FMT-coupler to the stapes head produces essentially the same footplate velocity responses in comparison to the CliP-FMT-coupler.

Round window stimulation with the Vibrant Soundbridge: Comparison of direct and indirect coupling

OBJECTIVES/HYPOTHESIS

The purpose of this study was to measure the degree of coupling between the floating mass transducer (FMT) and the round window membrane (RWM) in patients with conductive and mixed hearing loss implanted with the Vibrant Soundbridge (VSB) device. The efficiency of direct and indirect coupling of the FMT to the RWM was compared by measuring differences between the initial prescription targets and the final settings of the VSB audio processor after fine-tuning.

STUDY DESIGN

Retrospective study.

METHODS

Investigation of a group of subjects with either conductive or mixed hearing loss implanted with the VSB, a device that uses a FMT coupled to the RWM. There were two subgroups: subjects in which coupling was direct (no interposed material) or indirect (interposed material). The functional gain, insertion gain, and compression characteristics of the device were measured to assess the efficiency of coupling and to investigate the proximity of the fitting to prescriptive targets.

RESULTS

Coupling for the subgroup with indirect coupling of the RWM was higher (better) than for the subgroup with direct coupling. The gain deviation from prescriptive targets was smaller for the subgroup with indirect coupling.

CONCLUSIONS

The coupling method can have an effect on the coupling efficiency and the final electroacoustic settings of the device. The prescription targets were not accurate for the majority of subjects from either subgroup. Indirect coupling appears to provide more effective stimulation of the cochlea.

LEVEL OF EVIDENCE

4. Laryngoscope, 127:2843-2849, 2017.

A tri-coil bellows-type round window transducer with improved frequency characteristics for middle-ear implants

A number of methods to drive the round window (RW) using a floating mass transducer (FMT) have been reported. This method has attracted attention because the FMT is relatively easy to implant in the RW niche. However, the use of an FMT to drive the RW has been proven to produce low outputs at frequencies below approximately 1 kHz. In this study, a new tri-coil bellows-type transducer (TCBT), which has excellent low frequency output and is easy to implant, is proposed. To design the frequency characteristics of the TCBT, mechanical and electrical simulations were performed, and then a comparative analysis was conducted between a floating mass type transducer (like the FMT) and a fixed type transducer (like the TCBT). The features of the proposed TCBT are as follows. First, the TCBT's housing is fixed to the RW niche so that it does not vibrate. Second, the internal end of a tiny bellows is connected to a vibrating three-pole permanent magnet located within three field coils. Finally, the rim of the bellows bottom is attached to the end of the housing that hermetically encloses the three field coils. In this design, the only vibrating element is the bellows itself, which efficiently drives the RW membrane. To evaluate the characteristics of this newly developed TCBT, the transducer was installed in the RW niche of temporal bones and the velocity of the stapes was measured using a laser Doppler vibrometer. The experimental results indicate that the TCBT can produce 100, 111, and 129 dB SPL equivalent pressure outputs at below 1 kHz, 1-3 kHz, and above 3 kHz, respectively. Thus, the TCBT with one side coupled to the RW via a bellows will be easy to implant and offer better performance than an FMT.

Differential Intracochlear Sound Pressure Measurements in Human Temporal Bones with an Off-the-Shelf Sensor

The standard method to determine the output level of acoustic and mechanical stimulation to the inner ear is measurement of vibration response of the stapes in human cadaveric temporal bones (TBs) by laser Doppler vibrometry. However, this method is reliable only if the intact ossicular chain is stimulated. For other stimulation modes an alternative method is needed. The differential intracochlear sound pressure between scala vestibuli (SV) and scala tympani (ST) is assumed to correlate with excitation. Using a custom-made pressure sensor it has been successfully measured and used to determine the output level of acoustic and mechanical stimulation. To make this method generally accessible, an off-the-shelf pressure sensor (Samba Preclin 420 LP, Samba Sensors) was tested here for intracochlear sound pressure measurements. During acoustic stimulation, intracochlear sound pressures were simultaneously measurable in SV and ST between 0.1 and 8 kHz with sufficient signal-to-noise ratios with this sensor. The pressure differences were comparable to results obtained with custom-made sensors. Our results demonstrated that the pressure sensor Samba Preclin 420 LP is usable for measurements of intracochlear sound pressures in SV and ST and for the determination of differential intracochlear sound pressures.

Cone beam computed tomography after round window vibroplasty: do the radiological findings match the auditory outcome?

CONCLUSION

The cone beam computed tomography (CBCT) imaging technique has proved to be reliable for assessing the appropriate positioning of the floating mass transducer (FMT) in the round window (RW) niche, although some parameters do not seem to be essential for achieving a satisfactory functional outcome.

OBJECTIVES

To evaluate the role that specific imaging parameters derived from CBCT of the temporal bone have for predicting the functional outcome after RW vibroplasty (RW-VP).

METHODS

CBCT imaging was carried out in a homogeneous group of patients who presented with a mixed type of hearing loss after open tympanoplasty. Three arbitrary radiological parameters were taken into account: the FMT/RW membrane contact, bony contacts of the FMT margins, and the inferior FMT tissue support. The audiological assessment took into consideration the PTA4 (500-4000 Hz), the PTA2 (125-250 Hz), and the word recognition score (WRS) in quiet and in noise.

RESULTS

One subject presented with all positive CBCT parameters and showed a good, but not the best auditory performance among the study group. In the majority of the subjects, with a satisfactory postoperative hearing improvement, at least two of the three radiological parameters were present. In comparison with the unaided condition, an improvement in both the PTA4 and PTA2 was found in all the subjects.