Claudia Candreia

Factors improving the vibration transfer of the floating mass transducer at the round window

Objectives: With the placement of a floating mass transducer (FMT) at the round window, a new approach of coupling an implantable hearing system to the cochlea has been introduced. The aim of the present experimental study is to examine the influence of different ways of FMT placement at the round window on the vibration energy transfer to the cochlea. Material and Methods: Experiments were performed on 8 ears of human whole head specimens. A mastoidectomy and facial recess approach were performed to access the middle ear structures. Seven different conditions were compared, that is, a perpendicular or 90-degree rotated position of the FMT in the round window niche, overlaid or underlaid with connective tissue or with tight fixation and disrupted ossicular chain. The FMT was stimulated electrically and the movements at the FMT, the stapes head, and the promontory were measured using laser Doppler vibrometry. Results: Vibration transmission to the cochlear fluids was best with the FMT placed perpendicular to the round window membrane and underlaid with connective tissue. The energy transfer to the inner ear was up to 45 dB higher compared with tight fixation condition, where the poorest energy transfer was found. Underlaying the FMT with connective tissue improved energy transfer even for a suboptimal orientation of the FMT. Conclusion: The way of coupling of the FMT to the round window has a substantial influence on the vibration transmission. Energy transfer to the inner ear is highest with the FMT placed in the round window and underlaid with tissue.

The floating mass transducer at the round window: Direct transmission or bone conduction?

The round window placement of a floating mass transducer (FMT) is a new approach for coupling an implantable hearing system to the cochlea. We evaluated the vibration transfer to the cochlear fluids of an FMT placed at the round window (rwFMT) with special attention to the role of bone conduction. A posterior tympanotomy was performed on eleven ears of seven human whole head specimens. Several rwFMT setups were examined using laser Doppler vibrometry measurements at the stapes and the promontory. In three ears, the vibrations of a bone anchored hearing aid (BAHA) and an FMT fixed to the promontory (pFMT) were compared to explore the role of bone conduction. Vibration transmission to the measuring point at the stapes was best when the rwFMT was perpendicularly placed in the round window and underlayed with connective tissue. Fixation of the rwFMT to the round window exhibited significantly lower vibration transmission. Although measurable, bone conduction from the pFMT was much lower than that of the BAHA. Our results suggest that the rwFMT does not act as a small bone anchored hearing aid, but instead, acts as a direct vibratory stimulator of the round window membrane.

Low-dose temporal bone CT in infants and young children: effective dose and image quality.

If your institution is like ours, you must perform many temporal bone CT studies in children and worry about radiation exposure. These authors compared techniques using 80 kV/90–100 mAs (low dose) and 140kV/170 mAs (high dose) for temporal bone CT studies in children aged 5 years. Neuroradiologists and otologists evaluated 23 structures in those studies. Low-dose CT was given lower scores but these differences were only significant when otologists evaluated the studies. Thus, the image quality of low-dose CT was perceived as insufficient by our clinical colleagues. BACKGROUND AND PURPOSE: The temporal bone is ideal for low-dose CT because of its intrinsic high contrast. The aim of this study was to retrospectively evaluate image quality and radiation doses of a new low-dose versus a standard high-dose pediatric temporal bone CT protocol and to review dosimetric data from the literature. MATERIALS AND METHODS: Image quality and radiation doses were compared for 38 low-dose (80 kV/90–110 mAs) and 16 high-dose (140 kV/170 mAs) temporal bone CT scans of infants to 5-year-old children. The CT visualization quality of 23 middle and inner ear structures was subjectively graded by 3 neuroradiologists and 3 otologists by using a 5-point scale with scores 1–2 indicating insufficient and scores 3–5 indicating sufficient image quality. Effective doses of local and literature-derived protocols were calculated from dosimetric data by using NRPB-SR250 software. RESULTS: Insufficient image-quality scores were more frequent in low-dose scans versus high-dose scans, but the difference was only statistically significant for otologists (6.0% versus 3.4%, P = .004) and not for neuroradiologists (1.2% versus 0.7%, P = .84). Image quality was critical for small structures (such as the stapes or lamella at the internal auditory canal fundus). Effective doses were 0.25–0.3 mSv for low-dose scans, 1.4–1.8 mSv for high-dose scans, and 0.9–2.6 mSv for literature-derived protocols. CONCLUSIONS: The image quality of the new low-dose protocol remains diagnostic for assessing middle and inner ear anatomy despite a 3- to 8-fold dose reduction over previous and literature-derived protocols. However, image quality of small structures is critical and may be perceived as insufficient.

Laser Doppler vibrometric assessment of middle ear motion in Thiel-embalmed heads

Hypothesis Thiel-embalmed human whole head specimens represent an alternative model in middle ear research. Background Research into middle ear mechanics and the evaluation of active middle ear implants are generally performed on fresh human temporal bone specimens. A drawback of this method is the limited period during which the specimen can be used before tissue decay begins. Tissue conservation that preserves mechanical properties is desirable. Methods Using laser Doppler vibrometry, the movement of the tympanic membrane, stapes, and round window were measured in 23 ears from 15 human whole head specimens embalmed according to Thiel. The ears were acoustically stimulated through the intact external auditory canal. The measurement results were compared with data from the literature. Results The results were similar to those measured in living subjects and from fresh temporal bones, after excluding measurements with nontypical shapes or low amplitudes, that is, 9% for tympanic membrane, 38% for stapes, and 67% for round window. The best agreement was found for the tympanic membrane (mean difference between 0 and 5.2 dB) and for the stapes measurements (mean difference between 0 and 7.4 dB). Larger differences were found for the round window measurements (mean difference between 3 and 19 dB). For the stimulation levels used, the Thiel specimens behaved linearly in amplitude. The results remained reproducible for more than 20 hours in ambient air, and when the specimen was put back into Thiel solution, the measurements were stable for up to several months between measurements. Conclusion Our results showed that the middle ears of Thiel-embalmed human whole head specimens can be used to study human middle ear mechanics; however, significant differences in some frequencies, particularly at the round window, have to be considered.

Lamb Temporal Bone as a Surgical Training Model of Round Window Cochlear Implant Electrode Insertion

Objective: The preservation of residual hearing in cochlear implantation opens the door for optimal functional results. This atraumatic surgical technique requires training; however, the traditional human cadaveric temporal bones have become less available or unattainable in some institutions. This study investigates the suitability of an alternative model, using cadaveric lamb temporal bone, for surgical training of atraumatic round window electrode insertion. Intervention: A total of 14 lamb temporal bones were dissected for cochlear implantation by four surgeons. After mastoidectomy, visualization, and drilling of the round window niche, an atraumatic round window insertion of a Medel Flex24 electrode was performed. Electrode insertion depth and position were verified by computed tomography scans. Main Outcome Measure: All cochleas were successfully implanted using the atraumatic round window approach; however, surgical access through the mastoid was substantially different when compared human anatomy. The mean number of intracochlear electrode contacts was 6.5 (range, 4–11) and the mean insertion depth 10.4 mm (range, 4–20 mm), which corresponds to a mean angular perimodiolar insertion depth of 229 degrees (range 67–540°). Full insertion of the electrode was not possible because of the smaller size of the lamb cochlea in comparison to that of the human. Conclusion: The lamb temporal bone model is well suited as a training model for atraumatic cochlear implantation at the level of the round window. The minimally pneumatized mastoid as well as the smaller cochlea can help prepare a surgeon for difficult cochlear implantations. Because of substantial differences to human anatomy, it is not an adequate training model for other surgical techniques such as mastoidectomy and posterior tympanotomy as well as full electrode insertion.

Audiological monitoring in Swiss childhood cancer patients

Full audiological monitoring is the best strategy to detect hearing loss early and to provide timely intervention in the absence of a clinical method of otoprotection. Full monitoring requires audiological evaluation before, and then during and after ototoxic cancer treatment. In a worldwide context of monitoring protocols that vary substantially, we analyzed the audiological monitoring of childhood cancer patients over the last decade across treatment centers in Switzerland.

Single-Center Study Investigating Foreign Language Acquisition at School in Children, Adolescents, and Young Adults With Uni- or Bilateral Cochlear Implants in the Swiss German Population

OBJECTIVE To evaluate foreign language acquisition at school in cochlear implant patients. STUDY DESIGN Cohort study. SETTING CI center. PATIENTS Forty three cochlear implants (CI) patients (10-18 yr) were evaluated. CI nonusers and patients with CI-explantation, incomplete datasets, mental retardation, or concomitant medical disorders were excluded. INTERVENTION(S) Additional data (type of schooling, foreign language learning, and bilingualism) were obtained with questionnaires. German-speaking children with foreign tuition language (English and/or French) at school were enrolled for further testing. MAIN OUTCOME MEASURE(S) General patient data, auditory data, and foreign language data from both questionnaires and tests were collected and analyzed. RESULTS Thirty seven out of 43 questionnaires (86%) were completed. Sixteen (43%) were in mainstream education. Twenty-seven CI users (73%) have foreign language learning at school. Fifteen of these were in mainstream education (55%), others in special schooling. From 10 CI users without foreign language learning, one CI user was in mainstream education (10%) and nine patients (90%) were in special schooling. Eleven German-speaking CI users were further tested in English and six additionally in French. For reading skills, the school objectives for English were reached in 7 of 11 pupils (64%) and for French in 3 of 6 pupils (50%). For listening skills, 3 of 11 pupils (27%) reached the school norm in English and none in French. CONCLUSIONS Almost 75% of our CI users learn foreign language(s) at school. A small majority of the tested CI users reached the current school norm for in English and French in reading skills, whereas for hearing skills most of them were not able to reach the norm.

In situ Probe Microphone Measurement for Testing the Direct Acoustical Cochlear Stimulator

Hypothesis: Acoustical measurements can be used for functional control of a direct acoustic cochlear stimulator (DACS). Background: The DACS is a recently released active hearing implant that works on the principle of a conventional piston prosthesis driven by the rod of an electromagnetic actuator. An inherent part of the DACS actuator is a thin titanium diaphragm that allows for movement of the stimulation rod while hermetically sealing the housing. In addition to mechanical stimulation, the actuator emits sound into the mastoid cavity because of the motion of the diaphragm. Methods: We investigated the use of the sound emission of a DACS for intra-operative testing. We measured sound emission in the external auditory canal (PEAC) and velocity of the actuators stimulation rod (Vact) in five implanted ears of whole-head specimens. We tested the influence various positions of the loudspeaker and a probe microphone on PEAC and simulated implant malfunction in one example. Results: Sound emission of the DACS with a signal-to-noise ratio >10 dB was observed between 0.5 and 5 kHz. Simulated implant misplacement or malfunction could be detected by the absence or shift in the characteristic resonance frequency of the actuator. PEAC changed by <6 dB for variations of the microphone and loudspeaker position. Conclusion: Our data support the feasibility of acoustical measurements for in situ testing of the DACS implant in the mastoid cavity as well as for post-operative monitoring of actuator function.