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Biomedical subjects

E S Hochmair

Publications and source records attributed to E S Hochmair.

At least 19 recordsLinked to original sources
PubMed1999

Magnetic resonance imaging and cochlear implants: compatibility and safety aspects.

With cochlear implants, magnetic resonance imaging (MRI) has until recently been contraindicated due to excessive magnetic and electromagnetic interference. The aim of this study was to determine the MRI compatibility of the Med-E1 Combi 40/40+ cochlear implant, within a wide range of clinical MRI applications. In vitro experiments on a 1.5 T MR scanner were performed. Torque, force, demagnetization, artifacts, induced voltages, and temperature increase were measured in worst case scenarios for the implant. In addition, stabilization experiments were performed. It was shown that most of the electromagnetic interferences between the cochlear implant and the 1.5 T scanner remained within acceptable limits. One exception is the torque on the internal magnet, which represents a hazard for patients with these cochlear implants. Therefore, MRI examination should only be performed if there is a strong medical indication, and certainly some assessment of the relative risks involved versus the risk of not providing the diagnostic capabilities of MRI, will have to be made. Appropriate safety measures should be taken.

Artifacts↗
PubMed1999

Influence of automatic gain control parameter settings on speech understanding of cochlear implant users employing the continuous interleaved sampling strategy.

OBJECTIVE: The purpose of the present study was to gather data on the influence of compression ratio and attack and release times of slow-acting front-end automatic gain control (AGC) systems on speech understanding of cochlear implant users in various listening situations. The data should allow evaluation of the usefulness of front-end AGC in body-worn speech processors. DESIGN: Subjects were 12 experienced postlingually deafened adult users of the Med-El Combi-40 multichannel cochlear implant. Six different front-end configurations, including a linear setting, the standard AGC of the Med-El Combi-40 processor, and four slow-acting dual front-end AGCs (use of two instead of one level detector for improved transient handling), were evaluated in two experiments. In experiment 1, tests were performed at 55, 70 and 85 dB SPL, roughly corresponding to soft, medium and loud speech. Experiment 2 was intended to evaluate the quality of transient handling of the six configurations. In this experiment an intense transient ("chink") at 100 dB SPL was spliced onto the beginning of each sentence (presented at 85 dB SPL). RESULTS: At 55 dB SPL subjects performed significantly more poorly with the linear setting than with the AGC settings, but no differences in performance could be found for the AGC settings. At 70 dB SPL subjects showed the poorest performance with the high compression ratio dual front-end AGCs. No differences in performance of the six front-end configurations were found at 85 dB SPL. In the presence of intense chinks, performance of the standard AGC dropped significantly. CONCLUSIONS: The results indicate that slow-acting front-end AGC can be used effectively in speech processors for cochlear implants to expand the range of input levels that are audible for the cochlear implant user, without any need to adjust a processor control, and that incorporation of an additional fast-acting AGC component can improve performance under conditions where intense transients occur.

Adult↗
PubMed1998

Cochlear implants: in vitro investigation of electromagnetic interference at MR imaging--compatibility and safety aspects.

In vitro experiments were performed to determine the compatibility of a cochlear implant at 0.2- and 1.5-T magnetic resonance (MR) imaging. Except for the torque at 1.5 T, all electromagnetic interferences remained within acceptable limits. MR imaging should be performed only if there is a strong medical indication, by following appropriate safety procedures. MR imaging at 0.2 T should be safe; at 1.5 T, however, the relative risks will have to be assessed.

Cochlear Implants↗
PubMed1997

The advanced Combi 40+ cochlear implant.

A 12-channel cochlear implant (CI) for high-rate pulsatile stimulation strategies is presented. Symmetric biphasic current pulses can be generated up to a maximum pulse repetition rate of 18.18 kpulses/second. The stimulation pulse amplitude can be selected within 1.5 microA-1.5 mA. Data and power are transcutaneously transferred using a single radiofrequency (RF) channel. A fully digital data transfer format is employed at an overall data rate of 600 kBit/second. The implant contains a single mixed analog/digital CMOS-ASIC (Application Specific Integrated Description) for data synchronization and stimulus generation. Stimulation signals are applied via a monopolar intracochlear multichannel electrode. Output capacitors for each channel are employed for safety reasons. A self-calibrating back telemetry system is included for estimating the channel impedances and field distribution along the electrode array. Dimensions of the ceramic package of the implant are only 33.50 x 23.40 x 3.95 mm3.

Cochlear Implantation↗
PubMed1996

Geometric approach for coupling enhancement of magnetically coupled coils.

This paper presents a geometric approach for the enhancement of the coupling coefficient between two magnetically coupled coils. It is demonstrated that the coupling coefficient can be considerably enhanced, if the turns of the coils are not concentrated at the circumferences, but distributed across the diameters. For analysis, each of the two coils is assumed to be composed of concentric circular loops. The experimental results are in very good agreement with the theoretical results.

Equipment Design↗
PubMed1993

New hardware for analog and combined analog and pulsatile sound-encoding strategies.

Development for cochlear implants of primarily analog design focuses in two directions. The first direction is miniaturization. A behind-the-ear (BTE) speech processor has been developed which can replace the body-worn processor for approximately 90% of the users of a MED-EL cochlear implant and works with two 1.4 V hearing aid batteries for between seven and twelve days. Consonant, vowel and sentence testing and patient questioning revealed that the BTE speech processor demonstrates a significant improvement in speech understanding compared to the body-worn processor, and that the patients' device acceptance is superior for the BTE processor. The result of the second direction for our cochlear implant development is the multichannel cochlear implant, CAP, with combined analog and pulsatile stimulation. It aims at complementing the information from the broad-band analog signal by adding spectral information, that is, tonotopic information. This device is capable of simultaneously stimulating one electrode channel with a broad-band analog signal and one of eight electrode channels with a pulsatile signal. The system can also be used for purely analog or for purely pulsatile stimulation. Preliminary results with the first recipient of a CAP cochlear implant system demonstrate that the device works as expected.

Acoustic Stimulation↗
PubMed1993

A feedback control system for real-time formant estimation. I--Static and dynamic analysis for sinusoidal input signals.

This paper presents a novel analog scheme suitable for the real-time estimation of formant frequencies. Formant tracking is based on a feedback technique which uses both the amplitude and phase characteristics of two stagger-tuned bandpass filters to give an improved dynamic behavior. The implementation of the system requires a small number of components, and is practical for low-power applications. An analysis of the static and dynamic behavior is given for sinusoidal input signals. The transient response is independent of the amplitude level of the input signal. The system is designed for second formant detection in a cochlear prosthesis system.

Cochlear Implants↗
PubMed1993

A feedback control system for real-time formant estimation. II--Analysis of a hysteresis effect and F2 estimation.

This paper presents the second part of the analysis of a feedback control system for real-time formant estimation. The system behavior is analyzed for an input signal composed of two sinusoids. If the frequency difference between the two input spectral lines is sufficiently great and the amplitude ratio is within certain limits, a hysteresis effect occurs. Then the system shows a tendency to select one of the two input spectral lines. The existence of the second line has only little influence on the accuracy of the detection of the selected line. From the analysis, conclusions of the system behavior regarding formant estimation can be drawn. A design example for second formant detection is simulated and compared with the results obtained by simulation of a zero-crossing system for F2 estimation and LPC analysis.

Computer Simulation↗
PubMed1992

Transcutaneous transmission of digital data and energy in a cochlear prosthesis system.

This paper describes the inductive power and data link employed in the CAP Cochlear Prosthesis System (CAP stands for Combined Analog and Pulsative Stimulation Strategy). The inductive link consisting of a parallel-tuned receiver resonant circuit weakly coupled to a series-tuned transmitter resonant circuit, is driven by a self-oscillating class-E-tuned power amplifier. The class-E concept allows coupling-insensitive high-efficiency transcutaneous transmission of power. In the CAP implant, variations of the coil distance within a range of 0 to 9 mm result in changes of the implant supply voltage which are lower than 10%. Within this coil distance range, the mean overall efficiency is 49%. In view of the excellent switching properties of the class-E tuned power oscillator, a practical scheme for data transmission is ASK (Amplitude Shift Keying). To ensure constant energy flow and easy synchronization of the bitstream in the implant, a self-clocking bit format is employed.

Cochlear Implants↗
PubMed1990

High-efficiency coupling-insensitive transcutaneous power and data transmission via an inductive link.

This paper presents a new approach for transmitting RF power and signal via an inductive link. Such an approach optimizes the power efficiency of the overall transmission scheme comprising the power amplifier plus the inductive link. Power amplification is based on the single ended class E concept. The power amplification stage is self oscillating, the oscillation frequency thus being influenced by the coupling of the coils. The resulting operating frequency offset yields an improved power transmission performance of the circuit since the oscillation frequency tracks the absolute transmission efficiency maximum. A detailed analysis is given. Realization of the described approach requires a minimal number of circuit components. Experimental and theoretical results are in good agreement.

Amplifiers, Electronic↗
PubMed1990

Initial results with simultaneous analog and pulsatile stimulation of the cochlea.

An improved method has been developed for the coding of speech information into adequate signals for the stimulation of the auditory nerve. It combines the periodicity principle, which has been applied in single-channel analog stimulation in the Austrian cochlear prosthesis, with the place principle by simultaneous analog stimulation on one channel and pulsatile stimulation on other channels. The second formant frequency determines the place of stimulation for the pulsatile signals. Simultaneous stimulation of several channels can cause the currents emerging from different electrodes to interact because the fluid impedance in the cochlea is small. Therefore, an important aspect of the multichannel strategy is to maintain the temporal pattern transmitted via the analog channel by adequate repetition rates and phase relationships of the pulsatile signals. The signals were processed with finite impulse response digital filters. Vowel identification tests were performed with 6 patients implanted with a 4-channel intracochlear electrode. The test material was spoken by male and female speakers. With proper timing of the pulses the improvement over the single-channel stimulation was significant at the 1% level and this difference was due to a significant increase in second formant recognition.

Cochlear Implants↗
PubMed1984

A model for the electrostimulation of the nervus acusticus.

Electrostimulation of the nervus acusticus has been successfully used to achieve speech understanding. A model of nerve excitation due to Fitzhugh [(1961) Biophys. J. 1, 445-446] has been explored to show that the stochastic response of single acoustic mammalian fibers observed by Rose, Brugge, Anderson and Hind [(1967) J. Neurophysiol. 30, 769-793] may be due to the non-linear interaction of sub-threshold electrical nerve activity with the signal. Computations by means of an analogue computer also shows that a phase-locked response with a frequency dependence resembling behaviour observed with electrostimulation is obtained with the model. A dynamic range for single fiber excitation is produced by the non-linear interaction.

Cochlear Implants↗
PubMed1983

Percepts from the Vienna cochlear prosthesis.

This report includes psychophysical data on some of the 13 patients who have been equipped with intracochlear electrodes and the 6 patients who have received an extracochlear electrode. Thresholds and uncomfortable listening levels versus frequency, amplitude difference limens, and gap detection in noise and frequency difference limens have been determined and represent some essential characteristics of prosthetic hearing.

Adolescent↗