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Biomedical subjects

C H Chouard

Publications and source records attributed to C H Chouard.

At least 37 records · Page 2Linked to original sources
PubMed1997

[Nuclear magnetic resonance and cochlear implant].

Chou underlined that ive potential effects may be anticipated if MRI is realized on implantees: 1) force on the implant by strong magnetic field, 2) current induced by the implant in the radiofrequency (RF) field, 3) damage of implant by RF exposure, 4) MRI image distortion caused by the implant, 5) implant and adjacent tissue heating due to the absorption of RF energy. We studied the reality of the four first of these risks on the Digisonic cochlear implant from MXM using the Siemens Magneton 42 SP, which supplied the implants during 10 minutes with 1 Tesla magnetic field, RF 42 MHz, maximum intensity 10 kV. During T1 and T2 sequences we could notice that: 1) Provided the receiver is strongly attached in its skull niche as requested by normal surgical procedure, no deplacement may be observed: 2) No adverse current may been observed as well on the implanted electrodes as in the internal circuitry; 3) No damage or adverse magnetisation have been detected in the 3 studied receivers; 4) Cerebral imaging of the animal is moderately darkened by the implant. The volume of the shadow involved by the implant is approximately three times the volume of the implant. As Chou demonstrated that no observable heating could be detected after a long MRI sequence, and as Portnoy using Nucleus device observed also that neither adverse current nor implant damage could be detected, we estimate that there are no real contraindication to perform MRI on implantees, provided the surgical attachment has been correctly realised. Practical attitudes will be evoked and discussed.

Animals↗
PubMed1997

[Asynchronous sequential stimulation. A new signal treatment for cochlear implants].

Cochlear implants use a fixed or FO dependent stimulation rate, whatever the sound analysed (vowel or consonant) and its analysis procedure (fixed filters or FFT). We present a procedure which varies as a function of the nature of the input signal. This method is based on FFT analysis using a variable with analysis window. Short windows are applied on the transient part of the signal, providing poor frequency resolution but good time resolution; they accurately permit to follow the speech signal in time during its fast temporal variations. Large windows are applied on the stationary parts of the signal, providing better frequency resolution, but poor time resolution. Transient parts of the speech order this window switching; they are detected using the statistical properties of the FFT; moreover the narrow windowing is coupled with an increase of the stimulation frequency. This strategy has been implemented using the Digisonic cochlear implant software, and clinically assessed on 6 regular cochlear implant users, owing to a consonant-vowel-consonant test. This Asynchronous-Interleaved-Stimulation (AIS) strategy provides the patients with better discrimination than fixed window FFT analysis. The coding protocol are described and results presented.

Acoustic Stimulation↗
PubMed1995

Clinical results for the DIGISONIC multichannel cochlear implant.

The DIGISONIC is a digitized 15-channel cochlear implant. A special version of this implant has been designed for use in the totally obstructed cochlea. This device has 10 separate electrodes that may be inserted, one by one, into 10 different holes drilled in the bony cochlea. The device's 128-point Fast Fourier Transform analysis supplies the patient with the entire set of the sound information between 100 and 7800 Hz. The stimulation rhythm is set at a programmable frequency among 125 and 400 Hz or slaved to the fundamental pitch frequency. The flexibility of the microprocessor makes it possible to select the best width and mean value of each frequency band for each electrode. Many speech-coding strategies may be easily programmed as a function of scientific desiderata. The authors present clinical results for the first 28 patients they treated with this cochlear implant.

Adolescent↗
PubMed1995

Speech coding strategies of the digisonic fully digitized cochlear implant.

The Digisonic is a fully digitized cochlear implant. Because of its articulated array, its 15 electrodes can be inserted in the cochlea. Each electrode is recessed in a special silastic compartment of the array and has a very large stimulation area thanks to its large microrelief surface area. The small volume of its implanted receiver (flat cylinder diam 29 mm, 6.9 mm thick) allows it to be placed in 2-year-old children. The 128 point FFT of this device supply the patient with a full set of sound information between 64 and 7800 Hz. Electrode stimulation mode is sequential and stimulation rhythm is programmable. Electric crosstalk is decreased by the shape of the electrode array, and optionally by special programming of the neighboring electrodes. The speech therapist may select the width and peak value of each frequency band handled by each functional electrode. Because the versatility of this digitized emitter, many speech coding strategies can be easily programmed as a function of electrode responses or particular scientific considerations. A special version of this device, consisting of 10 separate electrodes, has been designed for use in patients with total obstruction of the cochlea. These insulated wires may be inserted one by one in the inner ear in 10 different recesses gently drilled in the bony cochlea. This device was placed in 46 patients between 1992 and 1994, including 8 young children (aged 2-9 years, mean 5 years) and 9 patients with total cochlear obstruction.

Child↗
PubMed1995

[Biocompatibility of cochlear implants].

Ceramic, titanium and platinum guarantee a perfect bio-compatibility for cochlear implants. Moreover the long term efficacy of the electrode nerve interface is obtained thanks to a limited electric current density. Failure risks of implanted electronic are decreased by use of carefully selected components.

Biocompatible Materials↗
PubMed1995

[Signal processing and clinical results with the French cochlear implant Digisonic].

The Digisonic is a totally digitised multichannel cochlear implant remarkable for the versatility of its sound signal processing. Owing to its flexible and articulated array, its 15 electrodes are usually introduced in the scala tympani. A special version of this device has been designed to be used in case of total obstructed cochlea. It consists of separated electrodes which may be inserted one by one in the inner ear in different holes gently drilled in the bony cochlea. The possibilities of the microprocessor allow the speech therapist to carefully select the best width and mean value of each frequency band respectively devoted to each functional electrode. These parameters may be adapted to progressively improve the patient's hearing performances as a function of his phonemic discrimination and or the number and the tonotopy of his functional electrodes. Moreover, owing to the versatility of this digitised emitter a lot of speech coding strategies may be easily programmed as a function of eventual desiderata. Its high miniaturisation leads this implant to be particularly useful for young children. Results of our 38 first implanted patients (age 2-74; mean 42) including 7 cases of totally obstructed cochlea are reported.

Adolescent↗
PubMed1995

[Cochlear implants and total cochlear obstruction].

Total cochlea obstruction is not a contraindication for cochlear implant. We report our experience owing to the single channel cochlear implant Monosonic (9 cases), partial insertion of the electrodes-array (3 cases: 1 Digisonic and 2 minisystem) and, more recently the separate electrodes version of the Digisonic (6 cases). This new device is encouraging because it supplies 2/5 patients with telephone use.

Adolescent↗
PubMed1995

[Evaluation protocol of cochlear implants in children under 5 years of age].

Special tests are necessary to assess the cochlear implant efficacy on a prelingually deaf child implanted before age 5 y. We propose to quantify comportment, comprehension, auditory perception and expression as percentage of a same age normally hearing child's scores. The particular items are detailed.

Age Factors↗
PubMed1994

[Test of electrical stimulation of the round window. Diagnostic and prognostic value of the rehabilitation of total deafness by cochlear implant].

The round window electrical stimulation (RWES) test has been performed in 708 cases of total deafness. Among them 244 have successfully benefited with a cochlear implant. Electrical Brain Stem Evoked (EBSE) potential elicited by this stimulation have been registrated in 283 cases, 113 of them during general anesthesia necessary in children. This test supplies the patient with a subjective sound sensation and/or EBSE in 93% of cases. The correlation between electrical data of this RWES test and clinical results of the cochlear implant is described. This test is discussed regarding the simple transtympanique promonotory stimulation test.

Adolescent↗
PubMed1994

[The French multi-electrode cochlear implant Digisonic: clinical results].

The Digisonic is a totally digitized and miniaturized multichannel cochlear implant. Owing to its flexible and articulated array, its 15 electrodes are usually introduced in the scala tympani. A special version of this device has been designed to be used in case of total obstructed cochlea. It consists of separated electrodes which may be inserted one by one in the inner ear in different holes gently drilled in the bony cochlea. The possibilities of the microprocessors allow the speech therapist to carefully select the best width and mean value of each frequency band respectively devoted to each functional electrode. These parameters may be adapted to progressively improve the patient's hearing performances as a function of his phonemic discrimination and or the number and the tonotopy of his functional electrodes. Moreover, owing to the versatility of this digitized emitter a lot of speech coding strategies may be easily programmed as a function of eventual desiderata. Owing to a special assessment protocol the scores presented by our 28 first patients including 5 young children are described. These scores inversely depend on the deafness duration. Thus the cochlear implant placement must be considered as an emergency. Special attention is devoted to the score of patients presenting a totally ossified cochlea.

Adult↗
PubMed1992

Clinical results of a 15-filter digital auditory prosthesis using selective amplification and compression.

Classical hearing aid efficiency was compared with that of a 15-filter digital auditory prosthesis in 23 patients suffering from partial sensorineural hearing loss. This device contains a microprocessor 320C25 from TEXAS Instruments. The sound signal is analysed at a sampling rate of 16 kHz. With the use of a Fast Fourier Transform (FFT), it provides the system with 15 energy levels at frequencies ranging from 0 to 8 kHz. The energy of each frequency band is multiplied by a coefficient stored in the device memory and directly dependent on the patient's audiometric specificities. The 15 signals are then synthesized by inverse FFT and mixed in a loudspeaker. The prosthesis is a rechargable battery powered 4 x 10 x 15 cm box programmable through a PC. The clinical results obtained with this 15-filter digital prosthesis are discussed and compared with the performances of present classical hearing aids.

Auditory Threshold↗
PubMed1992

[Improvement of clinical results by digitalization of a single channel cochlear implant].

For 1973 we have been among the first to claim the multichannel cochlear implant superiority regarding single channel efficacy. However we actually thing that single channel cochlear implant is indispensable in case of total ossified cochlea, and very useful when efficacy/coast ratio must be considered. In order to narrow the gap between multi and single channel device efficacy, we used the new microprocessors possibilities to digitalize the analogic emietter of the single channel system, which we designed in 1987. Owing to a PC keyboard the new emietter allows the speech therapist to select the frequency band width of the input signal, and to determine the threshold level and the dynamic value as a function of six steps values of the stimulus wave frequency. These improvements supply the patient with a better speech intelligibility excepted for vowels discrimination. Comparison of clinical results obtained through the two analogic and digital systems are reported on 4 post lingually and 4 pre lingually deaf patients.

Adolescent↗
PubMed1992

[Indications and results of cochlear implants in young children].

In order to determine the criteria for patient selection and the preoperative prognostic factors for hearing recovery after cochlear implants in young totally dead children, the results of hearing rehabilitation were studied in 15 children who had undergone cochlear implantation at from 2 to 9 years of age. The choice of implant is determined by the permeability of the cochlear duct. A multi-system should be used, except when the cochlea is totally ossified. The reliability and efficacy of mono and multi system implants make it possible to offer a solution to the urgent therapeutic problems posed by total deafness in the young child.

Age Factors↗