Objectives In this study, we compared the magnetic resonance (MR) image artifacts caused by a conventional metal-based cochlear implant and a newly developed liquid crystal polymer (LCP)-based device. Methods The metal-based cochlear implant system (Nurobiosys Co.) was attached to side of the head of a subject and the LCP-based device was attached to opposite side. In both devices, alignment magnets were removed for safety. Magnetic resonance imaging (MRI) was performed on a widely used 3.0 T and an ultra-high 7.0 T MRI machine. 3.0 and 7.0 T MR images were acquired using T1- and T2*-weighted gradient echo sequences, respectively. Results In the 3.0 T images, the metal-based device on the left side generated the significant amount of artifacts. The MR images in the proximity of the metal package were obscured by the artifacts in both axial and sagittal views. On the other hand, the MR images near the LCP-based device were relatively free from the artifacts and clearly showed the brain structures. 7.0 T MR images showed the more severe distortion in the both sides but the metal-based cochlear implant system caused a much larger obscure area than the LCP-based system. Conclusion The novel LCP-based cochlear implant provides a good MRI compatibility beyond present-day cochlear implants. Thus, MR images can be obtained from the subjects even with the implanted LCP-based neural prosthetic systems providing useful diagnostic information. Furthermore, it will be also useful for functional MRI studies of the auditory perception mechanism after cochlear implantations as well as for positron emission tomography-MRI hybrid imaging.

A simplified cochlear implant (CI) system would be appropriate for widespread use in developing countries. Here, we describe a CI that we have designed to realize such a concept. The system implements 8 channels of processing and stimulation using the continuous interleaved sampling (CIS) strategy. A generic digital signal processing (DSP) chip is used for the processing, and the filtering functions are performed with a fast Fourier transform (FFT) of a microphone or other input. Data derived from the processing are transmitted through an inductive link using pulse width modulation (PWM) encoding and amplitude shift keying (ASK) modulation. The same link is used in the reverse direction for backward telemetry of electrode and system information. A custom receiver-stimulator chip has been developed that demodulates incoming data using pulse counting and produces charge balanced biphasic pulses at 1000 pulses/s/electrode. This chip is encased in a titanium package that is hermetically sealed using a simple but effective method. A low cost metal-silicon hybrid mold has been developed for fabricating an intracochlear electrode array with 16 ball-shaped stimulating contacts

Cochlear implant system is one of the most advanced neural prosthetic devices, and a lot of hearing-impaired people have recovered their auditory functions by using these systems. However, there still exist personal differences in the patients’ speech perception performances after the cochlear implantations. To find and explain the reasons of these differences, the physiological response property and the central auditory plasticity after long-term cochlear implantation have been studied. In those studies, animal experiments have been preferred because the experiments with human subject are highly limited, and observing the behavioral response of the animal is very important. To do that, the animal cochlear implant system should provide complex stimulus similar to those of the human cochlear implant and also be small, light-weighted. In early animal experiments, simple cochlear stimulator or single channel human cochlear implant system were used. These are simple and light-weighted, but could not provide sound stimulations similar to natural and complex sounds. Alternatively, commercial multi-channel human cochlear implant systems can be adapted. These systems implement multi-channel digital coding strategies thus providing complex electrical stimulus according to natural sounds. However, they are too large and heavy for animals to move freely with them and need frequent replacement of batteries because of the high power consumption. In this paper, we suggest a new cochlear implant system for freely moving animals. In our system, the power demanding sound processor is located on the experimental cage where external power is available. The animal carries a small, lightweighted receiver/stimulator package with a small battery only, which communicates with the sound processor via the infra-red (IR) telemetry. This system enables animals move freely with still implementing multi-channel digital coding strategies, thus will be a very useful tools for various animal experiments.

A bidirectional digital data transmission system has been developed for neural prosthetic devices with a data transmission rate up to 500kbps at the 2.5MHz carrier frequency in case of both forward and backward data transmission. We use single pair of transcutaneous coil link for forward power transmission and bidirectional data transmission. The amplitude-shift keying (ASK) modulation protocol is selected for simple demodulation circuit in both bidirectional cases. Power amplification of external part is based on the single ended class E concept. The capacitive tuning circuit is introduced and analyzed for backward data transmission. Modulating tuning-capacitance of the implant enables one to modulate the current amplitude of the external coil without any additional circuit or antenna in implant. This circuit has the advantage of continuous power transmission to the implant relatively to conventional resistive load switching circuit. It permits the time for processing and transmitting of the backward data transmission to be unbounded. The experimental results show that the designed system is capable of delivering at least 30mW over a coil distance of 12mm. In neural prosthetic devices, this bidirectional digital data transmission is effective method for setting of stimulation parameters, recording of neural response after electrical stimulation, and monitoring of the implantable device.

This work was supported by KOSEF through NBS-ERC and its international collaboration program between NBS and Cornell Bioengineering program.

A new cochlear implant system for animal experiments is proposed. The system uses a DSP-based sound processor to implement the six-channel continuous interleaved sampling (CIS) speech processing strategy. An infra-red telemetry is designed to remotely connect the power-demanding sound processor to receiver/stimulator attached on the animal. This enables the animal to move freely. The receiver/stimulator consumes about 40 mW, thus can operates for about 200 hours without changing battery