Digital X-ray stereophotogrammetry for cochlear implantation

Multielectrode, intracochlear implant systems are effective treatment for profound sensorineural hearing loss. In some cases, these systems do not perform well, which may be partially due to variations in implant location within the cochlea. Determination of each electrode's position in a patient's inner ear provides an in vivo basis for both the cochlear modeling of electrical fields and the future design of electrode arrays that deliver electrical stimulation to surviving auditory neurons, and may improve speech processor programming for better speech recognition. We developed an X-ray stereophotogrammetric approach to localize implanted electrodes in three dimensions. Stereophotogrammetry of implanted electrodes is formulated in weak perspective geometry, with knowledge of a three-dimensional (3-D) reference structure and electrode positions in each of two digital stereo-images. The localization error is theoretically, numerically, and experimentally quantified. Both numerical and experimental results demonstrate the feasibility of the technique.     

Heart-surface reconstruction and ECG electrodes localization using fluoroscopy, epipolar geometry and stereovision: application to noninvasive imaging of cardiac electrical activity

To date there is no imaging modality for cardiac arrhythmias which remain the leading cause of sudden death in the United States (> 300000/yr.). Electrocardiographic imaging (ECGI), a noninvasive modality that images cardiac arrhythmias from body surface potentials, requires the geometrical relationship between the heart surface and the positions of body surface ECG electrodes. A photographic method was validated in a mannequin and used to determine the three-dimensional coordinates of body surface ECG electrodes to within 1 mm of their actual positions. Since fluoroscopy is available in the cardiac electrophysiology (EP) laboratory where diagnosis and treatment of cardiac arrhythmias is conducted, a fluoroscopic method to determine the heart surface geometry was developed based on projective geometry, epipolar geometry, point reconstruction, b-spline interpolation and visualization. Fluoroscopy-reconstructed hearts in a phantom and a human subject were validated using high-resolution computed tomography (CT) imaging. The mean absolute distance error for the fluoroscopy-reconstructed heart relative to the CT heart was 4 mm (phantom) and 10 mm (human). In the human, ECGI images of normal cardiac electrical activity on the fluoroscopy-reconstructed heart showed close correlation with those obtained on the CT heart. Results demonstrate the feasibility of this approach for clinical noninvasive imaging of cardiac arrhythmias in the interventional EP laboratory.     

Speech understanding performance of cochlear implant subjects using time-frequency masking-based noise reduction

Cochlear implant (CI) recipients report severe degradation of speech understanding under noisy conditions. Most CI recipients typically can require about 10-25 dB higher signal-to-noise ratio than normal hearing (NH) listeners in order to achieve similar speech understanding performance. In recent years, significant emphasis has been put on binaural algorithms, which not only make use of the head shadow effect, but also have two or more microphone signals at their disposal to generate binaural inputs. Most of the CI recipients today are unilaterally implanted but they can still benefit from the binaural processing utilizing a contralateral microphone. The phase error filtering (PEF) algorithm tries to minimize the phase error variance utilizing a time-frequency mask for noise reduction. Potential improvement in speech intelligibility offered by the algorithm is evaluated with four different kinds of mask functions. The study reveals that the PEF algorithm which uses a contralateral microphone but unilateral presentation provides considerable improvement in intelligibility for both NH and CI subjects. Further, preference rating test suggests that CI subjects can tolerate higher levels of distortions than NH subjects, and therefore, more aggressive noise reduction for CI recipients is possible.     

An advanced multiple channel cochlear implant

An advanced multiple channel cochlear implant hearing prosthesis is described. Stimulation is presented through an array of 20 electrodes located in the scala tympani. Any two electrodes can be configured as a bipolar pair to conduct a symmetrical, biphasic, constant-current pulsatile stimulus. Up to three stimuli can be presented in rapid succession or effectively simultaneously. For simultaneous stimulation, a novel time-division current multiplexing technique has been developed to obviate electrode interactions that may compromise safety. The stimuli are independently controllable in current amplitude, duration, and onset time. Groups of three stimuli can be generated at a rate of typically 500 Hz. Stimulus control data and power are conveyed to the implant through a single transcutaneous inductive link. The device also incorporates a telemetry system that enables electrode voltage waveforms to be monitored externally in real time. The electronics of the implant are contained almost entirely on a custom designed integrated circuit. Preliminary results obtained with the first patient to receive the advanced implant are included.     

Estimation of vowel recognition with cochlear implant simulations

Because there are many parameters in the cochlear implant (CI) device that can be optimized for individual patients, it is important to estimate a parameter's effect before patient evaluation. In this paper, Mel-frequency cepstrum coefficients (MFCCs) were used to estimate the acoustic vowel space for vowel stimuli processed by the CI simulations. The acoustic space was then compared to vowel recognition performance by normal-hearing subjects listening to the same processed speech. Five CI speech processor parameters were simulated to produce different degree of spectral resolution, spectral smearing, spectral warping, spectral shifting, and amplitude distortion. The acoustic vowel space was highly correlated with normal hearing subjects' vowel recognition performance for parameters that affected the spectral channels and spectral smearing. However, the acoustic vowel space was not significantly correlated with perceptual performance for parameters that affected the degree of spectral warping, spectral shifting, and amplitude distortion. In particular, while spectral warping and shifting did not significantly reshape the acoustic space, vowel recognition performance was significantly affected by these parameters. The results from the acoustic analysis suggest that the CI device can preserve phonetic distinctions under conditions of spectral warping and shifting. Auditory training may help CI patients better perceive these speech cues transmitted by their speech processors.     

The nerve-electrode interface of the cochlear implant: currentspread

One of the fundamental facets of the cochlear implant that must be understood to predict accurately the effect of an electrical stimulus on the auditory nerve is the nerve-electrode interface. One aspect of this interface is the degree to which current delivered by an electrode spreads to neurons distant from it. This paper reports a direct mapping of this current spread using recordings from single units from the cat auditory nerve. Large variations were seen in the degree to which the different units are selective in responding to electrodes at different positions within the scala tympani. Three types of units could be identified based on the selectiveness of their response to the different electrodes in a linear array. The first type of unit exhibited a gradual increase in threshold as the stimulating site was moved from more apical to more basal locations within the scala tympani. The second type of unit exhibited a sharp local minimum, with rapid increases in threshold in excess of 6 dB/mm in the vicinity of the minimum. At electrode sites distant from the local minima the rate of change of the threshold approached that of the first type of units. The final type of unit also demonstrated a gradual change in threshold with changing electrode position, however, two local minima, one apical and one basal, could be identified. These three types are hypothesized to correspond to units which originate apical to the electrode array, along the electrode array and basal to the electrode array     

Discrimination of synthetic vowels by using tactile vocoder and acomparison to that of an eight-channel cochlear implant

A vowel discrimination test using a tactual vocoder was administered and the results were compared to that of an eight-channel cochlear implant. Both the tactile vocoder and the cochlear implant divided the speech signals into 16 frequency components using band-pass filters and lateral inhibition circuits. In the tactile vocoder, these 16 components were converted into a vibration with 200 Hz frequency and applied to a 3 x 16 element vibrator array using bimorph piezoelectric elements. The vibratory patterns were sensed on the fingertip. In the cochlear implant, the 16 components were reduced to eight current stimulation signals, consisting of biphasic pulses with 200 Hz frequency, which were applied to an eight-channel electrode array implanted in the scala tympani. The electrode array passed through the round window into the scala tympani to a depth of 23 mm. These psychophysical experiments investigate the ability of human subjects to discriminate synthetic vowels as a function of the number of channels employed. The results suggested that an eight-channel and a 16-channel tactile vocoder provided essentially the same discrimination scores. However, the ability to discriminate synthetic vowels decreased rapidly when less than eight channels were employed. The ability of an eight-channel tactile vocoder is expected to be better than that of the eight-channel cochlear implant because it is supposed that vowel discrimination is degraded by a phenomenon known as "current spreading" in the case of cochlear stimulation. However, the comparison between the two devices was not done on the cochlear implant subject.     

Hearing with bionic ears [cochlear implant devices]

According to speech perception-rate data continuous interleaved sampling (CIS) and spectral maxima sound processor (SMSP) techniques are, and probably will be, the best speech processing strategies for multichannel electrode cochlear implant devices. From packaging and power-consumption viewpoints, today's speech processing systems are very big and are, therefore, worn on the body and consume large electric power. Next-generation cochlear implant devices would be more compact, low-power products that would be worn behind or in the ear. It is clear that mixed-signal, high-density, and low-power design techniques are required to satisfy compactness, as well as low-power consumption features to realize intelligent speech sensation for the implantees. The especially critical design consideration of power supply lifetime and efficiency might be increased by using new promising technologies like microelectromechanical systems (MEMS)     

Three-dimensional source localization in a waveguide

This paper deals with three-dimensional (3-D) passive localization of a narrowband point source in a 2½-dimensional waveguide using an array of sensors. Two different maximum likelihood (ML) procedures for estimating the source range, depth, and direction-of-arrival (DOA) based on the normal mode representation of the received data are studied. In the first procedure, ML estimation of range and depth is applied on the data collected by a vertical array, and DOA is estimated using the ML algorithm on the data received by a separate, horizontal array. In the second procedure, the ML algorithm is applied on the data received by a two-dimensional (2-D), hybrid array for simultaneously estimating of all three source location parameters. Our study shows that although a horizontal array is sufficient for 3-D localization, to reduce sensitivity of the localization algorithm, a 2-D array should be used. The presented performance analysis of the two algorithms enables one to determine the performance losses in using the stage-wise, suboptimal algorithm relative to the optimal one in any given scenario. Numerical examples with channel parameters, which are typical to shallow water source localization, show performance losses of 0-3 dB. Simulation results of the two ML algorithms and their comparison with the Cramer-Rao bound (CRB) support the theory     

Encoding frequency modulation to improve cochlear implant performance in noise

Different from traditional Fourier analysis, a signal can be decomposed into amplitude and frequency modulation components. The speech processing strategy in most modern cochlear implants only extracts and encodes amplitude modulation in a limited number of frequency bands. While amplitude modulation encoding has allowed cochlear implant users to achieve good speech recognition in quiet, their performance in noise is severely compromised. Here, we propose a novel speech processing strategy that encodes both amplitude and frequency modulations in order to improve cochlear implant performance in noise. By removing the center frequency from the subband signals and additionally limiting the frequency modulation's range and rate, the present strategy transforms the fast-varying temporal fine structure into a slowly varying frequency modulation signal. As a first step, we evaluated the potential contribution of additional frequency modulation to speech recognition in noise via acoustic simulations of the cochlear implant. We found that while amplitude modulation from a limited number of spectral bands is sufficient to support speech recognition in quiet, frequency modulation is needed to support speech recognition in noise. In particular, improvement by as much as 71 percentage points was observed for sentence recognition in the presence of a competing voice. The present result strongly suggests that frequency modulation be extracted and encoded to improve cochlear implant performance in realistic listening situations. We have proposed several implementation methods to stimulate further investigation. Index Terms-Amplitude modulation, cochlear implant, fine structure, frequency modulation, signal processing, speech recognition, temporal envelope.     

Real-time automatic tuning of noise suppression algorithms for cochlear implant applications

The performance of cochlear implants deteriorates in noisy environments compared to quiet conditions. This paper presents an adaptive cochlear implant system, which is capable of classifying the background noise environment in real time for the purpose of adjusting or tuning its noise suppression algorithm to that environment. The tuning is done automatically with no user intervention. Five objective quality measures are used to show the superiority of this adaptive system compared to a conventional fixed noise-suppression system. Steps taken to achieve the real-time implementation of the entire system, incorporating both the cochlear implant speech processing and the background noise suppression, on a portable PDA research platform are presented along with the timing results.     

基于TMS320VC5502的电子耳蜗CIS算法实现

针对电子耳蜗连续交替采样算法（CIS）实现中面临的所需刺激速率高、要求参数调整灵活等问题,提出了一种基于FFT的CIS算法实现方法,设计了一套基于TMS320VC5502的电子耳蜗体外处理器的硬件系统。利用单频信号和实际语音对系统进行了验证,结果表明系统高效地实现了CIS算法,刺激速率达到了8 000次以上,满足电子耳蜗的要求。因此该设计系统有着高灵活性、高实时性和低功耗等特点,对电子耳蜗的研究和工程实现具有一定的指导意义。     

pH measurements using polarizable electrodes

A model for the potential difference across a membrane bounded by an ion-injecting interface and an ideally polarizable interface is presented. Using this model the predicted pH response is compared with experimental data.     

Force application during cochlear implant insertion: an analysis for improvement of surgeon technique

Highly invasive surgical procedures, such as the implantation of a prosthetic device, require correct force delivery to achieve desirable outcomes and minimize trauma induced during the operation. Improvement in surgeon technique can reduce the chances of excessive force application and lead to optimal placement of the electrode array. The fundamental factors that affect the degree of success for cochlear implant recipients are identified through empirical methods. Insertion studies are performed to assess force administration and electrode trajectories during implantations of the Nucleus 24 Contour and Nucleus 24 Contour Advance electrodes into a synthetic model of the human Scala Tympani, using associated methods. Results confirm that the Advance Off- Stylet insertion of the soft-tipped Contour Advance electrode gives an overall reduction in insertion force. Analysis of force delivery and electrode positioning during cochlear implantation can help identify and control key factors for improvement of insertion method. Based on the findings, suggestions are made to enhance surgeon technique.     

Three-dimensional integrated optics using polymers

Some of the key components are demonstrated to make three-dimensional (3-D) optical integrated circuits possible using polymers. Fabrication techniques of shadow reactive ion etching, shadow photolithography, and gray-level photolithography to produce complex 3-D integrated optic structures are demonstrated. Vertical waveguide bends exhibit excess losses of <0.3 dB, and vertical power splitters possess predictable output splitting ratios between multiple core levels with excess losses of <0.5 dB. Vertical polarization splitters exhibit power extinction ratios of 15 dB between the output core layers. A 1×4 vertical-horizontal power splitter is also demonstrated. Additionally, these techniques are used to integrate different polymer materials into the same optical circuit while easily solving the mode mismatch problem. To show the technique, a polymer electrooptic modulator is vertically integrated with a low-loss waveguide     

Synthesis of acoustic-surface-wave filters using double electrodes

An extra degree of freedom becomes available in the design of s.a.w. bandpass filters using double electrodes if the electrodes are individually weighed. This procedure also removes fundamental synthesis problems encountered with more conventional structures.     

采用新型干电极的心电监护系统

为了提高个人健康的监护水平,降低人体病变的几率,提出并设计一种无线智能监护系统。此系统由采集前端、无线路由和上位机组成。针对湿电极与传统干电极的缺点,采集前端采用低成本新型干电极,增加了贴附的舒适度和佩戴时间。为了解决干电极引起的基线漂移和运动伪迹干扰,设计专门的自适应阈值R波提取算法,在较低计算复杂度的情况下提高了R波检测率。实验结果表明,该系统功能完善,且能够监测心电信号并准确地提取心率信息。     

未校准相机最小化重采样失真对极线校正方法

校正作为立体视觉的先决条件,通常会产生不必要的几何变形。文中提出一种新的针对未校准相机的立体图像校正方法以减少几何失真。在图像级上限制相机的单应性矩阵接近刚性变换,并引入一个惩罚项以进一步减少在像素级的失真。在不显示计算基本矩阵的前提下整个图像校正问题构成了一个函数能量最小化的问题。实验结果表明该方法实现了最小化重采样失真的校正。