Kyoung Won Nam

Application of Stereo-Imaging Technology to Medical Field

Objectives There has been continuous development in the area of stereoscopic medical imaging devices, and many stereoscopic imaging devices have been realized and applied in the medical field. In this article, we review past and current trends pertaining to the application stereo-imaging technologies in the medical field. Methods We describe the basic principles of stereo vision and visual issues related to it, including visual discomfort, binocular disparities, vergence-accommodation mismatch, and visual fatigue. We also present a brief history of medical applications of stereo-imaging techniques, examples of recently developed stereoscopic medical devices, and patent application trends as they pertain to stereo-imaging medical devices. Results Three-dimensional (3D) stereo-imaging technology can provide more realistic depth perception to the viewer than conventional two-dimensional imaging technology. Therefore, it allows for a more accurate understanding and analysis of the morphology of an object. Based on these advantages, the significance of stereoscopic imaging in the medical field increases in accordance with the increase in the number of laparoscopic surgeries, and stereo-imaging technology plays a key role in the diagnoses of the detailed morphologies of small biological specimens. Conclusions The application of 3D stereo-imaging technology to the medical field will help improve surgical accuracy, reduce operation times, and enhance patient safety. Therefore, it is important to develop more enhanced stereoscopic medical devices.

Nintendo Wii Remote Controllers for Head Posture Measurement: Accuracy, Validity, and Reliability of the Infrared Optical Head Tracker

PURPOSE To evaluate the accuracy, validity, and reliability of a newly developed infrared optical head tracker (IOHT) using Nintendo Wii remote controllers (WiiMote; Nintendo Co. Ltd., Kyoto, Japan) for measurement of the angle of head posture. METHODS The IOHT consists of two infrared (IR) receivers (WiiMote) that are fixed to a mechanical frame and connected to a monitoring computer via a Bluetooth communication channel and an IR beacon that consists of four IR light-emitting diodes (LEDs). With the use of the Cervical Range of Motion (CROM; Performance Attainment Associates, St. Paul, MN) as a reference, one- and three-dimensional (1- and 3-D) head postures of 20 normal adult subjects (20-37 years of age; 9 women and 11 men) were recorded with the IOHT. RESULTS In comparison with the data from the CROM, the IOHT-derived results showed high consistency. The measurements of 1- and 3-D positions of the human head with the IOHT were very close to those of the CROM. The correlation coefficients of 1- and 3-D positions between the IOHT and the CROM were more than 0.99 and 0.96 (P < 0.05, Pearsons correlation test), respectively. Reliability tests of the IOHT for the normal adult subjects for 1- and 3-D positions of the human head had 95% limits of agreement angles of approximately ±4.5° and ±8.0°, respectively. CONCLUSIONS The IOHT showed strong concordance with the CROM and relatively good test-retest reliability, thus proving its validity and reliability as a head-posture-measuring device. Considering its high performance, ease of use, and low cost, the IOHT has the potential to be widely used as a head-posture-measuring device in clinical practice.

Effect of counter-pulsation control of a pulsatile left ventricular assist device on working load variations of the native heart

BackgroundWhen using a pulsatile left ventricular assist device (LVAD), it is important to reduce the cardiac load variations of the native heart because severe cardiac load variations can induce ventricular arrhythmia. In this study, we investigated the effect of counter-pulsation control of the LVAD on the reduction of cardiac load variation.MethodsA ventricular electrocardiogram-based counter-pulsation control algorithm for a LVAD was implemented, and the effects of counter-pulsation control of the LVAD on the reduction of the working load variations of the left ventricle were determined in three animal experiments.ResultsDeviations of the working load of the left ventricle were reduced by 51.3%, 67.9%, and 71.5% in each case, and the beat-to-beat variation rates in the working load were reduced by 84.8%, 82.7%, and 88.2% in each ease after counter-pulsation control. There were 3 to 12 premature ventricle contractions (PVCs) before counter-pulsation control, but no PVCs were observed during counter-pulsation control.ConclusionsCounter-pulsation control of the pulsatile LVAD can reduce severe cardiac load variations, but the average working load is not markedly affected by application of counter-pulsation control because it is also influenced by temporary cardiac outflow variations. We believe that counter-pulsation control of the LVAD can improve the long-term safety of heart failure patients equipped with LVADs.

Enhanced beam-steering-based diagonal beamforming algorithm for binaural hearing support devices.

In order to improve speech intelligibility for hearing-impaired people in various listening situations, it is necessary to diversify the possible focusing directions of a beamformer. In a previous report, the concept of binaural beam-steering that can focus a beamformer in diagonal directions was applied to a binaural hearing aid; however, in the previously proposed protocol, the effective frequency range for consistent diagonal beam-steering was limited to the 200-750 Hz range, which is far narrower than that of normal speech signals (200-4000 Hz). In this study, we proposed a modified binaural diagonal beam-steering technique that can reduce the focusing-direction deviations at high input frequencies up to 4000 Hz by introducing a new correction factor to the original protocol that can reduce the differences in gradient between the signal and the noise components at frequencies up to 4000 Hz. In simulation tests, the focusing effect of the proposed algorithm was more consistent than conventional algorithms. The deviations between the target and the focusing directions were reduced 27% in the left device and 6% in the right device with 45° steering at a 4000 Hz input signal, and were reduced 3% in the left device and 25% in the right device with 135° steering. On the basis of the experimental results, we believe that the proposed algorithm has the potential to help hearing-impaired people in various listening situations.

Development of an Implantable Intrathecal Drug Infusion Pump

An intrathecal drug infusion system has been designed, manufactured and tested. The system is composed of a drug reservoir and a pump/controller assembly. The drug reservoir made of SUS316L is a negative pressure gas chamber enclosing a bellows type drug chamber. The pump/controller assembly includes a bacterial filter, a controller circuit board, a battery and a micropump, and is connected to a catheter for intrathecal infusion. The micropump implements a peristaltic pumping of the drug by a sequential motion of three pairs of cam and cam-follower. In vitro performance tests were conducted with prototypes.

An Environment‐Adaptive Management Algorithm for Hearing‐Support Devices Incorporating Listening Situation and Noise Type Classifiers

In order to provide more consistent sound intelligibility for the hearing-impaired person, regardless of environment, it is necessary to adjust the setting of the hearing-support (HS) device to accommodate various environmental circumstances. In this study, a fully automatic HS device management algorithm that can adapt to various environmental situations is proposed; it is composed of a listening-situation classifier, a noise-type classifier, an adaptive noise-reduction algorithm, and a management algorithm that can selectively turn on/off one or more of the three basic algorithms-beamforming, noise-reduction, and feedback cancellation-and can also adjust internal gains and parameters of the wide-dynamic-range compression (WDRC) and noise-reduction (NR) algorithms in accordance with variations in environmental situations. Experimental results demonstrated that the implemented algorithms can classify both listening situation and ambient noise type situations with high accuracies (92.8-96.4% and 90.9-99.4%, respectively), and the gains and parameters of the WDRC and NR algorithms were successfully adjusted according to variations in environmental situation. The average values of signal-to-noise ratio (SNR), frequency-weighted segmental SNR, Perceptual Evaluation of Speech Quality, and mean opinion test scores of 10 normal-hearing volunteers of the adaptive multiband spectral subtraction (MBSS) algorithm were improved by 1.74 dB, 2.11 dB, 0.49, and 0.68, respectively, compared to the conventional fixed-parameter MBSS algorithm. These results indicate that the proposed environment-adaptive management algorithm can be applied to HS devices to improve sound intelligibility for hearing-impaired individuals in various acoustic environments.

Clinical evaluation of the performance of a blind source separation algorithm combining beamforming and independent component analysis in hearing aid use

There have been several reports on improved blind source separation algorithms that combine beamforming and independent component analysis. However, none of the prior reports verified the clinical efficacy of such combinational algorithms in real hearing aid situations. In the current study, we evaluated the clinical efficacy of such a combinational algorithm using the mean opinion score and speech recognition threshold tests in various types of real-world hearing aid situations involving environmental noise. Parameters of the testing algorithm were adjusted to match the geometric specifications of the real behind-the-ear type hearing aid housing. The study included 15 normal-hearing volunteers and 15 hearing-impaired patients. Experimental results demonstrated that the testing algorithm improved the speech intelligibility of all of the participants in noisy environments, and the clinical efficacy of the combinational algorithm was superior to either the beamforming or independent component analysis algorithms alone. Despite the computational complexity of the testing algorithm, our experimental results and the rapid enhancement of hardware technology indicate that the testing algorithm has the potential to be applied to real hearing aids in the near future, thereby improving the speech intelligibility of hearing-impaired patients in noisy environments.

Optimal pressure regulation of the pneumatic ventricular assist device with bellows-type driver

The bellows-type pneumatic ventricular assist device (VAD) generates pneumatic pressure with compression of bellows instead of using an air compressor. This VAD driver has a small volume that is suitable for portable devices. However, improper pneumatic pressure setup can not only cause a lack of adequate flow generation, but also cause durability problems. In this study, a pneumatic pressure regulation system for optimal operation of the bellows-type VAD has been developed. The optimal pneumatic pressure conditions according to various afterload conditions aiming for optimal flow rates were investigated, and an afterload estimation algorithm was developed. The developed regulation system, which consists of a pressure sensor and a two-way solenoid valve, estimates the current afterload and regulates the pneumatic pressure to the optimal point for the current afterload condition. Experiments were performed in a mock circulation system. The afterload estimation algorithm showed sufficient performance with the standard deviation of error, 8.8 mm Hg. The flow rate could be stably regulated with a developed system under various afterload conditions. The shortcoming of a bellows-type VAD could be handled with this simple pressure regulation system.

Effect of the degree of sensorineural hearing impairment on the results of subjective evaluations of a noise-reduction algorithm

Performed subjective evaluations using subjects with various hearing impairments.Compared the perceptual effects of the three noise-reduction algorithms.No significant differences in the preference and intelligibility improvement.Significant differences in the quality improvement. Subjective evaluations of the perceptual effects of a specific noise-reduction (NR) algorithm for hearing-support devices have frequently been performed using normal-hearing (NH) participants because of financial, time, and ethical constraints. However, the perceptual effects of the same NR algorithm in a subjective evaluation may differ in accordance with the degree of hearing ability of the subjects. In this study, we performed subjective evaluations using 45 participants with different degrees of sensorineural hearing impairment to assess whether the perceptual effects of a certain NR algorithm in aspects of preference, quality, and intelligibility are affected by the degree of hearing ability. We recruited 15 NH subjects, 15 sensorineural hearing-impaired (SNHI) subjects with moderate hearing loss, and 15 SNHI subjects with moderately-severe hearing loss, and performed preference, intelligibility, and quality tests using three NR algorithms. Experimental results demonstrated that the perceptual effects of a certain NR algorithm were not significantly affected by the degree of hearing ability in regards to preference and improvement of speech intelligibility, but were significantly affected in regards to the improvement of speech quality.

A Diagonal‐Steering‐Based Binaural Beamforming Algorithm Incorporating a Diagonal Speech Localizer for Persons With Bilateral Hearing Impairment

Previously suggested diagonal-steering algorithms for binaural hearing support devices have commonly assumed that the direction of the speech signal is known in advance, which is not always the case in many real circumstances. In this study, a new diagonal-steering-based binaural speech localization (BSL) algorithm is proposed, and the performances of the BSL algorithm and the binaural beamforming algorithm, which integrates the BSL and diagonal-steering algorithms, were evaluated using actual speech-in-noise signals in several simulated listening scenarios. Testing sounds were recorded in a KEMAR mannequin setup and two objective indices, improvements in signal-to-noise ratio (SNRi ) and segmental SNR (segSNRi ), were utilized for performance evaluation. Experimental results demonstrated that the accuracy of the BSL was in the 90-100% range when input SNR was -10 to +5 dB range. The average differences between the γ-adjusted and γ-fixed diagonal-steering algorithms (for -15 to +5 dB input SNR) in the talking in the restaurant scenario were 0.203-0.937 dB for SNRi and 0.052-0.437 dB for segSNRi , and in the listening while car driving scenario, the differences were 0.387-0.835 dB for SNRi and 0.259-1.175 dB for segSNRi . In addition, the average difference between the BSL-turned-on and the BSL-turned-off cases for the binaural beamforming algorithm in the listening while car driving scenario was 1.631-4.246 dB for SNRi and 0.574-2.784 dB for segSNRi . In all testing conditions, the γ-adjusted diagonal-steering and BSL algorithm improved the values of the indices more than the conventional algorithms. The binaural beamforming algorithm, which integrates the proposed BSL and diagonal-steering algorithm, is expected to improve the performance of the binaural hearing support devices in noisy situations.