Yoshiki Nagatani

Numerical and experimental study on the wave attenuation in bone--FDTD simulation of ultrasound propagation in cancellous bone.

In cancellous bone, longitudinal waves often separate into fast and slow waves depending on the alignment of bone trabeculae in the propagation path. This interesting phenomenon becomes an effective tool for the diagnosis of osteoporosis because wave propagation behavior depends on the bone structure. Since the fast wave mainly propagates in trabeculae, this wave is considered to reflect the structure of trabeculae. For a new diagnosis method using the information of this fast wave, therefore, it is necessary to understand the generation mechanism and propagation behavior precisely. In this study, the generation process of fast wave was examined by numerical simulations using elastic finite-difference time-domain (FDTD) method and experimental measurements. As simulation models, three-dimensional X-ray computer tomography (CT) data of actual bone samples were used. Simulation and experimental results showed that the attenuation of fast wave was always higher in the early state of propagation, and they gradually decreased as the wave propagated in bone. This phenomenon is supposed to come from the complicated propagating paths of fast waves in cancellous bone.

Spectroscopic visualization of sound-induced liquid vibrations using a supramolecular nanofibre

The question of whether sound vibration of a medium can bring about any kind of molecular or macromolecular events is a long-standing scientific controversy. Although it is known that ultrasonic vibrations with frequencies of more than 1 MHz are able to align certain macromolecules in solution, no effect has yet been reported with audible sound, the frequency of which is much lower (20-20,000 Hz). Here, we report on the design of a supramolecular nanofibre that in solution becomes preferentially aligned parallel to the propagation direction of audible sound. This phenomenon can be used to spectroscopically visualize sound-induced vibrations in liquids and may find application in a wide range of vibration sensing technologies.

Propagation of two longitudinal waves in a cancellous bone with the closed pore boundary

Ultrasound propagation in cancellous bone (porous media) under the condition of closed pore boundaries was investigated. A cancellous bone and two plate-like cortical bones obtained from a racehorse were prepared. A water-immersion ultrasound technique in the MHz range and a three-dimensional elastic finite-difference time-domain (FDTD) method were used to investigate the waves. The experiments and simulations showed a clear separation of the incident longitudinal wave into fast and slow waves. The findings advance the evaluation of bones based on the two-wave phenomenon for in vivo assessment.

Effect of Boundary Condition on the Two-Wave Propagation in Cancellous Bone

The two-wave phenomenon in a cancellous bone surrounded by a cortical bone was investigated using the specimens obtained from large mammals. Measurements were performed using laboratory-built poly(vinylidene fluoride) (PVDF) transducers excited by a one-cycle sinusoidal wave at 1 MHz. In addition to the experimental ultrasonic measurements, the finite-difference time-domain (FDTD) simulation was performed using the X-ray micro computed tomography (micro-CT) images (resolution: 48 µm) of the specimens. The clear separation of fast and slow waves was not seen in a specimen where the boundary of the cancellous and cortical bones was ambiguous. On the other hand, the clear separation of fast and slow waves was observed in a specimen where the boundary of cancellous and cortical bones was clear. These results indicate that the boundary characteristics between the cancellous and cortical bones strongly affect the two wave phenomenon. We should pay attention to this point in the case of in vivo assessment using this phenomenon.

Wavelet Transform Analysis of Ultrasonic Wave Propagation in Cancellous Bone

Ultrasonic waves targeted on cancellous bone separates into fast and slow waves according to the alignment of bone trabeculae. The characteristics of the specimen, however, can sometimes result in ambiguous wave separation. In this study, we proposed using wavelet transform as a new method of analyzing ultrasonic waveforms. Using continuous wavelet transform, two components were separated by fitting two-dimensional Gaussian function in scalogram. The relationship between bone volume fraction and the peak amplitude of the lower- and higher-frequency components showed a clear negative correlation; conversely, the relationship between bone volume fraction and the peak value ratio of the lower- and higher-frequency components showed a positive correlation. We recoginized lower-frequency component as the multiple reflections (forward scattering) in cancellous bone.

Comparison between bone-conducted ultrasound and audible sound in speech recognition

Conclusion: This study showed that it is possible to transmit language information using bone-conducted ultrasound (BCU) in normal-hearing subjects. Our results suggest the possibility of a difference in speech recognition between BCU and air-conducted audible sound (ACAS). Objective: Ultrasound was audible when delivered by bone conduction. Some profoundly deaf subjects as well as normal-hearing subjects can discriminate BCU whose amplitude is modulated by different speech sounds. These findings suggest the usefulness of developing a bone-conducted ultrasonic hearing aid (BCUHA). However, the characteristics of BCU are still poorly understood. The aim of the present study was to compare BCU and ACAS in terms of their associated speech perception tendency and to investigate the different perceptual characteristics of BCU and ACAS. Subjects and methods: Speech discrimination tests using both BCU and ACAS were performed with normal-hearing subjects. BCU and ACAS were compared for intelligibility and hearing confusion. Results: With BCU, the maximum percentage correct totaled about 75%. Our comparison of the hearing confusion with ACAS and BCU according to the individual syllabic nuclear group showed a clear difference in the incorrect rates. In addition, the stimulus nuclear groups were often perceived in other nuclear groups in BCU.

Propagation of ultrasonic longitudinal wave in the cancellous bone covered by the subchondral bone of bovine femur

In order to understand the mechanism of two longitudinal wave propagation phenomena in the cancellous bone, we have tried to investigate the wave separation in the bone specimen by changing the main frequency of the longitudinal pulse wave. Here, we have used the specimens obtained from the end of bovine femur, which are covered by cartilage and subchondral bone. The pore size changed gradually in the specimens. We have then found the effect of the structure on the wave separation. The FDTD simulation with the CT image of the specimens showed similar behavior of wave propagation.

Evaluation of acoustic environments using deteriorated speech sound

Aged or hearing‐impaired people require better acoustical environments for higher QOL. Many methods of evaluating the quality of speech in acoustical environments have been developed. However, since they mainly focus on quality of speech in bad conditions (e.g. environments with huge noise or long reverberation), they are not suited for evaluations in generic environments such as normal houses or public facilities for aged people. For instance, the scores of D value (deutlichkeit) or speech transmission index (STI) are too high and not sensitive enough to refer to such environments. The intelligibility test using normal speech sounds cannot clarify the differences between different room environments because the intelligibility scores reach almost 100 percent in ordinary room environments. Therefore, we proposed a new evaluation method using deteriorated speech sounds. In this method, signal‐processed speech sounds are presented to trial subjects under target sound environments. In this study, Japanese mon...

Evaluation of prosodic and segmental change in speech-modulated bone-conducted ultrasound by mismatch fields

Speech-modulated bone-conducted ultrasound (BCU) can transmit speech sounds for some profoundly deaf individuals. Hearing aids using BCU are considered to be a novel hearing system for such individuals. In our previous study, the speech discrimination for speech-modulated BCU was objectively confirmed using a magnetoencephalography. Moreover, in our previous behavioral study, prosodic information for speech-modulated BCU could also be discriminated in the normal hearing. However, the prosodic discrimination for speech-modulated BCU has not objectively been studied. In order to evaluate the prosodic discrimination for speech-modulated BCU, mismatch fields (MMFs) elicited by prosodic and segmental change were measured for speech-modulated BCU and air-conducted speech. Ten Japanese participants with normal hearing took part in this study. Stimuli re-synthesized from the speech of a native Japanese female adult were used. Standard stimulus was /itta/ with a flat pitch pattern, and two deviant stimuli were /itta?/ with a rising pitch pattern and /itte/ with a flat pitch pattern. All and nine participants elicited the prominent MMF elicited by the prosodic and segmental change for the speech-modulated BCU, respectively. The moment of MMF components for speech-modulated BCU was significantly smaller than those for air-conducted speech, while no difference in the MMF latency elicited by the prosodic and segmental change were observed between both stimulus conditions. Comparing the MMFs elicited by prosodic and segmental change, no significant differences were observed for both stimulus conditions. Thus, it is suggested that the prosodic change can be discriminate to the same degree as segmental change even for speech-modulated BCU. However, discrimination capability for speech-modulated BCU is slightly inferior to that for air-conducted speech.

Duration-dependent growth of N1m for speech-modulated bone-conducted ultrasound

Bone-conducted ultrasound (BCU) modulated by speech sound is recognized as speech sound and activates the auditory cortex similar to audible sound. To investigate the mechanisms of perception, the effects of stimulus duration on N1m were compared among air-conducted audible speech sound (AC speech), AC speech with carrier BCU and speech-modulated BCU in eight native Japanese with normal hearing. The Japanese vowel sound /a/ was used as a stimulus with durations of 10, 15, 20, 30, 40 and 60 ms. Comparison between AC speech with and without carrier showed that the presentation of carrier had no effect on N1m evoked by AC speech. Comparison among the three conditions showed that N1m amplitude for speech-modulated BCU differed from that for the two AC speeches. Moreover, N1m amplitude growth saturated at 40 ms for speech-modulated BCU, and at 20 ms for two AC speeches. These results suggest a difference in temporal integration of N1m between speech-modulated BCU and AC speech. Considering these results, it is reasonable to conclude that N1m evoked by speech-modulated BCU is influenced mainly by the ultrasonic component rather than demodulated audible sound. Given this finding, the notion needs to be considered that the mechanisms underlying perception and recognition of speech-modulated BCU depend on the ultrasonic component to some extent.