Yasuhito Takeuchi

Numerical Analysis of Sound Pressure Fields Focused by Phase Continuous Fresnel Lens Using Finite Difference Time Domain Method

A convex lens using room temperature vulcanization (RTV) silicone rubber, whose acoustic impedance matches well with that of water, is a typical acoustic lens. However, some considerations are required to reduce the thickness of the lens because attenuation is very large in the RTV silicone rubber. Therefore, we have proposed a phase continuous Fresnel lens, which has some devices to keep the phase continuous in the entire lens aperture without an unequal phase on the exit side. This lens is fabricated by removing its thickness in a staircase shape in which the difference between each step is an integer multiple of wavelength. In this study, the sound fields focused by the phase continuous Fresnel lens are analyzed using a finite difference time domain (FDTD) method. Using a two-dimensional (2-D) FDTD method, we surveyed the sound pressure field of the focal region by changing the burst pulse length, angle of incidence, and frequency. Results show that the lens gain of the phase continuous Fresnel lens is greater than that of the convex lens, that focusing characteristics depend on the burst pulse length of sound source signal, and also that focal points strongly depend on frequency. In another analysis using a three-dimensional FDTD method, we found that the main lobe is the same as that indicated by 2-D analysis results and that the level outer of the main lobe is lower than that in the 2-D analysis results.

On the interaction between ultrasound and contrast agents during Doppler investigations

Knowledge of interaction mechanisms between ultrasound (US) and contrast agents (CA) suspended in blood is important for a correct interpretation of clinical investigation results. Experiments performed in different laboratories have shown that, as a consequence of primary radiation force, CA tend to move away from the US transducer. Accordingly, Doppler spectra produced by particles suspended in moving water turn out to be significantly altered from what is theoretically expected. The purpose of this paper is twofold. First, an original model describing the bubble dynamics as the outcome of the balance between US radiation force and fluid drag force is validated for the case in which bubbles are suspended in blood. The high fluid viscosity is shown to prevent significant bubble deviations from the unperturbed fluid streamlines so that, in large vessels, a residual spectral distortion may exist only at the highest intensity levels permitted by current regulations. Finally, the relative importance and differences between the effect of primary radiation force and streaming mechanisms that, in principle, could lead to similar effects, are discussed.

An experience of PNN-PT-PZ high-k piezoelectric ceramics aiming for medical imaging transducers

Beyond the k=0.7 class PZT families, our ever-lasting desire is to have more k to extend bandwidth and efficiency. A material within ceramic family, PNN-PT-PZ (PbNi/sub 1/3/Nb/sub 2/3/O/sub 3/-PbTiO/sub 3/-PbZrO/sub 3/), is an easier candidate, however, with k=0.8 around, in between PZT family and single crystal family. Although including a die-pressing step, the material can be prepared using conventional solid solution method similar to the one we used to make PZT. In this study, several pieces of 25 mm-dia., 1 mm-t, sintered, shaped, electrode-attached and poled PNN-PT-PZ discs are put up for evaluation. For control, almost same size PZT-5 (Fuji Ceramics C6) discs are hired for comparison. As single element air backed transducer, PNN-PT-PZ disc shows almost 20% more signaling bandwidth than conventional PZT, in air and with water loaded situations. 2-D half (or 2/3 thickness) diced structure also has been tried with similar conclusion, which suggests it could be also workable with such performance improvement, including 1D to 2D arrays for imaging and/or Doppler systems.

Effects of pulsed ultrasound on development and glucose uptake of preimplantation mouse embryos

The effects of pulsed ultrasound (US) on early mouse embryos were investigated. Two-cell embryos contained in oviducts were irradiated to US (1.875 MHz with an I (SPTA) of 2.96 W/cm(2)) in an experimental unit for either 1 or 5 min (exposure groups). The embryos were cultured to examine the rate of developing to blastocysts, and the uptake of 2-deoxyglucose (2-DG) into blastocysts was measured to evaluate their viability. The rates in the exposure groups were essentially the same, with those of the embryos treated similarly in the unit unless being exposed to US (nonexposure groups). However, they were lower than that of embryos not treated in the experimental unit (a control group). There were no significant differences of 2-DG uptake among the 1-min exposure, 1-min nonexposure, and control groups. The uptake in the 5-min exposure group did not differ from that in the 5-min nonexposure group; however, uptake in both groups was lower than that in the control group. Pulsed US for 1 min did not affect viability of preimplantation mouse embryos.

Comparison of Apodized Linear FM Chirp and Complementary Series Phase Encoding for Diagnostic Ultrasound Imaging by Reduced Peak Power Transmission Waveform

A cosine-square apodized linear FM chirp signal is proposed for a spread energy transmission wave form to be used in diagnostic ultrasound imaging with reduced peak power for insonification to improve patient safety. Comparison is made with complementary series phase encoding in terms of time sidelobe levels. Results indicate that apodized chirp waveform could have a time sidelobe of less than -60 dB under practical conditions, while being relatively robust against media dispersion. Since this waVe form can converge on each time by itself without aid of another sequence, inter-sequence Doppler shift is almost no problem for the time sidelobe.

Substitution of Vocal Folds for Voice Generation by Means of Intra-Oral Pulse Generator

Human beings vocal folds act as a carrier pulse (or pitch-pulse, as said) for normal voice, with that, other parameters such as oral cavity structure or its elements positioning, shape this signal in what we know as speech. This characterizes normal voice as signals with a high concentration of energy at the lower bands of the frequency spectrum [11]. This research defines and implements a device capable of generating a carrier signal (pitchpulse) capable of, eventually, acting as a substitute for the vocal folds. This device generates a constant low frequency periodic pulse that allows the user to shape it when used intra-orally, just as one would do for normal speech creation. This research also evaluates the results of using such substituting device, and compares it with the results of normal speech. Keywords—non-audible speech; voice generation; spectral energy; carrier; frequency spectrum; vocal folds I. PURPOSE The purpose of this study is to design a device capable of generating a periodic signal, which would be able of transmitting non-audible speech. Such generated signal acts as a carrier, emulating real-voice when transmitting non-audible speech; this is, as vocal folds do. Non-audible speech refers to the changes in the oral cavity which modulate vocal tract impulses to generate the voice. In this case, the human vocal tract is substituted by an artificial pulse-train generator specifically designed for such task. II. PREVIOUS STUDIES IN THE FIELD Although studies in non-audible speech data have a wide history, efforts are mainly centered on transmission of this data, or even in recognizing this data for later voice generation [8] and [10]. Vocal folds substitute devices is still an unpopulated area but has some precedents in studies achieved by N. MacLeod [14] for telephony or Katz et al. [13] for a larynx substitution device. However, the purpose of this study is to substitute vocal folds as they are, and enable the subject to create voice without its vocal folds. More recently, there has been an approach by A. Passos and Prof. Y. Takeuchi on the use of extra-oral low frequency signals as a substitute for the vocal folds [6]. Or researches on unvoiced signals properties like [2], [9] and [12], where the conclusion that in order to achieve pseudo-voice regeneration of unvoiced signals (whispering voice), only the higher segment of the speech frequency spectrum is necessary has been reached. III. FURTHER STUDIES Taking into account that the purpose of this study is to design a carrier signal capable of carrying non-audible speech data, the scope of this research is still far from achieving the generation of voice from this non-audible data. However, thru enabling a subject to transmit such data, generation of voice can, eventually, be achieved by means of the methods described in this study. Such pseudo-voice generation can be achieved by, for example, playback of the autocorrelation of this signal. Pseudo-voice regeneration has, by far, much more implications and issues to be solved than this study intends to solve. IV. DEVICE FOR PULSE GENERATION A. Design The device features a low frequency pitch-pulse period which can be varied on demand to provide different types of pulse signals with differences in pulse duration, pulse frequency, etcetera. Figure 1. Schema of usage of the pulse-train generator as an intra-oral device The device has been designed for intra-oral use. The device has to be positioned at either the right or the left side of the oral cavity but always touching the cavity wall and facing to the inside of it. 978-1-4244-4131-0/09/

Adaptive Scan Sequence for Real-Time Ultrasound 3-D Imaging

25.00 ©2009 IEEE

Ultrasound 3-dimensional image processing using power Doppler image

An adaptive scan sequence is proposed for real-time ultrasound three-dimensional (3-D) imaging. Generally, the refresh rate of 3-D imaging is limited by the view window, resolution and sound speed in the human body. If the object is transformed or moved during the data set acquisition, the 3-D image will be distorted. To realize a high refresh rate for 3-D imaging, a reduction of the number of transmissions is required. Using a small number of transmissions results in a small view window or low resolution. In this paper, we propose a method to adaptively modify the spatial and temporal beam density according to the local motion of the object. We present 3-D images of a phantom with high frame rate, high resolution and wide view-angle window, significantly reducing the size of the full real scan raw data set.

Three-dimensional power Doppler sonography of tumor vascularity.

A new ultrasound three dimensional (3D) reconstruction method is presented. It can show blood flow geometry (one promising application of 3D techniques). For this purpose, the authors adopt power Doppler ultrasound images of vascular flow because power Doppler has slow speed detectability and much less angle dependence. Here, the authors introduce this 3D processing method for ultrasonic diagnostic images. Furthermore, they propose an endoscopic view image. This power Doppler based endoscopic view image can display interior views of flow in arterial branches, curved vessels and so on.