Masasumi Yoshizawa

Development of Scanning Method for Puncture Needle-Type Ultrasonography

In this paper, we propose a scanning method for determining the acoustic impedance difference for puncture needle-type ultrasonography using a thin rod. The principle of the proposed scanning method is based on the movements of the end point of a lever. A thin rod is placed on the fulcrum, there by forming a lever. When the end point of the thin rod rotates clockwise forming a circle, the other side of the thin rod moves counterclockwise also forming a circle. By sensing the surface of the sample as a function of the angle made by the thin rod and center axis, scanning can be performed. First, we confirmed that the scanning is possible using the lever; moreover, the movement of the end of the rod is related to that of the other end of the lever. Next, we also confirmed that a one-dimensional image of the amplitude of an interference signal shows the difference in impedance between the polyethylene (PE), acrylic (AC), and polypropylene (PP). The experimental results show that the method is useful for scanning.

Imaging Method for Acoustic Impedance Difference for Puncture Needle-Type Ultrasonography using a Thin Rod with Focusing End Face

In this paper, we propose an imaging method for acoustic impedance difference for puncture needle-type ultrasonography. The difference in acoustic impedance between benign and malignant tissues will provide valuable diagnostic information. In this experiment, a thin rod that has a concave polished end face was constructed using a fused quartz with a diameter of 1 mm and a focus length of 0.3 mm. An ultrasonic wave emitted from the concave end face of the rod is focused on a tissue. The difference in acoustic impedance was determined by the reflection-type interference-based acoustic impedance measurement method. We confirmed that the image shows the difference in impedance between the polyethylene (PE) plate and acrylic rod with a diameter of 3.5 mm embedded therein. The experimental results show that the method is useful for puncture needle-type ultrasonography.

Transducer Vibration Method for Interference-Based Reflection-Type In Vivo Measurement for Acoustic Impedance of Bone

In this paper, we describe about a transducer vibration method for the measurement of acoustic impedance of bone, which enables to shorten the time of measurement without binding the patient. In the interference-based reflection-type measurement method, body motion is a problem; therefore, it is desirable to complete measurement in a short time. In addition, to eliminate the effect of motion, the part of the body to be measured is usually bound firmly. However, considering the burden on the subject, this is not desirable. This method allows acoustic impedance to be measured in 1/6 the time required by the conventional method without binding the patient firmly.

High Signal-to-Noise Ratio Ultrasonic Point Detection Method using a Fused Quartz Rod as a Pulse Compression Filter and a Sensor

In this paper we propose a method to detect ultrasound with high signal-to-noise ratio (S/N) at a point on the surface of a material. To obtain high S/N, we applied an frequency-modulation (FM) pulse compression method as used in radar. We also used a fused quartz rod for point detection, at the same time using it for the pulse compression filter. The concept is demonstrated with an image reconstructed using a computer tomography algorithm.

A Method for Suppressing the Unwanted Signal Due to the L(0, 2) Mode in an L(0, 3) Mode Pulse Compression Filter by Means of a Tapered Cylindrical Fused Quartz Rod

In an attempt to improve a pulse compression filter using a fused quartz rod, we devised a method to eliminate an unwanted L(0, 2) signal over a wide frequency range and, at the same time, obtain sufficient time dispersion. We found that the suppression of the L(0, 2) unwanted signal is realized using the freouency band where the change of patterns of L(0, 2) and L(0, 3) modes is slight. Sufficient time dispersion is obtained using a tapered cylindrical fused quartz rod.

Development of a bone-mimicking phantom and measurement of its acoustic impedance by the interference method

Fractures due to osteoporosis have increasingly become a problem. In order to investigate methods that measure osteoporosis using ultrasound, an appropriate bone-mimicking phantom is required. However, no appropriate phantom is currently available. Therefore, we have developed a bone-mimicking phantom that disperses calcium in oil jelly (a plasticizing material that contains oil and resin) and measured its acoustic impedance using the interference method. The phantoms were dispersed in oil jelly with calcium weight percentages of 50, 55 and 59%. The experiment was conducted at 3.5 MHz. The impedances of the phantoms were 2.0, 2.2 and 2.6 /spl times/ 10/sup 6/ kg/m/sup 2//spl middot/s, respectively. In order to confirm the change in acoustic impedance due to the varying calcium content, impedance measurements were also conducted by measuring the speed of sound and the density of the phantoms. The measured values for these two methods were similar with an error of around +10%.

Tissue imaging using the transmission of 100-MHz-range ultrasound through a fused quartz fiber

We have studied transmission methods of high-frequency ultrasonic waves through a thin fiber for direct observation of the microscopic image of the tissue. We reported previously that C-mode images of an artificial bone and an animal bone placed in water were obtained by reflection method using a fused quartz fiber as the probe. In this paper, we describe that the C-mode images of the tissue on the glass in water were obtained by penetration method.

Development of Robust Sensing System for Puncture Needle-Type Ultrasonography

In this paper, we propose a robust sensing system that protects a thin rod sensor used in the measurements of acoustic impedance in puncture needle-type ultrasonography. In this ultrasonograpy, an ultrasonic interference method using the thin rod sensor is applied. Since the thin rod made of fused quartz is not robust, a protector is required for the thin rod sensor in in vivo measurement. Therefore, the sensing system has consisted of a thin rod sensor and a hollow pipe with a top cover to protect the sensor. For the observation of a low-impedance material such as biological tissue, the measurement method requires an impedance-transforming layer as the top cover. However, since the optimum thickness of the layer decreases as the measurement frequency increases, the decrease in the thickness causes deformation of the layer. The deformation introduces an error in the measurement. To avoid such a problem, we developed a robust sensing system. The system consists of a quarter-wavelength layer that functions as an impedance transformer and a half-wavelength (or multiple times of a half-wavelength) layer that provides the robustness of the system. We confirmed experimentally the effectiveness of the robust sensing system for acoustic impedance measurement of a tissue sample by the acoustic impedance difference method. The experimental results show that the robust sensing system is useful for puncture needle-type ultrasonography.

A study for B-mode imaging using 100-MHz-range ultrasound through a fused quartz fiber

We have studied transmission methods of high-frequency ultrasonic waves through a thin fiber for direct observation of the microscopic image of the tissue. We reported previously that the C-mode images of the tissue on the glass placed in water were obtained by penetration method using a fused quartz fiber as the probe. In this paper, we describe that the B-mode image of a sample tissue in water was obtained by reflection method using the focused ultrasonic beam.

Attenuation Compensation of Ultrasonic Wave in Soft Tissue for Acoustic Impedance Measurement of In vivo Bone by Transducer Vibration Method

In this paper, we describe a method of compensating the attenuation of the ultrasound caused by soft tissue in the transducer vibration method for the measurement of the acoustic impedance of in vivo bone. In the in vivo measurement, the acoustic impedance of bone is measured through soft tissue; therefore, the amplitude of the ultrasound reflected from the bone is attenuated. This attenuation causes an error of the order of -20 to -30% when the acoustic impedance is determined from the measured signals. To compensate the attenuation, the attenuation coefficient and length of the soft tissue are measured by the transducer vibration method. In the experiment using a phantom, this method allows the measurement of the acoustic impedance typically with an error as small as -8 to 10%.