Precise correction for γ-ray attenuation in skull bone has been a significant problem in obtaining quantitative single photon emission computed tomography (SPECT) images. The correction for γ-ray attenuation is approximately proportional to the density and thickness of the bone under investigation. If the acoustic impedance and the speed of sound in bone are measurable using ultrasonic techniques, then the density and thickness of the bone sample can be calculated. Whole bone usually consists of three layers, and each layer has a different ultrasonic character. Thus, the speed of sound must be measured in a small section of each layer in order to determine the overall density of whole bone. It is important to measure the attenuation constant in order to determine the appropriate level for the ultrasonic input signal. We have developed a method for measuring the acoustic impedance, speed of sound, and attenuation constant in a small region of a bone sample using a fused quartz rod as a transmission line. In the present study, we obtained the following results: impedance of compact bone; 5.30(±0.40)×106 kg/(m2s), speed of sound; 3780±250 m/s, and attenuation constant; 2.70±0.50 Np/m. These results were used to obtain the densities of compact bone, spongy bone and bone marrow in a bovine bone sample and as well as the density of pig skull bone, which were found to be 1.40±0.30 g/cm3, 1.19±0.50 g/cm3, 0.90±0.30 g/cm3 and 1.26±0.30 g/cm3, respectively. Using a thin solid transmission line, the proposed method makes it possible to determine the density of a small region of a bone sample. It is expected that the proposed method, which is based on ultrasonic measurement, will be useful for application in brain SPECT.

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.

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.

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In this report, I describe an experimental analysis of the acoustic mechanism of the suikinkutsu. The sound of the suikinkutsu consists of an original sound generated by water drops striking the surface of the water in the suikinkutsu and a reverberant sound generated by the original sound. The reverberant sound is the sound we hear through the observation holes of the suikinkutsu. The body of the suikinkutsu also has its own natural frequencies and vibrates in synchronism with the natural frequencies of the oscillation modes of air inside it, affecting the tonal quality of the sound emitted from the suikinkutsu. If all of the natural frequencies and time constants of the reverberant sound are optimized, the suikinkutsu can produce a sound of good tonal quality. In this study, we investigate the relationships between the original sound and the reverberant sound emitted from the suikinkutsu. We propose an experimental formula representing the natural frequencies of the suikinkutsu and examine the validity of this formula.