Kunihiro Chihara

New Approach to Noninvasive Manometry Based on Pressure Dependent Resonant Shift of Elastic Microcapsules in Ultrasonic Frequency Characteristics

To measure physiological pressure in situ, we have developed a new technique based on the principle that an elastic microcapsule in liquid changes its resonant frequency depending on the surrounding pressure. The following results were ohtained: 1) The frequency characteristics of transmission wave through microcapsules showed marked attenuation with a specific spectral peak, indicating the resonance of the microcapsules. 2) Pressure dependent change in amplitude of the attenuation peak increased linearly with the increment of pressure. 3) Pressure dependent resonant shifts were also observed in proportion to the pressure increment.

Principle of High-Speed Digital Subtraction Echography and the Potential for Clinical Applications

To improve time and spatial resolution of echography, we have developed a High-speed Digital Subtraction Echography. The principle is serial image subtraction of successive frames of high-speed B-mode echograms. This system elucidated: 1) initial myocardial contraction originating from the pacing point of an experimental ventricular premature contraction (VPC) in dogs. Substantially the same initial contraction appeared from the VPC focus in a human patient. 2) Local elasticity of arterial wall was assessed as the systolic fine radial extension. 3) Utilizing echoic particles in blood, the streamlines were also visualized.

Colour Visualization of Two-Dimensional Distribution of Intracardiac Flow Abnormalities by Multigate Doppler Technique

The detection of flow disturbances in the heart and great vessels by pulsed Doppler echocardiography has great potentials in the noninvasive assessment of valvular and shunt disease (1,2). Recent investigations (3-5) have suggested that the extent or the area of the flow disturbances may reflect the severity of the valvular abnormalities. Current advent of real-time, two-dimensional duplex Doppler echocardiography has provided a more exact localization of the sample volume in the heart and great vessels, and enabled us to evaluate the extent of the flow disturbances very accurately. However, it is sometimes difficult to determine the presence or absence of the flow disturbance from a representation of the audio spectrum, the time interval histogram, since this analysis is easily modified by improper setting and is sensitive to noise and signal amplitude. Although the multifilter soundspectrogram could express all information available in the pulsed Doppler signal, it is also qualitative. Thus, recent interest has focused on Fourier analysis as a possible method of quantitating flow disturbances from Doppler signals (7–10).

Non-Invasive Visualization and Estimation of Severity of Aortic Regurgitation by Multigated Pulsed Doppler Technique

Pulsed Doppler flowmetry has proved to be very sensitive and specific in the diagnosis of intracardiac regurgitation. However, conventional pulsed Doppler flowmeters are to some extent limited in the evaluation of regurgitant flow. In order to accurately and extensively examine regurgitant flow, it would be necessary to locate a sampling site where blood flow is being measured, on a two-dimensional cardiac image. Furthermore, it would be very benefitial to measure intracardiac flow simultaneously at multiple sites along the Doppler beam. For these reasons, we have newly developed a computer-based multigated pulsed Doppler flowmeter combined with an electronic beam sector scanning echocardiograph.

The flow mapping method using color Doppler device

A method for displaying a 2-D intracardiac blood flow vector is presented. The flow velocity along the beam is measured by a color Doppler device, and the 2-D velocity vector is estimated by a method based on the continuity equation in flow mechanics. The experimental results show that the system is effective for determining the intracardiac blood flow state.<<ETX>>

Methods of Measuring Blood Velocity

The hot-film anemometer is based on heat transfer from a small body placed in the fluid flow. This is a very small metal film which is sputtered or burned on a substrate or a mount. This small film is connected to a bridge circuit (Fig. 13.1) for the generation of heat by an electrical current. A servoamplifier feeds back the error voltage of the bridge circuit, so that the electrical resistance, which is a function of the film temperature, is kept constant. This type of electrical equipment is called a constant temperature anemometer (CTA). If heat loss from the film increases, due to the high velocity of the surrounding fluid, the film temperature falls and the electrical resistance decreases, which leads to the increase of error voltage of the bridge. In this situation, the feedback current or output voltage of the servoamplifier becomes a nonlinear function of the fluid velocity. The metal film should be covered by a thin layer of insulating material, usually quartz, which does not interfere significantly with the heat transfer.

An intracardiac blood flow vector mapping method

A method is presented to estimate the flow vector from the Doppler frequency measured by a color Doppler device and to image a flow vector using an arrow line on a color display. A theoretical background is provided by the continuity equation. It is shown that experimental results in model flow and clinical application are effective to understand intracardiac blood flow dynamics.<<ETX>>