Kinya Takamizawa

Diagnostic ultrasound imaging using two-dimensional transducer array probe

A diagnostic ultrasound system capable of electronically controlling a beam width not only in a scan direction but also in a slice direction orthogonal to the scan direction despite a relatively small circuit scale. The system is provided with an ultrasonic probe having a plurality of ultrasonic transducers arranged two-dimensionally, and a transmitting/receiving unit for use in scanning an ultrasonic beam, which is transmitted and received by selectively driving the ultrasonic transducers, in the scan direction, and focusing the ultrasonic beam in the slice direction. A driving signal is supplied in common to a plurality of transducers elements adjoining in the slice direction. An echo signal converted by transducers is not only subjected to control of a specified delay time in the scan direction but also received in time sequence and then subjected to control of at least a specified delay time in the slice direction. The echo signal thus-processed is produced into an ultrasound image.

An evaluation of an in vivo local sound speed estimation technique by the crossed beam method

An in vivo local sound speed estimation technique, using the crossed beam method, has been proposed and its applicability was evaluated. At first, the potential of this technique was studied by a mapping simulation using the ray tracing technique followed by an experiment with a cylindrical agar phantom. The simulation result showed that an exact measurement of local sound speed values was difficult, but the sound speed information for the local region (its relative magnitude to the surrounding medium) was emphasized as a refraction mapping pattern. The experimental results agreed well with the calculation results. Furthermore, a clinical application was performed, using the clinical system (modified electronic linear scanner), on two liver tumor patients.

An investigation of wavefront distortion correction: correction using averaged phase information and the effect of correction in one and two dimensions (medical US imaging)

A method for estimating arrival time fluctuation for wavefront distortion correction is proposed and compared with the cross-correlation method. The improvement of image quality achieved by these methods is almost the same under normal conditions. However, the proposed method underestimates phase aberration in the presence of increased severe noise, while estimates from the cross-correlation method fluctuate more than expected under the same condition. the effect of phase aberration on received signals has been confirmed experimentally to be a decrease in the similarity between signals. Beam patterns distorted by two-dimensional phase aberration are not improved by one-dimensional correction but are improved by two-dimensional correction.<<ETX>>

Ultrasonic Mass-Screening System for Breast Examination

A new ultrasonic mass-screening system for the early detection of breast cancer without palpation is described. This system has been developed in order to detect a tumor larger than 5 mm in size. The entire region where breast cancer may develop can be scanned at one time by rotating the 5 MHz waterproof array transducer in a water bath. The real-time B-mode image with a wide viewing width of 190 mm can be obtained by electronic linear scanning. The screening time is less than 5 minutes per examinee. This trial system is confirmed to be effective for clinical mass-screening.

High resolution electronic-linear-scanning ultrasonic diagnostic equipment.

Abstract Electronic linear-scanning ultrasonic diagnostic equipment so far has suffered from low resolution. In the study presented here, improvement in resolution was obtained by electronic focusing and improved image quality by small-angle deflection. Electronic focusing is a method obtaining a narrow ultrasonic beam by means of phase control. Small-angle deflection is a method to increase scanning line density by deflecting slightly the ultrasonic beam also by means of phase control and thus to obtain information existing between the successive scanning lines of a conventional linear scanning system. Both experimental investigation and clinical application have shown that these techniques are highly effective in increasing lateral resolution and image quality. It has been confirmed that the equipment is practical for routine use.

A Fundamental Evaluation of In Vivo Local Velocity Measurement by Crossed Beam Method

The possibility of in vivo local velocity measurements by crossed beam method is described. The local velocity in the homogeneous medium is calculated from the known beam geometry and the difference in propagation time measured by several pairs of transducers. Each propagation time is determined by the center of moment for the echo from the cross region. Experimental results show the estimated error to be about 4%, but corrected values agree well with true values and the effectiveness of this new method is confirmed.

Maximum flow velocity estimation based on Doppler spectral analysis (haemodynamics)

A novel maximum-frequency estimator based on Doppler spectral analysis is presented and demonstrated on experimental results obtained by a newly constructed versatile pulse-echo Doppler system. The system employs a fast (12-b at 20 MHz) data-acquisition system that enables recording of raw RF data, which allows computation of Doppler spectra in software. Given a Doppler spectrum, the maximum-frequency estimator makes use of the total spectral power. This feature makes the estimator less susceptible to noise. The maximum-frequency estimator has been applied to a series of pulsatile flow phantom data obtained at 3.5 MHz. Maximum-frequency curves obtained from pulsatile flow velocities in the 2 m/s range are presented. The efficacy of the estimator is further demonstrated on preliminary results obtained from data taken from a human carotid artery using a real-time scanner.<<ETX>>

A Fundamental Evaluation of in Vivo Sound Speed Mapping Technique by Crossed Beam Method

Recently, several kinds of in vivo sound speed measurement techniques, using a pulse echo method, have been developed for the purpose of ultrasound tissue characterization.1,2,3The crossed beam method was proposed as a simple method by Haumschild and Greenleaf4 and Nishimura et al.5. This method uses two single probes. One probe is used for transmitting the ultrasound pulsed wave and the other for receiving the wave scattered from the region where the beams from the two probes cross. From the propagation time of the pulsed wave, the sound speed value is calculated. This method can also be realized using a linear array probe.6

A Fundamental Evaluation of In Vivo Local Sound Speed Measurement by Crossed Beam Method (2nd report)

The possibility of in vivo sound speed mapping by the crossed beam method was studied by a calculation using the ray tracing technique and a fundamental experiment. The calculation result is that the sound speed image is shown as a very characteristic pattern, which gives useful information about in vivo sound speed distribution. It was confirmed that experimental values agreed with calculated values.