S.-i. Umemura

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Among the nonthermal effects of ultrasound, acoustic cavitation may have the highest potential for therapeutic applications if it can be somehow controlled. Recent in vitro and in vivo experiments have demonstrated that sonochemically active cavitation can be enhanced an order of magnitude by superimposing the second harmonic onto the fundamental in(More)
We have developed a tissue-mimicking phantom for ultrasonic elastography. The phantom has tunable elastic and echographic properties. Polyacrylamide gel, a typical chemical gel in that it shows greater stability than physical gels such as gelatin or agar, provided the basis of the phantom. Fine metal-oxide particles were added to modify the echogenicity of(More)
The ultrasonic power absorbed by a microbubble in its continuous wave response is estimated through numerically solving a version of the Rayleigh-Plesset equation. At an ultrasonic frequency of 3 MHz, a resonant microbubble, approximately 1.1 /spl mu/m in radius, showed an absorption cross section of about 0.005 mm/sup 2/ in its low power response. This(More)
A preliminary study for therapeutic application of phase change nano droplet (PCND) in combination with low frequency ultrasound was performed. With gel phantom, it was found that the presence of PCND enhanced temperature elevation induced by 1.1-MHz ultrasound using albumin as the indicator of protein coagulation. Not like 2.2-MHz ultrasound, coagulation(More)
In studying a site-targeted contrast agent that can be administered as nano-particle (liquid droplet) and change its phase from liquid to gas by an external stimulus such as ultrasound to yield microbubbles, we have investigated if the phase shift can be achieved by using short pulses produced by a medical ultrasound scanner and probe. As expected in a(More)
Motion-compensated time-averaged imaging (MTI), a method of accumulating frames with a motion compensation technique using small subregions was conducted to improve power Doppler and B-mode imaging. In our previous study, MTI was shown to be able to clearly image vasculature with contrast agents without image blurring even if the target tissue was moving(More)
A new method is proposed to detect whether the sign of acoustic impedance change in space is positive or negative. Ultrasonic signed echoes are obtained by transmitting a pulse containing both the fundamental and second harmonic components, calculating the reference second harmonic phase carrying over the fundamental phase of received echoes, and(More)
Transcranial ultrasonic thrombolytic system has been developed, for acute ischemic stroke (AIS) therapy during hyper acute phase. The system aims to have a higher potential for early recanalization in the thrombo-embolism by accelerating the effect of thrombolytic agent with transcranial ultrasonication. Sub MHz ultrasound has less attenuation by several(More)
Therapy monitoring based on echo-time-shift imaging during high intensity focused ultrasound (HIFU) treatment was described. The echo shift estimated by radio frequency (RF) correlation between adjacent frames is potentially useful for mapping coagulation and tissue temperature. B-mode images are also useful for real-time monitoring, but cannot show the(More)
We investigated a high-contrast ultrasound imaging method by averaging multiple frames with motion correction. The purpose of this study is to visualize the vascularity of peripheral vessels filled with contrast agents by using an averaging method which cannot be imaged clearly in conventional contrast image because of low density of the agent. To average(More)