A hyperthermia thermometry system using an ultrasound. nonlinear effect caused by superposed pulses wzs developed and a feasibility study to obtain temperature mapping of tissue phantoms and anesthetized pigs heated by an ultrasound applicator was made. The thermometry system consists of a mechanical sector scanner and a main frame with a color monitor. The distribution of the temperature rise is calculated within 1 minute, and displayed on the monitor together with an ultrasound B-mode image. Experimental results show that reasonable temperature rise mapping was obtained in both objects and an agreed to within 2°C with the data obtained by thermocouples located in the phantom.
A new method for obtaining depth distribution of the nonlinearity parameter B/A and the frequency-dependent attenuation coefficient is outlined. In this method, the higher frequency probe pulse wave, superposed coaxially on the lower frequency pump pulse wave, is modulated nonlinearly due to their propagation, and is received as an echo signal. The relationship between these acoustic parameters and the modulation characteristics of the probe pulse wave is derived by the division of the spectra of modulated echo signals with each other. The possibility of canceling out of error factors, such as the frequency-dependent acoustic reflection coefficient of random scattering medium, in the above division process is discussed. A preliminary evaluation of this method is made by using an experimental system. B/A values are obtained for various kinds of sponge test targets immersed in water, n-propyl alcohol, isopropyl alcohol, ethylene glycol, or diethylene glycol; and for agar graphite phantom.
The method for measuring the distribution of the attenuation coefficient and the nonlinearity characteristic, using the nonlinear effect in superposed probe and pump pulse waves, is described. The relationship between these acoustic parameters, the measured crossing frequency (ωx) and the slope of the depth dependence of ω
x
is also described. The experimental result of using a pig liver as a lossy medium is reported.
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