Abstract
We propose a new contrast-echo method using the counter-crossed beams of two ultrasonic frequencies for ultrasound diagnosis of cancer and call it the counter-cross beam contrast echo (C-CBCE) method. In this C-CBCE method, the sum- or difference-frequency components generated by the nonlinear vibration of microbubbles driven by dual-frequency ultrasound are used for measuring flow velocity. The C-CBCE method has the potential to measure low blood flow velocities, since the echo from the blood flow is efficiently separated from the echo from the biological soft tissues using the sum- or difference-frequency component. Sonazoid is used as microbubbles, and the sum frequency is used in the experiments. We prototyped the measurement system, which consists of commercially available ultrasound diagnostic equipment with a convex array probe and another ultrasonic probe, in order to determine the feasibility of the C-CBCE method in clinical diagnosis. In this study, we employ the C-CBCE method to measure the flow velocity of microbubbles in a channel using the sum-frequency component generated by the nonlinear vibration of microbubbles. We demonstrate theoretically the relationship between the Doppler-shift frequency of the sum-frequency component and the flow velocity in a channel. In order to confirm the theory on which this method is based, we then determine flow velocities on the basis of the sum-frequency component, fundamental component, and second-harmonic component.
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