2016 Volume 43 Issue 2 Pages 265-277
Purpose: We propose a crossed beam contrast echo (CBCE) method, where the measurement of blood flow is achieved by analyzing the sum- or different-frequency components generated by nonlinear vibration of microbubbles under the radiation of two ultrasonic beams with different frequencies. This method allows us to measure only blood flow velocity separate from motion of biological soft tissue without using a high-pass filter such as MTI filter, because the sum- or different-frequency components can increase the contrast echo to tissue echo ratio (CTR). In this paper, we demonstrate the measurement of only blood flow velocity and show the advantage of this method. Subjects and Methods: In an experimental system comprised of steady flow with flow volume of approximately 126 mm3/s, we employed the CBCE method to measure the flow velocity. A commercially available contrast agent, Sonazoid, was injected into the channel surrounded by a gel phantom mimicking tissue. The flow velocity was evaluated by Doppler shift of fundamental, second harmonic, and sum-frequency components. Results and Discussion: CTR of the sum-frequency component was larger than that of the fundamental and second harmonic components when the echo signal from microbubbles was overlapped with that of the gel phantom in the range gate. The flow velocity measured by using the sum-frequency component was consistent with the reference value as compared with the fundamental and second harmonic components. Conclusion: In the CBCE method, the improvement of CTR with the sum-frequency component enables us to better evaluate the precious flow velocity as compared with other frequency components.
