Murakami, “ Nonlinear parameter tomography system using counterpropagating probe and pump waves,” Ultrason. Linzer, “ Imaging the nonlinear ultrasonic parameter of a medium,” Ultrason. Angelsen, “ Utilizing dual frequency band transmit pulse complexes in medical ultrasound imaging,” J. Angelsen, “ Transmit beams adapted to reverberation noise suppression using dual-frequency SURF imaging,” IEEE Trans. Hansen, “ SURF imaging: In vivo demonstration of an ultrasound contrast agent detection technique,” IEEE Trans. Angelsen, “ SURF imaging for contrast agent detection,” IEEE Trans. Hansen, “ SURF imaging: A new method for ultrasound contrast agent imaging,” in Proceedings of the IEEE Ultrasonics Symposium (2007), pp. The results demonstrate the high propagation complexity of dual-frequency pulses. By varying the low-frequency pressure, a shift of up to 0.5 MHz in center frequency of a 8.0 MHz transmitted high-frequency pulse is observed at the array focus. This makes the latter described effects also dependent on the array configuration. There is a phase shift between the low- and high-frequency pulse as it propagates from the array to the focus. The presence of the low-frequency pulse leads to compression, expansion, and a time delay of the high-frequency pulse. Activating both layers simultaneously, produce a well defined dual-frequency pulse. Activating the low- and high-frequency layers individually, results in less than −50 dB signal level from the high- and low-frequency layers respectively. The results show that the array works as intended. Water tank measurements demonstrate the function of the array by activating the low- and high-frequency layers individually and simultaneously. The dual-frequency band annular array, has been designed using a bi-layer piezo-electric stack. A designed and manufactured dual-frequency band annular array capable of transmitting 0.9/7.5 MHz center frequency wide-band pulses was used for this purpose. In this article, acoustic propagation effects of dual-frequency wide-band excitation pulses in a focused ultrasound system are demonstrated in vitro.
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