A two-pulse technique for extracting 3rd harmonic from ultrasound contrast agent echo signal.

ABSTRACT Multi-pulse techniques like CPS (contrast pulse sequence) and TPS (triplet pulse sequence) are the most popular methods for separating the 3rd harmonic signals from received signal. Those two methods, however, transmit a pulse at least three times along each scanline with different phase and amplitude, which results in the frame rate reduction. In this paper, we propose a technique using two pulses whose phase difference is 90 degrees and a simple digital filter. The second harmonic signal is eliminated by summing two received signals as their phase difference becomes 180 degrees and then the fundamental signals are eliminated by using a digital filter. Computer simulations are performed for different values of signal bandwidths and filter specifications. The results show the maximum error is -35.5 dB compared to TPS.

  • The Journal of the Acoustical Society of America 01/1998; 103(5). · 1.56 Impact Factor
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    ABSTRACT: A triplet pulse sequence is proposed for imaging with superior microbubble/tissue selectivity. This sequence utilizes the difference in nonlinearity between the nonlinear propagation in tissue and the nonlinear scattering by microbubbles. Three-time transmit/receive are performed with transmit pulses having the same envelope and a phase shift by 120°, and the received echo signals are summed. Numerical analysis of the microbubble scattering and the propagation in tissue predicted the selectivity superior to the conventional pulse inversion sequence by more than 20 dB in an ideal case. An experiment using a prototype scanner with a Doppler flow phantom and a contrast agent demonstrated an improvement in the selectivity by 15 dB at a typical acoustic amplitude in B-mode imaging at 2 MHz.
    Ultrasonics, 2003 IEEE Symposium on; 11/2003
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    ABSTRACT: For ultrasound contrast agents (UCA), nonlinear imaging now has become fundamental. All of the current contrast-imaging methods are dominantly based on the nonlinear response of UCA bubbles. The discrimination between the perfused tissue and the UCA is the challenge in the field of UCA-imaging. This differentiation is usually associated or expressed by the ratio of the scattered power from the contrast agent to the scattered power from the tissue and is termed "contrast-to-tissue ratio" (CTR). Second harmonic imaging showed a better discrimination between tissue and UCA than fundamental imaging because of a higher CTR. We demonstrate, in this study, that the CTR increases as a function of the order of the harmonic frequency. Currently, due to the limited bandwidth of the transducers, only the second harmonic is selectively imaged, resulting in images with a superior quality to fundamental images, but still degraded and not optimal because of the harmonic generation in the underlying tissue (due to nonlinear propagation) and hence giving a limited CTR. To increase the CTR and to take advantage of the higher harmonics (third, fourth, fifth and the ultraharmonics and termed here super harmonics), we have developed a new phased array transducer. The array transducer contains two different types of elements arranged in an interleaved pattern (odd and even elements). The total number of elements is 96. The elements can operate separately and at a distinct frequency, enabling separate transmission and reception modes. The odd elements (48) operate at typically 2.8 MHz center frequency and 80% bandwidth. The even elements (48) have a center frequency of 900 kHz with a bandwidth of 50%. In vitro measurements using the dual frequency probe show an increase of 40 dB in the CTR for super harmonic components over the conventional second harmonic system. The increase in CTR is in agreement with the calculations using existing models for the response of encapsulated bubbles and known theory of nonlinear propagation. Animal experiments have demonstrated the feasibility of this approach using commercially available UCA and showed a similar increase of the CTR.
    Ultrasound in Medicine & Biology 02/2002; 28(1):59-68. · 2.10 Impact Factor