Che-Chou Shen

National Taiwan University of Science and Technology, T’ai-pei, Taipei, Taiwan

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Publications (48)54.66 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: In our previous studies we explored the potential of using a combined US/magnetic resonance (MR) multimodality contrast agent, albumin-gadolinium-diethylenetriaminepentacetate (Gd-DTPA) MBs, to induce BBB opening and for distinguishing between FUS-induced BBB opening and intracerebral hemorrhage in MR T1-weighted contrast imaging. According to the previous study in the literature, 1-2 µm bubbles have more pronounced acoustic activity at frequencies above 10 MHz. The present study developed a new targeted US/MR multimodality MB and the acoustic properties were compared with two commercial MBs, SonoVue and Targestar SA. The acoustic activities of these 1.15-2.78 µm MBs with different shells at 10 MHz were investigated. The feasibility of designing a new targeted US/MR multimodality MB was investigated. The lifetime (survival of MBs in the liquid suspension) and attenuation properties of lipid MBs (SonoVue and Targestar SA), albumin-(Gd-DTPA) MBs, and avidin-conjugated albumin (avidin-albumin)-(Gd-DTPA) MBs at 10 MHz were investigated with the pulse-echo substitution method. It was found that incorporating avidin into the albumin MBs and avidin-albumin-(Gd-DTPA) MBs affects the size distribution but does not affect the concentration of MBs produced. The avidin-albumin-shelled MBs had more significant nonlinear activity at 4-18 MHz (p=0.025), while the nonlinear activity of the other MBs peaked at 6-24 MHz (p=0.003-0.044). Moreover, the incorporation of paramagnetic metal ions into the MB shells increased their attenuation coefficients. With regard to the lifetime of these agents, the attenuations of the SonoVue and Targestar SA lipid MBs were 87.96% and 8.74%, respectively, while those of albumin MBs, avidin-albumin MBs, albumin-(Gd-DTPA) MBs, and avidin-albumin-(Gd-DTPA) MBs were 49.52%, 41.38%, 74.69%, and 100%, respectively. Avidin conjugation decreased the lifetime of the albumin MBs, but not that of the lipid MBs. The incorporation of paramagnetic metal ions into the shells of albumin MBs did not decrease the lifetime.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 07/2013; 2013:6965-6968.
  • Che-Chou Shen, Hui-Ting Wang
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    ABSTRACT: BACKGROUND: The presence of tissue harmonic generation during acoustic propagation is one major limitation in nonlinear detection of microbubble contrast agents. However, conventional solutions for tissue harmonic suppression are not applicable in dual-frequency (DF) harmonic imaging. In DF harmonic imaging, the second harmonic signal at second harmonic (2f(0)) frequency and the inter-modulation harmonic signal at fundamental (f(0)) frequency are simultaneously generated for imaging and both need to be suppressed to improve contrast-to-tissue ratio (CTR). In this study, a novel phase-coded pulse sequence is developed to accomplish DF tissue harmonic suppression. METHODS: Phase-coded pulse sequence utilizes multiple firings with equidistant transmit phase for harmonic cancellation in the sum of respective echoes. For the f(0) transmit component, the transmit phase comes from the equidistant set of {-2π/3, 0, 2π/3} to suppress the second harmonic signal at 2f(0) frequency. Moreover, in order to provide the inter-modulation harmonic suppression at f(0) frequency, the 2f(0) transmit phase has to be particularly manipulated for the corresponding f(0) transmit phase. RESULTS: The proposed three-pulse sequence can remove not only the second-order harmonic signal but also other higher-order counterparts at both f(0) and 2f(0) frequencies. Measurements were performed at f(0) equal to 2.25MHz and using hydrophone in water and contrast agents in tissue phantom. Experimental results indicate that the sequence reduces the tissue harmonic magnitude by about 20dB along the entire axial depths and the corresponding CTR improves at both frequencies. CONCLUSION: In DF harmonic imaging, the proposed phase-coded sequence can effectively remove the tissue harmonic background at both f(0) and 2f(0) frequencies for improvement of contrast detection.
    Ultrasonics 11/2012; · 2.03 Impact Factor
  • Che-Chou Shen, Chin-Hsiang Lin
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    ABSTRACT: Dual-frequency (DF) transmit waveforms comprise signals at two different frequencies. With a DF transmit waveform operating at both fundamental frequency ( f(0)) and second-harmonic frequency 2f((0)), tissue harmonic imaging can be simultaneously performed using not only the conventional 2f(0) second-harmonic signal but also using the f(0)frequency difference harmonic signal. Nonetheless, when chirp excitation is incorporated into the DF transmit waveform for harmonic SNR improvement, a particular waveform design is required to maintain the bandwidth of the f(0) harmonic signal. In this study, two different DF chirp waveforms are proposed to produce equal harmonic bandwidth at both the f(0) and 2f(0) frequencies to achieve speckle reduction by harmonic spectral compounding and to increase harmonic SNR for enhanced penetration and sensitivity. The UU13 waveform comprises an up-sweeping f(0) chirp and an up-sweeping 2f(0) chirp with triple bandwidth, whereas the UD11 waveform includes an up-sweeping f(0) chirp and a down-sweeping 2f(0) chirp with equal bandwidth. Experimental results indicate that the UU13 tends to suffer from a high range side lobe level resulting from 3f(0) interference. Consequently, the 2f(0) harmonic envelopes of the UD11 and the UU13 waveforms have compression qualities of 87% and 77%, respectively, when the signal bandwidth is 30%. When the bandwidth increases to 50%, the compression quality of the 2f(0) harmonic envelope degrades to 78% and 54%, respectively, for the UD11 and the UU13 waveforms. The compression quality value of the f0 harmonic envelope remains similar between the two DF transmit waveforms for all signal bandwidths. B-mode harmonic images also show that the UD11 is less contaminated by range side lobe artifacts than is the UU13. Compared with a short pulse with equal bandwidth, the UD11 waveform not only preserves the same spatial resolution after compression but also improves the image SNR by about 10 dB. Moreover, the image contrast-to-noise ratio (CNR), defined as the ratio of the mean to the standard deviation of image intensity in the speckle region, can be increased from 1.0 to about 1.2 when DF spectral compounding is performed. Therefore, it is concluded that the UD11 waveform is a potential solution for chirp-encoded DF harmonic imaging.
    IEEE transactions on ultrasonics, ferroelectrics, and frequency control 11/2012; 59(11):2420-30. · 1.80 Impact Factor
  • Po-Wen Cheng, Che-Chou Shen, Pai-Chi Li
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    ABSTRACT: Using software for beamforming in ultrasound systems provides high flexibility, and the large number of computations required in a software-based system can be performed in real time on a PC. However, the very large data transfer rate required from the ultrasound front-end to the PC host for real-time operation is a bottleneck which cannot be overcome without appropriate compression. Previous studies have examined JPEG compression of ultrasound RF channel data, but the schemes do not exploit temporal redundancy between adjacent frames. This study utilized MPEG technology to process the ultrasound RF data to increase the compression efficiency. Our results indicate that MPEG compression generally provides a better compression ratio than does JPEG compression. As an example, the compression ratio of MPEG compression in an 8-bit channel A/D data under 5 μm interframe displacement is smaller than 0.13, thus allowing real-time data transfer requirements to be met. Moreover, the compression efficiency for motions in different directions is shown to be highly dependent on the frame-to-frame correlation.
    IEEE transactions on ultrasonics, ferroelectrics, and frequency control 07/2012; 59(7):1413-20. · 1.80 Impact Factor
  • Chin-Hsiang Lin, Che-Chou Shen
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    ABSTRACT: Dual-frequency (DF) transmit waveform comprises of signals at both fundamental frequency (f0) and second harmonic frequency (2f0). With the DF transmit waveform, tissue harmonic imaging can be simultaneously performed not only using the conventional 2f0 second harmonic signal but also the f0 frequencydifference harmonic signal. Nonetheless, when chirp excitation is incorporated into the DF transmit waveform for improvement of harmonic SNR, particular waveform design is required to maintain the bandwidth of the f0 harmonic signal. In this study, two different chirp waveforms (i.e., UD11 and UU13) are proposed to provide the desired signal bandwidth. Experimental results indicate that the UU13 tends to suffer from high range side lobe level due to severe 3f0 interference. Consequently, the 2f0 harmonic envelope of the UD11 is consistently superior to that of the UU13 while the quality of the f0 harmonic envelope remains similar between the two DF transmit waveforms. B-mode harmonic images also show that the UD11 is less susceptible to range side lobe artifacts than the UU13. Therefore, it is concluded that the UD11 waveform is a better solution for chirp-encoded DF harmonic imaging.
    Ultrasonics Symposium (IUS), 2012 IEEE International; 01/2012
  • Tai-yu Shi, Che-chou Shen
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    ABSTRACT: Ultrasound tissue harmonic signal generally provides superior image quality as compared to the linear signal but with limited penetration and the sensitivity due to low signal-to-noise ratio (SNR). The method of third harmonic (3f0) transmit phasing can improve the tissue harmonic SNR by transmitting at both the fundamental and the 3f0 frequencies to provide mutual enhancement between the second harmonic components. To further increase the SNR without excessive transmit pressure, the phase-encoded Golay excitation can be incorporated in 3f0 transmit phasing to boost the tissue harmonic generation. The resultant frequency-sum and frequency-difference components of tissue harmonic signal can be simultaneously Golay-encoded for SNR improvement. Results indicate that the tissue harmonic SNR increases by about 11 dB without noticeable compression artifacts.
    01/2012;
  • Hui-Ting Wang, Che-Chou Shen
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    ABSTRACT: The presence of tissue harmonic generation during acoustic propagation is one major limitation in nonlinear detection of microbubble contrast agents. However, conventional solutions for suppression of tissue harmonic background are not directly applicable when dual-frequency (DF) waveform is utilize for transmit. In DF harmonic imaging, the second harmonic signal at second harmonic frequency (2f0) and the inter-modulation harmonic signal at fundamental frequency (f0) are simultaneously produced and both need to be suppressed for imaging of contrast agents. In this study, novel phase-coded pulse sequences are developed to accomplish DF harmonic suppression. The proposed three-pulse sequence can effectively remove the second-order harmonic signal by producing equidistant phases for cancellation in the sum of different firings. Therefore, the tissue background in DF harmonic imaging can be mostly suppressed. Experiments have been performed to validate the efficacy of the proposed sequence. It is shown that the sequence effectively suppresses the tissue harmonic signal at both f0 and 2f0 frequencies to improve CTR.
    Ultrasonics Symposium (IUS), 2012 IEEE International; 01/2012
  • Che-Chou Shen, Hsin-Hsien Wu
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    ABSTRACT: High-frequency Doppler imaging is highly potential for detection of blood flow in microcirculation. In a swept-scan system, however, the spectral broadening of tissue clutter limits the detectability of low-velocity flow signal. Conventionally, the scanning speed of transducer has to be reduced to alleviate the clutter interference but at the cost of imaging frame rate. For example, the blood velocity of 0.5mm/s becomes detectable only with a scanning speed lower than 1mm/s. In this study, an alternative method is examined by suppressing the clutter magnitude to reduce the interference to flow signal without sacrificing scanning speed. The method of third harmonic (3f(0)) transmit phasing can suppress the tissue harmonic clutter by transmitting at the fundamental and the additional 3f(0) frequencies to achieve mutual cancellation between the frequency-sum and the frequency-difference components of the second harmonic signal. With 3f(0) transmit phasing, the cut-off frequency of wall filtering can be reduced to preserve low-velocity flow without compromising the frame rate. Our results indicate that the 3f(0) transmit phasing effectively reduces the harmonic clutter magnitude and thus improves the flow signal-to-clutter ratio. Compared to the conventional counterpart, the clutter-suppressed color flow and power Doppler images show fewer clutter artifacts and is capable of detecting more low-velocity flow of microbubbles. The resultant color-pixel-density also improves with clutter suppression. For the swept-scan high-frequency (>20MHz) system, 3f(0) transmit phasing is capable of providing effective clutter suppression. With the same achievable scanning speed, the resultant Doppler image has higher sensitivity for low-velocity flow and is less susceptible to clutter artifacts.
    Ultrasonics 08/2011; 52(2):238-43. · 2.03 Impact Factor
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    ABSTRACT: The goal of this work is to examine the effects of pulse-inversion (PI) technique in combination with dual-frequency (DF) excitation method to separate the high-order nonlinear responses from microbubble contrast agents for improvement of image contrast. DF excitation method has been previously developed to induce the low-frequency ultrasound nonlinear responses from bubbles by using the composition of two high-frequency sinusoids (f(1) and f(2)). Although the simple filtering was conventionally utilized to provide signal separation, the PI approach is better in the sense that it minimizes the mutual interferences among these high-order nonlinear responses in the presence of spectral overlap. The novelty of the work is that, in addition to the common PI summation, the PI subtraction was also applied in DF excitation method. DF excitation pulses having an envelope frequency of 3MHz (i.e., f(1)=8.5MHz and f(2)=11.5MHz) with pulse lengths of 3-10μs and the pressure amplitudes from 0.5 to 1.5MPa were used to interrogate the nonlinear responses of SonoVue™ microbubbles in the phantom experiments. The high-order nonlinear responses in the DF excitation were extracted for contrast imaging using PI summation for even-order nonlinear components or PI subtraction for odd-order nonlinear ones. Our results indicated that, as compared to the conventional filtering technique, the PI processing effectively increases the contrast-to-tissue ratio (CTR) of the third-order nonlinear response at 5.5MHz and the fourth-order nonlinear response at 6MHz by 2-5dB. For these high-order nonlinear components, the CTR increase varies with the transmission pressures from 0.5 to 1.5MPa due to the microbubbles' displacement induced by the radiation force of DF excitation. For DF excitation technique, the PI processing can help to extract either the odd-order or the even-order nonlinear components for higher CTR estimates.
    Ultrasonics 06/2011; 52(1):25-32. · 2.03 Impact Factor
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    ABSTRACT: This report describes a system that utilizes a single high-intensity focused ultrasound (HIFU) transducer for both the localization and ablation of arteries with internal diameters of 0.5 and 1.3 mm. In vitro and in vivo tests were performed to demonstrate both the imaging and ablation functionalities of this system. For imaging mode, pulsed acoustic waves (3 cycles for in vitro and 10 cycles for in vivo tests, 2 MPa peak pressure) were emitted from the 2-MHz HIFU transducer, and the backscattered ultrasonic signal was collected by the same transducer to calculate Doppler shifts in the target region. The maximum signal amplitude of the Doppler shift was used to determine the location of the target vessel. The operation mode was then switched to the therapeutic mode and vessel occlusion was successfully produced by high-intensity continuous HIFU waves (12 MPa) for 60 s. The system was then switched back to imaging mode for residual flow to determine the need for a second ablation treatment. The new system might be used to target and occlude unwanted vessels such as vasculature around tumors, and to help with tumor destruction.
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 05/2011; · 1.82 Impact Factor
  • Source
    Chih-Hao Cheng, Che-Chou Shen, Chih-Kuang Yeh
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    ABSTRACT: The method of dual-frequency (DF) difference excitation is capable of generating a low-frequency envelope component as the driving force of commercial contrast microbubbles by using a high-frequency pulse. Although the DF difference excitation method provides good lateral resolution in high-frequency contrast imaging, it suffers from degraded axial resolution because a longer-than-usual envelope component is required to induce the oscillation of microbubbles. In this study, a coded excitation technique (i.e. chirp waveform) is combined with the DF difference excitation method (also referred to as the DF chirp excitation method) to improve the axial resolution of contrast imaging while maintaining the impinging insonation energy. B-mode images were constructed to compare the performance of the DF chirp excitation method with the conventional tone-burst pulse method. Results indicate that the proposed DF chirp excitation method can provide better axial resolution after pulse compression. Moreover, as compared to the tone-burst pulse with the same pulse duration, the pulse compression results in a higher signal-to-noise ratio because of the temporal concentration of the received energy. Nevertheless, images with the DF chirp excitation method demonstrated noticeable image artefacts resulting from the range sidelobes. The DF chirp excitation method also produced obvious tissue harmonic generation that could degrade the contrast-to-tissue ratio at higher acoustic pressures.
    Physics in Medicine and Biology 04/2011; 56(9):2767-78. · 2.70 Impact Factor
  • Che-Chou Shen, Tai-Yu Shi
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    ABSTRACT: Golay-encoded excitation in combination with the third harmonic (3f<sub>0</sub>) transmit phasing is examined for both signal-to-noise ratio (SNR) and contrast-to-tissue ratio (CTR) improvements in harmonic imaging of contrast microbubbles. To produce the cancellation pair of tissue harmonic signal in 3f<sub>0</sub> transmit phasing, the phase of the bit waveform is properly designed for both the fundamental and the 3f<sub>0</sub> transmit signals to provide the Golay encoding of the received harmonic responses. Results indicate that the proposed Golay excitation can effectively suppress the tissue harmonic amplitude to increase CTR. Meanwhile, the SNR of the contrast harmonic signal also improves because of the elongated waveform of Golay excitation. Nevertheless, the generation of marked range side-lobes of the bubble region would degrade the achievable SNR improvement and the image contrast, especially when the bit of Golay excitation increases. The range side-lobes could result from the nonlinear resonance of the microbubbles that interferes with the phase modulation of the Golay encoding.
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 03/2011; · 1.82 Impact Factor
  • Che-Chou Shen, Chih-Hao Cheng, Chih-Kuang Yeh
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    ABSTRACT: Sub-harmonic imaging techniques have been shown to provide a higher contrast-to-tissue ratio (CTR) at the cost of relatively low signal intensity from ultrasound contrast agents (UCAs). In this study, we propose a method of dual-frequency excitation to further enhance the CTR of subharmonic imaging. A dual-frequency excitation pulse is an amplitude-modulated waveform which consists of two sinusoids with frequencies of f₁ (e.g., 9 MHz) and f₂ (e.g., 6 MHz) and the resulting envelope component at (f₁ - f₂) (e.g., 3 MHz) can serve as a driving force to excite the nonlinear response of UCAs. In this study, the f₂, at twice of the resonance frequency of UCAs, is adopted to efficiently generate a sub-harmonic component at half of the f₂ frequency, and f₁ is included to enhance the high-order nonlinear response of UCAs at the sub-harmonic frequency. The second- and third-order nonlinear components resulting from the envelope component would spectrally overlap at the sub-harmonic frequency when f₁ and f₂ are properly selected. We further optimize the generation of the sub-harmonic component by tuning the phase terms between second- and third-order nonlinear components. The results show that, with dual-frequency excitation, the CTR at sub-harmonic frequency improves compared with the conventional tone-burst method. Moreover, the CTR changes periodically with the relative phase of the separate frequency component in the dual-frequency excitation, leading to a difference of as much as 9.1 dB between the maximal and minimal CTR at 300 kPa acoustic pressure. The echo produced from the envelope component appears to be specific for UCAs, and thus the proposed method has the potential to improve both SNR and CTR in sub-harmonic imaging. Nevertheless, the dual-frequency waveform may suffer from frequency-dependent attenuation that degrades the generation of the envelope component. The deviation of the microbubble's resonance characteristics from the selection of dual-frequency transmission may also decrease the CTR improvement.
    IEEE transactions on ultrasonics, ferroelectrics, and frequency control 02/2011; 58(2):379-88. · 1.80 Impact Factor
  • Po-Wen Cheng, Che-Chou Shen, Pai-Chi Li
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    ABSTRACT: Using software for beamforming in ultrasound systems provides high flexibility, and it has been demonstrated that the large amount of computations required in a software-based system can be performed in real time on a personal computer. However, the current bottleneck is in the very high data transfer rate required from the ultrasound front-end to the computer, which generally cannot be achieved without appropriate data compression. Previous studies have examined JPEG compression of ultrasound RF channel data, but the schemes do not exploit temporal redundancy between adjacent frames. This study utilized MPEG to process the ultrasound RF data in order to increase the compression efficiency. Our results indicate that the compression ratio of MPEG under the 5 μm interframe displacement is smaller than 0.13 and meets the real-time data transfer requirement. The MPEG generally provides a better compression ratio than does JPEG, and the compressed data size reduced at least 38% than JPEG when the interframe displacement is 5 μm. Moreover, the compression efficiency for motions in different directions is highly dependent on the frame-to-frame correlation.
    Ultrasonics Symposium (IUS), 2011 IEEE International; 01/2011
  • Che-Chou Shen, Hsin-Hsien Wu, Chih-Kuang Yeh
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    ABSTRACT: In high-frequency swept-scan Doppler system, the spectral broadening of tissue clutter limits the detectability of low-velocity flow signal. Conventionally, the scanning speed of transducer has to be reduced to alleviate the clutter interference but at the cost of imaging frame rate. With third harmonic (3f0) transmit phasing, the tissue harmonic clutter is suppressed and the cut-off frequency of wall filtering can be reduced to preserve low-velocity flow without compromising the frame rate. Our results indicate that the 3f0 transmit phasing effectively reduces the harmonic clutter magnitude and thus improves the flow signal-to-clutter ratio. Compared to the conventional counterpart, the clutter-suppressed color flow and power Doppler images show fewer clutter artifacts and is capable of detecting more low-velocity flow of microbubbles. The resultant color-pixel-density also improves with clutter suppression. For the swept-scan high-frequency system, 3f0 transmit phasing is capable of providing effective clutter suppression. With the same achievable scanning speed, the resultant Doppler image has higher sensitivity for low-velocity flow and is less susceptible to clutter artifacts.
    Ultrasonics Symposium (IUS), 2011 IEEE International; 01/2011
  • Che-Chou Shen, Tai-Yu Shi
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    ABSTRACT: Ultrasound tissue harmonic signal generally provides superior image quality as compared to the linear signal. However, since the generation of the tissue harmonic signal is based on finite amplitude distortion of the propagating waveform, the penetration and the sensitivity in tissue harmonic imaging are markedly limited because of the low signal-to-noise ratio (SNR). The method of third harmonic (3f(0)) transmit phasing can improve the tissue harmonic SNR by transmitting at both the fundamental (2.25MHz) and the 3f(0) (6.75MHz) frequencies to achieve mutual enhancement between the frequency-sum and the frequency-difference components of the second harmonic signal. To further increase the SNR without excessive transmit pressure, coded excitation can be incorporated in 3f(0) transmit phasing to boost the tissue harmonic generation. Our analyses indicate that the phase-encoded Golay excitation is suitable in 3f(0) transmit phasing due to its superior transmit bandwidth efficiency. The resultant frequency-sum and frequency-difference components of tissue harmonic signal can be simultaneously Golay-encoded for SNR improvement. The increase of the main-lobe signal with the Golay excitation in 3f(0) transmit phasing are consistent between the tissue harmonic measurements and the simulations. B-mode images of the speckle generating phantom also demonstrate the increases of tissue harmonic SNR for about 11dB without noticeable compression artifacts. For tissue harmonic imaging in combination with the 3f(0) transmit phasing method, the Golay excitation can provide further SNR improvement. Meanwhile, the axial resolution can be effectively restored by pulse compression while the lateral resolution remains unchanged.
    Ultrasonics 12/2010; 51(5):554-60. · 2.03 Impact Factor
  • Che-Chou Shen, Tai-Yu Shi
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    ABSTRACT: Golay-encoded excitation in combination with the third harmonic (3f<sub>0</sub>) transmit phasing is examined for both signal-to-noise ratio (SNR) and contrast-to-tissue ratio (CTR) improvements in harmonic imaging of contrast microbubbles. To produce the cancellation pair of tissue harmonic signal in 3f<sub>0</sub> transmit phasing, the phase of the bit waveform is properly designed for both the fundamental and the 3f<sub>0</sub> transmit signals to provide the Golay encoding of the received harmonic responses. Results indicate that the proposed Golay excitation can effectively suppress the tissue harmonic amplitude to increase CTR. Meanwhile, the SNR of contrast harmonic signal also improves due to the elongated waveform of Golay excitation. Nevertheless, the generation of marked range side-lobes of the bubble region would degrade the achievable SNR improvement and the image contrast especially when the bit of Golay excitation increases. The range side-lobes could result from the nonlinear resonance of the microbubbles that interferes with the phase modulation of the Golay encoding.
    Ultrasonics Symposium (IUS), 2010 IEEE; 11/2010
  • Ai-Ho Liao, Che-Chou Shen, Pai-Chi Li
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    ABSTRACT: Ultrasound nonlinear imaging using microbubble- based contrast agents has been widely investigated. Nonetheless, its contrast is often reduced by the nonlinearity of acoustic wave propagation in tissue. In this paper, we explore the use of empirical mode decomposition (EMD) and ensemble empirical mode decomposition (EEMD) in the Hilbert-Huang transform (HHT) for possible contrast improvement. The HHT is designed for analyzing nonlinear and nonstationary data, whereas EMD is a method associated with the HHT that allows decomposition of data into a finite number of intrinsic modes. The hypothesis is that the nonlinear signal from microbubbles and the tissue nonlinear signal can be better differentiated with EMD and EEMD, thus making contrast improvement possible. Specifically, we tested this method on pulse-inversion nonlinear imaging, which is generally regarded as one of the most effective nonlinear imaging methods. The results show that the contrast-to-tissue ratios at the fundamental and second-harmonic frequencies were improved by 10.2 and 4.3 dB, respectively, after EEMD. Nonetheless, image artifacts also appeared, and hence further investigation is needed before EMD and EEMD can be applied in practical applications of ultrasound nonlinear imaging.
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 03/2010; · 1.82 Impact Factor
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    ABSTRACT: OBJECTIVE AND MOTIVATION: The goal of this work was to test experimentally that exposing air bubbles or ultrasound contrast agents in water to amplitude modulated wave allows control of inertial cavitation affected volume and hence could limit the undesirable bioeffects. Focused transducer operating at the center frequency of 10 MHz and having about 65% fractional bandwidth was excited by 3 micros 8.5 and 11.5 MHz tone-bursts to produce 3 MHz envelope signal. The 3 MHz frequency was selected because it corresponds to the resonance frequency of the microbubbles used in the experiment. Another 5 MHz transducer was used as a receiver to produce B-mode image. Peak negative acoustic pressure was adjusted in the range from 0.5 to 3.5 MPa. The spectrum amplitudes obtained from the imaging of SonoVue contrast agent when using the envelope and a separate 3 MHz transducer were compared to determine their cross-section at the -6 dB level. The conventional 3 MHz tone-burst excitation resulted in the region of interest (ROI) cross-section of 2.47 mm while amplitude modulated, dual-frequency excitation with difference frequency of 3 MHz produced cross-section equal to 1.2mm. These results corroborate our hypothesis that, in addition to the considerably higher penetration depth of dual-frequency excitation due to the lower attenuation at 3 MHz than that at 8.5 and 11.5 MHz, the sample volume of dual-frequency excitation is also smaller than that of linear 3-MHz method for more spatially confined destruction of microbubbles.
    Ultrasonics 02/2010; 50(7):698-703. · 2.03 Impact Factor
  • Che-Chou Shen, Min-Yan Pan, Meng-Lin Li
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    ABSTRACT: Speckle tracking is capable of searching the complete vector velocity but is susceptible to the frame-to-frame image de- correlation. With plane-wave excitation (PWE), the high frame- rate reduces the scatterer displacement and thus increases the signal correlation. Nevertheless, the lower image quality with PWE may suffer from spatial velocity gradient outside the sample volume and reduce the achievable accuracy of speckle tracking. In this study, we propose a recursive PWE compounding technique to improve the image quality for accuracy of vector velocity estimation while the high-frame-rate nature of PWE for vector velocity estimation is retained. In the proposed compounding, several PWE images from different steering angles are combined coherently to suppress the beam sidelobes at the cost of longer acquisition time. The coherent PWE compounding is further combined with a recursive technique to generate high-resolution images with different features at a frame rate of pulse repetition frequency; thus retaining the high frame-rate nature. The neighboring high-resolution image pairs with the same image feature are utilized for velocity detection with speckle tracking. Extensive simulations were performed to test the recursive PWE compounding method for its performance in speckle-tracking based vector velocity estimation. Results indicate that, the lateral estimation is more susceptible to the spatial flow velocity gradient than the axial estimation is. When the Doppler angle is 0°, it is shown that the mean axial velocity remains close to the ideal parabolic profile while the detection of lateral velocity is markedly interfered by the flow gradient. In the case of large Doppler angle, it is also evident that an accurate lateral estimation is achieved with the coherent PWE compounding method. Note that the standard deviation with the PWE compounding is generally smaller as compared to the conventional PWE image, indicating the improved robustness in both lateral and axial estimation. Nevertheless, the error of lateral estimation is still larger than that of axial estimation. It is demonstrated that the recursive PWE compounding with speckle tracking is capable of improving estimation of vector velocity with high frame rate. In addition to vector velocity estimation, the proposed method can also be potentially applied to elastography.
    01/2010;

Publication Stats

134 Citations
54.66 Total Impact Points

Institutions

  • 2007–2012
    • National Taiwan University of Science and Technology
      • Department of Electrical Engineering
      T’ai-pei, Taipei, Taiwan
  • 2000–2012
    • National Taiwan University
      • • Graduate Institute of Biomedical Electronics and Bioinformatic
      • • Department of Electrical Engineering
      Taipei, Taipei, Taiwan
  • 2011
    • Taipei Medical University
      • Department of Physical Medicine and Rehabilitation
      T’ai-pei, Taipei, Taiwan
  • 2009–2011
    • National Tsing Hua University
      • Department of Biomedical Engineering and Environmental Sciences
      Hsinchu, Taiwan, Taiwan