Abstract
Background
Capon-based beamformers are well-known methods to improve the SNR and quality of medical ultrasound images. Furthermore, they can improve the resolution of the images unexpectedly more than conventional DAS beamformers. Another method used in radar, sonar, and ultrasound imaging to increase the SNR is coded excitation with linear frequency-modulated signal (chirp).
Method
In this paper, we illustrate that the combination of coded excitation with a Capon beamformer provides better resolution and higher SNR. However, this combination suffers from high sidelobe levels. We propose a weighted Capon beamformer (WCB) with chirp excitation to suppress the sidelobes and obtain a higher contrast with approximately the same resolution as the standard Capon beamformer (SCB). The weights of the WCB are obtained using element-wise multiplication of the weights of the SCB and a desired window (Hanning) with the same dimension.
Results
The results show a 20 dB reduction in the sidelobe levels in simulated point targets and a 6 dB increase in background contrast in simulated cyst phantoms.
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References
Bennett S, Peterson DK, Corl D, et al. A realtime synthetic aperture digital acoustic imaging system. In: 10th International Symposium on Acoustic Imaging 1982; vol. 10, pp. 669–92.
Holm S, Yao H. Improved framerate with synthetic transmit aperture imaging using prefocused subapertures. Ultrason Symp 1997;2:1535–8.
Hassan MA, Kadah YM. K3 Synthetic transmit aperture medical ultrasound imaging. NRSC. 2012;641–8.
Bae M-H, Jeong M-K. A study of synthetic-aperture imaging with virtual source elements in B-mode ultrasound imaging systems. IEEE Trans Ultrason Ferroelectr Freq Control. 2000;47:1510–9.
Chang C-H, Chang Y-F, Ma Y, et al. Reliable estimation of virtual source position for SAFT imaging. IEEE Trans Ultrason Ferroelectr Freq Control. 2013;60:356–63.
Gammelmark KL, Jensen JA. Multielement synthetic transmit aperture imaging using temporal encoding. IEEE Trans Med Imag. 2003;22:552–63.
Misaridis T, Jensen JA. Space-time encoding for high frame rate ultrasound imaging. Ultrasonics. 2002;40:593–7.
Chiao RY, Thomas LJ. Synthetic transmit aperture using orthogonal golay coded excitation. In: IEEE Ultrasonics Symposium 2000, pp. 1469–72.
Gran F, Jensen JA. Frequency division transmission imaging and synthetic aperture reconstruction. IEEE Trans Ultrason Ferroelectr Freq Control. 2006;53:900–11.
Montaldo G, Aubry JF, Tanter M, et al. Spatio-temporal coding in complex media for optimum beamforming: the iterative time-reversal approach. IEEE Trans Ultrason Ferroelectr Freq Control. 2005;52:220–30.
Misaridis T, Jensen JA. Use of modulated excitation signals in medical ultrasound Part II: design and performance for medical imaging applications. IEEE Trans Ultrason Ferroelectr Freq Control. 2005;52:192–207.
Gran F, Hansen KL, Nielsen MB, et al. 1K–3 Preliminary In-vivo results for spatially coded synthetic transmit aperture ultrasound based on frequency division. In: IEEE Ultrasonics Symposium; 2006. pp 1087–90.
Frost OL. An algorithm for linearly constrained adaptive array processing. Proc IEEE. 1972;60:926–35.
Widrow B, Duvall KM, Gooch RP, at al. Signal cancellation phenomena in adaptive antennas: causes and cures. IEEE Transactions on Antennas and Propagation 1982; vol AP-30, pp 469–78.
Ali ME, Schreib F. Adaptive single snapshot beamforming: a new concept for the rejection of nonstationary and coherent interferers. IEEE Trans Signal Process. 1992;40:3055–8.
Bethel R, Shapo B, Van Trees HL. Single snapshot spatial processing: optimized and constrained. In: Sensor Array and Multichannel Signal Processing Workshop Proceedings; 2002. pp 508–12.
Mann JA, Walker WF. A constrained adaptive beamformer for medical ultrasound: Initial results. IEEE Ultrason Symp Proc. 2002;2:1807–10.
Sasso M, Cohen-Bacrie C. Medical ultrasound imaging using the fully adaptive beamformer. ICASSP05.2005;2.
Synnevåg JF, Austeng A, Holm S. Minimum variance adaptive beamforming applied to medical ultrasound imaging. IEEE Int Ultrason Symp. 2005;1199–202.
Wang Z, Li J, Wu R. Time-delay and time-reversal-based robust Capon beamformers for ultrasound imaging. IEEE Trans Med Imaging. 2005;24:1308–22.
Holfort IK, Gran F, Jensen JA. Broadband Minimum Variance Beamforming for Ultrasound Imaging. IEEE Trans Ultrason Ferroelectr Freq Control 2009;56:314–25.
Asl BM, Mahloojifar A. Minimum variance beamforming combined with adaptive coherence weighting applied to medical ultrasound imaging. IEEE Trans Ultrason Ferroelectr Freq Control. 2009;56:1923–31.
Capon J. High resolution frequency-wavenumber spectrum analysis. Proc IEEE. 1969;57:1408–18.
Synnevåg JF, Austeng A, Holm S. Adaptive beamforming applied to medical ultrasound imaging. IEEE Trans Ultrason Ferroelectr Freq Control. 2007;54(8):1606–13.
Shan TJ, Kailath T. Adaptive beamforming for coherent signals and interferences. IEEE Trans Acoust Speech Signal Process. 1985;33:527–36.
Asl BM, Mahloojifar A. Contrast enhancement and robustness improvement of adaptive ultrasound imaging using forward-backward minimum variance beamforming. IEEE Trans Ultrason Ferroelectr Freq Control. 2011;58:858–67.
Synnevåg JF, Austeng A, Holm S. A low-complexity datadependent beamformer. IEEE Trans Ultrason Ferroelectr Freq Control. 2011;58:281–9.
Asl BM, Mahloojifar A. A low-complexity adaptive beamformer for ultrasound imaging using structured covariance matrix. IEEE Trans Ultrason Ferroelectr Freq Control. 2012;59:660–7.
Jensen A, Austeng A. An approach to multibeam covariance matrices for adaptive beamforming in ultrasonography. IEEE Trans Ultrason Ferroelectr Freq Control. 2012;59:1139–48.
Toosi TK, Behnam H. Combined pulse compression and adaptive beamforming in coded excitation ultrasound medical imaging. In: International Conference on Signal Processing Systems. 2009;210–14.
Nikolov SI. Synthetic aperture tissue and flow ultrasound imaging. Ph.D. dissertation, Ørsted DTU, Technical University of Denmark, Lyngby; 2001.
Jensen JA. Field: a program for simulating ultrasound systems. Med Biol Eng Comput. 1996;34:351–3.
Synnevåg JF, Nilsen CIC, Holm S. Speckle statistics in adaptive beamforming. IEEE Ultrasonics Symp. 2007:1545–8.
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Izadi, S.A., Mahloojifar, A. & Asl, B.M. Weighted Capon beamformer combined with coded excitation in ultrasound imaging. J Med Ultrasonics 42, 477–488 (2015). https://doi.org/10.1007/s10396-015-0640-6
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DOI: https://doi.org/10.1007/s10396-015-0640-6