Modified synthetic transmit aperture algorithm for ultrasound imaging.

The modified synthetic transmit aperture (STA) algorithm is described. The primary goal of this work was to assess the possibility to improve the image quality achievable using synthetic aperture (SA) approach and to evaluate the performance and the clinical applicability of the modified algorithm using phantoms. The modified algorithm is based on the coherent summation of back-scattered RF echo signals with weights calculated for each point in the image and for all possible combinations of the transmit-receive pairs. The weights are calculated using the angular directivity functions of the transmit-receive elements, which are approximated by a far-field radiation pattern of a narrow strip transducer element vibrating with uniform pressure amplitude over its width. In this way, the algorithm takes into account the finite aperture of each individual element in the imaging transducer array. The performance of the approach developed was tested using FIELD II simulated synthetic aperture data of the point reflectors, which allowed the visualization (penetration) depth and lateral resolution to be estimated. Also, both simulated and measured data of cyst phantom were used for qualitative assessment of the imaging contrast improvement. The experimental data were obtained using 128 elements, 4MHz, linear transducer array of the Ultrasonix research platform. The comparison of the results obtained using the modified and conventional (unweighted) STA algorithms revealed that the modified STA exhibited an increase in the penetration depth accompanied by a minor, yet discernible upon the closer examination, degradation in lateral resolution, mainly in the proximity of the transducer aperture. Overall, however, a considerable (12dB) improvement in the image quality, particularly in the immediate vicinity of the transducer's surface was demonstrated. The modified STA method holds promise to be of clinical importance, especially in the applications where the quality of the "near-field" image, that is the image in the immediate vicinity of the scanhead is of critical importance such as for instance in skin- and breast-examinations.

[1]  J. Goodman.  Introduction to Fourier optics , 1969 .

[2]  W. E. Engeler,et al.  Windowing of wide-band ultrasound transducers , 1996, 1996 IEEE Ultrasonics Symposium. Proceedings.

[3]  B. S. Robinson,et al.  Synthetic focus imaging using partial datasets , 1994, 1994 Proceedings of IEEE Ultrasonics Symposium.

[4]  A Trucco,et al.  A stochastic approach for the apodization of very short arrays. , 2004, Ultrasonics.

[5]  J.A. Jensen,et al.  Ultrasound research scanner for real-time synthetic aperture data acquisition , 2005, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[6]  G.R. Lockwood,et al.  Real-time 3-D ultrasound imaging using sparse synthetic aperture beamforming , 1998, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[7]  Jørgen Arendt Jensen,et al.  Synthetic aperture ultrasound imaging. , 2006, Ultrasonics.

[8]  M. Fink,et al.  Coherent plane-wave compounding for very high frame rate ultrasonography and transient elastography , 2009, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[9]  M. Tanaka,et al.  A new system for real-time synthetic aperture ultrasonic imaging , 1988, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[10]  J. Arendt.  Paper presented at the 10th Nordic-Baltic Conference on Biomedical Imaging: Field: A Program for Simulating Ultrasound Systems , 1996 .

[11]  K. Nagai,et al.  A New Synthetic-Aperture Focusing Method for Ultrasonic B-Scan Imaging by the Fourier Transform , 1985, IEEE Transactions on Sonics and Ultrasonics.

[12]  K. Boone,et al.  Effect of skin impedance on image quality and variability in electrical impedance tomography: a model study , 1996, Medical and Biological Engineering and Computing.

[13]  G. Kino.  Acoustic waves : devices, imaging, and analog signal processing , 1987 .

[14]  P. J. 't Hoen.  Aperture apodization to reduce the off-axis intensity of the pulsed-mode directivity function of linear arrays , 1982 .

[15]  J-F Synnevåg,et al.  A low-complexity data-dependent beamformer , 2011, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[16]  Tai-Kyong Song,et al.  Effects and limitations of motion compensation in synthetic aperture techniques , 2000, 2000 IEEE Ultrasonics Symposium. Proceedings. An International Symposium (Cat. No.00CH37121).

[17]  W.F. Walker,et al.  Optimal apodization design for medical ultrasound using constrained least squares part II simulation results , 2007, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[18]  K. Thomenius,et al.  Evolution of ultrasound beamformers , 1996, 1996 IEEE Ultrasonics Symposium. Proceedings.

[19]  H. Ghassemian,et al.  A transformation based method to design ultrasound array. , 2009, Ultrasonics.

[20]  Masayuki Morimoto,et al.  Sound radiation from an unbaffled elastic plate strip of infinite length , 2000 .

[21]  Gordon S. Kino,et al.  A theory for the radiation pattern of a narrow‐strip acoustic transducer , 1980 .

[22]  R. F. Wagner,et al.  Statistics of Speckle in Ultrasound B-Scans , 1983, IEEE Transactions on Sonics and Ultrasonics.

[23]  J. Jensen,et al.  Calculation of pressure fields from arbitrarily shaped, apodized, and excited ultrasound transducers , 1992, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.