One of the challenges of phased array (PA) ultrasonic imaging systems is their limited capability to deal with real-time applications, such as echocardiography and obstetrics. In its most basic outline, these systems require emitting and receiving with the entire array for each image line to be acquired; therefore, with many image lines, a higher acquisition time and a lower frame rate. This constraint requires one to find alternatives to reduce the total number of emissions needed to obtain the whole image. In this work, we propose a new PA scheme based on the Code Division Multiple Access (CDMA) technique, where a different code is assigned to each steering direction, allowing the array to emit in several directions simultaneously. However, the use of encoding techniques produces a reduction of the image contrast because of the interferences between codes. To solve this, a new scheme based on merging several images is proposed, allowing the system to get close to the theoretical maximum frame rate, as well as to limit the loss of contrast, intrinsic to the technique.
References
[1]
Démoré, E.M.; Joyce, A.; Wall, K.; Lockwood, G.R. Real-time volume imaging using a crossed electrode array. IEEE Trans. Ultrason. Ferroelectr. Freq. Control Soc. 2009, 56, 1252–1261.
[2]
O'Donnel, M. Coded excitation system for improving the penetration of real-time phased-array imaging systems. IEEE Trans. Ultrason. Ferroelectr. 1992, 39, 341–351.
[3]
Toosi, T.K.; Behnam, H. Combined Pulse Compression and Adaptive Beamforming in Coded Excitation Ultrasound Medical Imaging. Proceedings of the International Conference on Signal Processing Systems, Singapore, 15–17 May 2009; pp. 210–214.
[4]
Moo-Ho, B.; Woo-Youl, L.; Mok-Kun, J.; Sung-Jae, K. Orthogonal golay code based ultrasonic imaging without reducing frame rate. IEEE Trans. Ultrason. Ferroelectr. Freq. Control Soc. 2009, 56, 1252–1261.
[5]
Kim, B.H.; Song, T.K. Multibeam Simultaneous Transmit Multizone (MB-STMZ) focusing method using modulated orthogonal codes for ultrasound imaging. Proc. SPIE 2004, 5373, 315–323.
[6]
De Marziani, C.; Ure？a, J.; Mazo, M.; Hernández, A.; García, J.J.; Pérez, M.C.; Aparicio, J.; Alcoleas, R. Simultaneous round-trip time-of-flight measurements with encoded acoustic signals. IEEE Sens. J. 2012, 12, 2931–2940.
[7]
Klaus-Werner, J.; Berg, M.; Müller, M. Using Pseudo-Random Codes for Mobile Robot Sonar Sensing. Proceedings of the 3rd IFAC Symposium on Intelligent Autonomus Vehicles, IAV, Madrid, Spain, 25–27 March 1998; pp. 25–27.
[8]
Shen, J. A new coded-excitation ultrasound imaging system. IEEE Trans. Ultrason. Ferroelectr. Freq. Control Soc. 1996, 43, 131–140.
[9]
Diego, C.; Hernández, A.; Jiménez, A.; J álvarez, F.; Sanz, R.; Aparicio, J. Ultrasonic array for obstacle detection based on CDMA with Kasami codes. Sensors 2011, 11, 11464–11475.
[10]
Kasami, T. Weight Distribution Formula for Some Class of Cyclic Codes. Technical Report; Coordinated Science Lab, University of Illinois: Urbana, IL, USA, 1966.
[11]
Golomb, S.W. Shift Register Sequences; Aegean Park Press: Laguna Hills, CA, USA, 1981.
[12]
Gold, R. Optimal binary sequences for spread spectrum multiplexing. IEEE Trans. Inf. Theory 1967, 13, 619–621.
[13]
Misaridis, T.; Jensen, J.A. Use of modulated excitation signals in medical ultrasound. Part I: Basic concepts and expected benefits. IEEE Trans. Ultrason. Ferroelectr. Freq. Control Soc. 2005, 52, 177–191.
[14]
Pérez, M.C.; Ure？a, J.; Hernández, A.; Jiménez, A.; Ruí, D.; álvarez, F.J.; de Marziani, C. Performance Comparison of Different Codes in an Ultrasonic Positioning System Using DS-CDMA. Proceedings of the IEEE International Symposium on Intelligent Signal Processing WISP, Budapest, Hungary, 26–28 August 2009; pp. 125–130.
[15]
Von Ramm, O.T.; Smith, S.W. Beam steering with linear arrays. IEEE Trans. Biomed. Eng. 1983, BME-30, 438–451.
[16]
Yao, H. Synthetic Aperture Methods for Medical Ultrasonic Imaging. MS.c. Thesis, University of Oslo, Oslo, Norway, December 1997.
