Spatial encoding using a code division technique for fast ultrasound imaging

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control Vol. 55; no. 1; pp. 12 - 23
• Main Authors: Gran, F., Jensen, J.A.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01-01-2008; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Acoustic signal processing; Acoustics; Algorithms; Apertures; Data Compression - methods; Decoding; Encoding; Error correction; Error correction codes; Exact sciences and technology; Firing; Fundamental areas of phenomenology (including applications); Image Enhancement - methods; Image Interpretation, Computer-Assisted - methods; Imaging; Noise levels; Numerical Analysis, Computer-Assisted; Physics; Random sequences; Reproducibility of Results; Sensitivity and Specificity; Sidelobes; Signal Processing, Computer-Assisted; Signal to noise ratio; Simulation; System testing; Transducers; Transduction; acoustical devices for the generation and reproduction of sound; Transmitters; Ultrasonic imaging; Ultrasonography - methods; Ultrasound; Lateral lobe; Ultrasound imaging; Linear array; Experimental study; Pulse code modulation; Modeling; Point spread function; Aperture antenna; Linear antenna; Synthetic aperture; Code division multiple access; Error correcting code; Feasibility; Sinusoidal excitation; Acoustic image; Transducer network; Signal to noise ratio
• ISSN: 0885-3010; 1525-8955
• DOI: 10.1109/TUFFC.2008.613

This paper describes a method for spatial encoding in synthetic transmit aperture ultrasound imaging. This allows several ultrasonic sources to be active simultaneously. The method is based on transmitting pseudorandom sequences to spatially encode the transmitters. The data can be decoded after only one transmission using the knowledge of the transmitted code sequences as opposed to other spatial encoding techniques, such as Hadamard or Golay encoding. This makes the method less sensitive to motion, and data can be acquired using fewer transmissions. The aim of this paper is to analyze the underlying theory and to test the feasibility in a physical system. The method has been evaluated in simulations using Field II in which the point-spread functions were simulated for different depths for a 7 MHz linear array transducer. A signal-to-noise ratio (SNR) simulation also was included in the study in which an improvement in SNR of ~1.5 dB was attained compared to the standard synthetic transmit aperture (STA) firing scheme. Considering the amount of energy transmitted, this value is low. A plausible explanation is given that is verified in simulation. The method also was tested in an experimental ultrasound scanner and compared to a synthetic transmit aperture ultrasound imaging scheme using a sinusoidal excitation. The performance of the proposed method was comparable to the reference with respect to axial and lateral resolution, but it displayed poorer contrast with sidelobe levels at ~ - 40 dB compared to the mainlobe.