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Proceedings Paper

Coded ultrasound for blood flow estimation using subband processing
Author(s): Fredrik Gran; Jesper Udesen; Michael Bachmann Nielsen; Jørgen Arendt Jensen
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Paper Abstract

This paper further investigates the use of coded excitation for blood flow estimation in medical ultrasound. Traditional autocorrelation estimators use narrow-band excitation signals to provide sufficient signal-to-noise-ratio (SNR) and velocity estimation performance. In this paper, broadband coded signals are used to increase SNR, followed by sub-band processing. The received broadband signal, is filtered using a set of narrow-band filters. Estimating the velocity in each of the bands and averaging the results yields better performance compared to what would be possible when transmitting a narrow-band pulse directly. Also, the spatial resolution of the narrow-band pulse would be too poor for brightness-mode (B-mode) imaging and additional transmissions would be required to update the B-mode image. In the described approach, there is no need for additional transmissions, because the excitation signal is broadband and has good spatial resolution after pulse compression. Two different coding schemes are used in this paper, Barker codes and Golay codes. The performance of the codes for velocity estimation is compared to a conventional approach transmitting a narrow-band pulse. The study was carried out using an experimental ultrasound scanner and a commercial linear array 7 MHz transducer. A circulating flow rig was scanned with a beam-to-flow angle of 60°. The flow in the rig was laminar and had a parabolic flow-profile with a peak velocity of 0.09 m/s. The mean relative standard deviation of the reference method using an eight cycle excitation pulse at 7 MHz was 0.544% compared to the peak velocity in the rig. Two Barker codes were tested with a length of 5 and 13 bits, respectively. The corresponding mean relative standard deviations were 0.367% and 0.310%, respectively. For the Golay coded experiment, two 8 bit codes were used, and the mean relative standard deviation was 0.335%.

Paper Details

Date Published: 12 March 2007
PDF: 10 pages
Proc. SPIE 6513, Medical Imaging 2007: Ultrasonic Imaging and Signal Processing, 651309 (12 March 2007); doi: 10.1117/12.703345
Show Author Affiliations
Fredrik Gran, Technical Univ. of Denmark (Denmark)
Jesper Udesen, Univ. Hospital of Copenhagen (Denmark)
Michael Bachmann Nielsen, Univ. Hospital of Copenhagen (Denmark)
Jørgen Arendt Jensen, Technical Univ. of Denmark (Denmark)

Published in SPIE Proceedings Vol. 6513:
Medical Imaging 2007: Ultrasonic Imaging and Signal Processing
Stanislav Y. Emelianov; Stephen A. McAleavey, Editor(s)

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