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Proceedings Paper

Spatio-temporal encoding using narrow-band linear frequency modulated signals in synthetic aperture ultrasound imaging
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Paper Abstract

In this paper a method for spatio-temporal encoding is presented for synthetic transmit aperture ultrasound imaging (STA). The purpose is to excite several transmitters at the same time in order to transmit more acoustic energy in every single transmission. When increasing the transmitted acoustic energy, the signal to noise ratio will increase. However, to focus the data properly using the STA approach, the transmitters have to be separated from each other. This is done by dividing the available spectrum into several subbands with a small overlap. Separating different transmitters can be done by bandpass filtering. Therefore, the separation can be done instantaneously without the need for further transmissions, unlike spatial encoding relying on Hadamard or Golay coding schemes, where several transmissions have to be made before the decoding can be done. Motion artifacts from the decoding can, thus, be avoided. To further increase the transmitted energy, the excitation waveforms are designed as linear frequency modulated (FM) signals. This makes it possible to maintain the full excitation amplitude during most of the transmission. The design of the separation filters will also be discussed. The method was tested using the experimental ultrasound scanner RASMUS and evaluated using a reference setup with a linear FM excitation waveform and STA beamforming. The point spread function (PSF) was measured on a wire phantom in water. A wire phantom with an attenuating medium was also measured, where the proposed method achieved approximately 2 cm improvement in penetration depth. The signal to noise ratio was also measured, where the gain was approx. 7 dB in comparison to the reference.

Paper Details

Date Published: 12 April 2005
PDF: 12 pages
Proc. SPIE 5750, Medical Imaging 2005: Ultrasonic Imaging and Signal Processing, (12 April 2005); doi: 10.1117/12.592352
Show Author Affiliations
Fredrik Gran, Technical Univ. of Denmark (Denmark)
Jorgen Arendt Jensen, Technical Univ. of Denmark (Denmark)

Published in SPIE Proceedings Vol. 5750:
Medical Imaging 2005: Ultrasonic Imaging and Signal Processing
William F. Walker; Stanislav Y. Emelianov, Editor(s)

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