17 March 2015 Synthetic aperture imaging using a semi-analytic model for the transmit beams
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Abstract
Many modern high-end scanners use some form for coherent synthesis of image lines by combining beams acquired with different transmissions, such as retrospective dynamic transmit focusing (Acuson / Siemens), nSIGHT (Philips), and Zone imaging (Zonare). There are two major strategies described in the literature to uniformly focus both transmit and receive beams throughout the field of view - using virtual sources, and by applying spatial matched filtration. The virtual source model is precise, when the transmit is either strongly focused (f-number ~ 1, 2) or images are formed using circular or spherical waves. The spatial matched filtration can be used also with weakly focused transmissions, but requires the measurement and storage of the response of point targets within the limits of the transmit beam.

This paper presents a semi-analytic model for the transmitted field, which can be applied to synthetic transmit imaging. The model is more precise than the virtual source concept, does not require the measurement of the transmit field as matched filtration methods do, and can be applied to both strongly and weakly focused transmissions. Furthermore, the model is applicable to tissue harmonic and contrast enhanced ultrasound imaging.

The paper presents the development of the model using the principles of diffraction, and its validation using computer simulations and measurements on a phantom. Finally, the model is demonstrated for synthetic aperture tissue harmonic in-vivo imaging.
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Jens Munk Hansen, Svetoslav Ivanov Nikolov, "Synthetic aperture imaging using a semi-analytic model for the transmit beams", Proc. SPIE 9419, Medical Imaging 2015: Ultrasonic Imaging and Tomography, 94190K (17 March 2015); doi: 10.1117/12.2081936; https://doi.org/10.1117/12.2081936
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