Designing Non-linear Frequency Modulated Signals For Medical Ultrasound Imaging

Fredrik Gran, Jørgen Arendt Jensen

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    Abstract

    In this paper a new method for designing non-linear frequency modulated (NLFM) waveforms for ultrasound imaging is proposed. The objective is to control the amplitude spectrum of the designed waveform and still keep a constant transmit amplitude, so that the transmitted energy is maximized. The signal-to-noise-ratio can in this way be optimized. The waveform design is based on least squares optimization. A desired amplitude spectrum is chosen, hereafter the phase spectrum is chosen, so that the instantaneous frequency takes on the form of a third order polynomial. The finite energy waveform is derived by minimizing the summed squared error between the desired spectrum and the obtained spectrum of the waveform. Having total control of the waveform spectrum has two advantages: First, it facilitates efficient use of the transducer passband, so that the amount of energy converted to heat in the transducer can be decreased. Secondly, by choosing an appropriate amplitude spectrum, no additional temporal tapering has to be applied to the matched filter to achieve sufficient range sidelobe suppression. Proper design results in waveforms with a range sidelobe level beyond -80 dB. The design method is tested experimentally using the RASMUS ultrasound system with a 7 MHz linear array transducer. Synthetic transmit aperture ultrasound imaging is applied to acquire data. The proposed design method was compared to a linear FM signal. Due to more efficient spectral usage, a gain in SNR of 4.3plusmn1.2 dB was measured resulting in an increase of 1 cm in penetration depth. Finally, in-vivo measurements are shown for both methods, where the common carotid artery on a 27 year old healthy male was scanned.
    Original languageEnglish
    Title of host publicationIEEE Ultrasonics Symposium
    PublisherIEEE
    Publication date2006
    Pages1714-1717
    ISBN (Print)1-4244-0201-8
    DOIs
    Publication statusPublished - 2006
    Event2006 IEEE Ultrasonics Symposium - Vancouver, Canada
    Duration: 2 Oct 20066 Oct 2006
    https://ieeexplore.ieee.org/xpl/conhome/4151855/proceeding

    Conference

    Conference2006 IEEE Ultrasonics Symposium
    Country/TerritoryCanada
    CityVancouver
    Period02/10/200606/10/2006
    Internet address

    Bibliographical note

    Copyright: 2006 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE

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