Ultrasound imaging is an inexpensive method which provides an accurate
diagnosis tool.
This thesis provides elements to characterise the acoustic pressure
generated by ultrasound transducers as well as signal processing method
that could improve modern echography. The first measurement method to
assess transducers characteristics consists in deducing the absolute
amplitude of the acoustic pressure from a distortion measurement. Using
this method, the acoustic pressure was determined within 20% of the
calibrated hydrophone measurement. Another measurement method of
harmonic acoustic beams was developed based on Schlieren photography.
For some patients, ultrasound imaging presents difficulties. Super
harmonic imaging (SHI) improves further the compromise between
penetration and resolution. A description of the strategy to fulfil the
bandwidth requirements of such an exigent method is provided. The
detailed piezomaterial selection is depicted as well as the optimization
of the array configuration for transthoracic and abdominal
applications.
Furthermore, two signal processing techniques are described to improve
the SHI point spread function. The first technique consists in a dual
pulse method and second uses chirp compression. Both methods permit to
recover a good axial resolution. Those two methods present different
performances.
Finally, for contrast echography, two methods are described in order to
further enhance the contrast to tissue ratio. The first one uses source
pre-biasing technique. Improvement of contrast to tissue ratio (CTR)
yields to 7.4 dB. The second technique consists in applying a power
modulation scheme on a filtered population of bubbles. An improvement of
13 dB in CTR compared was observed.http://repub.eur.nl/res/pub/21748/101125_Matte%2C%20Guillaume%20Matthieu.pdf
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