Motion-compensation for complementary-coded medical ultrasonic imaging
View/ Open
Cannon2010_files.zip (22.31Mb)
Date
2010Author
Cannon, Cormac
Metadata
Abstract
Ultrasound is a well-established tool for medical imaging. It is non-invasive and relatively
inexpensive, but the severe attenuation caused by propagation through tissue limits its effectiveness
for deep imaging. In recent years, the ready availability of fast, inexpensive computer
hardware has facilitated the adoption of signal coding and compression techniques to counteract
the effects of attenuation. Despite widespread investigation of the topic, published opinions
vary as to the relative suitability of discrete-phase-modulated and frequency-modulated (or
continuous-phase-modulated) signals for ultrasonic imaging applications. This thesis compares
the performance of discrete binary-phase coded pulses to that of frequency-modulated pulses
at the higher imaging frequencies at which the effects of attenuation are most severe.
The performance of linear and non-linear frequency modulated pulses with optimal side-lobe
characteristics is compared to that of complementary binary-phase coded pulses by simulation
and experiment. Binary-phase coded pulses are shown to be more robust to the affects of attenuation
and non-ideal transducers. The comparatively poor performance of frequency-modulated
pulses is explained in terms of the spectral characteristics of the signals and filters required to
reduce side-lobes to levels acceptable for imaging purposes.
In theory, complementary code sets like bi-phase Golay pairs offer optimum side-lobe performance
at the expense of a reduction in frame rate. In practice, misalignment caused by
motion in the medium can have a severe impact on imaging performance. A novel motioncompensated
imaging algorithm designed to reduce the occurrence of motion artefacts and
eliminate the reduction in frame-rate associated with complementary-coding is presented. This
is initially applied to conventional sequential-scan B-mode imaging then adapted for use in
synthetic aperture B-mode imaging. Simulation results are presented comparing the performance
of the motion-compensated sequential-scan and synthetic aperture systems with that of
simulated systems using uncoded and frequency-modulated excitation pulses.
Collections
The following license files are associated with this item: