Projects per year
Abstract
Many attempts to find a non-invasive procedure to measure the blood pressure locally in the
body have been made. This dissertation focuses on the approaches which utilize highly compressible
ultrasound contrast agents as ambient pressure sensors. The literature within the topic
has been reviewed. From this, the appropriate pressure dependent acoustic properties of the
microbubbles can be summarized to be the resonance frequency, the disappearance time, and
the subharmonic response.
During this thesis, the ambient pressure sensitivity of the subharmonic response has been investigated
through simulations and initial experimental measurements.
By simulations, a parameter study has investigated what mechanisms of the driving pulse are
important to optimize the ambient pressure sensitivity when utilizing the subharmonic component.
Investigating two different types of microbubbles clearly showed that two factors are
important when striving for an optimum sensitivity. First, the amount of subharmonic energy
reduction, when increasing the ambient pressure, is very sensitive to the acoustic excitation
pressure. Second, the study also indicated that the amount of reduction in subharmonic energy
is increased as the length of the excitation pulse is extended.
To carry out measurements in the laboratory, an experimental setup has been established. As
the focus has been on preparations for future in vivo measurements, the setup was designed
to match a clinical situation. Under the current measurement conditions, this setup showed
that the subharmonic component by itself cannot be used as an ambient sensitivity measure.
Instead, a new technique looking at the ratio of the subharmonic energy to the energy of the
fundamental component was used. Doing so, an ambient pressure dependent behavior of the
microbubbles was observed, indicating this to be a more robust measure. When increasing the
ambient pressure, the relation decreases linearly. Likewise, decreasing the ambient pressure
makes the relation increase linearly. Although the approach seems to reduce factors like time
dependency, a high standard deviation was still observed. This could be caused by several
reasons and more measurements are needed to investigate it further.
Original language | English |
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Place of Publication | Kgs. Lyngby, Denmark |
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Publisher | Technical University of Denmark |
Number of pages | 120 |
Publication status | Published - Sep 2009 |
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Projects
- 1 Finished
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Non-invasive in-vivo Spatial Pressure Measurement in Real Time
Andersen, K. S., Jensen, J. A., Ferkinghoff-Borg, J., Hoff, L. & Jansson, T.
15/02/2006 → 23/09/2009
Project: PhD