| Περίληψη: | Ultrasound contrast agents (UCA) is a relatively new tool, used in medical
ultrasound imaging to enhance the diagnostic abilities of ultrasound and potentially offer a therapeutic value in medical ultrasounds. UCAs are bi or single-layered bubbles, that
contain a highly backscattering gas. By injecting them into the blood flow, we locally increase the echogenicity and therefor enhance the contrast of the blood-tissue interface.
This way we can provide a improved image of the structure of the organs, we can more
accurately diagnose abnormal of defected areas on them, and if the containing gas is
replaced with an appropriate drug, focus drug delivery can be achieved, providing potential healing of the disease.
! Up to now, most of the studies done in order to investigate the microbubbles -
ultrasound interaction are mostly population studies, which due to their roughly approach
cannot clearly diagnose and explain the complex nonlinear and dynamic properties of
UCAs and their response to ultrasound field. Because of that, our knowledge on the
UCAsʼ, is yet limited although the potential improvements at imaging and therapeutic
technics that would be gained from a thorough understanding of this interactions can be very big.
! In this thesis, a study of single microbubbles is presented, using a system
developed by the group of Ultrasound imaging in Edinburgh University. The system uses a
specially modified commercial ultrasound machine, phased array probes and a specially
designed single microbubbles measuring system. The system has the ability to feed,
insonify and capture the backscattered echo from a single microbubble, with the use of
fully calibrated and characterized ultrasound - probe system. The aim of the project is to
contribute in the understanding of the behavior of the UCAs when insonified with an
ultrasound wave, and the underlying physical mechanism behind that.
The response of two different commercially available UCAs under insonification by
ultrasound waves of varying acoustical pressure is presented. The UCAs used are Definity
and biSphere. In total echoes from 842 biSphere and 1994 Definity microbubbles have
ben captured and the data have been analyzed with in house made matlab codes.
Also the response of the bubbles when insonified by consequent pulses of different
repetition frequency has been investigated. For this reason, echoes from other 1221
Definity and 459 biSphere microbubbles have been captured and analyzed.
The fully understanding of the agent - ultrasound interaction mechanisms can be the basis
for creating improved signal processing tools for ultrasound imaging contrast enhancement
that would improve imaging abilities of the modality, and potentially use of UCAs as a
therapeutic mean.
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