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Dissertation
Modeling and characterization of ultrasound contrast agents
Doctor of Philosophy (Ph.D.), Drexel University
1998
DOI:
https://doi.org/10.17918/00000640
Abstract
In harmonic imaging using ultrasound contrast agents, the backscattered second harmonic has been the component of choice for differentiating blood from surrounding tissue. On the other hand, the work reported here investigates the possibility of utilizing the subharmonic of the insonating frequency for such applications. It is experimentally shown that the subharmonic can be generated from modern ultrasonic contrast agents (Levovist and Optison) at acoustic pressures in the 10 kPa range with insonation at twice the resonance frequency of the contrast agent. The theoretical basis of subharmonic generation from coated microbubbles is examined as a function of the damping associated with such microbubbles. It is shown that the subharmonic is easiest to excite if the total damping associated with the microbubble is low. Further it is shown that, for the subharmonic to be generated at pressures seen in the experiments, the total damping associated with the contrast agent should be lesser than 0.01, which is significantly lower than current estimates (0.4). The feasibility of subharmonic imaging is investigated theoretically and experimentally, by examining the generation of the subharmonic with burst insonations (5 and 10 cycles). It is shown that the subharmonic gain observed, for insonation at twice the resonance frequency, is higher than the second harmonic gain for insonation at the resonance frequency of the contrast agent (by approximately 8 dB for 5 cycle burst insonation of Optison at 225 kPa). The ability to measure flow velocities using subharmonic Doppler is experimentally verified for flow rates in the range of 0.05 to 0.4 m/sec using continuous wave as well as burst insonation. The ability to measure volumetric flow rates by using subharmonic washout curves is demonstrated for a flow rate of 0.065 ml/sec and a technique for quantifying tissue perfusion is suggested.
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Details
- Title
- Modeling and characterization of ultrasound contrast agents
- Creators
- Praveen Dalakrishna
- Contributors
- P. Mohana Shankar (Advisor)Vernon Leopold Newhouse (Advisor)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xii, 128 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- School of Biomedical Engineering, Science, and Health Systems (1997-2026); Drexel University
- Other Identifier
- 991014970212604721