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Dissertation
Characterization of a new class of surfactant stabilized ultrasound contrast agents, and investigation of ultra-harmonics as a new diagnostic tool
Doctor of Philosophy (Ph.D.), Drexel University
Mar 2000
DOI:
https://doi.org/10.17918/00000470
Abstract
Ultrasound contrast agents are intravenously injected, and are used to enhance the received signal. A new surfactant-based contrast agent 'ST68' has been developed, which was prepared by insonating buffered mixtures of Span-60 and Tween-80 in either air, Sulfurhexafluoride (SF 6), or Decafluorobutane (PFC). These gas-filled agents showed excellent in-vivo and in-vitro enhancements (>25 dB). In-vivo enhancements from ST68-PFC lasted much longer (7 to 10 minutes), in comparison to ST68-SF6 (3 to 5 minutes) and ST68-Air (1 to 2 minutes). One of the possible reasons being that air is highly soluble in water, while PFC and SF6 are essentially insoluble. In-vitro experiments were conducted to explain the influence of environmental parameters such as gas diffusion, solubility, and ionic strength variation. These in-vitro results were later compared and analyzed with the in-vivo results. A unique distinction between ST68 and tissue is the enhanced ability of the agent to generate non-linear frequencies such as sub-harmonics (f0/2), higher-harmonics (2 f0, 3f0, 4f 0, ...), and ultra-harmonics (3f0/2, 5f0/2, 7f0/2, ...), when insonated (with fundamental frequency f0). Currently, 2nd harmonics (2f0) have been predominantly researched, to exploit the diagnostic benefits of the contrast-specific non-linear imaging. However, we found that at normal imaging pressures (100 kPa to 1 MPa), the agent-generated 2nd harmonic enhancements dropped to ~8dB at 100 kPa and ~2dB at 1 MPa. Moreover, at these pressures water (or tissue) produced strong 2nd harmonics due to propagation non-linearity. Ultra-harmonics and sub-harmonics on the other hand, were generated only by the agent, and were not produced due to the non-linear propagation of ultrasound in either water or tissue. Additionally, ultra-harmonic (3f0/2) enhancements of ~23dB at 100 kPa, ~35dB at 0.5 MPa and ~41dB at 1.1 MPa for ST68-PFC, offer much greater signal to noise ratio than higher-harmonics. Finally, ultra-harmonics by virtue of their higher frequency provide greater Doppler and image resolution than fundamental or sub-harmonics. Hence, this thesis identifies ultra-harmonics as a potential ultrasound contrast agent-based diagnostic tool.
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Details
- Title
- Characterization of a new class of surfactant stabilized ultrasound contrast agents, and investigation of ultra-harmonics as a new diagnostic tool
- Creators
- Raghuveer Basude
- Contributors
- Margaret A. Wheatley (Advisor)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xvii, 200 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- School of Biomedical Engineering, Science, and Health Systems (1997-2026); Drexel University
- Other Identifier
- 991014970311804721