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Title page for ETD etd-11192014-203717


Type of Document Dissertation
Author Jarrett, Christopher William
Author's Email Address christopher.w.jarrett@vanderbilt.edu
URN etd-11192014-203717
Title Physical Basis of Acousto-Optical Imaging
Degree PhD
Department Chemical and Physical Biology
Advisory Committee
Advisor Name Title
Thomas E. Yankeelov Committee Chair
John C. Gore Committee Co-Chair
Henry C. Manning Committee Member
Melissa C. Skala Committee Member
Todd E. Peterson Committee Member
Wellington Pham Committee Member
Keywords
  • acousto
  • optical
  • acousto-optical
  • ultrasound
  • modulated
  • ultrasound modulated
  • light
  • imaging
Date of Defense 2014-10-24
Availability unrestricted
Abstract
Acousto-Optical Imaging (AOI) is an emerging hybrid multi-modal imaging technique that combines the high spatial resolution of ultrasound with the versatile molecular sensitivity of optical detection to improve upon the limited spatial resolution of purely optical techniques. However, the precise mechanisms that contribute to the contrast in AOI have been relatively little explored, and the influence of several physical factors are not well understood. Kobayashi et al. previously reported observations of modulated fluorescence capable of locating fluorescent regions of interest within turbid media, suggesting the ability to use incoherent light for AOI. This research aimed to develop and extend such an approach for applications in biomedical imaging. We aimed to demonstrate the modulation of incoherent light by ultrasound and investigate what factors affect the magnitude of such effects. We proposed the following specific aims: (1) To design and develop instrumentation to detect and quantify Acousto-Optical interactions; (2) To evaluate the contributions of different mechanisms of ultrasonic modulation of fluorescence and the factors that influence these effects in turbid media like tissues; (3) To test a variety of fluorescent contrast agents to determine if their light output may be directly affected by ultrasonic modulation, which would suggest a novel approach to AOI. This work achieved these aim. We were successful in designing and developing an experimental apparatus capable of detecting and quantifying Acousto-Optical Interactions. We determined this signal scales linearly with squared ultrasound pressure but unlike the interpretation of Kobayashi et al., we found the apparent modulated fluorescence is dominated by acoustic modulation of the excitation light. In addition, we report a novel finding that ultrasound can modulate incoherent light via modulation of tissue absorption and density, incidentally providing a new way to image sound fields. Lastly, we failed to detect direct acoustic effects on common optical agents but successfully observed the direct modulation of light output of ZnS and ZnCdS suspensions. We conclude the observations by Kobayashi cannot be reproduced, and the effects of the modulation of a coherent exciting source must be considered. The potential remains for designing agents whose optical output may be affected by sound fields.
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