Static and dynamic light and ultrasound measurements for the elucidation of biological and biomaterial structure and function

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The objective of the proposal is to develop optical and ultrasound techniques to characterise the functional state of cells and tissues using optical, ultrasound and photoacoustic techniques. My work to date has been focused on using static optical and ultrasound scattering. In the proposed work these static techniques will be refined based on new knowledge generated from recent theoretical and experimental findings. The main novelty of the new work proposed will be a) to extend the techniques developed to include photoacoustic tissue characterization and b) to extended the static ultrasound and optical scattering measurements to include dynamic scattering measurements (fluctuations of scattering intensity as a function of time) to infer the states of cells and tissues. Whereas the field of photoacoustic imaging has recently gained a lot of attention, fundamental questions as to the origin of the photoacoustic signal and how to characterize the signal when blood vessels (the main generator of photoacoustic signals) are unresolved remain unanswered. As for most clinically relevant ultrasound frequencies blood vessels of interest cannot be resolved, a new technique is required to analyze the photoacoustic signals. New techniques based on modeling the photoacoustic signals generated by individual blood vessels will be used to develop methods for photoacoustic tissue characterization. In parallel, techniques will be also developed based on the fluctuations of (optical / ultrasound) scattering intensity as a function of time. We recently discovered that dying cells exhibit significantly shorter optical coherence tomography speckle decorrelation times (faster fluctuations of scattering intensity as a function of time), and that the speckle decorrelation time can be used to assess intracellular motion of the main scattering sources within cells / tissues. While the most common application relates to blood flow measurements, in these new techniques signals from blood are supressed so as to assess motion in tissues and cells alone. The optical and ultrasound techniques developed will aid in the non-invasive monitoring of the functional states of cells and tissues.