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15 March 2016 Nanoparticle-enhanced spectral photoacoustic tomography: effect of oxygen saturation and tissue heterogeneity
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Molecular imaging for breast cancer detection, infectious disease diagnostics and preclinical animal research may be achievable through combined use of targeted exogenous agents – such as nanoparticles – and spectral Photoacoustic Tomography (PAT). However, tissue heterogeneity can alter fluence distributions and acoustic propagation, corrupting measured PAT absorption spectra and complicating in vivo nanoparticle detection and quantitation. Highly absorptive vascular structures represent a common confounding factor, and variations in vessel hemoglobin saturation (SO2) may alter spectral content of signals from adjacent/deeper regions. To evaluate the impact of this effect on PAT nanoparticle detectability, we constructed heterogeneous phantoms with well-characterized channel-inclusion geometries and biologically relevant optical and acoustic properties. Phantoms contained an array of tubes at several depths filled with hemoglobin solutions doped with varying concentrations of gold nanorods with an absorption peak at 780 nm. Both overlying and target network SO2 was tuned using sodium dithionite. Phantoms were imaged from 700 to 900 nm using a custom PAT system comprised of a tunable pulsed laser and a research-grade ultrasound system. Recovered nanoparticle spectra were analyzed and compared with results from both spectrophotometry and PAT data from waterimmersed tubes containing blood and nanoparticle solutions. Results suggested that nanoparticle selection for a given PAT application should take into account expected oxygenation states of both target blood vessel and background tissue oxygenation to achieve optimal performance.
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William C. Vogt, Congxian Jia, Keith A. Wear, Brian S. Garra, and T. Joshua Pfefer "Nanoparticle-enhanced spectral photoacoustic tomography: effect of oxygen saturation and tissue heterogeneity", Proc. SPIE 9708, Photons Plus Ultrasound: Imaging and Sensing 2016, 97081H (15 March 2016);

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