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11 March 2015 Design and phantom-based validation of a bimodal ultrasound-photoacoustic imaging system for spectral detection of optical biomarkers
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The construction of photoacoustic tomography (PAT) systems that combine tunable laser sources and ultrasound systems for bimodal imaging and spectroscopic applications such as oximetry presents novel challenges to the biophotonics researcher. We address some of the design issues, including system synchronization, cross-platform integration, and image reconstruction algorithms, and present techniques for device performance validation. Our system comprises a pulsed Nd:YAG laser-pumped optical parametric oscillator for near-infrared tunability and a research-grade ultrasound acquisition system compatible with multiple clinical transducers to enable wide variation in operating parameters. Considerations such as pulse energy variability, ultrasound transducer properties, and spectral energy compensation, and their impact on measurements are presented. Spectral imaging was performed on tissue-simulating phantoms made of a custom polyvinyl chloride (PVC) plastisol gel designed to mimic both the optical properties (absorption, scattering) and acoustic properties (sound velocity, attenuation) of human breast tissue. Phantoms contained fluid channels at various depths which were injected with either oxyhemoglobin or organic dye solutions as absorptive targets. Spectral analysis of these solutions was performed for channel depths from 0.5 to 3 cm and at radiant exposures up to the ANSI maximum permissible exposure. Recovered photoacoustic spectra are compared with absorption spectra measured using spectrophotometry. Results provide insight into the influence of factors that impact the quality of spectroscopic measurements and reconstructed images in ultrasound-PAT systems.
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William C. Vogt, Congxian Jia, Keith A. Wear, Brian S. Garra, and Joshua Pfefer "Design and phantom-based validation of a bimodal ultrasound-photoacoustic imaging system for spectral detection of optical biomarkers", Proc. SPIE 9315, Design and Quality for Biomedical Technologies VIII, 931502 (11 March 2015);

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