Dr. Jinjun Xia Profile

Dr. Jinjun Xia

Assistant Professor at Lawrence Technological Univ

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Proceedings Article | 16 March 2020 Paper

Photoacoustic signal waveform numerical simulation

Jinjun Xia, Yuehua Wang, Na Yu

Proceedings Volume 11240, 112404M (2020) https://doi.org/10.1117/12.2541755

KEYWORDS: Absorption, Wave propagation, Photoacoustic spectroscopy, Signal detection, Sensors, Acoustics, Spherical lenses, Interfaces, Diffraction, Signal generators

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In this paper, we numerically simulate the photoacoustic signal waveforms based on the Huygens-Fresnel principle. In this model, laser absorption medium which is the source of generating photoacoustic signal is divided into microspheres. A N-shaped carrier ultrasonic spherical wave is generated by each microsphere due to the absorption of short laser pulse and propagates outwards from the sphere center. The N-shaped waves reach the detection point through the direct propagation and the reflection from the medium interface. The photoacoustic signal generated by the overall absorption medium detected in the observation point is calculated as the summation of all these individual N-shaped photoacoustic waves including the original and reflected waves by considering the temporal delay and attenuation induced by the propagation distance. The envelope of the resulted summation is the transducer-detectable photoacoustic signal waveform. The photoacoustic signal profiles and spectra under different media interface boundary conditions and propagation distances are studied. The effect of optical absorption to photoacoustic signal bandwidth is studied as well. This numerical investigation demonstrates the formation of the detected photoacoustic signals and improves the understanding of the mechanism of the photoacoustic signal generation.

Proceedings Article | 20 March 2017 Paper

Polarization enhanced laser speckle contrast imaging for vascular dynamic study

Ashley Julin, Jinjun Xia

Proceedings Volume 10063, 1006315 (2017) https://doi.org/10.1117/12.2249928

KEYWORDS: Polarization, Laser speckle contrast imaging, Speckle, Blood vessels, Solids, Imaging systems, Laser speckle imaging, Polarization control, Particles, Linear polarizers

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The contrast in laser speckle imaging with controlled polarization conditions for illumination and imaging was studied in a blood vessel mimic flow phantom. Either linear or circular polarization was used to illuminate samples. The polarization in imaging was controlled, to be either orthogonal (cross) or parallel to the polarization of the illumination beam. Temporal contrast imaging, was obtained by calculating the pixelwise contrast among a series of successfully recorded snapshot images. Then, temporal-spatial contrast imaging was calculated from temporal contrast imaging by calculating the spatial contrast among the pixels in a temporal contrast image. The results have shown that the parallel polarization setting had a near doubled contrast dynamic range compared to the cross polarization setting. Linear polarization and circular polarization did not show significant differences in contrast dynamic range. The results obtained here can be generally applied to all laser speckle based imaging, because they are all interference based imaging, and it is suggested that parallel polarization imaging setting can be considered for a better imaging contrast between flow and solid tissue background. In addition, in a preliminary flow speed test, the temporal-spatial contrast values did not show a statistical difference among different flow speeds due to the current experiment settings.

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