We characterized a commercially available LED-based photoacoustic system (Prexion Inc. Japan) that offered a tunable LED pulse repetition rate (1K Hz, 2K Hz, 3K Hz, and 4K Hz) and found that the temporal resolution of the scanner is dependent on the choice of repetition rate. The LED system have lower power, and averaging is used to minimize the noise. The power from the LED arrays at 690 nm and 850 nm with 70 ns pulse width was measured to be 9.85 mW/cm2 and 31.55 mW/cm2. Beam profiling showed that the average intensity at the center of the transducer was ~ 18% higher than the power on the edges of the transducer. The system had axial and lateral resolution of 268 μm and 590 μm, respectively. This system has frame rates of 30 Hz and 0.15 Hz. Pencil lead inside chicken breast could be detected up to 3.2 cm deep with a frame rate of 15 Hz. Indocyanine green (ICG), methylene blue (MB), and DiR were used as exogenous contrasts to measure the limit of detection using PLED-PAI. The limit of detection values for ICG, MB, and DiR are 9 μM, 0.75 mM, and 68 μM, respectively. For in vivo experiments, DiR (positive control), 400,000 stem cells labeled with DiR, and bare stem cells (negative control) were subcutaneously injected on the spinal cord of male mice. Results shows difference between labeled and unlabeled cells in photoacoustic intensity using PLED-PAI. This experiment shows the capability of this LED-based system to perform molecular imaging at a price point and device footprint nearly a log order smaller than systems based on an optical parametric oscillator laser.
Ali Hariri, Jeanne Lemaster, and Jesse Jokerst, "A portable and economical LED-based photoacoustic imaging system for molecular imaging (Conference Presentation)," Proc. SPIE 10494, Photons Plus Ultrasound: Imaging and Sensing 2018, 104942C (Presented at SPIE BiOS: January 30, 2018; Published: 15 March 2018); https://doi.org/10.1117/12.2288563.5752219217001.
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Study of self-shadowing effect as a simple means to realize nanostructured thin films and layers with special attentions to birefringent obliquely deposited thin films and photo-luminescent porous silicon