Abstract
This demonstration of photoacoustics involves a focused light-emitting diode (LED) pulse (620 nm wavelength) which illuminates an optically absorbing target. The rapid expansion generates an ultrasonic pulse detected by an immersion transducer. An LED is a cost-effective alternative to the traditional neodymium-doped Yttrium-Aluminum Garnet (Nd:YAG) laser and laser diode- that is most effective in near-infrared. The LED is driven by a home-made MOSFET driver capable of 100 A pulses. Focused pulses illuminate a horizontal 1.2 mm capillary tube filled with Fast Green Dye. A highly-diffuse Teflon cylindrical cavity (9 cm tall, 6 cm diam) contains the mounted capillary tube. A 2.25 MHz immersion transducer with four low-noise amplifier gain blocks (combined 86 decibel gain, 0.5- 30 MHz bandwidth), detects a time-averaged signal from over 1000 trials. Comparisons are made using India ink. Earlier, T. J. Allen and P. C. Beard used 35 percent hematocrit blood in a capillary tube at a 620 nm wavelength demonstrating the feasibility of photoacoustic medical imaging of vascular systems under the skin or shallow-tissue cancerous tumors (using tomography) as an alternative to radioactive medical imaging. Our work precedes a photoacoustic tomography demonstration using three targets in an open acrylic tank.
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