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12 February 2009 Design, fabrication, and testing of a dual-band photoacoustic transducer
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The absorption coefficients in most biological tissues range from 1 cm-1 to 10 cm-1, which produce photoacoustic signal with peak frequency lower than 5 MHz. However, the lower operating frequencies mean equivalently larger wavelengths, which are incapacitation to resolve smaller objects. In order to obtain the excellent performance of images in both sensitivity and resolution, this study discusses the design and fabrication of the dual frequencies photoacoustic transducer (DFPT) with 36°-rotated, Y-cut lithium niobate (LiNbO3) material. The DFPT had a diameter of 6 mm and comprised two concentric rings of equal area with center frequency of the outer and inner elements as 4.9 MHz and 14.8 MHz, respectively. Moreover, there was a 0.65 mm hole in the DFPT surface for insertion of an optical fiber, which solved conventional light-placing problem. The experiment was performed with an agarose phantom which mixed glass beads with various concentration of black stain to create different optical absorptions. The absorption coefficients of absorbers are 5.6 cm-1 and 11.8 cm-1, respectively. The mean amplitude between the two absorbers differs by 0.5 dB at band 0-5 MHz, while the difference increases to 5.9 dB at band 6-15 MHz. The results show that the DFPT not only provides high ultrasonic resolution but also enhances the contrast based on higher frequency subbands for photoacoustic imaging. The potential of improving the contrast between biological tissues and contrast agent with a significant higher absorption is revealed. In the future, the DFPT will be applied to in vivo investigation with gold nanoparticles. Bioconjugated gold nanoparticles have been used as a photoacoustic contrast agent as well as a molecular probe to target cancer cells in a small animal model. The denseness of targeted gold nanoparticles on tumor results in a higher absorptions, which means higher frequency signals comparing to those of surrounding tissues. Thus, DFPT will assist in recognizing the tumor region for a better diagnosis.
© (2009) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Jian-Hung Liu, Chen-Wei Wei, Yae-Lin Sheu, Yu-Tsung Tasi, Yu-Hsin Wang, and Pai-Chi Li "Design, fabrication, and testing of a dual-band photoacoustic transducer", Proc. SPIE 7177, Photons Plus Ultrasound: Imaging and Sensing 2009, 717712 (12 February 2009);

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