Su Shin-Yuan, Li Pai-Chi
Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan.
Opt Express. 2011 Jan 17;19(2):1174-82. doi: 10.1364/OE.19.001174.
A Q-switched Nd:YAG laser providing nanosecond pulse durations and millijoule pulse energies is suitable for typical biomedical PA applications. However, such lasers are both bulky and expensive. An alternative method is to use a diode laser, which can achieve a higher pulse repetition frequency. Although the energy from a diode laser is generally too low for effective PA generation, this can be remedied by using high-speed coded laser pulses, with the signal intensity of the received signal being enhanced by pulse compression. In this study we tested a version of this method that employs coded excitation. A 20-MHz PA transducer was used for backward-mode PA detection. A frequency-coded PA signal was generated by tuning the interval between two adjacent laser pulses. The experimental results showed that this methodology improved the signal-to-noise ratio of the decoded PA signal by up to 19.3 dB, although high range side lobes were also present. These side lobes could be reduced by optimizing the compression filter. In contrast to the Golay codes proposed in the literature, the proposed coded excitation requires only a single stimulus.
提供纳秒脉冲持续时间和毫焦耳脉冲能量的调Q Nd:YAG激光适用于典型的生物医学光声应用。然而，这种激光器体积庞大且价格昂贵。另一种方法是使用二极管激光器，它可以实现更高的脉冲重复频率。虽然二极管激光器产生的能量通常太低，无法有效地产生光声信号，但可以通过使用高速编码激光脉冲来弥补这一不足，通过脉冲压缩增强接收信号的信号强度。在本研究中，我们测试了这种采用编码激励方法的一个版本。使用一个20MHz的光声换能器进行反向模式光声检测。通过调整两个相邻激光脉冲之间的间隔来产生频率编码的光声信号。实验结果表明，这种方法将解码后的光声信号的信噪比提高了19.3dB，尽管也存在高范围旁瓣。通过优化压缩滤波器可以减少这些旁瓣。与文献中提出的格雷码不同，所提出的编码激励只需要一次刺激。
