Quantification of optical attenuation coefficient based on continuous wavelet transform of photoacoustic signals measured by a focused broadband acoustic sensor
Quantification of optical attenuation coefficient based on continuous wavelet transform of photoacoustic signals measured by a focused broadband acoustic sensor
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DOI：
10.1117/12.2041676
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发表时间：
2014-03
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影响因子：
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通讯作者：
T. Hirasawa;S. Okawa;M. Fujita;T. Kushibiki;M. Ishihara
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文献类型：
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作者：
T. Hirasawa;S. Okawa;M. Fujita;T. Kushibiki;M. Ishihara
提出了一种量化光吸收材料有效衰减系数的方法，该方法利用连续小波变换计算光声信号的时间分辨频谱。为了将该方法应用于血管血氧监测，本研究探讨了如何减小血管直径对PA信号时间分辨频谱的影响。对不同直径的血管模体产生的功率放大器信号进行了数值模拟。模拟结果表明，通过测量小范围的PA信号，PA信号的频率与血管直径无关。当测量面积为0.035 mm，频率为1.5 MHz时，模拟功率放大器信号的频率与有效衰减系数成正比，相关系数为0.99，斜率为0.035 MHz/cm-1。因此，我们使用了聚焦声学传感器，其聚焦于上述测量区域。它由一层P(VDF-TrFE)薄膜组成，具有宽频带的特点。利用聚焦声传感器进行的实验结果表明，血管模体产生的PA信号的频率与有效衰减系数成正比，相关系数为0.96，但频率偏差为0.135 MHz，对应的有效衰减系数为3.46 cm-1。由于传感器对准等实验因素造成了较大的偏差，因此需要提高对实验因素的鲁棒性。
We proposed a method of quantifying the effective attenuation coefficients of optical absorbers which uses the continuous wavelet transform to calculate the time-resolved frequency spectra of photoacoustic (PA) signals. In order to apply the method to blood oxygenation monitoring of blood vessels, this study discusses how to reduce the effects of blood vessel diameters, which influences on the time resolved frequency spectra of PA signals. Numerical simulations which calculate the PA signals produced from blood vessel phantoms with various diameters were performed. The simulations revealed that the frequency of PA signal became independent from the vessel diameters by measuring the PA signal from small area. The frequencies of simulated PA signals were proportional to the effective attenuation coefficients with a correlation coefficient of 0.99, and a slope of 0.035 MHz/cm-1 under condition that the measurement area was 4.0 mm at a frequency of 1.5 MHz. Thus we used the focused acoustic sensor of which focusing the foregoing measurement area. It consisted of a P(VDF-TrFE) film, which was characterized by broad frequency band. As results of experiments using the focused acoustic sensor, the frequencies of PA signals produced from blood vessel phantoms were proportional to the effective attenuation coefficients with correlation coefficient of 0.96 although the frequencies were suffered from deviations of 0.135 MHz, which corresponded to the effective attenuation coefficient of 3.46 cm-1. Since the large deviations were caused by experimental factors such as sensor alignment, it is required to improve robustness to the experimental factors.