Cardiovascular and cerebrovascular diseases, mainly caused by vessel blockage and degeneration, remain major causes of death worldwide. Therefore, there is an increasing demand for photoacoustic measurement and imaging techniques based on laser excitation to non-invasively evaluate vascular conditions. Our group has focused on the photoacoustic evaluation of liquid-filled sub-millimeter tubes using a semiconductor laser. Previous studies have shown that by utilizing acoustic resonance within the tube, the photoacoustic signal can be enhanced by selecting an appropriate laser pulse width, and that this resonance phenomenon can be used to assess tube deformation and wall stiffness. However, pulsed excitation limits measurement precision. In this study, to improve the accuracy of evaluating physical parameters such as inner diameter, we developed a system that uses amplitude-modulated continuous-wave laser excitation combined with lock-in detection. A semiconductor laser with a wavelength of 690 nm and an average power of 15 mW was used, and the modulation frequency was swept from 0.75 to 3 MHz. The amplitude and phase frequency responses of the photoacoustic signal were measured. The results indicated a relationship between structural dimensions, such as inner diameters, and the resonance frequency, suggesting that this method could be effective for evaluating the physical properties of sub-millimeter tubes.
Misutani et al. (Wed,) studied this question.