| Photoacoustic imaging(PAI) inspection has advantages of non-contact, high contrast, high resolution and great depth of detection, which has great potential in the field of biomedical diagnosis. Frequency-domain photoacoustic imaging(FD-PAI) inspection technique uses low-energy and continuously modulated laser for sample excitation and acoustic detector for inspection of the laser-induced modulated acoustic signal. By analyzing the acoustic characteristics(amplitude and phase) of the acoustic signal, FD-PAI conducts non-destructive detection of biological tissue or material properties. PAI has the contrast of optical inspection methods and the depth of acoustic inspection methods, which will play an indispensable role in the field of biomedical detection. In this paper, research for the FD-PAI of simulated biological tissue has been carried out, including modulated laser-induced one-dimensional mathematical model of photoacoustic pressure, simulation analyses of photoacoustic frequency characteristics, system for photoacoustic imaging inspection and inspection tests for simulated biological tissue.First, we used translucent optical scattering medium for simulation of biological tissue. Based on diffusion transmission approximation theory, equation of heat conduction and theory of elastic wave, a one-dimensional frequency-domain optical sound pressure mathematical model has been established. By using the model, simulation analyses of the effect of parameters(optical absorption coefficient, scattering coefficient, thermal conductivity, thermal diffusivity, thermal expansion coefficient, bulk modulus and absorption layer thickness) to the photoacoustic signal’s frequency-domain characteristics have been carried out. Meanwhile, the Monte Carlo method has been used for simulation of optical field in biological tissue.Secondly, system for FD-PAI has been built, including establishing of hardware platform, software programming based on Lab VIEW for automatic control of displacement platform, feature acquisition and analysis of acoustic signal programming, which can make planning and selection for the scanning path, set scan parameters, and make acquisition for the amplitude and phase of the photoacoustic signal.Lastly, by using the system established, frequency-domain photoacoustic imaging inspections for simulated biological tissue have been carried out. When given a certain modulation frequency, optical absorption and structural changes have been detected in position scan inspection by the phase and amplitude of the acoustic signal. When given a certain position,reflection characteristics of biological tissue at different depths have been inspection in frequency response(amplitude-frequency and phase-frequency) test. |
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