Effects of diameter of optical absorber visualized by an annular array AR-PAM system on spectrum characteristics of photoacoustic signals

Spectrum characteristics of photoacoustic signals are potential indicators to assess the structural information of optical absorbers. This study investigated whether a spectrum analysis approach can evaluate microvascular diameters obtained by an annular array AR-PAM system. First, 2D numerical simulations were performed to estimate spectral changes in five absorbers with different diameters from 30 to 200 μm. Slope and intercept values from the regression line of the spectrum curve were calculated. Second, the estimated changes were validated by acquiring photoacoustic signals from tungsten wires with five different diameters. Both in numerically and experimentally, spectrum analysis showed the larger the diameter, the greater the lower frequency components, resulting in steeper slope and greater intercept values. Finally, photoacoustic signals acquired from cutaneous microvessels were analyzed. The FWHM diameter of the vessels were corresponded to the slope (r = −0.595; p < 0.05) and intercept (r = 0.657; p < 0.05) values, respectively.