Time and frequency-domain biomedical photoacoustic imaging: a comparative study

In this study, we compare the time-domain (pulsed laser) and frequency-domain (FD) photoacoustic (PA) imaging techniques with respect to their signal-to-noise ratio (SNR), contrast and axial resolution. Experiments are performed using a dual-mode PA system and under the condition of maximum permissible exposure (MPE) for both methods. An analytical model of photoacoustic effect and a Krimholtz-Leedom-Matthaei (KLM) model for employed transducers are developed and used to analyze the experimental results. Experiments reveal that the contrast of the pulsed method suffers from the oscillating baseline and the resolution of the FD-PA is limited by the finite bandwidth as well as combining the in-phase and quadrature signals to generate the envelope signal; both are the requirements to maximize the SNR. It is shown that by increasing the laser power and decreasing the chirp duration within the safety limits, the SNR of the FD-PA method can be enhanced. Also it is demonstrated that the axial resolution of the FD method can be improved by combining its two channels; amplitude and phase. The improved resolution competes with the high resolution generated by pulsed technique.