Dual-Contrast Nonlinear Photoacoustic Sensing and Imaging Based on Single High-Repetition- Rate Pulsed Laser

Photoacoustic imaging (PAI) is a fast-developing non-invasive imaging technique, which provides optical contrast in deep scattering tissue with high spatial resolution. Conventional photoacoustic (PA) imaging has been widely studied based on linear PA effect, which is induced by single short laser pulse. Recently, nonlinear photoacoustic effect has been proposed by using two consecutive laser pulses with two laser sources. In this paper, we report a dual-contrast nonlinear photoacoustic (dNPA) sensing and imaging technique by single high-repetition-rate laser induced nonlinear PA effect. Using the high-repetition-rate pulsed laser, two different kinds of imaging contrasts can be extracted: optical and thermal contrasts. Unlike conventional PA imaging that exhibits optical absorption only, we could extract thermal contrast that is reflected by the rising slope/trend of temperature and consequent PA signals. In this paper, the high-repetition-rate nonlinear PA effect and dual-contrast mechanism were proposed in theory with detailed mathematical modeling. The dual-contrast PA sensing and imaging were demonstrated by experimental results with both in vitro phantom and ex vivo porcine tissues. The results indicate both optical absorption and thermal accumulation properties of different samples, which could enhance the image contrast significantly.