Toward dual-wavelength functional photoacoustic endoscopy: laser and peripheral optical systems development

Photoacoustic endoscopy (PAE) provides unique functional information with high spatial resolution at super depths. The provision of functional information is predicated on its strong spectroscopic imaging ability, and its deep imaging capability is derived from its ultrasonic detection of diffused photon absorption. To accurately image functional physiological parameters, it is necessary to rapidly alternate laser pulses of sufficient energy and different wavelengths. In this study, we developed peripheral optical systems for PAE based on two identical pulsed-laser systems to achieve the fast laser wavelength switching that is essential for accurate functional imaging. Each laser system was comprised of a tunable dye laser pumped by a solid-state, diode-pumped Nd:YLF laser. Both systems deliver adequate energy at the scanning head of the endoscope for imaging biological tissue in the optically diffusive regime (~0.3-0.6 mJ per pulse with a repetition rate of ~1 kHz). In this paper, we introduce the employed laser systems and design of the light delivery optics, and present results from an ex vivo animal imaging experiment that validates the system's multi-wavelength functional imaging capability.