Real-time optical-resolution photoacoustic microscopy using fiber-laser technology

Abstract

Optical-resolution photoacoustic microscopy (OR-PAM) is an emerging technology providing visualization of superficial structures in vivo with optical-absorption contrast. High resolution is possible as the lateral spatial resolution is determined by the optical spot size rather than acoustic detection. The imaging speed is dictated by both the beam scanning speed and the laser pulse repetition rate. We are developing a realtime OR-PAM system that uses a high repetition rate pulsed laser and high speed XY mirror galvanometers. We have demonstrated OR-PAM imaging by employing a diode-pumped pulsed Ytterbium fiber laser with a pulse repetition rate ranging from 20 kHz - 600 kHz, second harmonic generation at a wavelength of 532 nm and average output power up to 13 W. In our study, we utilized 0.13μJ ~1-ns pulses. A photoacoustic probe consisting of a 45-degree glass prism in an optical index-matching fluid is used to transmit the focused output of the laser to the sample and also to reflect exiting photoacoustic signals to an ultrasound transducer. Phantom studies with a ~7.5-μm carbon fiber demonstrate the ability to image with ~7-μm optical lateral spatial resolution. Combined with a fast-scanning mirror oscillating at 800 (B-scan) lines per second, we demonstrate a system capable of C-scan imaging at 4 frames per second. These near-realtime frame-rates should permit clinical applications.