Ultrafast laser-scanning optical resolution photoacoustic microscopy at up to 2 million A-lines per second

The imaging speed of optical resolution photoacoustic microscopy (OR-PAM) using pulsed excitation is fundamentally limited by the range ambiguity condition, which defines the maximum laser pulse repetition frequency (PRF). To operate at this theoretical upper limit and maximize acquisition speed, a custom-built fiber laser capable of operating at a PRF of up to 2 MHz was combined with a fast laser scanning optical OR-PAM system based on a stationary fiber-optic ultrasound sensor. A large area (10 mm × 10 mm) of the mouse ear was imaged within 8 s, when acquiring 16 million A-lines and operating the laser at a PRF of 2 MHz. This corresponds to a factor of four improvement in imaging speed compared to the fastest OR-PAM system previously reported. The ability to operate at high-imaging frame rates also allows the capture of hemodynamic events such as blood flow. It is considered that this system offers opportunities for high throughput imaging and visualizing dynamic physiological events using OR-PAM.