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

Abstract

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.

Miniature probe for dual‐modality photoacoustic microscopy and white‐light microscopy for image guidance: A prototype toward an endoscope

“…In this study, the laser energy used for tissue imaging (Figures and ) was ~305 and ~750 nJ (per pulse) for 532 and 680 nm lasers, respectively. The fluence at the focus can thus be calculated as ~0.75 J/cm 2 (532 nm) and ~0.64 J/cm 2 (680 nm), which is comparable to that used in other OR‐PAM studies . In addition, as mentioned previously, the laser was focused below the tissue surface to conform to the ANSI safety limit.…”

“…The high resolution is provided by either a focused laser beam or a focused acoustic transducer. The former is termed as optical‐resolution PAM (OR‐PAM) , and the latter acoustic‐resolution PAM (AR‐PAM) . Over the past few years, many attempts have been made to implement PAM as miniature probes, also called photoacoustic endoscopy (PAE) , which enables PAM of internal organs.…”

High-Throughput Platform for Optoacoustic Probing of Genetically Encoded Calcium Ion Indicators

“…The use of a fast, wavelength-tunable dye laser for OA excitation increases probing and imaging speed of this setup by several orders of magnitude compared with previously reported design using optical parametric oscillator lasers (Li et al., 2016). Although mirror-based OA microscopy scanners can image at higher speeds, their effective FOV is diminished due to a highly non-uniform sensitivity field of an ultrasound (US) detector remaining in a constant position (Allen et al., 2018). In contrast, our mechanical scanning approach allowed for attaining uniform sensitivity field in detecting the generated US signals over large FOVs, an ideal trait for high-throughput protein screening.…”

Ultra-widefield photoacoustic microscopy with a dual-channel slider-crank laser-scanning apparatus for in vivo biomedical study

“…The present trends of OR-PAM imaging highly focused on the extended field of view (FOV) with reduced scanning time while maintaining a highly sensitive detection. Although the scanning time technically depends on the pulse repetition rate (PRR) of the laser and scanning mechanism, it is theoretically limited by the sound speed of the PA waves in biological tissues [ 23 ]. Several high-speed scanning techniques for OR-PAM have been reported, such as galvanometer scanner, microelectromechanical system (MEMS) scanner, hexagon-mirror scanner, and voice-coil scanning system [ 8 , [24] , [25] , [26] , [27] , [28] , [29] , [30] ].…”