In recent years, many methods have been investigated to improve imaging speed in photoacoustic microscopy (PAM). These methods mainly focused upon three critical factors contributing to fast PAM: laser pulse repetition rate, scanning speed, and computing power of the microprocessors. A high laser repetition rate is fundamentally the most crucial factor to increase the PAM speed. In this paper, we review methods adopted for fast PAM systems in detail, specifically with respect to light sources. To the best of our knowledge, ours is the first review article analyzing the fundamental requirements for developing high-speed PAM and their limitations from the perspective of light sources.

Acoustically probing biological tissues with light or sound, photoacoustic and ultrasound imaging can provide anatomical, functional, and/or molecular information at depths far beyond the optical diffusion limit. However, most photoacoustic and ultrasound imaging systems rely on linear-array transducers with elevational focusing and are limited to two-dimensional imaging with anisotropic resolutions. Here, we present three-dimensional diffractive acoustic tomography (3D-DAT), which uses an off-the-shelf linear-array transducer with single-slit acoustic diffraction. Without jeopardizing its accessibility by general users, 3D-DAT has achieved simultaneous 3D photoacoustic and ultrasound imaging with optimal imaging performance in deep tissues, providing near-isotropic resolutions, high imaging speed, and a large field-of-view, as well as enhanced quantitative accuracy and detection sensitivity. Moreover, powered by the fast focal line volumetric reconstruction, 3D-DAT has achieved 50-fold faster reconstruction times than traditional photoacoustic imaging reconstruction. Using 3D-DAT on small animal models, we mapped the distribution of the biliverdin-binding serpin complex in glassfrogs, tracked gold nanoparticle accumulation in a mouse tumor model, imaged genetically-encoded photoswitchable tumors, and investigated polyfluoroalkyl substances exposure on developing embryos. With its enhanced imaging performance and high accessibility, 3D-DAT may find broad applications in fundamental life sciences and biomedical research.

Photoacoustic microscopy (PAM) is an important imaging tool that can noninvasively visualize the anatomical structure of living animals. However, the limited scanning area restricts traditional PAM systems for scanning a large animal. Here, we firstly report a dual-channel PAM system based on a custom-made slider-crank scanner. This novel scanner allows us to stably capture an ultra-widefield scanning area of 24 mm at a high B-scan speed of 32 Hz while maintaining a high signal-to-noise ratio. Our system's spatial resolution is measured at ∼3.4 μm and ∼37 μm for lateral and axial resolution, respectively. Without any contrast agent, a dragonfly wing, a nude mouse ear, an entire rat ear, and a portion of mouse sagittal are successfully imaged. Furthermore, for hemodynamic monitoring, the mimicking circulating tumor cells using magnetic contrast agent is rapidly captured in vitro. The experimental results demonstrated that our device is a promising tool for biological applications.

Photoacoustic imaging (PAI) has become a powerful biomedical imaging technique in the last decades, combining optical and ultrasound imaging (USI) principles. Among the various configurations, optical-resolution photoacoustic microscopy (OR-PAM) served as a vital tool for high-resolution and high-sensitivity imaging of small animals in vivo. However, the current systems have limited mobility, which hinders preclinical and clinical research in cramped spaces. Here, we propose a compact ( $510\times 660\times1660$ mm3) transportable PAI system with stimulated Raman scattering (SRS) spectroscopy to address this challenge. The proposed system is designed for complete mobility, overcoming space restrictions. We demonstrate the feasibility of the system by imaging in vitro phantoms and in vivo mice. Additionally, we verify its functional imaging capabilities by visualizing oxygen saturation levels in vivo mice ears. Our results indicate that the proposed transportable PAI system maintains fast data acquisition time, superior image quality, and multispectral imaging capabilities. This shows great potential for expanding the applications of OR-PAM to a wider range of research and clinical scenarios.

We demonstrate a novel electro-optic swept source for wavenumber-linear interferometric sensing and imaging applications. The electro-optic swept source based on an acousto-optic tunable filter (AOTF) provides high environmental stability and arbitrary drive function sweeping because the electro-optic wavelength selection does not depend on a mechanical moving component to tune the output lasing wavelength. We show improved stability of the suggested electro-optic swept source, compared to a conventional swept source based on a fiber Fabry–Perot tunable filter (FFP-TF). Various types of wavelength sweeping are demonstrated by applying the programmed drive function to the applied radio frequency (RF) of the AOTF. We demonstrated improved image quality of optical coherence tomography (OCT) by using the wavenumber-linear drive function of a simple triangular signal, which has a high wavenumber-linearity with an R-square value of 0.99991.

Photoacoustic (PA) imaging (PAI) has emerged as a promising biomedical technique based on the PA effect, wherein ultrasonic emission occurs upon the absorption of a short-pulsed laser by irradiating objects, such as biological tissues.^{1 – 3} The resultant ultrasonic waves, termed PA waves, are captured by a transducer to form PA images for diverse applications [Fig. 1(a)]. PA microscopy (PAM) is a prevalent form of PA imaging that achieves micron-level spatial resolution by focusing either the optical or acoustic beam or both. According to the focusing type, the PAM system is categorized into optical-resolution PAM (OR-PAM) and acoustic-resolution PAM (AR-PAM).^5,6 Using wide-field optical excitation, AR-PAM can achieve a 3 to 5 times larger penetration depth than OR-PAM [Fig. 1(b)]. By contrast, because an optical focus is approximately 10 times tighter than an acoustic focus, OR-PAM excels in delivering higher resolution, which has the capability to image physiological and pathological changes in single capillaries.⁷ Furthermore, the remarkable optical absorption contrast makes PAM a promising imaging tool across various research domains including biology, dermatology, neurology, oncology, ophthalmology, and pathology.⁸