Optimization of light source parameters for photoacoustic imaging: trade-offs, technologies, and clinical considerations

The selection of light sources for photoacoustic imaging, a biomedical imaging technology, remains a critical yet under-informed topic. This review discusses the key trade-offs in light source parameters (e.g. wavelength, pulse energy, repetition frequency), safety, and practical considerations. We analyse these factors in the context of underlying imaging physics and the limits imposed by regulatory standards across various wavelength ranges. Attention is given to light source selection for photoacoustic tomography, optical and acoustic resolution microscopy, and endoscopy, which pose different requirements for pulse energies and repetition frequencies, to achieve real-time imaging at the desired depth. Current PA imaging light sources, including high-power lasers with optical parametric oscillators, fibre lasers, laser diodes, vertical-cavity surface-emitting lasers, and light-emitting diodes, are reviewed in terms of wavelength availability, energy, repetition frequency, beam quality, portability, and safety. Clinically viable systems require careful consideration of fibre coupling limitations, maximum permissible exposure at the tissue interface, imaging field of view, and signal-to-noise ratio. Further practical considerations include energy efficiency and thermal management in clinical settings. We also outline the present gaps in the available light source technologies, where the development of new sources may enable new PA imaging capabilities, both scientific and clinical. By offering an overview of these considerations, this review aims to guide researchers, industry, and clinicians in selecting optimal light sources and advancing the development of light sources that address current gaps in available technology.