Fig. 5.

Embodiments of forward-viewing photoacoustic endoscopy (PAE) systems. (a) Schematic diagram of an optical-resolution PAE system based on a multi-core coherent fibre bundle and 2D galvanometer mirrors. Excitation light was focused at the proximal end of the fibre bundle and raster-scanned by the galvanometer mirrors for photoacoustic (PA) excitation. M, mirror; GS, glass; PD, photodiode; C1, C2, controllers; DX, DY, X and Y axis mirror drivers; OL, objective lens. (b) PA image of carbon fibre network. (c) PA image of the microvascular of a mouse ear. (a)-(c) were adapted from Ref. [65] with permission. (d) Schematic diagram of an optical-resolution PAE system based on a multimode optical fibre and a spatial light modulator (SLM). After calibration, the SLM modulated the incident light field to focus light through the multimode fibre for PA excitation. CMOS, complementary metal oxide semiconductor camera; BS1, beam splitter; L1, tube lens; OBJ, objective. (e) White light optical image and (f) PA image of a wire knot. (d)-(f) were adapted from Ref. [67] with permission. (g) Schematic diagram of an optical-resolution PAE system based on a multimode optical fibre and speckle illuminations. Pre-recorded speckle patterns were generated by a digital micro-mirror device at the distal end of the fibre for PA excitation. A model-based algorithm was used for image reconstruction. f1, tube lens; SMF, single-mode fibre; MMF, multimode fibre; CMOS, complementary metal oxide semiconductor camera. (h) Bright-field microscopy and (i) PA images of an absorbing micro-structure. Scale bar, 30 μm. (g)-(i) were adapted from Ref. [92] with permission. (j) Schematic diagram of an acoustic-resolution PAE system that is based on a multi-core coherent fibre bundle with a Fabry-Pérot (FP) cavity at its distal end to serve as a 2D array of ultrasound detectors. (k-l) PA images of the mouse abdominal skin microvasculature. (j)-(l) were adapted from Ref. [66] with permission.