Fig. 1. NIR-I fluorescence confocal microscopic images of blood vessels of the mouse brain stained with IR820^[26]. (a) Fluorescence microscopic images of blood vessels in the mouse brain at various vertical depths (0-500 µm); (b) 3D reconstructive images of blood vessels of the mouse brain. Scale bar: 50 μm

Fig. 2. The application of NIR-II spinning-disc confocal microscopy^[31]. (a) Optical layout of the NIR-II spinning-disc confocal microscopy; (b) Comparison of wide-field (left) and spinning-disc(right) confocal microscope imaging for (186±48) nm NIR fluorescent beads. Scale bar: 1 µm; (c) Z-stack projection of wide-field (top) and confocal (bottom) microscopic images of the fluorescent beads. Scale bar: 2 µm

Fig. 3. (a) Optical diagram of the stage-scanning NIR-II fluorescence confocal microscopic device^[32]; (b) Ex vivo NIR-II fluorescence confocal imaging in large area (3000 µm×2 000 µm) of brain in a mouse injected with p-FE^[33]; (c) 3D reconstruction of ex vivo NIR-II fluorescence confocal imaging of vasculatures in brain of mouse within a small volume (left side, 200 µm×200 µm×200 µm) and (d) a large volume (right side, 400 µm×400 µm×400 µm)^[33]; (c) Two-color fluorescence confocal microscope imaging of a tumor tissue and blood vessels in the NIR-II window^[33]

Fig. 4. (a) Schematic illustration of NIR-II fluorescence confocal scanning microscopic imaging system; (b) Invivo NIR-II fluorescence confocal scanning microscopic imaging of cerebrovasculature in a mouse with craniotomy at various depths from 40 to 300 µm^[34]

Fig. 5. (a) Schematic illustration of NIR-II fluorescence confocal scanning microscopic imaging system; (b) Three-dimensional images of cerebral vessels of a living mouse using NIR-II fluorescence confocal microscope^[35]

Fig. 6. (a) The schematic illustration of the NIR-II fluorescence confocal microscopic imaging system. Red arrows: fine adjustment. Blue arrows: rotation. Green arrows: coarse adjustment. The excitation and imaging light paths are showed on the right panel; (b) In vivo NIR-II fluorescence confocal microscopic imaging of cerebral blood vessels of the rhesus macaque with large penetration depth^[41](Scale bar: 100 µm)

Fig. 7. (a) In vivo noninvasive NIR-IIb fluorescence confocal imaging of the mouse tumor^[42]. Scale bar: 500 µm. (b)-(c) High-resolution fluorescence confocal imaging of tumor vessels at a depth of 180 μm: (b) Scale bar: 200 µm; (c) Scale bar: 50 µm

Fig. 8. (a) Schematic illustration of the NIR-II reflectance confocal microscope; (b) Confocal images of white matter under CW and pulsed laser illumination with the same power at 1310 nm, 1610 nm, 1630 nm, and 1650 nm; (c) In vivo reflectance confocal microscope images at various depths^[43] （Scale bars: 30 μm）

Fig. 9. (a) Schematic of NIR-II fluorescence mesoscopic system; (b) In vivo through-skull cerebral vascular imaging of a local cerebral ischemia mouse with photochemically induced thrombosis^[51]

Fig. 10. In vivo imaging of an adult mouse brain vasculature at various depths with PbS/CdS quantum dots^[52]. Scale bar: 50 μm

Fig. 11. Non-invasive in vivo confocal microscopic imaging of intact mouse head in NIR-IIc window^[53]. (a) Schematic of intact mouse confocal microscopic head imaging in NIR-IIc window; (b) Three-dimensional volumetric images of blood vessels in an intact mouse head visualized through the scalp; (c) High-resolution fluorescence confocal images of blood vessels at various depths through intact mouse head imaged with a PMT or SNSPD in NIR-IIb or NIR-IIc window

Fig. 12. (a) A simplified optical diagram of NIR-II confocal fluorescence lifetime microscopic imaging system; (b) Anin vivo NIR-II FLIM image of cerebral vessels in mouse, which was intravenously injected with TB1 dots; (c) Fluorescence decay curves measured at the arrow in (b), showing the fluorescence lifetime of TB1 dots in vessels is 1.5 ns^[35]

Fig. 13. In vivo three-dimensional NIR-II fluorescence imaging of mouse ear vessels labeled with IR820-BSA^[54]. The fluorescence intensity attenuation curve of the blood vessel at the yellow line is shown in the lower right corner