TABLE 1.

The current technical state of the art in three-photon microscopy (3PM).

Advanced modules	Advantages	Limitations	References
The optimization of 3PM (4.1)	Optimization of Excitation; Fluorescence, Emission, Microscope, Optical power	–
Adaptive excitation source (4.2)	Less power requirement	System complexity; Improvement coefficient depends on the area of the ROI size relative to the entire FOV	Li et al., 2020
Adaptive optics (4.3)	Better spatial resolution Larger fluorescence signal	System complexity; Requires correction time	Rodríguez et al., 2021; Streich et al., 2021; Qin et al., 2022; Sinefeld et al., 2022
Bessel beam (4.4)	Higher speed for volumetric imaging	Lacks resolution along the axial dimension	Chen et al., 2018; Rodríguez et al., 2018
Remote focusing (4.5)	Faster axial scanning	Used to introduce artificial aberration	Mok et al., 2019; Weisenburger et al., 2019; Klioutchnikov et al., 2022
Temporal focusing (4.6)	Higher frame rate	Tissue penetration capability was restricted	Toda et al., 2017
Light-sheet (4.7)			Escobet-Montalbán et al., 2018
Miniaturization (4.8)	Allows for freely moving	Limited imaging FOV	Klioutchnikov et al., 2020, 2022
Resonant enhancement (4.9)	One wavelength can excite fluorescence of multiple colors at the same time	Only some specific dyes and fluorophores process this property.	Hontani et al., 2021