Imaging deeper than the transport mean free path with multiphoton microscopy

Area of Science:

• Biomedical Optics
• Microscopy Technology
• In Vivo Imaging

Background:

• Multiphoton fluorescence microscopy offers deep in vivo imaging by utilizing long excitation wavelengths and nonlinear excitation.
• Tissue scattering and absorption fundamentally limit imaging depth in multiphoton microscopy.
• Two-photon microscopy's depth limitations are well-established, prompting development of three-photon microscopy.

Purpose of the Study:

• To extend the theoretical framework for two-photon microscopy depth limits to three-photon microscopy.
• To experimentally verify theoretical predictions for three-photon microscopy depth.
• To assess the feasibility of high-resolution imaging at extended depths.

Main Methods:

• Theoretical modeling of depth limits for three-photon microscopy.
• Experimental validation using tissue phantoms.
• Characterization of imaging resolution at significant depths.

Main Results:

• Theoretical framework for two-photon microscopy depth limits successfully extended to three-photon microscopy.
• Experimental results from tissue phantoms confirmed theoretical predictions.
• Achieved diffraction-limited imaging at 10 scattering mean free paths, exceeding previous limits.

Conclusions:

• Three-photon microscopy demonstrates potential for significantly deeper in vivo imaging than previously achieved.
• Current imaging depths are well below the theoretical limits of three-photon microscopy.
• Further technological development is necessary to fully exploit the capabilities of three-photon microscopy for biological applications.