Penetration depth of single-, two-, and three-photon fluorescence microscopic imaging through human cortex...

Area of Science:

• Neuroscience
• Biophysics
• Optical Imaging

Background:

• Fluorescence microscopy is crucial for visualizing neural structures.
• Penetration depth and image quality are key limitations in deep tissue imaging.
• Understanding the performance of multiphoton microscopy in human cortical tissue is essential.

Purpose of the Study:

• To investigate the penetration depth, image resolution, and signal level of single-, two-, and three-photon fluorescence microscopy in human cortex.
• To compare the performance of two- and three-photon excitation in different cortical tissue layers.
• To evaluate the influence of numerical aperture on imaging performance.

Main Methods:

• Simulations were performed on a double-layer human cortex model (gray and white matter).
• Analysis focused on signal level and transverse image resolution.
• Performance was assessed under single-, two-, and three-photon excitation.
• The effect of numerical aperture was also simulated.

Main Results:

• Three-photon excitation signal level is significantly affected by white matter presence.
• Two-photon excitation maintains a better signal level than three-photon excitation, with only a slight decrease in image resolution.
• A penetration depth of 1500 microm with near-diffraction-limited resolution is achievable in thick gray matter using three-photon excitation.
• Numerical aperture has a minimal impact on image resolution and signal level due to the nonlinear excitation process.

Conclusions:

• Three-photon microscopy enables deeper penetration in human cortical gray matter.
• Two-photon microscopy offers a favorable balance between signal level and resolution for certain applications.
• The choice between two- and three-photon excitation depends on the specific imaging depth and tissue composition.
• Numerical aperture has a limited effect on multiphoton imaging performance in the human cortex.