2-photon Endoscopic System with 2 Gradient-index Lenses for Deep and High-speed 3D Brain Imaging

Yu-Feng Chien^1*, Jyun-Yi Lin^1,2, Yu-Hsuan Tsai^1,2, Shi-Wei Chu^1,3

¹Department of Physics, National Taiwan University, Taipei, Taiwan
²Brain Research Center, National Tsing Hua University, Hsinchu, Taiwan
³Molecular Imaging Center, National Taiwan University, Taipei, Taiwan

* Presenter:Yu-Feng Chien, email:h63062005@gmail.com

Studying functional neural connections in vivo is essential to understand mechanisms of brain. Given cm-size and three-dimensional (3D) active neural circuits, deep-tissue and high-speed 3D imaging is necessary for brain study. With sub-μm spatial resolution, intrinsic optical sectioning, and deep-tissue imaging ability, 2-photon microscopy (2PM) has gained a special niche in neuroscience. However, state-of-the-art 2PM currently relies on slow axial scan for volumetric imaging, and the deepest imaging depth it could reach is only ~ 1 mm. Here, we demonstrate that by integrating two gradient-index (GRIN) lenses into 2PM, both imaging depth and volume-imaging rate can be significantly enhanced. More specifically, the imaging depth is improved to 1 cm by a thin rod-like GRIN lens, while a tunable acoustic GRIN (TAG) lens provides sub-second volume rate via 100 kHz ~ 1 MHz axial scan. This technique allows, for the first time, the study of calcium dynamics in cm-deep brain regions with sub-cellular and sub-second spatiotemporal resolution, thus paving the way for construction of deep-brain functional connectome.

Keywords: Gradient-index lenses, Endoscopic imaging, Functional monitoring and imaging, Three-dimensional microscopy, Nonlinear microscopy