High-speed Volumetric Two-photon Endoscopic Imaging of Deep Brain Regions

Yu-Feng Chien^1,2*, Jyun-Yi Lin^1,2, Kuo-Jen Hsu^1,2, Yu-Hsuan Tsai^1,2, Po-Ting Yeh³, Shih-Kuo Chen³, Shi-Wei Chu^1,4

¹Department of Physics, National Taiwan University, Taipei, Taiwan
²Brain Research Center, National Tsing Hua University, Hsinchu, Taiwan
³Department of Life Science, National Taiwan University, Taipei, Taiwan
⁴Molecular Imaging Center, National Taiwan University, Taipei, Taiwan

* Presenter:Yu-Feng Chien, email:r05222023@ntu.edu.tw

Studying neural connections and activities in vivo is fundamental to understand brain functions. Given the cm-size brain and three-dimensional neural circuit dynamics, deep-tissue, high-speed volumetric imaging is necessary for brain study. With sub-micrometer spatial resolution, intrinsic optical sectioning, and deep-tissue penetration capability, two-photon microscopy (2PM) has found a special niche in neuroscience. However, current state-of-the-art 2PM typically relies on slow axial scan for volumetric imaging, and the maximal penetration depth is only about 1 mm. Here, we demonstrate that by integrating two gradient-index (GRIN) lenses into 2PM, both penetration depth and volume-imaging rate can be significantly improved. More specifically, the penetration depth is enhanced to 1 cm by a thin rod-like GRIN lens, while a tunable acoustic gradient-index (TAG) lens provides sub-second volume rate via 100kHz-1MHz 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