In vivo deep-brain blood flow speed measurement through third-harmonic generation imaging excited at the 1700-nm window.

Hongji Liu,Ke Wang,Jia Li,Ziwei Zhuang,Shen Tong,Weixin Xie,Xiangquan Deng,Ping Qiu,Xinlin Chen

doi:10.1364/boe.389662

Abstract

Measurement of the hemodynamic physical parameter blood flow speed in the brain in vivo is key to understanding brain physiology and pathology. 2-photon fluorescence microscopy with single blood vessel resolution is typically used, which necessitates injection of toxic fluorescent dyes. Here we demonstrate a label-free nonlinear optical technique, third-harmonic generation microscopy excited at the 1700-nm window, that is promising for such measurement. Using a simple femtosecond laser system based on soliton self-frequency shift, we can measure blood flow speed through the whole cortical grey matter, even down to the white matter layer. Together with 3-photon fluorescence microscopy, we further demonstrate that the blood vessel walls generate strong THG signals, and that plasma and circulating blood cells are mutually exclusive in space. This technique can be readily applied to brain research.

Highlights

The cells in the brain rely on circulating blood for continuous oxygen and nutrient supply
In order not to incur the exogenous fluorescent label which might be toxic to the animals, it is desirable to develop a label-free technique for measuring blood flow speed through multiphoton microscopy (MPM)
First we verify that blood vessel walls yield third-harmonic generation (THG) signals

Summary

Introduction

The cells in the brain rely on circulating blood for continuous oxygen and nutrient supply. Two groups demonstrated that label-free third-harmonic generation (THG) microscopy can be used for measuring blood flow speed in animals in vivo [3,4]. We demonstrate that THG microscopy exited at the 1700-nm window can be used to visualize and measure blood flow speed in the mouse brain in vivo down to the white matter layer.

Results

Conclusion