Grüneisen-relaxation photoacoustic microscopy at 1.7 µm and its application in lipid imaging.

Abstract
We report the first, to the best of our knowledge, demonstration of Grüneisen relaxation photoacoustic microscopy (GR-PAM) of lipid-rich tissue imaging at the 1.7 µm band, implemented with a high-energy thulium-doped fiber laser and a fiber-based delay line. GR-PAM enhances the image contrast by intensifying the region of strong absorbers and suppressing out-of-focus signals. Using GR-PAM to image swine-adipose tissue at 1725 nm, an 8.26-fold contrast enhancement is achieved in comparison to conventional PAM. GR-PAM at the 1.7 µm band is expected to be a useful tool for label-free high-resolution imaging of lipid-rich tissue, such as atherosclerotic plaque and nerves.

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Fig. Swine muscular tissue images under (a)-(c) OR-PAM and (d)-(f) GR-PAM at (a), (d) 1700; (b), (e) 1725; and (c), (f) 1750 nm. (g) Reference confocal microscopy image at the same region.

Jiawei Shi, Can Li, Huade Mao, Yuxuan Ren, Zhi-Chao Luo, Amir Rosenthal, and Kenneth K. Y. Wong