Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139.
Optical Materials Engineering Laboratory, ETH Zurich, 8092 Zurich, Switzerland.
Proc Natl Acad Sci U S A. 2018 Sep 11;115(37):9080-9085. doi: 10.1073/pnas.1803210115. Epub 2018 Aug 27.
Recent technology developments have expanded the wavelength window for biological fluorescence imaging into the shortwave infrared. We show here a mechanistic understanding of how drastic changes in fluorescence imaging contrast can arise from slight changes of imaging wavelength in the shortwave infrared. We demonstrate, in 3D tissue phantoms and in vivo in mice, that light absorption by water within biological tissue increases image contrast due to attenuation of background and highly scattered light. Wavelengths of strong tissue absorption have conventionally been avoided in fluorescence imaging to maximize photon penetration depth and photon collection, yet we demonstrate that imaging at the peak absorbance of water (near 1,450 nm) results in the highest image contrast in the shortwave infrared. Furthermore, we show, through microscopy of highly labeled ex vivo biological tissue, that the contrast improvement from water absorption enables resolution of deeper structures, resulting in a higher imaging penetration depth. We then illustrate these findings in a theoretical model. Our results suggest that the wavelength-dependent absorptivity of water is the dominant optical property contributing to image contrast, and is therefore crucial for determining the optimal imaging window in the infrared.
最近的技术发展将生物荧光成像的波长窗口扩展到了短波近红外区域。在这里，我们展示了对荧光成像对比度如何因在近红外区域稍微改变成像波长而发生剧烈变化的机制理解。我们在 3D 组织模型和体内小鼠中证明，由于生物组织内水的光吸收会衰减背景光和高度散射光，因此图像对比度会增加。在荧光成像中，传统上会避免强组织吸收的波长，以最大限度地提高光子穿透深度和光子收集，然而我们证明，在水的峰值吸收波长（近 1450nm）处成像会在近红外区域产生最高的图像对比度。此外，我们通过对高度标记的离体生物组织进行显微镜检查，表明来自水吸收的对比度提高能够分辨更深的结构，从而实现更高的成像穿透深度。然后，我们通过理论模型说明了这些发现。我们的结果表明，水的波长依赖性吸光度是导致图像对比度的主要光学性质，因此对于确定红外光中的最佳成像窗口至关重要。
