Chu Shi-Wei, Tai Shih-Peng, Liu Tzu-Ming, Sun Chi-Kuang, Lin Chi-Hung
Department of Physics, National Taiwan University, Taipei 10617, Taiwan.
J Biomed Opt. 2009 Jan-Feb;14(1):010504. doi: 10.1117/1.3080722.
As a novel modality of optical microscopy, second-harmonic generation (SHG) provides attractive features including intrinsic optical sectioning, noninvasiveness, high specificity, and high penetrability. For a biomedical application, the epicollection of backward propagating SHG is necessary. But due to phase-matching constraint, SHG from thick tissues is preferentially forward propagation. Myosin and collagen are two of the most abundant fibrous proteins in vertebrates, and both exhibit a strong second-harmonic response. We find that the radiation patterns of myosin-based muscle fibers and collagen fibrils are distinct due to coherence effects. Based on these asymmetric radiation patterns, we demonstrate selective imaging between intertwining muscle fibers and type I collagen fibrils with forward and backward SHG modalities, respectively. Thick muscle fibers dominate the forward signal, while collagen fibril distribution is preferentially resolved in the backward channel without strong interference from muscle. Moreover, we find that well-formed collagen fibrils are highlighted by forward SHG, while loosely arranged collagen matrix is outlined by backward signal.
作为一种新型光学显微镜技术，二次谐波产生（SHG）具有诸多吸引人的特性，包括固有的光学切片、非侵入性、高特异性和高穿透性。对于生物医学应用而言，收集向后传播的SHG至关重要。但由于相位匹配限制，来自厚组织的SHG优先向前传播。肌球蛋白和胶原蛋白是脊椎动物中最丰富的两种纤维蛋白，两者都表现出强烈的二次谐波响应。我们发现，由于相干效应，基于肌球蛋白的肌纤维和胶原纤维的辐射模式截然不同。基于这些不对称的辐射模式，我们分别用向前和向后的SHG模式展示了在交织的肌纤维和I型胶原纤维之间的选择性成像。厚肌纤维主导向前信号，而胶原纤维分布在向后通道中优先得到分辨，且不受肌肉的强烈干扰。此外，我们发现排列良好的胶原纤维被向前的SHG突出显示，而排列松散的胶原基质则由向后信号勾勒出来。
