Hesse Bernhard, Stier Deborah, Cotte Marine, Forien Jean-Baptiste, Zaslansky Paul
European Synchrotron Radiation Facility, Grenoble, France.
Xploraytion GmbH, Berlin, Germany.
Biomed Opt Express. 2018 Dec 3;10(1):18-28. doi: 10.1364/BOE.10.000018. eCollection 2019 Jan 1.
For biomedical research, successful imaging of calcified microstructures often relies on absorption differences between features, or on employing dies with selective affinity to areas of interest. When texture is concerned, e.g. for crystal orientation studies, polarization induced contrast is of particular interest. This requires sufficient interaction of the incoming radiation with the volume of interest in the sample to produce orientation-based contrast. Here we demonstrate polarization induced contrast at the calcium K-edge using submicron sized monochromatic synchrotron X-ray beams. We exploit the orientation dependent subtle absorption differences of hydroxyl-apatite crystals in teeth, with respect to the polarization field of the beam. Interaction occurs with the fully mineralized samples, such that differences in density do not contribute to the contrast. Our results show how polarization induced contrast X-ray fluorescence mapping at specific energies of the calcium K-edge reveals the micrometer and submicrometer crystal arrangements in human tooth tissues. This facilitates combining both high spatial resolution and large fields of view, achieved in relatively short acquisition times in reflection geometry. In enamel we observe the varying crystal orientations of the micron sized prisms exposed on our prepared surface. We easily reproduce crystal orientation maps, typically observed in polished thin sections. We even reveal maps of submicrometer mineralization fronts in spherulites in intertubular dentine. This Ca K-edge polarization sensitive method (XRF-PIC) does not require thin samples for transmission nor extensive sample preparation. It can be used on both fresh, moist samples as well as fossilized samples where the information of interests lies in the crystal orientations and where the crystalline domains extend several micrometers beneath the exposed surface.
对于生物医学研究而言，钙化微结构的成功成像通常依赖于特征之间的吸收差异，或者依赖于使用对感兴趣区域具有选择性亲和力的染料。当涉及纹理时，例如用于晶体取向研究，偏振诱导对比度特别受关注。这需要入射辐射与样品中的感兴趣体积有足够的相互作用，以产生基于取向的对比度。在此，我们使用亚微米尺寸的单色同步加速器X射线束展示了钙K边处的偏振诱导对比度。我们利用牙齿中羟基磷灰石晶体相对于光束偏振场的取向依赖性细微吸收差异。这种相互作用发生在完全矿化的样品上，使得密度差异不会对对比度产生影响。我们的结果表明，在钙K边的特定能量下进行偏振诱导对比度X射线荧光映射，如何揭示人类牙齿组织中的微米和亚微米晶体排列。这有助于在反射几何结构中相对较短的采集时间内实现高空间分辨率和大视野的结合。在牙釉质中，我们观察到在我们制备的表面上暴露的微米尺寸棱柱体的不同晶体取向。我们能够轻松重现通常在抛光薄片中观察到的晶体取向图。我们甚至揭示了管间牙本质中球粒内亚微米矿化前沿的图谱。这种钙K边偏振敏感方法（XRF - PIC）既不需要用于透射的薄样品，也不需要广泛的样品制备。它可用于新鲜、潮湿的样品以及化石样品，这些样品中感兴趣的信息在于晶体取向，并且晶体域在暴露表面下方延伸数微米。
