Schneider Julio V, Rabenstein Renate, Wesenberg Jens, Wesche Karsten, Zizka Georg, Habersetzer Jörg
1Department of Botany and Molecular Evolution, Senckenberg Research Institute and Natural History Museum Frankfurt, Senckenberganlage 25, 60325 Frankfurt, Germany.
2Institute of Ecology, Evolution and Diversity, Goethe-University, Max-von-Laue-Str. 13, 60439 Frankfurt, Germany.
Plant Methods. 2018 Jan 19;14:7. doi: 10.1186/s13007-018-0274-y. eCollection 2018.
Leaf venation traits are important for many research fields such as systematics and evolutionary biology, plant physiology, climate change, and paleoecology. In spite of an increasing demand for vein trait data, studies are often still data-limited because the development of methods that allow rapid generation of large sets of vein data has lagged behind. Recently, non-destructive X-ray technology has proven useful as an alternative to traditional slow and destructive chemical-based methods. Non-destructive techniques more readily allow the use of herbarium specimens, which provide an invaluable but underexploited resource of vein data and related environmental information. The utility of 2D X-ray technology and microfocus X-ray computed tomography, however, has been compromised by insufficient image resolution. Here, we advanced X-ray technology by increasing image resolution and throughput without the application of contrast agents.
For 2D contact microradiography, we developed a method which allowed us to achieve image resolutions of up to 7 µm, i.e. a 3.6-fold increase compared to the industrial standard (25 µm resolution). Vein tracing was further optimized with our image processing standards that were specifically adjusted for different types of leaf structure and the needs of higher imaging throughput. Based on a test dataset, in 91% of the samples the 7 µm approach led to a significant improvement in estimations of minor vein density compared to the industrial standard. Using microfocus X-ray computed tomography, very high-resolution images were obtained from a virtual 3D-2D transformation process, which was superior to that of 3D images.
Our 2D X-ray method with a significantly improved resolution advances rapid non-destructive bulk scanning at a quality that in many cases is sufficient to determine key venation traits. Together with our high-resolution microfocus X-ray computed tomography method, both non-destructive approaches will help in vein trait data mining from museum collections, which provide an underexploited resource of historical and recent data on environmental and evolutionary change. In spite of the significant increase in effective image resolution, a combination of high-throughput and full visibility of the vein network (including the smallest veins and their connectivity) remains challenging, however.
叶脉特征在系统学、进化生物学、植物生理学、气候变化和古生态学等众多研究领域中都很重要。尽管对叶脉特征数据的需求不断增加，但由于能够快速生成大量叶脉数据的方法发展滞后，相关研究往往仍受数据限制。最近，无损X射线技术已被证明是传统缓慢且具有破坏性的化学方法的有效替代方案。无损技术更便于使用植物标本，而植物标本提供了宝贵但未得到充分利用的叶脉数据及相关环境信息资源。然而，二维X射线技术和微焦点X射线计算机断层扫描的效用因图像分辨率不足而受到影响。在此，我们通过提高图像分辨率和通量且不使用造影剂改进了X射线技术。
对于二维接触式微射线照相术，我们开发了一种方法，可实现高达7微米的图像分辨率，即与工业标准（25微米分辨率）相比提高了3.6倍。我们针对不同类型的叶片结构和更高成像通量的需求专门调整了图像处理标准，进一步优化了叶脉追踪。基于一个测试数据集，与工业标准相比，在91%的样本中，7微米分辨率的方法在小叶脉密度估计方面有显著改进。使用微焦点X射线计算机断层扫描，通过虚拟3D - 2D转换过程获得了非常高分辨率的图像，优于三维图像。
我们分辨率显著提高的二维X射线方法推动了快速无损批量扫描，其质量在许多情况下足以确定关键叶脉特征。连同我们的高分辨率微焦点X射线计算机断层扫描方法，这两种无损方法将有助于从博物馆藏品中挖掘叶脉特征数据，博物馆藏品提供了关于环境和进化变化的历史及近期数据的未充分利用资源。然而，尽管有效图像分辨率显著提高，但实现高通量与叶脉网络（包括最小叶脉及其连通性）的完全可视化相结合仍然具有挑战性。
