A new episcopic method for rapid 3-D reconstruction: applications in anatomy and embryology

The topographic relations of complex structures and the morphogenesis of organ systems can only be fully understood in their three-dimensional context. Three-dimensional (3-D) reconstruction of physically sectioned specimens has become an indispensable tool in modern anatomical and embryological research. Teaching also makes increasingly use of 3-D representations, in particular in the case of embryonic systems that undergo complicated transformations of form and shape. At present no cheap and simple technique is available that generates accurate 3-D models of sectioned objects. In this study we describe a novel technique that rapidly provides faithful 3-D models of sectioned specimens. The images are captured directly from the cutting surface of the embedding block after each sectioning and "on block" staining step. Automatic image processing generates a stack of binary images of the specimen contour. Binary images of internal structures are obtained both by automatic segmentation and manual tracing. Since these image series are inherently aligned, they can be reconstructed three-dimensionally without time-consuming alignment procedures. The quality and the flexibility of the method are demonstrated by reconstructing three kinds of specimens of different histological composition and staining contrast: a 4 mm mouse embryo together with several of its inner organs, a cavernous sinus region of a human infant, and a segment of a human carotid artery. Very short processing times and the faithful representation of complex structural arrangements recommend this technique for routine use in morphological research and for creating embryologic teaching models or 3-D embryonic staging series.