Three‐dimensional models once again: For research and teaching of early human development
Naoki Shiraishi, Shigehito Yamada, Tetsuya Takakuwa · Congenital Anomalies · 2012
Many people – some scientists, others not – are interested in early human development because it is closely related to the basic and important question: What are we and where have we come from? Classically, histological serial sections were prepared for microscopic two-dimensional (2D) analysis as well as for understanding the three-dimensional (3D) development of external and internal structures (O'Rahilly and Müller 1987). 3D plaster or wax models, constructed by technical specialists since the late 19th century, have been indispensable in research as well as teaching (Morgan 2004). The histological models of Ziegler, Blechshmidt, and Heard are famous worldwide. The construction process of these models used to be so complicated that a team of scientists, technicians, artists and photographers spent several months to years to complete one model. Then, application of newer modeling techniques produced much more detailed models and contributed to vivid understanding of early human development. With the advent of magnetic resonance imaging (MRI), the imaging of embryos has become highly effective, providing a resolution of 40 μm/pixel or more with long scan times. MRI is a non-invasive and non-destructive method that has many possibilities, not only for precise morphological observations but also for morphometric evaluations of internal structure (Yamada et al. 2006). A beautiful image on the 2D screen can be easily drawn from MRI digital data using computer graphics. However, we think it still fails to illuminate dynamic morphogenesis, particularly spatial changes and anatomical relationships. A 3D printer is a tool for making 3D solid objects from digital data. Stereolithography was developed in 1986 and attracted much attention (Jacobs 1992). It did not become very popular because it involved very expensive equipment and many other incidental facilities. In recent years, fused deposition modeling (FDM) method has been developed. It has enabled creation of inexpensive 3D models in engineering, medical and dental fields as well as the academic area (Dimitrov et al. 2006). We constructed a series of 3D precise models of the central nervous system and cerebral ventricle of human embryo from MR data. We created the models according to the manufacturer's operation manual (BFB-3000, Bristol, UK). These were 3D models of the cerebral ventricle between Carnegie stage (CS) 13 and 23. The printed 3D models allowed us to directly visualize the 3D appearance, touch and feel. Comparison of successive specimens enabled us to recognize the dynamic still precise morphological change during development, and to understand the spatial relationship and dynamism of morphogenesis more intuitively, as expected (Fig. 1). (A) 3D model of cerebral ventricles at Carnegie Stage (CS) 23 printed by Fused Deposition Modeling method. (B) 3D models of the rhombencephalon (a,b) and rhombencephalic ventricle (c) at CS 17. (a) Right lateral surface view of the rhombencephalon. (b) Internal surface view of the left half of the rhombencephalon. (c) Right lateral view of the rhombencephalic ventricle with the same scale. Development of the rhombencephalon will be better understood by comparing the 3D model of the rhombencephalic ventricle with the rhombencephalon. (C) Internal views of the left halves of the 3D models of the rhombencephalon between CS17 and 23. Comparison of successive specimens enabled recognition of the dynamic still precise morphological changes about the cerebellum, brainstem and roof of the rhombencephalic ventricle and their effects on the rhombencephalic ventricle and pontine flexure. The cerebellar hemisphere arose from the rhombic lip and grew in thickness between CS17 and 23. The pons and medulla grew in thickness rapidly, thereby developing the pontine flexure. Mesencephalon and rhombencephalon were separated by the isthmic canal, which was narrowed by development of medullary velum and pons. ch, cerebellar hemisphere; ic, isthmic canal; me, medulla; mv, medullary velum; po, pons; θpf; pontine flexure. The use of 3D printed models is expected to compensate the faults and limits of computed graphical pictures reconstructed on 2D display. The models are also expected to act as attractive and intelligible tools for teaching. We plan to teach the whole process from MRI data to visible embryonic models. The plaster model played a substantial role at the dawn of research and teaching of human embryos. We expect that the 3D printed model will again be available and play an important role in the near future.