In Three Small Dimensions: X-Ray Microtomography as a Way of Seeing

Direct three-dimensional imaging of small biological samples with resolution down to the size of individual cells is now possible using x-ray microtomography (micro-CT). The principle is identical to medical computed tomography, but the technology has recently been developed commercially for micron-scale imaging. As the conceptual offspring of labor-intensive methods of reconstructing sectioned samples, micro-CT offers a solution to some technical problems of 3-D imaging of embryos and other small soft-tissue specimens. Tomographic imaging automatically provides exactly-aligned slices and reconstructed volumes at high resolution, and it produces microscopic images of internal features without destroying the specimen. But imaging is not seeing: imaging is technical and computational, while seeing is perceptual and cognitive. This technology for direct microscopic 3-D imaging makes small biological structural systems visible to us, but we must also learn how to visualize 3-D structures and relationships in our own minds, and how to incorporate them into our theories and models. X-ray microtomography offers quantifiable data on morphological development, for comparisons between different developmental stages, and between developing embryos of different species, between offspring of mutant or transgenic lines, or between embryos subjected to different experimental treatments. Ultimately, we will be able to register morphological and molecular information in a single volumetric image.