3-D Imaging of Embryos with Micro-CT

High-resolution three-dimensional images of embryos are a valuable tool for comparative embryology, mutant phenotyping, and other kinds of developmental studies. We are testing micro-computed tomography (micro-CT) as a method for high-resolution, high-throughput imaging of embryonic and other small soft tissue specimens. Like standard CT scanning, micro-CT imaging relies on differential x-ray absorption among tissues and structures in the sample, so imaging of soft tissues such as embryos poses a particular challenge. A test scan of a 12.5-day mouse embryo stained with osmium tetroxide shows extremely high contrast of neural tissues, and more subtle but useable contrast between epithelial layers and underlying mesenchyme. The images from this scan demonstrate objects as small as 10 microns or less, and can distinguish single-cell epithelial layers from their adjacent tissues. Another test scan of a mouse embryo stained with phosphotungstic acid, performed by a different facility, also gave high contrast among tissues, but with much lower spatial resolution, likely due to less advantageous use of the scanner¿s capability. A third scan of an alum-hematoxylin stained embryo showed only very limited contrast. Here we compare the potentials of micro-CT with other 3-D imaging methods, and delineate a number of possibl