Until recently, a common technique for creating a 3D image of an embryo was to slice it into hundreds of thin sections, photograph each section, and then computationally recombine the images to produce a 3D representation of the embryo.  But during this process, the specimen may become deformed, and information about the alignment of the sections – the third dimension – is lost.

Optical projection tomography (OPT) overcomes these problems, as Laura Quintana and James Sharpe (Centre for Genomic Regulation, Barcelona) explain in a featured article in the latest issue of Cold Spring Harbor Protocols.  OPT is ideal for analyzing the morphology of fixed embryos – especially for analyzing mutant phenotypes, for developing anatomical atlases, and for analyzing gene expression patterns.

During OPT, the whole embryo is mounted on a stage that rotates 360 degrees.  As the embryo rotates, visible light is projected through it, and a detector on the other side records the amount of light that penetrates.  Images are captured at different angles as it revolves, and computer software combines the images to create a 3D image.

Sharpe, the lead author of the article, describes OPT in this video:

The article, freely accessible here, is published in the June issue.  The issue also contains a detailed step-by-step protocol, written by the same authors, for the preparation of mouse embryos for OPT imaging.