Virtual Histology: No Frozen Sections, No Wax, No Mess

MicroCT-based virtual histology is being touted as a new method to study and analyse embryos, their development and effect of new drugs on the developing organisms. An example of the new method, developed by a scientific team from the University of Utah and reported at PLoS Genetics, is a mouse embryo, illustrated above.
From the University of Utah press office:

Scientists often use mouse embryos both to learn what genes do and to test the safety of new drugs and household chemicals. By disabling or “knocking out” a gene, researchers can see what goes wrong in the mouse embryo and thus learn the gene’s normal function, or learn how a mutant gene can cause cancer. Mouse embryos also are sensitive to toxicity from chemicals, so new medicines and chemicals are tested on them to see if any defects develop, indicating the safety for humans and their unborn embryos.
But the traditional method of histology – the anatomical study of the microscopic structure of living tissues – has been difficult and time-consuming. Mouse embryos with genetic mutations or damage from toxic chemicals are killed, embedded in wax, sliced into thin sections, then stained and placed on slides for examination under a microscope.
The new, faster and inexpensive method is called “virtual histology” because it uses computer visualization techniques to convert X-ray CT scans of mouse embryos into detailed 3-D images showing both the mouse’s exterior and interior.
Instead of being sliced up physically, mouse embryos are stained with special dyes. Traditional CT scans take a series of X-ray images representing “slices” through the body, and they primarily “see” bone and other hard tissues such as cartilage. In the new microCT virtual histology, the special dyes permeate the skin and other membranes, which are still permeable in an embryo.
“This technique allows us to get at a lot more tissues other than bone, such as internal organs, which [conventional] CT scans can’t pick up,” Johnson says.
Johnson and his team wrote a computer algorithm – a problem-solving formula in computer software – to take the CT scan data and automatically distinguish various organs and structures in the mouse embryo. The “virtual rendering” of the CT scan data also includes a virtual light source so the 3-D embryo image includes shadows that make it easier for the human eye to understand and interpret the image.
The embryo images can be made transparent or have cutaways so that internal organs and body parts are visible. And the detail they show is exquisite – revealing features as small as one-tenth the thickness of a human hair.
The idea is to allow geneticists to quickly examine large numbers of embryos, each with a different gene disabled, so that the normal function of many genes can be determined faster than with existing methods.

The press release…
Online videos of “virtual histology”: video #1 (.mov); video #2 (.mov)…
The article @ PLoS Genetics: Virtual Histology of Transgenic Mouse Embryos for High-Throughput Phenotyping