Last year, we wrote about scientists developing ways to see-through organisms. Now, a team of researchers from the Howard Hughes Medical Institute have found a way to peer into the heart (and lungs, and brain) of developing embryos with a keener eye. Their microscopy technique produces crisper images of living specimens and allows detailed visualizations of organisms in later stages of development.

A Nature Methods paper describes how scientists refined an imaging technique called ‘digital scanned laser light sheet fluorescence microscopy’. In the traditional version of this process, specimens are scanned with a laser beam and a camera records the resulting fluorescent image. This standard method has worked fine for zebrafish embryos in early stages of development, but researchers found it difficult to take clear photos after 24 hours. The dense thicket of cell membranes in the more complex embryo scattered the photons from the laser, blurring the images.

But, by modulating the frequency of the laser beam during the scanning process, the scientists were able to solve the light-scattering issue, resulting in images that attained a higher degree of contrast than ever before. This meant they were also able to use the technique on species like Drosophila, where the yolk surrounding the embryo had previously confounded the efforts of the laser even in early stages of development.

The resulting images were combined to create time lapse movies of embryonic development. Here, neurogenesis in the zebrafish embryo is rendered in minute detail:

And here’s another, showing Drosophila development from several angles:

This method holds great promise for researchers studying cell fate and morphogenesis. Philipp Keller, an HHMI biophysicist and lead author of the paper, says there’s always the possibility for further refinement — within reason.

“It is still a light microscope,” Keller says. “It has to obey the laws of physics.”

Videos courtesy of Philipp Keller. You can see more on his website.