Imaging hat trick: Sharper, deeper and faster

Ashley N. Paddock, ashley.paddock@photonics.com

An imaging technique that simultaneously achieves high speed, high resolution and deep penetration using 3-D samples could redefine optical imaging of live biological tissues.

Scientists must capture high-quality 3-D images of living tissues and organisms over time to solve problems in fields ranging from neurobiology to genomics. State-of-the-art techniques often excel only in one of the three key parameters – speed, resolution or depth – necessary for high-quality images suitable for research.

Now, scientists at California Institute of Technology have developed a technique that makes it possible to accomplish all three goals without damaging, killing or adversely affecting live biological samples.

First, the team used light-sheet microscopy, a method in which a thin flat sheet of light illuminates a biological sample from the side, creating a single illuminated optical section through the sample. The light emitted is captured with a camera oriented perpendicular to the light sheet so that it harvests data from the entire illuminated plane at once. This technique allows millions of pixels to be captured at the same time while the light intensity used for each pixel is reduced. This approach increases imaging speed while decreasing the light-induced damage to the living samples – in this instance, zebra fish and fruit fly embryos.

Next, to achieve sharper image resolution with light-sheet microscopy farther inside the sample, the researchers used two-photon excitation for the illumination. Although the technique has been used previously for deeper imaging of biological samples, it typically would collect the image only one pixel at a time. The team’s discovery that it could be carried out in sheet-illumination mode could make it suitable for a variety of in vivo applications. Its report was published online July 14 in Nature Methods (doi: 10.1038/nmeth.1652).

The researchers hope that their hat trick imaging technique will open the door to many biomedical research and life sciences applications requiring noninvasive observation of dynamic biological processes in 3-D, with cellular or subcellular resolution. One example would be constructing 3-D movies of an embryo throughout its development. These “digital embryos” could advance medical applications such as tissue engineering, stem cell therapy and robotic surgery.