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Imaging Natural History

07/21/2011
Bow Young Kim

Bow Young Kim looks at how the latest microscopy and imaging techniques are allowing museum researchers to make new discoveries about the past and present.

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With a 4-foot-long jaw and 6-inch-long teeth, the fossil skeleton of a Tyrannosaurus rex stands in a crouching position, ready to attack the thousands of visitors to the American Museum of Natural History (AMNH) on New York’s Upper West Side. In another of the museum’s halls, the model of a blue whale over 70 feet long hangs suspended from the ceiling as visitors learn about various oceanic ecosystems. In total, the museum is home to over 32 million biological specimens and cultural artifacts as well as over 4 million fossils.

Atlantic Spotted Mackerel: Associate Curator in the Museum’s Division of Vertebrate Zoology John Sparks, an ichthyologist, highlights details of cichlids and other small fish using biological dyes.

The Hitachi S-4700 field emission SEM—provides conventional SEM imaging at 2-nm resolution for fine details on samples that have been coated with an electrically conducting material to prevent the accumulation of a static electrical charge on the sample during scanning that can cause imaging artifacts. Source: AMNH

Using the Hitachi SEM, Siddall has imaged in fine detail the three jaws, which have 50–60 denticles each, that the leech Macrobdella decora utilizes to bite into its host. Source: AMNH

“I think imaging technology is presently awesome,” says Mark Siddall, curator of Annelida and Protozoa at AMNH. “We have the ability now to visualize not just in 2-D with pixels, but in 3-D with voxels.”       Source: AMNH

Most visitors assume that these collections are static, on display to educate and expose the population of city-dwellers to the diversity of life in the world. Behind the walls of the exhibit hall, however, museum scientists are continuously conducting research on this concentrated collection of biodiversity. The AMNH research facilities and equipment include a molecular systematics laboratory, a frozen tissue collection, a biodiversity informatics facility, and a conservation genetics center, as well as a microscopy and imaging facility.

“I think imaging technology is presently awesome,” says Mark Siddall, curator of Annelida and Protozoa at AMNH. “We have the ability now to visualize not just in 2-D with pixels, but in 3-D with voxels.”

Because of this “awesomeness”, Siddall has put together an exhibit featuring aesthetically compelling images taken by 27 AMNH scientists, students, and staff to give visitors a behind-the-scenes look at the research performed at the museum. By constantly using the latest imaging techniques, these researchers are rewriting our understanding of biodiversity.

Behind the Curtain

At AMNH, Siddall and his team are interested in blood suckers. Specifically, the team is interested in the taxonomy of leeches as well as the bacterial symbioses of microbes with leeches. Siddall has travelled around the world collecting leech specimens, bringing them back to his lab for standard microscopic analysis.

When he and his AMNH colleagues need to get a better view of their specimens, however, they turn to the AMNH Microscopy and Imaging Facility (MIF). Led by laboratory manager Rebecca Rudolph, the MIF staff is trained in various microscopic techniques, a necessity for AMNH researchers who are not interested in the method as much as the final picture these techniques can provide.

The MIF houses two scanning electron microscopes (SEMs) that serve different purposes. One of the microscopes—a Hitachi S-4700 field emission SEM—provides conventional SEM imaging at 2-nm resolution for fine details on samples that have been coated with an electrically conducting material to prevent the accumulation of a static electrical charge on the sample during scanning that can cause imaging artifacts. Using the Hitachi SEM, Siddall has imaged in fine detail the three jaws, which have 50–60 denticles each, that the leech Macrobdella decora utilizes to bite into its host.

The other SEM—a Zeiss Evo 60 environmental SEM—can image uncoated as well as wet samples by creating a nondestructive coating of pressurized air across the sample’s surface to prevent charge build-up. But this lack of sample preparation comes at a cost in resolution; the Evo 60 can only resolve down to 50 nm.

Both instruments also include X-ray spectrometer detectors that allow museum scientists to obtain insights into how certain cultural artifacts were made and handled as well as electron microprobes to determine the chemical compositions of meteorite samples.

The MIF also has a Zeiss LSM 710 confocal laser scanning microscope (CLSM) used for optical sectioning of transparent, fluorescently stained specimens. The series of 2-D optical sections obtained can then be reconstructed into a 3-D image for analysis of the specimen’s exterior as well as its interior.

In 2010, the MIF added a GE Phoenix v|tome|x dual-tube computed tomography (CT) scanner for high-resolution 3-D tomography imaging and 2-D X-ray inspection. There are only four such powerful systems in the country.

Now, AMNH scientists and staff can examine their specimens without having to go off-site to other imaging facilities, which is especially important for specimens that are fragile and rare. Specifically, the CT scanner has been incredibly useful for producing 3-D images of fossil interiors without having to cut open and destroy the fossil.

“The advantage of having a CT scanner inside the museum is that museum scientists have more control over what they’re looking at and what information they are harvesting from a particular object,” says Siddall. “Full speed ahead, we’re going to continue to use these technologies to the best of our ability.”

While these techniques have allowed researchers new ways to examine their specimens, the public has had a much more limited view of the lab’s work at the AMNH.

As Siddal prepared to curate the exhibit of images from the museum’s microscopy lab, he was presented with multiple problems. For one, many of the images at the MIF could not be blown up into a poster-size format for display in the museum since they were not captured at high enough resolutions. So Siddall worked with the design team to present instead a series of smaller images of a particular figure that would convey the same idea as a poster-sized image.

Another challenge was to actually pick which images would be included in the exhibit. The MIF’s imaging systems are operating almost every day, producing thousands of images every year for the different research departments.

So Siddall recruited the museum’s scientists from every division to individually select a couple of their most aesthetically pleasing and interesting images for consideration in the exhibit. From there, Siddall and the graphics and design team looked through the submissions to find the right balance between aesthetics and scientific content for the exhibit.

“The point of the exhibit, although we do highlight various technologies, is to convey this unfettered beauty in the eyes of the scientist,” says Siddall.

The exhibition is located in the Museum’s second-floor Akeley Gallery and will be on view from June 25, 2011 to June 24, 2012.

Keywords:  microscopy