"Forever—since Darwin—people have tried to figure out how fossils look in 3-D, when they're embedded in rock and it's hard to get them out," Maloof said. "People did serial sections just like this way back then—but perhaps not at this scale—where they would grind away a little rock, draw it, grind a little more, draw it. ... It can be incredibly time-consuming."
Enter GIRI, which can cut slices as thin as a few microns (less than 1 percent of a millimeter) and can run 24 hours a day for weeks on end. As each slice takes about 90 seconds to cut and image, researchers have to choose between speed and scale. Most of the specimens Maloof and Mehra have imaged are cut into 30-micron slices, about a third the thickness of a human hair. A typical inch-thick, 1,500-slice sample takes about a day and a half to grind and image; during this time, the operator needs to replace machine fluids and clean the wipers (which clear the surface after each cut) only once.
"The process is destructive," Maloof said. "Dinosaur bones, lunar samples—there are certain specimens that people are less likely to give us. It hasn't really stopped us, because most samples are not precious. Cloudina, there are zillions of them—we could never grind them all."
"From the ground up, Akshay has designed machine-learning solutions to make the process of image segmentation—differentiating fossils from matrix, cement, etc., in every slice—automated and reliable," said Maloof. "He has developed techniques that ultimately will be important for any tomographic applications, including X-ray CT. Akshay also has developed ways to make quantitative measurements in the reconstructed 3-D volumes. You'd be surprised how much 3-D modeling out there only leads to visualization and qualitative interpretation, whereas Akshay actually measures the size, shape and 3-D orientation of these critters."
The embedded movie is pretty neat, and there are more here : http://www.pnas.org/content/suppl/2018/02/22/1719911115.DCSupplemental
I'll have to find some time to play around with those...
https://phys.org/news/2018-02-princeton-geologists-fossil-mystery-d.html
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