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  • CT scanner peers into soil and sustainable materials

Photonics Spectra
Dec 2009
Anne L. Fischer, Senior Editor,

Imagine looking at the inner structure of pretty much anything – and getting ultrahigh-quality, high-resolution images that show it changing over time. Researchers at the University of Nottingham in the UK are doing just that with a three-dimensional x-ray micro-CT system.

Sacha Mooney from the university’s division of agricultural and environmental sciences previously had to borrow time on hospital scanners to look at soil structure. By taking an interdisciplinary approach and pooling resources, the university was able to purchase a Nanotom from phoenix x-ray, based in Germany, a division of GE Sensing and Inspection Technologies. Researchers from various departments – including veterinary, geography, archaeology, engineering and biology – all use the Nanotom.

“There’s a lot of interest in [seeing] how things look inside without disturbing them,” Mooney noted. The scanner can image objects measuring up to 15 × 15 cm and weighing up to 1 kg. It comes with a digital 5-megapixel detector and a 180-kV/15-W nanofocus tube. There are a lot of x-ray tomography systems around, but what’s significant with the Nanotom, Mooney said, is that it produces resolution to a half a micron, “and you can scan in a matter of minutes instead of hours.”

A CT scan taken at 18 μm shows roots from a wheat plant (in purple) in a sandy loam soil. Image courtesy of Rob Davidson/Sacha Mooney.

In the soil studies, the researchers can now scan whole plants. By scanning roots in soil at 10- or 15-minute intervals, they’re able to see the growth process. And with the high-resolution capability, they can see the complexity of soil better than they ever have with previous scanners.

The engineering department has had the same results with sustainable building materials. They can see the internal pore structure to better understand heat flow, heat loss and moisture retention.

The output is a series of image slices separated by very fine intervals. Mooney explained that scanner operators can open up a stack of images and examine each in any orientation or level of zoom with VGStudio Max visualization software from Volume Graphics of Heidelberg, Germany. The result is a model of the structure that is useful for studying the transportation process.

For example, looking at sustainable building materials, scanner users can determine the size and shape of pores in a structure and understand the flow of heat or moisture. Or in soil studies, they can see how water flows around roots. “We no longer have to guess,” Mooney said.

The greatest challenge with the Nanotom so far has been “just getting it in the building,” according to Mooney. During actual use, there’s a steep learning curve, as with any type of computed tomography, he noted. He added that a secondary component is image analysis.

“Image quality is everything in image analysis.” With many options throughout the scanning process, the researchers have to understand more about it. He indicated that, although the operators are still learning how to get the best results, they’ve already gotten some that are very good. “We’re amazed by the images of some structures that we didn’t know even existed.” The results of this understanding can be used in food security and sustainable food production, and in developing more energy-efficient building materials.

image quality
A measure of the closeness with which an optical image is capable of resembling the original object. The factors that affect image quality are lens aberrations, diffraction, dirt and stray light within the system, and atmospheric turbulence and haze outside it. If the image is recorded photographically, it can become further degraded by image motion during exposure and by light diffusion in the emulsion. At one time image quality was expressed by its resolving power, but today a more meaningful...
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