3D x-ray film

Rapid movements in real time

weevil

weevil hip joint
In a weevil’s hip joint, skeleton parts interlock like a screw and a nut. Credit: dos Santos Rolo et al., PNAS, 2014

Mar 13, 2014 — How does the hip joint of a crawling weevil move? Scientists have developed a new technique to find out. The method records 3D X-ray films showing precise internal movements. Researchers at ANKA, the Karlsruhe Institute of Technology’s Synchrotron Radiation Source, developed the technique. The scientists applied this technique to a living weevil and generated complete 3D film sequences in real time and slow motion. To do so, they genererated up to 100,000 2-D radiographs per second. The results are: now published in the Proceedings of the National Academy of Sciences (PNAS).

Three-dimensional radiographs represent internal structures, but do not provide any information about movement sequences. Conventional computer tomography is not efficient enough to reproduce movement in a spatially precise manner and, at the same time, in the temporal dimension. Every individual three-dimensional image (“tomogram”), is reconstructed from hundreds of two-dimensional radiographs.

“To produce highly resolved tomograms at such recording speed, we had to adjust every setting screw, from the X-ray source to the pixel detector and we optimally attuned all process steps to each other,” says Tomy dos Santos Rolo, lead author on the study. By making the 3D image frequencies approach the image rates known for 2D cine films, he reached the world record in high-speed tomography, i.e. a real 3D film with microscopic magnification.

For scientific evaluation, the three-dimensional contours of anatomic structures have to be clearly visible. This is achieved by the so-called phase contrast. If highly parallel X-rays pass the biological examination object, wave optics phenomena occur, which highlight the inner and outer contours.

“It is these contours that matter to us. We want to distinguish individual functional elements that move relative to each other. That is why we need sharp contours,” Alexey Ershov, the expert for image analysis in the team, says. From the X-ray source to movement analysis, all process stages are designed to filter out image noise without reducing contrast. This also applies to the mathematic algorithms optimized for radiography. They reconstruct three spatial and one temporal dimension and derive exact movement patterns from the data.

In line with the first moving images – cinematography – the scientists call their method “cinetomography.” In the late 19th century, movements of big animals were studied. Today, researchers can analyze internal biological processes of small organisms, as is now demonstrated for the recently discovered screw joint of the weevil. Insects, spiders, and crustaceans make up more than 80% of all species.

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Source: Karlsruhe Institute of Technology