Colour X-ray machine sees so much more

A colour X-ray machine that can detect the chemical make-up as well as the structure and shape of a sample has been demonstrated by UK researchers. They say the new technique could be better at spotting smuggled substances or abnormal body tissue.

Regular X-ray machines and CT scanners can produce images in 2 or 3D, but only in monochrome. In the same way that black-and-white film is blind to other wavelengths of light, these techniques cannot distinguish between different wavelengths of X-ray.

"We have miniaturised a detector that can differentiate those different wavelengths," says Robert Cernik, a materials scientist at Manchester University, UK, who developed the device with colleagues Kern Hauw Khor and Conny Hansson.

The detector has 256 silicon pixels that are each 50 microns wide and can pick up different X-ray frequencies. A 20 cm-thick protective tungsten filter, with 256 holes that correspond to the pixels, sits over the top of the detector.

After a sample is hit with an X-ray beam, the device collects the scattered X-rays onto the different pixels of the detector. "Each looks at one area of the sample, you move the sample through the scanner to get a full 3D image," says Cernik. The new technique is called Tomographic Energy Dispersive Diffraction Imaging, or TEDDI.

Diffraction 'fingerprint'

A previous TEDDI prototype used a single pixel to slowly build an image over about 20 hours. By using an array of X-ray sensors the prototype can do it in just two hours. With improved detectors Cernik says it should be possible to reduce this to a few minutes.

Being able to sense the colour of the X-rays scattered by the sample means much more information can be extracted, the researchers say. For example, the diffraction pattern of different wavelengths can reveal material properties or chemical make-up in more detail.

"If you were looking for abnormal tissue, you would know the particular diffraction 'fingerprint' you were looking for," says Cernik. "The pattern can also measure changes in the crystal structure of materials like aluminium, for example, to look at the strain in a weld."

Cernik and colleagues have tested their machine on pieces of polymer, bone and aluminium, but the current prototype can only examine samples to a depth of 1 to 2 millimetres. This is because its silicon detector cannot sense the high-power X-rays needed to make it through thicker or denser materials.

"We know exactly how to do that," says Cernik, who suggests that a detector made from a heavier semiconductor than silicon, like cadmium zinc telluride, would do the trick. Physicists using synchrotron particle accelerators already use such detectors, which could perhaps be modified for the job, he says.

Source: http://technology.newscientist.com/article/dn12977