17:31 21 January 2008
NewScientist.com news service
Tom Simonite
A set of simple silicon filters could dramatically improve the quality of X-ray images produced in hospitals and at airport checkpoints.
The technique provides a more detailed picture of fractured bone and could help airport security scanners distinguish plastic explosives from harmless substances.
X-ray images normally reveal the way different materials, including body tissue, absorb X-ray radiation. Strongly absorbing areas are white and weakly absorbing ones black. But finer details are often lost in a fog caused by areas with intermediate radiation-absorbing ability.
Now researchers led by Franz Pfeiffer of the Paul Scherrer Institute, in Villigen, Switzerland, and including colleagues at the Niels Bohr Institute in Copenhagen, Denmark, have figured out a way to produce much clearer snapshots for little extra cost.
The team adapted a technique known as dark-field microscopy, which is normally used by biologists to get a clearer view of cells under a light microscope.
Higher dose
Dark-field microscopy improves the contrast of an image by using only scattered light. Pfeiffer and colleagues have shown that the same principle can be applied to X-ray images.
This is done by ignoring conventional X-rays passing through an object and only collecting those that scatter off it instead. The team has developed a set of silicon filters that make this possible: radiation that passes straight through an object can be ignored, and rays bent through a tiny angle, as a result of scattering, are collected.
The process involves taking four separate images, each with the three filters in a slightly different arrangement. Software then compares each snapshot to produce a final high-contrast picture.
Although the process means exposing the subject to a higher total dose of radiation, Pfeiffer says this can be justified in some circumstances.
The resulting images reveal physical details that would normally be invisible. For example, since soft tissue and bone differ strongly in their ability to scatter X-ray, the dark-field technique could help a doctor spot small splinters of bone or cartilage after a bad fracture.
X-ray scans of a fish and a chicken wing reveal the level of detail revealed (see images, top and middle right).
Live tests
The technique also makes it possible to distinguish between substances that would otherwise look identical, which may be useful for security screening.
For example, some kinds of cheese absorb X-rays in a similar way to plastic explosive, but they scatter them differently, making it easy to tell them apart using the new method (see image, bottom right).
The technique is not yet ready for deployment in hospitals as it only works with relatively low-intensity X-rays.
However it could be used for some clinical investigations like mammography and Pfeiffer's team is working on making it suitable for more powerful X-ray machines. They plan to test it on live animals within the next 12 months.
*www.blogsmithmedia.com/www.engadget.com/media/2008/01/dark-field-x-ray.jpg
Enlarge image
The new method could help doctors spot bone fragments that traditional X-rays don't reveal. This chicken wing (right) clearly shows the difference (Image: Franz Pfeiffer/Nature)
