Scientists at the University of Twente in the Netherlands have found a way to see through opaque barriers, Nature reports. This is done by recording wavelengths from visible light, which can pass through solid material like paint or skin. Researchers are now working on methods to reassemble scattered light that has passed through opaque barriers to create a useable image on the other side.

In 2007, scientists Allard Mosk and Ivo Vellekoop attempted to shine a beam of visible light through a glass slide covered with white paint and focus the beam on the other side. They didn't expect it to work — but it did. "I really just wanted to try this because it had never been done before," Mosk said. Mosk and his team used a "spatial light modulator" to control the transmission of different parts of a light beam as it passed through the painted glass slide. A detector on the other side of the slide picked up light transmissions and a computer monitored wavelengths picked up by the detector.

They didn't expect it to work — but it did

Following two independent studies, researchers have had luck with optical focusing by beaming light through thin material like mouse ears, but some biological tissue — especially tissue that moves and stretches — is more difficult to work with. But the potential to work with biological tissue means visible light images of a person's internal organs could eventually eliminate the need for intrusive surgeries.

Visible light images tend to have a higher resolution than images produced by x-rays, because the wavelengths can interact with organic molecules. But it is exactly these interactions that makes visible light difficult to work with. When visible light interacts with organic molecules, its photons can be scattered or absorbed by the material. Absorption will alter the resulting image, making it unusable, but scattering means there is an opportunity for scientists to unscramble the photons.

Astronomers have previously solved the problem of scrambling photons using "adaptive optics," a technology that uses an algorithm to calculate how exactly the atmosphere has blurred the imaging of a particular star. The algorithm then eliminates atmospheric distortions using a special "deformable" mirror. But human bodies are not internally illuminated the way stars are, so adaptive optics is difficult to apply to internal medicine.

Practical applications are a long way off

Last year, Sylvain Gigan, a physicist at the Kastler Brossel Laboratory in Paris, managed to reconstruct a hidden image using single-shot imaging. Lihong Wang, a biomedical engineer at Washington University in Saint Louis, managed to reconstruct an image in 5.6 milliseconds, down from Mosk's original hour.

For now, the exercise is still a lab study, and practical applications are a long way off. Scientists suggest than in addition to medical treatments, the technology could be used in the military or in art restoration to see underneath layers of paint. Although many scientists have tried different types of optical imaging, no one technique has proven more effective than the rest.