Look four times deeper into tissue with light waves

The new method optical imaging by means of light waves from the TU-Delft can provide valuable information about certain diseases in the future. For example, to follow the development of a disease over time and thus study the effect of drugs or potentially toxic substances on tissue. This can in turn provide useful insights to develop better treatment.

“We have been working on this for almost ten years with a whole team of researchers, so it gives us a huge kick that we have finally achieved this,” explains TU Delft researcher Jeroen Kalkman.

Light waves penetrate tissue

One of the techniques that the researchers are using in the development of the new optical imaging method is Optical Coherence Tomography (OCT). This technique is used by ophthalmologists to image the retina. It is a form of ultrasound in which sound waves are replaced by light waves. This allows images to be made with a higher resolution. An algorithm can then create a cross-section of tissue using the information from the reflected light waves.

The TU Delft researchers have further developed the OCT technique. Instead of using reflected light, the light waves are now sent straight through the tissue. A special sensor then captures the light on the other side of the tissue. The difference in the ‘arrival time’ of the light waves is important for optical imaging.

“The light that takes longer to travel is scattered through the tissue and arrives at the detector relatively late. Normally this causes blurry pictures. But by looking at the time of arrival we can separate this scattered light from the light that passed straight through the sample. We can create a sharp picture with that early light, ”explains Jeroen Kalkman.

The researchers then use computer tomography techniques to process the ‘light information’ into a so-called tomogram. The best known of these is the CT-scan. “You measure a projection of the X-rays that pass through the object at many different angles and positions. Then you can connect all those different projections with the help of a computer into a three-dimensional image. We do something similar, but with light ”, says Kalkman.

Four times deeper ‘look’

The theory of the new method has been tested in practice on dead zebrafish. This showed that the maximum penetration depth was about four millimeters. That is a factor of four better than what is possible with the usual reflection approach in OCT. By looking at both the strength and arrival time of the light, the researchers succeeded in imaging the organs of the zebrafish in high contrast with the new technique.

In addition to forming images with a higher quality, the researchers see another possible application; the analysis of biopsies. “Currently, labs often add fluorescent labels to biopsies or they are cut into small slices and clarified with a liquid. This takes a long time, and such a biopsy can deform when clarified and sliced. Our technique is expected to be able to display the biopsies in their three-dimensional shape and thus help the doctor to make a good diagnosis, ”says Kalkman.