New techniques for tissue become transparent

If people have visible skin like jellyfish, it is easy to detect a disease like cancer. You just need to look and observe a tumor forming or developing.

But of course people cannot become transparent. According to Mr. Changhuei Yang of the California Institute of Technology, 'the reason why people don't become transparent is because human tissues are in different positions' , making light waves wriggle. through those tissues rather than going straight through like with jellyfish.

In addition to preventing us from becoming transparent, this scattered distribution makes it more difficult to detect diseases, requiring a range of diagnostic tests and procedures. But perhaps we will no longer have to wait for new optical techniques developed by Yang and his colleagues (he is an assistant professor of electronics engineering and biological engineering). This technique can prevent scattered dispersion of light and make images more accurate.

The phenomenon of dispersing light in matter is not necessarily a random, unpredictable process as everyone thinks. In fact, the dispersion of light has been predetermined, when going to a specific tissue layer, light will bounce off the cell, and the path it passes through is completely predictable. If you let a light ray pass through the same group of cells again, it will disperse again.

Chart of chicken breast tissue (about 250 micrometers thick) with photoluminescent plate to prevent scattered light scattered to create a more accurate image.The lower the chart, the better the image will be.(Photo: Caltech Biophotonics Laboratory)

The process is even reversible. If collecting photons of light scattered throughout the tissues and taking them out, they will bounce back to the old path and converge at the original point where the light emits. Yang explained: 'This process is similar to when dispersing billiard balls on a table. If you can accurately reverse the old path with the old speed of the ball, you can assemble them into the rack. Yang and colleagues at Laussanne Federal University of Technology (Caltech, Switzerland) and MIT have exploited this phenomenon to compensate for the disadvantages of tissues in our bodies. "

Their technique carries a name made transparent by combining optical steps ; though it's very simple. They used crystals to record interference patterns to capture patterns of light dispersion in a chicken breast 0.46 mm thick. They then redo the dispersion pattern from the tissue area to restore the original light ray. Yang said: 'This is like holding the direction and time and reversing it. Reversed photons must find their path through the tissues again. However, the job is very difficult, equivalent to playing a game of billiards with 10 to 18 balls (or photons). You beat them all over the table and try to put them back into the rack. '

'Until we do this study, we are not sure if any results will be achieved with biological tissues. But then we were surprised by the remarkable results and successes achieved. Research opens countless opportunities in using reverse optical time in biological therapies'.

Another application of the technique is optical dynamic therapy , in which a light beam converges to cancer cells that absorb light-sensitive compounds that destroy cells. When light hits the cancer cells, the compound is stimulated and destroyed. Photodynamic therapy is most effective in treating cancers on the skin surface. However, Yang's technique offers a way to focus light on cancer-healing compounds deep within the tissues.

Yang had the idea of ​​injecting powerful light-dispersing molecules surrounded by light-activated cancer drugs into the diseased tissue. Shining a ray of light into the cell, it will be reflected when exposed to light-dispersing compounds during light rays bouncing in the tissues. Some scattered rays will return to the starting point, where it will produce a hologram.

This hologram contains information about the pathways of scattered light rays passing through the tissue, thereby re-describing the optimal path to dispersing molecules as well as cancer treatment compounds. Thanks to the road signs, a powerful beam of light is released that activates the therapeutic compounds and destroys cancer cells.

In addition, the technique also offers a method to power microcapsules buried deep inside the tissue . Yang said: 'If you conduct a small survey of what's available, you'll find the implants quite large. For example, pacemakers are about the size of a mobile phone. Why are they so big? Part of the reason is because they need to carry the energy supply department '.

The key to creating smaller, pen-sized implants, for example, lies in restraining energy supplies. Yang said: 'I think implants that carry photovoltaic receivers have very good blocking. The effect can be applied to light-emitting devices that help it direct light efficiently to cell tissues and to the implant. '

The study describes the process published in the February issue of Nature Photonics. Zahid Yaqoob, postdoctoral in electronics engineering at Caltech, has done most of the experiments included in the research article. Another author of the paper is Demetri Psaltis (professor of optics and head of the technical department at the University of Federal Polytechnic Lausanne in Switzerland), along with Michael S. Feld (MIT physics professor again).