A new method lets researchers send laser light deeper into bodily tissues than ever before. A tenth of an inch (2.5 millimeters) may not sound very deep, but previous efforts to send laser light through tissue worked only to a depth of a few hundredths of an inch (about 1 millimeter).
The new method paves the way for making better images of individual cells or molecules inside the body. In the farther future, the technique may create a laser scalpel that goes deep into the body without requiring any cuts the way metal scalpels do, said Changhuei Yang, an engineer at the California Institute of Technology who led the research.
"It enables the possibilities of doing incisionless surgery," he says.
It's difficult to take images inside tissue because when light enters tissue, it scatters. To focus the laser light, Yang and his colleagues employed ultrasound waves – the same waves doctors use to take images of fetuses.
Where ultrasound waves and laser light waves meet, the light focuses to create an image of that point. To get images of the tissue at other points, the researchers simply aim the ultrasound waves elsewhere. [ iPhones Transform into Medical Imaging Devices ]
Biologists commonly aim laser light at cells to take pictures of them and study them. Because light doesn't penetrate far into biological tissue, however, scientists have always had to isolate very thin layers of cells for their studies.
To show how well their technique works, Yang and his colleagues used their laser-ultrasound method to take pictures of tiny bits of tumors embedded in a piece of tissue at a depth of a 2.5 millimeters. They also took a picture of fluorescent material spelling out "CIT" (for California Institute of Technology) that was embedded in tissue.
"It's a very new way to image into tissue, which could lead to a lot of promising applications," Yang said.
Yang said that in the future, deep-penetrating laser imaging could help doctors search for cells or molecules not just in the lab but in living patients. The laser imaging might work something like ultrasound does today.
In addition, by using a higher-powered laser light, researchers in the future might be able to create a laser scalpel that works only at the depth doctors want, without disturbing the surrounding tissue. "By generating a tight laser-focus spot deep in tissue, we can potentially use that as a laser scalpel that leaves the skin unharmed," Yang said.
Yang and his team now plan to work on increasing how deep their laser light can go. They hope to be able to take images in tissue at a depth of almost 4 inches (10 centimeters) within a few years.
They published the results from their current laser-imaging work June 26 in the journal Nature Communications.