"Biologists currently have to look at things on the cellular level through microscopes. With this technology, we now can detect things on the cellular level and the tissue scale at the same time. In this case, the whole is greater than the sum of its parts. Tissue is more than just an accumulation of cells. It is a communication network in 3-D that behaves differently than 2-D cell cultures."

In addition to realizing the diagnostic applications of the shimmer, the group has simplified and reduced the cost of the system.

In 2002 Nolte's group was the first to use holography to produce images inside of tissue. The original technique used special semiconductor holographic film developed by the team as opposed to a CCD chip.

"At the time, the only way to capture the image was on this very expensive, very difficult to make film," Nolte said. "But the CCD cameras kept getting better and better and reached the point where we could make the transition from holographic film to the CCD."

Light waves have peaks and valleys that offer information about depth undetected by the human eye. By shining a second laser directly on the CCD chip, bright and dark fringes occur corresponding to the relationship of these peaks and valleys. These fringes, or interference patterns, can be recorded directly onto the camera.

"This extra laser light wave, called the reference wave, acts like a yardstick," Nolte said. "It provides depth information and measurement. It gives us the original image layered with the fringes and the specific locations of these fringes tell us about the 3-D structure of the object."

The team combines this holography technique with "laser ranging," a method similar to radar that measures the time it takes for a laser pulse to travel to an object and be reflected back.

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Contact: Elizabeth K. Gardner
ekgardner@purdue.edu
765-494-2081
Purdue University
6-Mar-2007