Surgeons also need to be able to see the surface of the tissue and the tumor underneath before cutting away, which requires visible light imaging. So researchers have been developing systems that can see in both fluorescent and visible light modes.
The trouble is that the two modes have opposing needs, which makes integration difficult. Because the fluorescent glow tends to be dim, a near-infrared light camera needs to have a wide aperture to collect as much fluorescent light as possible. But a camera with a large aperture has a low depth of field, which is the opposite of what's needed for visible-light imaging.
"The other solution is to put two different imaging systems together side by side," Liang says. "But that makes the device bulky, heavy and not easy to use."
To solve this problem, Liang's group and that of his colleagues, Samuel Achilefua and Viktor Gruev at Washington University in St. Louis, created the first-of-its-kind dual-mode imaging system that doesn't make any sacrifices.
The new system relies on a simple aperture filter that consists of a disk-shaped region in the middle and a ring-shaped area on the outside. The middle area lets in visible and near-infrared light but the outer ring only permits near-infrared light. When you place the filter in the imaging system, the aperture is wide enough to let in plenty of near-infrared light. But since visible light can't penetrate the outer ring, the visible-sensitive part of the filter has a small enough aperture that the depth of field is large.
Liang's team is now adapting its filter design for use in lightweight goggle-like devices that a surgeon can wea
|Contact: Lyndsay Meyer|
The Optical Society