Dai and graduate students Sarah Sherlock and Kevin Welsher, who are also coauthors of the PNAS paper, observed the fluorescent nanotubes passing through the lungs and kidneys within seconds after injection. The spleen and liver lit up a few seconds later.
The group also did some "post-production" work on digital video footage of the circulating nanotubes to further enhance the image quality using a process called "principal component analysis."
"In the raw imaging, the spleen, pancreas and kidney might appear as one generalized signal," Sherlock said. "But this process picks up the subtleties in signal variation and resolves what at first appears to be one signal into the distinct organs."
"You can really see things that are deep inside or blocked by other organs such as the pancreas," Dai said.
There are some other imaging methods that can produce deep tissue images, such as magnetic resonance imaging (MRI) and computer tomography (CT) scans. But fluorescence imaging is widely used in research and requires simpler machinery.
Dai said that the fluorescent nanotubes are not capable of reaching the depth of CT or MRI scans, but nanotubes are a step forward in broadening the potential uses of fluorescence as an imaging system beyond the surface and near-surface applications it has been restricted to up until now.
Since nanotube fluorescence was discovered about ten years ago, researchers have been trying to make the fluorescence brighter, Dai said. Still, he has been a little surprised at just how well they now work in animals.
"I did not imagine they could really be used in animals to get deep images like these," he said. "When you look at images like this, you get a sense that the body almost has some transparency to it."
Source: Stanford University