BUILDING A BETTER ENDOSCOPE
Joseph Kahn is best known for his record-setting work in fiber-optic communications—increasing the distance over which signals can be transmitted at high bit rates. But two years ago, Kahn and fellow Stanford electrical engineer Olav Solgaard, MS '87, PhD '92, began exploring the potential of light-based technologies for studying biological systems. The result? A prototype endoscope no thicker than a human hair that can resolve details as small as 2.5 microns. (A micron is one thousandth of a millimeter.)
Fibers through which light travels via many different paths—known in optics as Eigenmodes or simply modes—are good at transmitting complex information. The trouble with such multimode fibers is that light tends to get scrambled along the way. Kahn and graduate student Reza Nasiri Mahalati, MS '10, developed a computer program to teach a spatial light modulator (basically a miniature LCD display) how to make sense of the scrambled signal.
They also figured out a way to speed up image processing by projecting a random pattern of light through the fiber to sample the object of interest. The reflected light returns through the fiber to a computer, which uses algorithms developed by Nasiri Mahalati and fellow graduate student Ruo Yu Gu, MS '12, to reconstruct an image. The resulting endoscope can resolve four times as many image features as previous single-fiber endoscopes.
The hair-thin endoscope could open a door to unprecedented views inside living organisms. The limiting factor, for now, is that it has to be rigid; bending a multimode fiber causes light traveling through it to become scrambled beyond reconstruction. (Current flexible endoscopes are made up of bundles of single mode fibers.) Kahn feels up to the challenge: "No one knows if a flexible single-fiber endoscope is even possible, but we're going to try."
FUKUSHIMA BOOSTS FISH FORENSICS
The March 2011 Tohoku earthquake and tsunami, which led to the meltdown at the Fukushima Dai-ichi nuclear power facility in Japan, has had lasting global impacts. Last summer, Stanford researchers led by Mark Z. Jacobson, '87, MS '88, reported that, based on atmospheric and health-effects models, the radioactive material released may cause on the order of 130 deaths and 180 cases of cancer. And last spring researchers from Stanford and Stony Brook University measured elevated levels of radioactive isotopes from Fukushima in Bluefin tuna caught off Southern California.
This latter observation provides perhaps the one potentially productive outcome of the disaster: It may enable scientists to reliably track the movements of juvenile Pacific Bluefin tuna.
Bluefin tuna are an important commercial species; they also play a key role in maintaining the health of ocean ecosystems. Their popularity has led to severe overfishing; Pacific Bluefin numbers are down 96 percent from unfished levels, according to the Tuna Research and Conservation Center—a joint project of Stanford's Hopkins Marine Station and the Monterey Bay Aquarium.
Researchers have been tracking adult Bluefin using electronic data recording tags for more than a decade. The migratory fish travel thousands of miles to hunt and feed before returning to spawn in the waters where they were born. But little is known about their movements during their first year or so of life when they are most vulnerable.
Daniel Madigan, a doctoral candidate working in the lab of Fiorenza Micheli, collaborated with researchers at Stony Brook and the National Oceanic and Atmospheric Administration to sample 50 Bluefin tuna born near Japan within the last four years—meaning that the youngest fish would have swum only in contaminated waters. Cesium-134, one of two telltale radioactive isotopes from the spill, was detected in every one of the smaller fish. Madigan further showed that the ratio of two Cesium isotopes (134 and 137) could serve as an indicator of how much time a fish spent in Japanese waters and when it left.
"We plan to look for this tracer in hundreds of samples of Pacific Bluefin tuna," he says. "It's not that easy to tell what a fish did in the past, but this gives us a forensic tool."
