Brain imaging shifts focus from learning to homeland security
Using technology based on a continuous-wave near-IR imager first demonstrated in 1996 by Britton Chance, emeritus faculty at University of Pennsylvania (Philadelphia, PA), and colleagues, a research team headed by Chance is looking for signs of blood vessels generated by tumors in cancerous breasts.
Using technology based on a continuous-wave near-IR imager first demonstrated in 1996 by Britton Chance, emeritus faculty at University of Pennsylvania (Philadelphia, PA), and colleagues, a research team headed by Chance is looking for signs of blood vessels generated by tumors in cancerous breasts. The researchers are also comparing vascularization in the musculature of healthy astronauts and athletes, such as Neal Armstrong and Greg LeMond, with that of people suffering from diabetes or vascular disease.
The main focus for Chance's work is in the brain, however, where a near-IR-detectable signal called a "sudden insight" occurs in a student who has solved a problem (see figure). "Our goal is to make an unfettered, untethered device for use in the classroom to help teachers monitor student comprehension," he said.
Unlike optical brain-imaging systems that use fiberoptic light guides, and in which subjects have been said to resemble the mythical Medusa, the University of Pennsylvania researchers image remotely and noninvasively. Using near-IR illumination, they are monitoring blood flow in the so-called Brodman's Areas 9 and 10 in the prefrontal cortex of the human brain "where decisions are made, where social inhibitions reside, and where problem-solving ability resides," Chance said.
Around the time of the terrorist attacks on Sept. 11, 2001, Chance's brain research program on learning in a summer program for minority high school students was diverted to security-related issues. "Certainly since Sept. 11 and maybe a little bit before, we became interested in seeing whether we could detect the disturbed or malevolent brain," he said.
Each summer for the past two years, about 10 students are included in a protocol that involves showing them disturbing images such as angry faces or the World Trade Center disaster, while their forebrain responses are optically monitored. The experiments are replicated 500 times with each student, and are similar to experiments also being performed with magnetic-resonance imaging, which, unlike optical imaging, requires that the subject be immobilized.
The ultimate goal of this effort is essentially to develop an optical version of a polygraph or lie detector that could be used remotely or even covertly. The Pennsylvania researchers are currently performing functional near-IR imaging from as far as a meter away, and they presented a report on the progress of their research to DARPA (the Defense Advanced Research Projects Agency) last January. Chance also said that in terms of civilian applications the remote imaging capability may help widen acceptance of medical procedures such as mammography in which patients might prefer to undergo a noncontact procedure.
Currently, the light sources for the experiments are laser diodes, but Chance expects rapid improvements in commercially available source technology to enable a switch to light-emitting diodes. He noted recently developed near-IR gallium arsenide photosurfaces from Hamamatsu (Hamamatsu City, Japan) with a 21% quantum yield that rolls over at 850 nm as one example of developments that will enable increasingly portable and sensitive systems. One of the next steps will be to use nano-optical and nano-electronic technology to design optical-imaging telemetry devices that are wearable, he said.
The primary interest for Chance, as well as for the high school educators is to return to the learning research, however, which Chance describes as the long-term goal. "That's our peacetime project," he said, "to get into the classroom."
- B. Chance et al., Optics Express 2(10) 411 (May 11, 1998).