Current heart-imaging techniques can identify arterial plaques, but they can't distinguish stable plaques from unstable ones likely to break off and cause clots.

A relatively new laser imaging technology called optical-coherence tomography, on the other hand, can.

[For an image from this new imaging technology, click here.]

An early version of the technology, developed by James Fujimoto's research group at MIT, is already used in several countries to diagnose eye disease. A laser beam is split in two; one beam is reflected off eye tissue. The reflection and the other beam are combined to create interference patterns that can be converted into an eye image. But in an artery, the technology can image only about three centimeters in 30 seconds, since that's the maximum time that blood flow can be safely blocked.

MIT postdoc Robert Huber and Fujimoto describe using a laser whose light frequency can be tuned extremely rapidly to enhance imaging speed. To allow faster tuning, the researchers built a laser with a coil of optical fiber several kilometers long.

The round-trip time of the light in the coil precisely matches the time between frequency adjustments, so the beams provide a ready supply of photons for each adjustment, eliminating the delays normally required to build up enough photons at a new frequency.

The technology can scan three centimeters of artery in just 2.5 seconds -- at a high enough resolution to diagnose plaques and distinguish cancerous cells from normal ones.

LightLabs Imaging, an MIT spinoff, is working on a prototype and hopes to be ready for clinical trials before 2008.