In the last few years, researchers including Pan and his colleagues have developed another method called optical coherence Doppler tomography (ODT). In this technique, laser light hits the moving blood cells and bounces back. By measuring the shift in the reflected light's frequencythe same Doppler effect that causes the rise or fall of a siren's pitch as it moves toward or away from youresearchers can determine how fast the blood is flowing.
It turns out that ODT offers a wide field of view at high resolution. "To my knowledge, this is a unique technology that can do both," Pan said. And, it doesn't require fluorescent dyes, which can trigger harmful side effects in human patients or leave unwanted artifactsfrom interactions with a drug being tested, for examplewhen used for imaging animal brains.
Two problems with conventional ODT right now, however, are that it's only sensitive to a limited range in blood-flow speeds and not sensitive enough to detect slow capillary flows, Pan explained. The researchers' new method described in today's Biomedical Optics Express paper incorporates a new processing method called phase summation that extends the range and allows for imaging capillary flows.
Another limitation of conventional ODT is that it doesn't work when the blood vessel is perpendicular to the incoming laser beam. In an image
|Contact: Angela Stark|
The Optical Society