Stanford scientists develop new technique to visualize blood flow

SCIENTISTS from Stanford University have developed a fluorescence imaging technique that allows visualization of pulsing blood vessels in living animals with unprecedented clarity. The technique also has a fast image acquisition rate, allowing for near real time measurement of blood flow.

The technique, called near infrared-2 imaging, or NIR-2, involves injection of water-soluble carbon nanotubes into the living subject’s bloodstream. A laser with light in the near-infrared range (wavelength of about 0.8 micron) is then shone over the subject; in this case, a mouse. Because of the light, the nanotubes then fluoresce at a longer wavelength of 1 to 1.4 microns, which is then detected to determine the structure of blood vessels.

The longer wavelengths at which the nanotubes fluoresce allow for the sharper images, due to less light scattering. Less background noise is also registered, since the body does not produce autofluorescence in this wavelength range.

The technique was developed by Stanford scientists Hongjie Dai, Ph.D., professor of chemistry; John Cooke, M.D., Ph.D., professor of cardiovascular medicine; and Ngan Huang, Ph.D., acting assistant professor of cardiothoracic surgery. A paper detailing the study was published online in Nature Medicine.

Because NIR-2 can only penetrate a centimeter, at most, into the body, it won’t replace other imaging techniques for humans, but will be a powerful method in the study of animal models, replacing or complementing other techniques such as X-ray, CT, MRI, and laser Doppler techniques. Further research will be done on alternative fluorescent molecules with the potential for human use.