Even with all the modern imaging techniques, visualizing blood flow within narrow vessels is a problem that makes studying vascular diseases a drag. MRI is bulky and expensive, while ultrasound and infrared produce poor resolutions.
Scientists at Stanford University have developed a new technique, called near infrared-2 imaging, that provides substantially greater detail and that should be highly useful in animal studies. It relies on using injected carbon nanotubes that fluoresce under infrared light. The nanotubes are water soluble, and so travel along with blood, while the color they emit when energized is of a different wavelength from that coming from the infrared source, making blood flow readily distinguishable.
That the nanotubes fluoresce at substantially longer wavelengths than conventional imaging techniques is critical in achieving the stunningly clear images of the tiny blood vessels: longer wavelength light scatters less, and thus creates sharper images of the vessels. Another benefit of detecting such long wavelength light is that the detector registers less background noise since the body does not produce autofluorescence in this wavelength range.
The ability to obtain both blood flow information and blood vessel clarity was not previously possible, and will be particularly useful in studying animal models of arterial disease, such as how blood flow is affected by the arterial blockages and constrictions that cause, among other things, strokes and heart attacks.
Because NIR-2 can only penetrate a centimeter, at most, into the body, it won’t replace other imaging techniques for humans, but it will be a powerful method for studying animal models by replacing or complementing X-ray, CT, MRI and laser Doppler techniques.
The next step for the research, and one that will make the technology more easily accepted for use in humans, is to explore alternative fluorescent molecules, Dai said. “We’d like to find something smaller than the carbon nanotubes but that emit light at the same long wavelength, so that they can be easily excreted from the body and we can eliminate any toxicity concerns.”
Press release: Researchers develop new technique for visualizing blood flow
Study in Nature Medicine: Multifunctional in vivo vascular imaging using near-infrared II fluorescence