WASHINGTON, Aug. 28, 2014 — A variant of optical coherence tomography has provided the first images of blood flow disruption in the brain caused by cocaine use. In a study involving mice repeatedly injected with cocaine over a 30-day period, researchers from Stony Brook University and the National Institutes of Health documented dramatic drops in blood flow speed, as well as microischemia, a precursor to a stroke. The researchers used optical coherence Doppler tomography (ODT) to produce the blood-flow images. In this technique, laser light hits the moving blood cells and bounces back. Determining the Doppler shift in the reflected light’s frequency provides a measurement of how fast the blood is flowing. The top image shows the mouse brain blood vessels before cocaine. The bottom image shows the blood vessels after, revealing that many of the vessels are now darker, which signifies lower blood flow. Courtesy of Biomedical Optics Express. The researchers incorporated a new processing method called phase summation that extends the imaging range and allows for imaging smaller capillary flows. The technique offers a wide field of view at high resolution and does not require fluorescent dyes, which can trigger harmful side effects in human patients or leave unwanted artifacts when used for imaging animal brains. ODT penetrates 1 to 1.5 mm below the surface, so the method for now is limited to smaller animals. But it could be useful when the brain is exposed in the operating room, said Dr. Yingtian Pan of Stony Brook University, to help surgeons operate on tumors, for example. The new method is best-suited for looking at small blood vessels and networks, such as capillaries in the eye. Bioengineers can also use it to monitor the growth of new blood vessels when engineering tissue. Information about blood flow in the brain could also be applied to developing new treatment options for recovering drug addicts, the researchers said. The work was published in Biomedical Optics Express (doi: 10.1364/boe.5.003217).