Doctors would really like to be able to watch blood flowing in any part of the body in real time—that would allow them to see blockages, tumors and a host of other medical problems in their patients. Unfortunately, that is still not possible, though ultrasound and light microscopy are constantly improving, leading perhaps to that ultimate goal.

In this new effort, the researchers in the journal Nature report that they have taken a step closer using an approach that involves combining ultrasound and microscopic bubbles injected into the bloodstream of a living rat.

In their approach, extremely small gas bubbles, on the order of 2 micrometers, are injected into the bloodstream in a given area, such as an organ. Once they are inside the blood vessels, high frequency ultrasound waves are fired through the skin and into the area under study. When the waves hit the bubbles, some of the energy is bounced back. That energy is captured by an imaging system that operates at several thousand frames per second, allowing for distinguishing between echoes and bubble data. As each individual bubble moves, its progress is captured—putting all the individual images together allows for creating a single image of the entire vessel or network of vessels.
 
The researchers report that it took just ten seconds to build such an image of the blood vessels in a rat's brain, with a resolution of 10 micrometers—the best that has ever been achieved using any technique.
 
The researchers believe their new technology will make it into the medical community, helping doctors not only find problems and treat them, but to learn more about how they unfold. One such example would be tracking the growth of new vessels surrounding a tumor, which could help predict how fast it is growing.

http://www.nature.com/nature/journal/v527/n7579/full/nature16066.html