A new ultrasound technique that uses tiny micro-bubbles to help improve the contrast of its images is capable of producing highly detailed pictures of blood vessels inside living animals.
The new technique, developed by researchers at the Langevin Institute in Paris, uses gas-filled bubbles that are just a couple of microns in diameter. While injecting gas into the blood can be dangerous when the volumes are large, these tiny bubbles are harmless, and in fact serve to improve ultrasound images. That's because the differences in acoustic properties between a bubble and surrounding blood and tissue is huge, which means that ultrasound hitting one of the bubbles is strongly reflected — providing a nice, clear image.
What the team from the Langevin Institute has done is use high-frequency ultrasound to trace the bubbles as they move through the blood vessels at rates of up to several thousand frames per second. That allows the team to trace the movement of bubbles with incredible accuracy, and in turn generate a highly detailed image of the blood vessel structure that they're passing through. Really, then, they're images the movement of the bubbles rather than the vessel itself — but the end result is the same.
In these images, you can see the blood vessels in the brain of a rat. Each pixel is about the size of a single red blood cell. The researchers claim that they have been able to to improve the resolution of their ultrasound images by over an order of magnitude — usually, they can image structures that are about 150 microns in size, while the new technique lets them study objects as small as 10 microns. The results are published in Nature.
Speaking to New Scientist, the team claims that it already knows it can do better. In fact it plans to begin imaging structures as small as 3 microns, and it hopes the technique will be used to better understand cancerous tumours in the near future.
Image by ESPCI/Inserm/CNRS