Understanding the fine structure of blood vessels in the heart, kidneys and other organs is an ongoing problem for surgeons and anatomists. While conventional imaging techniques clearly show the scale and structure of large blood vessels, photographing the vascular structure on smaller scales is tricky.

The problem is one of contrast. One conventional way to image the blood vessels in the heart is with x-ray tomography which produces beautiful 3D pictures of the large scale vasculature.

To make this work, the blood vessels have to be filled with a contrast agent that absorbs X-rays more than the surrounding tissue. But the limited absorption of conventional contrast agents means that only the largest vessels show up.

That looks set to change thanks to the work of Qian Wang and Yang Yu at Tsinghua University in Beijing and a couple of pals who have found a way to create 3D X-ray images of even the smallest blood vessels in the heart. And they’ve done it by filling the vessels with liquid metal.

Conventional contrast agents are based on iodine because it has a high electron density and so absorbs x-rays. A more effective way to absorb X-rays is by using a denser fluid. But until now nobody had tried the obvious solution: using a liquid metal.

That’s where Qian and co come in. These guys have tried it for the first time with gallium, a metal which melts at about 29 degrees centigrade and so is liquid at body temperature. Gallium is also chemically stable and does not react with water at this temperature and so ought to flow easily through the vessels.

Of course, this kind of early stage research cannot be done on humans so Qian and co injected the liquid metal into a pig’s heart which they then x-rayed.

The results are impressive. The image below shows two pig hearts, one injected with liquid gallium (left) and the other with a standard iodine-based contrast agent.

The gallium more clearly shows blood vessels large and small. Indeed, the technique reveals capillaries with a diameter of only 0.07 millimetres and the team say that higher resolution techniques should show even smaller vessels. “The capillaries that used to be hardly detectable are now easily seen on the image with outstanding clarity,” say Qian and co.

That’s impressive work that has the potential to dramatically improve the 3D imaging of organs.

Qian and co say it will help to better understand the variation in vasculature that can occur in humans, something that has not been studied in detail. It should contribute to the Virtual Physiological Human project which aims to better understand the structure of the body. And since cooling the metal freezes it, the vessels can act as a mould to create a detailed solid copy of their 3D structure.

Qian and co also suggest the technique could be used in other cavities such as the digestive tract and various plant tube structures. The opportunities are clearly many.

An even bigger question is whether liquid metal can be used to image living tissue, perhaps even in humans.

Qian and co are optimistic. They point out that gallium is chemically inert and believed to be non-toxic in humans. And they say a small amount of the metal can be injected into the target vessels and sucked out afterwards without leaving a residue.

So that doesn’t immediately rule out the possibility of injecting it into living humans. Indeed, Qian and co go further: “It suggests the possibility for localized in vivo vascular-enhanced radiological imaging in the near future.”

That’s an interesting idea but one that will need significant testing in advance. If that goes well, who knows what kind of detail this kind of imaging will reveal.

Ref: arxiv.org/abs/1311.6717 : Liquid Metal Angiography for Mega Contrast X-ray Visualization of Vascular Network