By Paul Rincon
Science reporter, BBC News
The US military plans a portable device that uses focused sound waves to treat troops bleeding internally from wounds sustained on the battlefield.
The technology could potentially save lives on the battlefield
Ultrasound can seal ruptured blood vessels deep within the body without the need for risky surgery.
The lightweight device has to be designed so that soldiers can operate it with minimal training.
Blood loss from wounds to the extremities is regarded as a major, preventable cause of battlefield death.
The ability to treat soldiers with internal bleeding on the battlefield could prevent combat deaths and amputations, according to a US military presentation on the project.
These occur, it says, due to the delay involved in evacuating soldiers from the battlefield to a surgical facility.
The device would first use ultrasound imaging technology, in particular "Doppler ultrasound", to locate internal bleeding. This employs a physical phenomenon known as the Doppler effect to look for a characteristic signature of bleeding vessels.
It would then deliver a focused beam of high-powered ultrasound to those sites in order to cauterise the damaged vessels.
The Deep Bleeder Acoustic Coagulation (DBAC) programme is sponsored by the US Defense Advanced Research Projects Agency (Darpa).
Darpa envisages the device as a "cuff" containing an array of ultrasound transducers, different elements of which will detect bleeding and deliver focused, high-powered energy to the wound. This cuff would be flexible enough to be wrapped around the treatment area.
Competing teams - one headed by the multinational Philips, the other by Seattle-based AcousTx Corporation - have both been awarded contracts by Darpa to develop the technology.
The AcousTx team includes Siemens Corporate Research and medical ultrasound company Therus. The Philips team includes researchers at the University of Washington, Seattle, responsible for a number of early studies showing that ultrasound could halt bleeding.
Together, the contracts are worth a potential $51m (£28m) over four years.
"This is a pretty serious effort. These groups are working on making this an autonomous system that any soldier, or first responder, could use in an emergency," said Lawrence Crum, a member of the team headed by Philips and an engineering research professor at the University of Washington, Seattle.
Randy Serroels, general manager of AcousTx told the BBC News website: "High-intensity focused ultrasound is already used in a number of areas such as cancer treatment, fibroid treatment, and in breaking up kidney stones, so the technology is available today. The unique part is to combine that with imaging ultrasound and to automate the procedure."
Ultrasound stops bleeding partly by heating the damaged area and partly through mechanical effects.
The heating produced when this energy is absorbed prompts an insoluble protein called fibrin to precipitate from blood, forming a network of fibres that promotes clotting and plugs the wound. Heating also denatures the blood vessel's connective tissue (collagen) which helps form mechanical plugs and thermally "welds" tissue.
One mechanical effect is called streaming; the high intensity beam pushes blood away from the injury, either back into the vessel itself or to the sides.
In addition, the pressure changes induced by ultrasound lead to the formation of bubbles in the blood - an effect known as cavitation. This in turn may lead to the formation of free radicals - highly reactive charged molecules - which accelerate the clotting process.
While the science is reasonably well understood, it is the engineering that will determine success or failure.
Making the detection and treatment of bleeding an automatic process perhaps poses the biggest challenge of the project, according to Professor Crum.
"We've demonstrated in our laboratory that we can detect internal bleeding and that you can stop it using ultrasound. But you need a very intelligent, skilled administrator to do that," he told the BBC News website.
Describing the project as "high-risk, high-return", he explained: "It's a grand challenge but we're keen to have a go at it.
"If one of these big companies could make one of these it could be something like the [automated external] defibrillator. That was also a remarkable challenge, now everyone has one. They are even selling them for the home market."
In about a year-and-a-half, the prototype technologies will be put through their paces on a Stanford University testbed. This is expected to involve "blind "tests on lab tissue.