The hope is that the device, known as the Deep Bleeder Acoustic Coagulation cuff (or DBAC), will be able to non-invasively clot blood vessels and stop internal bleeding from combat limb injuries - the leading preventable cause of death of soldiers in action. Longer term, Siemens believes the technology will also find applications in civilian care.

Partners at the University of Washington's Center for Industrial and Medical Ultrasound (Seattle, WA), Texas A&M University's Institute for Preclinical Studies (College Station, TX) and Siemens Corporate Research will work with Siemens Healthcare to deliver a prototype to DARPA within 18 months.

So how does the DBAC work? Once the device is applied to the limb, says Siemens, silicon transducers within the cuff automatically detect the location and severity of the bleeding. High-intensity focused ultrasound (HIFU) pulses are then directed towards the bleeding, so as to speed coagulation at the injury site.

The technical challenges in this ambitious project are daunting. DARPA wants a system that will operate fully automatically on the battlefield while being able to detect, localize and coagulate the full range of life-threatening "bleeders" without requiring a soldier to interpret an image displayed by the device. The system must not cause damage to the skin or the tissue surrounding the wound. And the whole set-up must be portable and rugged enough to survive battlefield conditions.

With those specifications in mind, the developers will collaborate with future users of the technology, including the Combat Casualty Care Group at the US Army Medical Research and Material Command, surgeons from the Madigan Army Medical Center, and the US Army Institute for Surgical Research.

Briefing: HIFU haemostasis

HIFU has been shown to provide an effective method of haemostasis in animal studies, for both solid organs and blood vessels. Moderate to profuse bleeding from major blood vessels, liver and spleen can be stopped within 1-2 min of HIFU application.

Both thermal and mechanical mechanisms of HIFU appear to be responsible for achieving haemostasis. The thermal mechanism, due to ultrasound absorption, raises the tissue temperature in excess of 70 °C in less than 1 s, leading to shrinkage of the tissue and collapse of small blood vessels. Ultrasound also appears to induce a range of mechanical mechanisms that prevent bleeding, including acoustic streaming (where blood is pushed away from the injury) and cavitation (where bubbles are formed in the blood).

Both the thermal and mechanical mechanisms result in coagulative necrosis of tissue and arrest of bleeding.