A proposed lifesaving cuff would use sound to cauterize a bleeding blood vessel on the battlefield. The U.S. Defense Advanced Research Projects Agency (DARPA) earlier this year launched a four-year project to develop such a device, which would use ordinary ultrasound imaging technology to detect a broken vessel and intensely focused ultrasound to effectively seal its ends with heat. Much of the vessel would remain unharmed, thanks to the cooling effect of the blood inside it. Seattle-based Therus has been developing a similar system to seal punctures in the femoral artery that result from catheterizations. And high-intensity ultrasound technology is already approved in some parts of the world to ablate prostate tumors. The challenge: getting everything working in one small, rugged instrument.