HIFU is already approved in parts of the world for treating prostate cancer, while clinical trials are underway to use it to treat liver and kidney cancer. For cancer treatment, the tumor tissue is ablated using the HIFU.
Applying it to bleeding seems like a sensible next step, says Gail ter Haar, a physicist at the Institute of Cancer Research’s Therapeutic Ultrasound Team in the Royal Marsden Hospital, near London. “It is ambitious but it’s quite realizable,” she says.
Surrounding tissue may be damaged in the process, since it will be heated close to the boiling point. But the blood vessels remain functional because “the blood flow in the vessel cools the wall and so protects it,” says ter Haar. So the blood around the opening coagulates, while the blood passing through the vessels keeps on flowing.
The biological feasibility of this technology is well established, says Joseph Eichinger, president of Seattle-based AcousTx, which was spun out of another company, Therus, to take part in DARPA’s research program. Therus, also in Seattle, has also been developing ways to use ultrasound to stop bleeding. In particular, its acoustic hemostasis system is being developed to seal punctures in the femoral artery of the groin that are caused as part of cardiac catheter treatments. Normally, these punctures have to have continuous pressure applied to them, and can take from 30 minutes to several hours to seal, says Eichinger. With the HIFU approach, they seal in just a few seconds.
In its final form, the acoustic cuff will consist of a lightweight, flexible device with both ultrasonic imaging transducers and therapeutic transducers lining its insides. The imaging transducers, which function in the same way as sonograms, will be used to first identify the vasculature within a limb and locate any bleeds. The therapeutic transducers are then focused to stem the blood flow.
these capabilities have been demonstrated as separate parts, says
Eichinger – now comes the engineering hurdle of putting them together
in a package capable of surviving the rigors of a battlefield. “It is a
very challenging environment,” he says. “It’s hard enough to take an
iPod into Iraq and make it work.” Indeed, the heat, humidity, dust, and
noisy electromagnetic environment of combat couldn’t be further from a
safe and clean hospital treatment room.