Ultrasound waves are high in frequency, lying beyond the human range of hearing. The technology is similar to sonar used by submarines and the ability of dolphins and bats to echolocate objects by emitting high-pitched sounds and tracking their reflections.

"The advantages of ultrasound are that it's a non-invasive way of looking in the body and it's non-ionizing radiation that can otherwise cause damage," said Ronald Silverman, an ultrasound researcher of ophthalmology at Cornell University's Weill Medical College in New York.

In ultrasound, typically millions of sound pulses are emitted a second. The pulses travel into the body and reflect off physical boundaries, such as those between organs.

By analyzing the intensities and times of return of these echoes, ultrasound machines can deduce the appearance of the body's interior. The higher the sound frequency, the more likely a machine can make out minuscule differences in return times of echoed sounds -- and the more detailed ultrasound images can be.

Doctors first began using ultrasound in medicine more than a half-century ago. Now, more than 135 million ultrasound scans are performed worldwide per year, for instance, to monitor growing fetuses without using X-ray scans than can damage genes.

Ultrasound is not just used to scan the body, however -- it can cure it as well. For decades, medics have employed ultrasound vibrations either to crush kidney stones to powder without surgery, warm aching muscles or stimulate healing. Since the 1990s, doctors also have developed high-intensity ultras ound devices to kill tumors, focusing two or more beams to heat a single point inside the body without invading surrounding tissue, as would conventional surgery.

Therapeutic ultrasound has shown success in treating tumors in the prostate gland and other organs, but until now it could not treat all tumors.

"For certain tumors, ultrasound is hard to apply, such as those buried too deep to reach from the outside, or those too close to gaseous pockets," Cyril Lafon, an ultrasound researcher in gastroenterology at the French Institute of Health and Medical Research INSERM in Lyon told UPI. "Ultrasound does not propagate through the gas pockets."

Lafon and colleagues have developed a method to destroy tumors deep in the body via ultrasound. Instead of attacking a tumor from outside the body, they are sending a transmitter inside to kill tumors up close.

"It's minimally invasive, precise and safe, repeatable, bloodless, and economical, with a short recovery time and hospital stay," Lafon said recently at the annual Acoustical Society of America meeting in New York.

The research team examined bile duct tumors.

"The prognosis is very, very bad," Lafon said. "By the time the tumor is diagnosed, they have approximately six months to live. Radiotherapy is totally inefficient against them, so the only treatment is surgery, from which few see benefits."

First an endoscope -- a medical periscope -- is extended from the mouth into the body. The endoscope carries a miniature flat ultrasound transducer, which emits ultrasound pulses to heat tumors to 175 to 195 degrees Fahrenheit. In a clinical trial with 10 patients, on average 75 years old, the method helped completely cure one patient. The researchers are considering using it for kidney and prostate tumors as well.

Medical physicist Kullervo Hynynen of Harvard Medical School In Boston has been working with General Electric and the therapeutic ultrasound company InSightec at Tirat Carmel, Israel, to destroy 700 uterine fibroids to date. Uterine fibroids are the main cause for one-third of the 600,000 hysterectomies performed in the United States each year. Commercially available in Europe and Israel, the researcher team now is working toward Food and Drug Administration approval in the United States after phase III trials.

Hynynen said they also are experimenting in animals, using their method on the brain, the most difficult part of the body at which to aim ultrasound. The skull causes ultrasound to bounce around, making it very difficult to focus on a desired location. Moreover, skull bone absorbs a lot of ultrasound, leading to unwanted heat.

Bringing ultrasound to the brain, however, could be extremely beneficial. Therapeutic ultrasound could remove brain tumors without surgical incision or X-rays that can lead to unwanted complications.

Experiments on animals, involving removal of the skull bone between the brain and ultrasound emitters, showed the researchers were "able to produce nice focused spots (of ultrasound-caused heat) in many, many experiments," Hynynen said. "A few more experiments and we should be able to start clinical trials."

Hynynen added his team is experimenting with intravenously injecting micro-bubbles that enhance ultrasound's searing effects on brain tissue. When hit with ultrasound, the bubbles rapidly expand and collapse, releasing heat. The hope is this will allow therapeutic ultrasound on the brain using 10 to 100 times less power, to reduce skull heating and make it "really feasible to treat any tumors in the brain" without needing to remove skull bone or making a surgical incision.

Medical physicist Lisa Treat at Harvard Medical School said her team is working to use ultrasound to help drugs and genetic therapies in the brain. The blood-brain barrier or is the filter that keeps virtually all drugs from reaching the brain, greatly hampering anti-tumor chemotherapy. In rats, the researchers found ultrasound can temporarily open the BBB's gates for between two to seven hours, a technique they currently are trying on rats.

"No one knows for sure how it works. It's very mysterious," Treat told UPI.

Scientists at Riverside Research Institute in New York are trying to develop therapeutic ultrasound for the living heart, no mean feat given the beating organ is a moving target. So far their work is at the animal experimentation stages, timing each searing pulse on roughly every beat of the heart.

Ultrasound monitoring is not just about taking pictures of fetuses anymore. Silverman said his team is monitoring the eye with ultrasound without damaging the lens, retina or optic nerve as ionizing radiation could. High-frequency 50-megahertz ultrasound, whi ch began use in the 1990s, has allowed researchers to map the eye at a near-microscopic resolution of 30 microns, or a third the width of a human hair.

"Ultrasound allows precision monitoring in refractive surgery, meaning various types of procedures so patients can have perfect vision without eyeglasses," Silverman said. "The first form, LASIK, now has over 1 million patients in the U.S. per year."

Using devices from Ultralink, based in St. Petersburg, Fla., surgeons can examine the eye to determine if the cornea is thick enough for surgery or monitor the eye for abnormalities afterward.

"These structures cannot be seen or measured properly with optical techniques," Silverman said.

Ultrasound also can help with lens implants and cataract surgery, the latter resulting in more than 2 million cataract extractions in the United States per year.

Researcher Joel Mobley and colleagues at the U.S. Army Research Laboratory at Adelphi, Md., are working on ultrasound to detect brain injury. Traumatic brain injury is a leading cause of accidental death in North America for people under age 45. Proper assessment of head injuries could prevent serious, hidden damage in accidents and for soldiers wounded in battle. A small ultrasound emitter is placed behind the ear, connected to a small portable computer.

"The primary thing we want to be able to find are epidural hematomas that can happen before any physical signs of them manifest. They're arterial bleeds that continue to grow and press on the back of the brain," Mobley said.

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