University of Rochester

Distorted Ultrasound Waves Produce Clearer Images: University Technology Licensed to Medical Ultrasound Company

July 29, 2002

A technology that greatly sharpens ultrasound images by capitalizing on a distortion that arises in tissue has been licensed to Acuson Corporation in Mountain View, Calif. The technique was developed at the University of Rochester's Center for Biomedical Ultrasound by several researchers over the course of three decades. Acuson, which has been granted a nonexclusive right to the patent, is a leading worldwide manufacturer and service provider of diagnostic medical ultrasound systems that generate, display, archive, and retrieve ultrasound images.

"This imaging technology has revolutionized echocardiography by improving the quality of our exams and by extending the type of exams we can perform," says Dr. Karl Q. Schwarz, cardiologist and director of the Echocardiography Laboratory at the University of Rochester Medical Center. "Many more of our exams now yield fully diagnostic information, so health care is improved while at the same time lowering costs by eliminating other diagnostic tests that might have been needed."

The new technology utilizes harmonics, the complex upper pitches that in musical instruments make a French horn sound distinct from a tuba or a trumpet. Doctors will be able to utilize dramatically sharper ultrasound images, such as when screening for breast cancer or for fetal checkups, regardless of the kind of tissue being examined because these harmonics travel through tissue in different ways than the regular emitted ultrasound signal, revealing once-hidden structures in the tissue.

"I feel both fortunate and gratified to have been able to help develop an improved medical imaging technique," says Ted Christopher, principal inventor of the technology. "The prospect of providing clearer biomedical ultrasound images keeps drawing me back to the research. Such practical innovation is very rewarding."

Traditionally, ultrasonic imagers emit short high-frequency sound pulses and build images from the echoes they receive, a bit like bats or dolphins use sonar to get a fix on their environment. The new technology builds its images by taking advantage of a special distortion that arises as the pulse moves through tissue. The two megahertz (2MHz) pulse used by most ultrasound imagers travels into the body, bouncing off different tissues in a way that can be processed to form a picture. Pulses of higher frequencies, such as 4MHz, could in theory provide clearer pictures, but tissue tends to deform their shorter wavelengths, so the conventional wisdom was to concentrate only on the regular 2MHz signal.

Christopher, however, found a way to image at 4MHz while still using the regular 2MHz signal by building on the University's 30 years of ultrasound research.

In the late 1960s, David Blackstock, then professor of electrical engineering in the Acoustical Physics Laboratory at the University, crafted a way to predict a subtle kind of distortion that occurs when using ultrasound. Like any sound, ultrasound slightly compresses and expands the medium through which it travels. Normally, this phenomenon is of little interest, but Blackstock found that when the ultrasound wave compressed tissue, it made the tissue a little denser, and sound waves propagate through dense material more quickly than through less dense material. The result is that the part of the ultrasound wave that compresses tissue ends up traveling through it faster than the part of the wave that decompresses it, distorting the original sound wave. That distortion creates a harmonic-a signal similar to the original, but at 4MHz.

Edwin Carstensen, professor of electrical engineering at the University, investigated the possibility of tissue damage from this distortion throughout the 1980s. His research not only showed that the distortion was quite safe, but he removed much of the mystery surrounding the distorted wave and the harmonics it generated. His research associate at the time was a young Ted Christopher.

"In 1993, a week before my doctoral defense, I was lying awake in bed trying to think of a way to keep the boredom level at my defense as low as possible, when it hit me," says Christopher. "I had heard at a University of Rochester conference that one of the great hurdles in ultrasound was in trying to improve the contrast of images, and suddenly I realized I could use the harmonics caused by the distortion to do it."

After four years of research, Christopher discovered that the 4MHz-and even a 6MHz-signal was indeed being generated by the distortion inside the tissue in such a way that it could be read by a scanner and processed to create a much clearer ultrasonic picture of the inside of a living body than had ever been done before. The University patented the process through Research Corporation Technologies (RCT), an independent technology investment and commercialization company. RCT has now granted Acuson, a Siemens company, and its affiliates a nonexclusive license to patent rights for the tissue harmonic ultrasound imaging technology.

Acuson is part of the Siemens Medical Solutions Ultrasound Division, a leader in the U.S. ultrasound market. The division provides ultrasound solutions across a wide range of clinical environments, including general radiology, cardiology, obstetrics, gynecology, urology, and vascular imaging.

Hospitals, clinics, and health care delivery systems worldwide use Siemens' Acuson and SONOLINE ultrasound products. These include the Acuson Sequoia, Aspen and 128XP ultrasound systems with the Native Tissue Harmonic Imaging (THI) option, and the SONOLINE Antares, Elegra and Omnia systems with the Ensemble THI option.

The Rochester Center for Biomedical Ultrasound ( at the University of Rochester was created in 1986 to unite professionals from both the medical and engineering communities. The center provides a unique environment where professionals can join together to investigate the use of very high frequency sound waves in medical diagnosis and treatment along with other medical imaging bioeffects endeavors. Current projects include nonlinear acoustics, contrast agents, 3D sonoelastography, ultrasound and MRI fusion, scattering, bioeffects, therapeutics, advanced imaging systems, and other areas.