New Technology Has Ultrasound Poised for Renaissance
New quantitative methods are augmenting ultrasound's traditional role as a safe, fast and easy-to-perform modality and giving it new life and increased relevance in medical imaging, according to one of the leading experts in the field.
By Richard S. Dargan
The presenter of the RSNA 2014 New Horizons Lecture, Jonathan M. Rubin, M.D., Ph.D., described how quantitative ultrasound techniques like volume flow estimation and elasticity imaging provide insight into the function of some of the body's major organs.
Though still in its infancy, elasticity imaging—a measure of the mechanical properties of tissue—has many applications that will develop over time, Dr. Rubin said. "Elastography has grown beyond strain and shear wave speed imaging to include shear viscosity imaging, non-linear strain and non-linear shear wave imaging," he said. "The applications are expanding rapidly, and the impact will almost certainly be major."
One of the newest and most exciting potential applications is in lung imaging, where researchers have developed a new technique to monitor respiratory motion by measuring lung strain. The technique takes advantage of the fact that the lung's surface expands like a balloon when filled with air. A transducer is placed on the skin and used to track speckle on the lung surface. The lung strain is positive when the patient inhales, and negative when the patient exhales.
"People with lung disease have no strain because there's no aeration," Dr. Rubin said. "This technique enables us to measure local lung ventilation, which is almost impossible with current methods."
Though still in its early stages, the technique has been successfully accomplished in mice with pulmonary fibrosis. Potential applications include assessing and monitoring patients with pulmonary fibrosis and other lung conditions.
Elasticity imaging has also shown the ability to differentiate between inflammation and fibrosis in people with Crohn's disease. Intestinal fibrosis occurs in the majority of patients with Crohn's disease patients, Dr. Rubin said, and distinguishing it from inflammation is important because the medical therapies used to treat the conditions are different. A study performed on rats showed that elastography could noninvasively measure how much of intestinal stenosis, or narrowing, is due to fibrosis.
"The non-linearity of the strain can, at least in this experiment, separate inflammation from fibrosis with very high power," he said.
Elasticity imaging has already established a role in assessing liver fibrosis and cirrhosis, or scarring from liver damage. Biopsy is invasive, carries risks and can easily miss diseased tissue because of its highly localized nature. As a more global and benign measure, shear wave imaging is a likely candidate to replace biopsy for fibrosis and cirrhosis assessment, Dr. Rubin said.
Volume Flow Has Applications in Transplant Evaluation, Cerebral Perfusion
Dr. Rubin also discussed the multiple applications of volume blood flow estimation, a field in which he was a pioneer. A combination of 3D and 4D ultrasound with an angle-independent technique has made flow estimation viable, with multiple physiological and pathological implications, Dr. Rubin said.
Volume flow estimation has proven to be very accurate in animal studies and has been used clinically to measure umbilical cord blood flow. In one patient, the technique even predicted preeclampsia, a potentially dangerous pregnancy complication. Other potential volume flow applications include transplant evaluations, cardiac output measurements and cerebral perfusion.
"We are at the cusp of a renaissance in ultrasound," said Dr. Rubin. "There are many things going on in the field that will have a major impact on medical care."
Emanuel Welcomes RSNA 2014 Attendees
Before Monday's New Horizons Lecture, Chicago Mayor Rahm Emanuel welcomed the attendees to the city and congratulated the RSNA on the centennial anniversary of its first meeting. He described his personal connection to radiology, noting that his mother was working as an x-ray technologist at Mt. Sinai Hospital in Chicago in the 1950s when she met his physician-father.
In closing, the mayor had a special announcement for people intending to participate in Tuesday morning's 5K Fun Run to benefit the RSNA Research & Education Foundation. "By executive order, we made sure the temperature will be a little warmer tomorrow morning," he said.