Old Tech, New Tricks

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Imaging enables researchers to peer deeply into the functioning of the human body. But even well-known modalities such as ultrasound and magnetic resonance imaging may have untapped potential. Researchers at the Mayo Clinic and University of Pennsylvania are leading the push to find out, exploring experimental technologies that may alter the research landscape. Here are snapshots of their efforts--and the thought leaders behind them.

Technology: Vibro-acoustography
Organization: Mayo Clinic College of Medicine, Rochester, MN
Researcher: Jim Greenleaf, PhD, director ultrasound research laboratory

When Jim Greenleaf says that ultrasound is the "wave of the future," he's making both an academic pun and a serious statement about clinical research. For more than a decade, Greenleaf has been leading research into how ultrasound can be used to analyze tissues and gain insight into breast cancer. Under Greenleaf's guidance, the Ultrasound Research Laboratory at Mayo Clinic has developed a technique called "vibro-acoustography."

In essence, the technique uses two intersecting ultrasound beams to impart a force on tissue. It then measures the acoustic emission of the impact, producing an image of cancerous tissue that contains far more detail than conventional ultrasound can yield. "Regular ultrasound records the reflection of the actual ultrasound," he explains. "This method records variation due to change in the reflectivity of the tissue." To date, Mayo researchers have used the technology to perform breast scans on nearly 40 patients. The high-contrast images often have remarkable clarity, Greenleaf observes. "On some of the cancers, you can see how it is pulling nearby tissue," he says.

In a related project, Greenleaf's 14-member department is developing an "ultrasound biopsy." This technology measures how fast a wave propagates when tissue is "hit" by the ultrasound beam. "We can quantitatively measure stiffness and viscosity in tissue," he says. "It could also work with prostate and thyroid tissue."

Mayo is working with GE Healthcare to develop a commercial application of the vibro-acoustography technology. But Greenleaf is cautious about predicting widespread acceptance, despite its potential. "In the past I have predicted things that would be outstanding that have fizzled," he concedes.

Technology: MRI with polarized carbon-13
Organization: University of Pennsylvania School of Medicine, Philadelphia (part of Penn Medicine)
Researcher: Rahim Rizi, PhD, associate professor of radiology

The context of Rahim Rizi's work is the growth of lung disease globally. "By 2012, chronic obstructive pulmonary disease will be the third-leading cause of death in the world," he says. But imaging the lungs has proven to be a challenge. CT scans give a detailed structural view but offer little insight into function. Thus, for the past 15 years, Rizi has been developing MRI-based techniques to gather images of how the lungs function all the way down to the alveoli, the small air sacs that serve as the intersection of inhalation and exhalation. "As lung diseases progress, the alveoli collapse and the lung cannot ventilate as well."

Unlike the brain and other parts of the body, the lungs do not contain water, thus limiting conventional MRI images of lung functioning, Rizi explains. As a result, Penn researchers have looked at alternative substances to introduce into the lungs, enabling the MRI to capture more detailed images. Since 1994, Penn researchers have experimented with hyperpolarized helium, a specially treated gas that the patient inhales before undergoing a scan. The images enable physicians to measure the diffusion of the helium molecules, and thus understand lung function down to areas of one millimeter or less.

Hyperpolarized helium can be difficult to produce, Rizi says, although xenon may be used as a substitute. That's one reason Penn researchers have looked at other alternatives. Most recently, they have experimented--on animals only--with polarized carbon-13 molecules. After injecting the molecules into a rabbit, researchers then run the animal through an MRI. The MRI can measure changes in metabolic activity as the carbon-13 breaks down in the body. Understanding the metabolism of cancerous cells could open many doors for researchers, Rizi says. "By imaging metabolic activity, you gather information to analyze the cause and symptoms of disease," he says.

-Gary Baldwin

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