Physicians use hi-tech scanners all the time to produce crisp
and detailed images to help them diagnose illness. But they may not
be getting the whole picture.
CT or MRI scanners are unable to provide potentially important
clues about a tissues health namely, how it feels. Duke University
biomedical engineers believe information about the stiffness of
particular tissue such as organs or arteries can add an important
dimension to the diagnostic process.
The trick is how to make measurements of stiffness without
actually opening the patient up surgically.
One approach, in the early stages of development in labs at
Dukes Pratt School of Engineering, uses sound waves. Among other
areas of research, Gregg Trahey, professor of biomedical
engineering, and his students are applying Duke-developed
modifications to existing ultrasound technology to more completely
understand the health of the heart and its arteries.
Underlying this approach is the assumption that healthy tissue
should be soft and elastic, while damaged tissue will be stiff. In
the case of the heart, stiffness means the muscle is dead or
damaged hindering its ability to contract. In arteries, stiffness
may indicate the presence of an atherosclerotic plaque that could
dislodge from the vessel wall, potentially causing a heart attack
or stroke.
Traheys method pushes the tissue with sound waves and measures
how quickly it returns to its previous state, much like the rebound
of the Pillsbury dough boy after his belly is poked. Trahey uses a
sound wave-based technology, called Acoustic Radiation Force
Impulse (ARFI) imaging, to capture how the tissue responds these
sound-wave pokes.
Using ARFI, we have shown that we can make measurements of
tissues stiffness, Trahey. Our next task is to compare our results
with those of other approaches to see if our data is really
reflective of the situation, and once we can do that, well need to
determine if our measurements are actually predictive of the degree
of disease in a patient.
The National Institutes of Health believes that this line of
research holds promise and has backed it with a five-year MERIT
(Method to Extend Research in Time) award to Trahey.
The prestigious MERIT awards provide long-term, stable support
to investigators whose research and productivity are likely to
continue in the future. The awards are intended to foster continued
creativity and lessen the administrative burdens associated with
the preparation and submission of research grant applications.
Traheys award came from the NIHs National Heart, Lung Blood
Institute,
Conventional ultrasound focuses high frequency sound waves into
the body either to create images of internal tissues or to heat
them. ARFI is a special kind of ultrasound that employs two
different sound pulses — one pulse is a high-energy beam that
pushes on tissues like sonic fingers and the other is a tracking
beam that measures the resulting tissue motion.
To accomplish this, Trahey and his students use the latest
ultrasound scanners available and modify them to perform ARFI
studies. These modifications range from physically altering the
transducers, which collects the rebounding waves, to writing new
computer language to collect and synthesize the data.
One use of the technology currently being conducted is the study
of atherosclerosis. Normal arteries are pliable, since they help
move blood throughout the circulatory system. However, when the
arteries get clogged, they lose these elastic capabilities.
“We hypothesize that we can tell the difference between hard and
soft plaques with ARFI, since it essentially a stiffness-imaging
modality,” said Trahey. “We also hypothesize that in healthy people
we will detect soft vessels, and that in patients with known
vascular disease we will see stiff vessels.
Clinical trials are already underway assessing ARFIs ability to
characterize vascular plaques as stable or vulnerable and to
measure the stiffness of blood vessels. Ongoing trials are also
being conducted to assess the ability of ARFI imaging to guide
cardiac ablation surgeries and to characterize the stiffness of the
myocardium throughout the cardiac cycle.
With NIH support, Trahey is also using ARFI to detect and
characterize liver cancers and to guide minimally invasive
surgeries of liver and kidney cancer.
