 At issue is the plaque that builds up in arteries as we age. Some
types of plaque are deemed "vulnerable," meaning that they are more
likely to detach from the artery wall and cause heart attack or
stroke."Existing state-of-the-art technologies are capable of
determining if plaque is present in the arteries but can't tell
whether it's vulnerable. And that makes it difficult to assess a
patient's risk," says Dr. Paul Dayton, co-author of a paper on the
new device and professor in the joint biomedical engineering
department at NC State and Chapel Hill. "Our goal was to develop
something that could effectively identify which plaques are
vulnerable."
There are two ultrasound techniques that can help identify
vulnerable plaques, but both depend on the use of contrast agents
called microbubbles.
The first technique is to identify "vasa vasorum" in arteries.
These are clusters of small blood vessels that often infiltrate
arterial plaque and are considered indicators that a plaque is
vulnerable. When microbubbles are injected into an artery, they
follow the flow of the blood. If vasa vasorum are present, the
microbubbles will flow through these blood vessels as well,
effectively highlighting them on ultrasound images.
The second technique is called molecular imaging and relies on
the use of "targeted" microbubbles. These microbubbles attach
themselves to specific molecules that are more likely to be found in
vulnerable plaques, making the plaques stand out on ultrasound
images.
"The problem is that existing intravascular ultrasound technology
does not do a very good job in detecting contrast agents," says Dr.
Xiaoning Jiang, an NC State associate professor of mechanical and
aerospace engineering, adjunct professor of biomedical engineering,
and co-author of the paper.
"So we've developed a dual-frequency intravascular ultrasound
transducer which transmits and receives acoustic signals," Jiang
says. "Operating on two frequencies allows us to do everything the
existing intravascular ultrasound devices can do, but also makes it
much easier for us to detect the contrast agents — or microbubbles — used for molecular imaging and vasa vasorum detection."
The prototype device has performed well in laboratory testing,
but the researchers say they are continuing to optimize the
technology. They hope to launch preclinical studies in the near
future.
The paper, "A preliminary engineering design of intravascular
dual-frequency transducers for contrast enhanced acoustic
angiography and molecular imaging," is published in the
May issue of IEEE Transactions on Ultrasonics, Ferroelectrics,
and Frequency Control. Lead author of the paper is Jianguo Ma, a
mechanical engineering Ph.D. student at NC State. The paper was
co-authored by Heath Martin, a Ph.D. student in the joint biomedical
engineering program.
[to top of second column] |
The research was supported by the National Institutes of Health,
under grant 1R01EB015508.
___
The study abstract follows:
(Copy)
"A preliminary engineering design of intravascular
dual-frequency transducers for contrast enhanced acoustic
angiography and molecular imaging"
Authors :
Jianguo Ma and Xiaoning Jiang, North Carolina State University;
Heath Martin and Paul A. Dayton, North Carolina State University and
the University of North Carolina at Chapel Hill
Published : May 2014,
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency
Control
Abstract:
Current intravascular ultrasound (IVUS) probes are not optimized for
contrast detection due to their design for high-frequency
fundamental mode imaging. However, data from transcutaneous contrast
imaging suggests the possibility of utilizing contrast ultrasound
for molecular imaging or vasa vasorum assessment to further
elucidate atherosclerotic plaque deposition. This paper presents the
design, fabrication, and characterization of a small aperture (0.6 x
3 mm2), IVUS probe optimized for high-frequency contrast
imaging. The design utilizes a dual-frequency (6.5 MHz/30 MHz)
transducer arrangement for exciting microbubbles at low frequencies
(near their resonance) and detecting their broadband harmonics at
high frequencies, minimizing detected tissue backscatter. The
prototype probe is able to generate nonlinear microbubble response
with more than 1.2 MPa of rarefractional pressure (mechanical index:
0.48) at 6.5 MHz, and also able to detect microbubble response with
a broadband receiving element (center frequency: 30 MHz, -6 dB
fractional bandwidth: 58.6%). Nonlinear super-harmonics from
microbubbles flowing through a 200 μm diameter micro-tube were
clearly detected with a signal-to-noise ratio higher than 12 dB. The
preliminary phantom imaging at the fundamental frequency (30 MHz)
and dual frequency super-harmonic imaging results suggest the
promise of small aperture, dual-frequency IVUS transducers for
contrast enhanced IVUS imaging.
[Text from
news release received from NC
State News Services]
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