Thermal sensor deployed by angiogram catheter detects early
13 March 2011
A micro heater and thermal sensor small enough to deploy by an angiogram
catheter can detect the earliest stages of atherosclerosis in blood
The thermal sensor uses convective heat transfer to detect
pre-atherosclerotic regions of arteries that otherwise show no
clinical signs of atherosclerosis. The sensor method has the
advantage of being both minimally invasive and sensitive. The
technology has the potential for widespread and rapid application
during diagnostic angiograms.
The study’s lead author, Dr. Tzung Hsiai, an Associate Professor
of Biomedical Engineering and Cardiology at the University of
Southern California, said, “The innovation of this study lies in the
convective heat transfer strategy to detect changes in output
voltage signals in the non-obstructive, albeit inflammatory and
otherwise considered normal arterial regions.”
Frictional force acting on the walls of vessels by blood flow,
known as shear stress, is intimately involved in oxidative stress
and inflammatory responses that lead to atherosclerosis. In
athero-prone regions, the flow is disturbed, yet detection of
changing flow patterns in real-time remains a challenge.
Dr. Hsiai’s group developed a micro-electro-mechanical system
(MEMS) by depositing titanium and platinum on a flexible polymer
membrane and patterning them to form the sensing elements. They
deployed the sensor via an angiogram catheter into the aortic and
abdominal arteries of rabbits that had eaten a high fat, high
cholesterol diet, and a control group that had eaten a normal diet.
An electric current passed through the sensing element generates
a thermal layer in the flow field, from which convective heat
transfer is measured as a function of the voltage signals. In the
regions of atherosclerotic lesions, blood flow is disturbed. This
causes changes in convective heat transfer from the sensing element
to the flow field, and thus, changes in voltage signals.
In the study, The sensor measured a high voltage upstream from
the part of the blood vessel that harbored the atherosclerotic
plaque, and a low voltage downstream.
The scientists concluded that the MEMS thermal sensor method
could sensitively detect pre-atherosclerotic regions that otherwise
showed no clinical signs of atherosclerosis. The authors integrated
mathematical simulations, fluoroscopic images, and dissection of the
aortas to verify their results.
Once the MEMS thermal sensors have identified the atherosclerotic
lesion, doctors can identify whether this lesion is a vulnerable or
stable plaque. A vulnerable plaque could rupture, which blocks the
arteries and causes heart attacks and strokes. Doctors perform
angioplasty and implant stents to prevent blockage of vessels.
Lifestyle changes and medication can manage stable plaque.
According to Dr Hsiai, “Despite imaging modalities, we have yet to
develop a means to differentiate vulnerable from stable plaque. If
we can differentiate vulnerable from stable plaque during a
diagnostic angiogram, we can avoid unnecessary complications from
angioplasty and stenting, and deliver an enhanced risk-to-benefit
profile for our patients. It could also reduce health costs by
eliminating unnecessary procedures and for treating
Fei Yu, Lisong Ai, Wangde Dai, Nora Rozengurt, Hongyu Yu, Tzung
Keith Hsiai. MEMS Thermal Sensors to Detect Changes in Heat Transfer
in the Pre-Atherosclerotic Regions of Fat-Fed New Zealand White
Rabbits. Annals of Biomedical Engineering. DOI