Cross-sectional view of an artery made with laser/ultrasound imaging process. Fatty plaque deposits are highlighted in green. (Ji-Xin Cheng, Purdue University)
5 November 2014. A process to capture high-speed three-dimensional images of plaque deposits in arteries and analyze their chemical makeup for diagnosing heart conditions is being developed by Purdue University in West Lafayette, Indiana. The team from the lab of Purdue biomedical engineer and chemist Ji-Xin Cheng, with colleagues from Indiana University School of Medicine, University of California campuses in Davis and Irvine, and sensor technology company Spectral Energies in Ohio, reported yesterday on recent advances in the journal Scientific Reports.
Purdue filed a patent application for the technology. Cheng and first author Pu Wang, a postdoctoral researcher in Cheng’s lab, founded the company Vibronix Inc. to take the technology to market.
The build-up of plaque in the arteries is a major cause of heart attacks and strokes, when plaque either breaks off or forms clots that block the arteries to the heart or brain. Plaque is made up of cholesterol and other fatty substances, as well as calcium, cellular waste and fibrin, the material that helps blood clot. Not all plaque is the same, however, and being able to identify the nature of plaque in the arteries can determine if the plaque may break off and trigger a heart attack.
Evaluating plaque in arteries requires knowing not only the amount of build-up, but also its composition, which up to now is hampered by the lack of high-speed imaging. Current technologies can take low-resolution images of the arterial wall, or test samples of plaque in lab cultures, such as in an autopsy, but none can yet accurately and reliably identify risky plaque deposits in live patients.
The technique developed by Cheng and colleagues combines laser and ultrasound processes. The laser process emits 2,000 pulses per second, a rate the researchers say is a 100-fold increase over current technologies. Each pulse of the laser, generated in the near infrared spectrum, is capable of capturing an image. In addition, the process does not require dyes to highlight targets for the images.
The laser also heats the tissue, causing it to expand and produce non-damaging pressure waves that can be detected by ultrasound and converted by a transducer into electrical signals for measurement. Signals returned by the ultrasound act as indicators of the carbon and hydrogen bonds in molecules making up fatty plaque deposits on the arterial wall, and their risk of breaking loose.
In the paper, the team tested the technique on a pig’s artery with atherosclerosis, or hardening of the arteries from plaque deposits. The combination of laser and ultrasound processes returns 3-D images of plaque build-up in the artery, highlighting the higher (10-fold) densities of carbon-hydrogen bonds in the fatty substances contained in the plaque, which indicate vulnerability of deposits to break apart and cause a heart attack.
The researchers plan to extend the tests to live animals and eventually clinical trials. Cheng says the system can be made small enough to fit on an endoscope, a device to produce images inside an artery, inserted and guided by a catheter. Vibronix, the company commercializing the technology, aims to produce such a device.
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