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Using Nanosecond Laser Pulses to Image Plaques Lining Arteries in 3D
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Ji-Xin Cheng, associate professor of biomedical engineering and chemistry at Purdue University, and his research group have developed a new type of imaging technology to take precise three-dimensional images of plaques lining arteries.
The new technique uses nanosecond laser pulses in the near-infrared range of the spectrum. The laser generates molecular "overtone" vibrations, or wavelengths that are not absorbed by the blood. The pulsed laser causes tissue to heat and expand locally, generating pressure waves at the ultrasound frequency that can be picked up with a device called a transducer.
The results will be published in Physical Review Letters and expected to appear in the June 17 issue.
Other imaging methods that provide molecular information are unable to penetrate tissue deep enough to reveal the three-dimensional structure of the plaques, but being able to do so would make better diagnoses of cardiovascular disease possible, Cheng said.
"You would have to cut a cross section of an artery to really see the three-dimensional structure of the plaque," Cheng said. "Obviously, that can't be used for living patients."
The imaging reveals the presence of carbon-hydrogen bonds making up lipid molecules in arterial plaques that cause heart disease. The method also might be used to detect fat molecules in muscles to diagnose diabetes and for other lipid-related disorders, including neurological conditions and brain trauma. The technique also reveals nitrogen-hydrogen bonds making up proteins, meaning the imaging tool also might be useful for diagnosing other diseases and to study collagen's role in scar formation.
"Being able to key on specific chemical bonds is expected to open a completely new direction for the field," Cheng said
"We are working to miniaturize the system so that we can build an endoscope to put into blood vessels using a catheter," Cheng said. "This would enable us to see the exact nature of plaque formation in the walls of arteries to better quantify and diagnose cardiovascular disease."
Lihong Wang, Gene K.
Imaging & Microscopy Issue 4 as free epaper or pdf download
Beare Distinguished Professor of Biomedical Engineering at Washington University in St. Louis, is a pioneer of using the "photoacoustic" imaging of blood vessels based on the absorption of light by the electrons in hemoglobin.
The Purdue researchers are the first to show that a strong photoacoustic signal can arise from the absorption of light by the chemical bonds in molecules. The near-infrared laser causes enough heating to generate ultrasound but not enough to damage tissue.
"You can measure the time delay between the laser and the ultrasound waves, and this gives you a precise distance, which enables you to image layers of the tissues for three-dimensional pictures," Cheng said. "You do one scan and get all the cross sections. Our initial target is cardiovascular disease, but there are other potential applications, including diabetes and neurological conditions."
The approach represents a major improvement over another imaging technique, called coherent anti-Stokes Raman scattering, or CARS, which has been used by the Purdue-based lab to study three-dimensional plaque formation in arteries.
http://www.purdue.edu
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Keywords: 3D Imaging CARS microscopy coherent anti-Stokes Raman scattering Diagnostic Imaging Ji-Xin Cheng laser Nanosecond Laser Pulses Near-infrared Laser Photoacoustic Imaging Plaques Lining Arteries Purdue University Transducer
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