Intravascular Imaging Technique Characterizes Key Heart Attack Risk

A Massachusetts General Hospital-based research team has introduced an intravascular laser speckle imaging (ILSI) technique that showed the ability to identify the distinct mechanical features of plaques that are most apt to rupture under the physiological conditions of cardiac motion, blood flow, and breathing. The rupture of unstable coronary plaques can cause arterial blockage, leading to heart attack.

The research charts a course for scientists to obtain the visual information necessary to deliver pharmacological insights that could aid in the development of treatments and preventative approaches for the prevention of heart attacks.

The researchers deployed a small-diameter intravascular catheter device that delivered light into the coronary artery wall. The catheter incorporated an optical fiber (fiber bundle), under which they placed an illumination fiber. The catheter also included a GRIN lens to image the reflected speckle patterns onto an external CMOS sensor, as well as a mirror and circular polarizer component.

ILSI uses laser speckle patterns to estimate a source’s (in this case, coronary plaques’) mechanical properties. These patterns form when laser light scatters from tissue, and within those patterns, individual speckles fluctuate in time due to a plaque’s viscoelastic properties when viewed with a high-speed camera.

A new technique known as intravascular laser speckle imaging could one day be used to detect coronary plaques that are likely to lead to a heart attack. The researchers developed a small-diameter intravascular catheter that incorporates a small-diameter fiber bundle, polarizer, and GRIN lens to image the reflected speckle patterns onto a CMOS sensor. Courtesy of Seemantini Nadkarni, Wellman Center for Photomedicine.

Viscous materials naturally resist flow when stress is applied. Viscoelasticity is the property of materials exhibiting viscous and elastic characteristics together when undergoing deformation that could be caused by stress.

The researchers gauged the efficiency and performance capabilities of their instrument to detect unstable plaques in a human coronary artery in a swine xenograft model; the team sutured human coronary arteries onto the beating heart of a pig to perform its preclinical tests. Team members assessed the mechanical properties of plaque inside the arteries by calculating the rate of fluctuations in the intensity of the speckle pattern and then comparing results with histopathological determinations they had previously obtained.

The team reported that the rates, or “time constants,” in the unstable plaques were significantly lower than other, stable plaques in the coronary wall. The results, in other words, showed high diagnostic sensitivity and specificity of ILSI in detecting lipid pool plaques in humans that were most likely to rupture under physiological conditions, said Seemantini Nadkarni, research team leader from the Wellman Center for Photomedicine at Massachusetts General Hospital.

“By providing the unique capability to measure mechanical stability — a critical metric in detecting unstable plaques — ILSI is poised to provide a new approach for coronary assessment,” Nadkarni said.

Medical personnel could easily integrate the new technique with existing intracoronary technologies such as OCT and/or intravascular ultrasound, the researchers said. Such a combination would pair ILSI’s information about mechanical features and properties with the morphological information that those other methods deliver to comprehensively improve plaque stability evaluations.

Recent studies have shown that mechanical features as well as microstructural and compositional features influence plaque rupture.

Following additional planned evaluations in live animals, the researchers will assess the safety of using their device in humans and begin the process of gaining regulatory approval for clinical use.

The research was published in Biomedical Optics Express (www.doi.org/10.1364/BOE.418939).