Better Images of Dangerous Coronary Plaques

Three-dimensional visualization of OCT-NIRAF imaging data acquired from a patient's coronary artery- (Source: Wellman Center for Photomedicine)

Three-dimensional visualization of OCT-NIRAF imaging data acquired from a patient’s coronary artery. (Source: Wellman Center)

Combing optical coherence tomography (OCT) with another advanced imaging technology may more accurately identify coronary artery plaques that are most likely to rupture and cause a heart attack. In a new report investi­gators from the Wellman Center for Photo­medicine at Massa­chusetts General Hospital MGH describe the first use in patients of a catheter-based device utilizing both OCT and near-infrared auto­fluorescence (NIRAF) imaging.

“OCT provides images of tissue micro­structure but not of its chemical and molecular composition”, says Gary Tearney of the Wellman Center and the MGH Pathology Department, co-senior author of the paper. “Since both of those charac­teristics are needed to fully understand coronary artery disease, the combi­nation of OCT with NIRAF could provide a more powerful tool for investi­gating coronary pathology.”

The detailed images provided by OCT are created by bouncing near-infrared light off the internal surfaces of blood vessels and can identify plaques that have the appea­rance of rupture-prone “vulnerable” plaques with the potential to cause a heart attack or sudden cardiac death. Fluores­cence imaging techniques like NIRAF illuminate an artery with a specific wavelength of light to excite certain molecules, which respond by emitting different wave­lengths. Since only certain molecules respond, the resulting signal provides infor­mation on the molecular compo­sition of analyzed tissue.

Tearney’s team has been investi­gating whether the additional data provided by NIRAF could identify rupture-prone sites within arterial plaques – particularly fibroatheromas, advanced lesions consisting of a core of dead cells covered by an often-thin fibrous cap, which are particularly prone to rupture. In a previous study using coronary artery segments from cadavers, the investi­gators showed that the NIRAF signal was elevated in fibroa­theromas and highest in those with thin fibrous caps. The current study is the first to inves­tigate the use of NIRAF in living patients.

The study enrolled 12 patients receiving cardiac catheteri­zation at the MGH between July 2014 and January 2015. In addition to the clinical procedures conducted to diagnose and/or treat the patients’ cardiac disease, Farouc Jaffer, director of MGH Coronary Inter­vention and co-senior author of the paper, used the novel device developed by the Wellman/MGH team that acquires both OCT and NIRAF data to construct images of coronary arterial segments. The investi­gational procedure was identical to that used for conven­tional OCT imaging.

“Performing OCT-NIRAF imaging is just like conducting standalone coronary OCT imaging, and we are now able to obtain near-infrared fluores­cence biological plaque information seamlessly integrated with OCT anatomical images, with no additional time required,” Jaffer says. “The clinical success of OCT-NIRAF should further pave the way forward for targeted near-infrared fluores­cence molecular imaging using injectable molecular- or cellular-specific agents.”

The primary results of the study were confirmation that the procedure was as safe and as feasible to perform as conventional OCT. The OCT-NIRAF images revealed that the NIRAF signal was elevated in areas in which OCT results suggested the presence of a fibroa­theroma, and even higher in lesions with thin caps or at sites of plaque rupture and clot formation. Several aspects of the NIRAF signal were different from the patterns produced by other coronary vascular imaging modalities, and more investi­gation is needed to determine the molecular under­pinnings and clinical signi­ficance of NIRAF signal results. NIRAF was also elevated in sites showing evidence of inflammation, another potential bio­marker of plaques likely to rupture.

“Overall we believe that the combined OCT-NIRAF examination provides infor­mation on molecules within arterial plaques and other features associated with a higher risk of an acute coronary event,” says Tearney, a professor of Patho­logy at Harvard Medical School and the Mike and Sue Hazard Family MGH Research Scholar. “But right now this is a hypo­thesis, and our findings need to be borne out in larger studies, which we plan to have underway later this year.” (Source: MGH)

Reference: G. J. Ughi et al.: Clinical Characterization of Coronary Atherosclerosis With Dual-Modality OCT and Near-Infrared Autofluorescence Imaging, JACC: Cardio. Ima., online 9 March 2016, DOI:10.1016/j.jcmg.2015.11.020

Link: Wellman Center for Photo­medicine at Massa­chusetts General Hospital, Boston, Massachusetts, USA

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