FL-IVUS combines intravascular ultrasound with fluorescence lifetime imaging to obtain morphologic and biochemical details from the arterial wall. Ultrasound measurements alone provide morphologic information (plaque burden, remodeling index and presence of calcium). Fluorescence lifetime can determine the presence of a thick fibrous cap, macrophage infiltration, and lipid cores beneath thin fibrous caps. These details are important to assess plaque vulnerability. In this study, we focused on the ability of FL-IVUS to differentiate between early and advanced lipid cores-advanced cores are vulnerable to rupture. We imaged N=12 ex vivo human coronary arteries and performed hematoxylin and eosin, Movat’s pentachrome and CD68 immunohistochemistry at 500 micron intervals throughout the length of the vessels. We found only N=1 thin-capped fibroatheroma (TCFA) with an advanced necrotic core and N=7 cases of foam cell infiltration, early lipid cores or deep necrotic cores. IVUS was able to observe the increased plaque burden and calcification of the advanced and deep necrotic cores, but could not identify early lipid cores, foam cell infiltration or discriminate between deep necrotic cores and TCFA. The addition of FLIm to IVUS allowed the TCFA to be discriminated from early lipid accumulation, particularly at 542±50 nm (355 nm pulsed excitation): 7.6 ± 0.5 ns compared to 6.6 ± 0.4 ns, respectively (P<0.001 by ANOVA analysis). These differences need to be validated in a larger cohort, but exist due to specific lipid content in the necrotic core as well as increased extracellular matrix in early lesions.
Jennifer E. Phipps, Julien Bec, Deborah Vela, L. Maximilian Buja, Jeffrey A. Southard, Kenneth B. Margulies, and Laura Marcu, "Fluorescence lifetime intravascular ultrasound (FLIm-IVUS) and the quest to discriminate between early and advanced lipid cores in atherosclerosis (Conference Presentation)," Proc. SPIE 10042, Diagnostic and Therapeutic Applications of Light in Cardiology, 100420C (Presented at SPIE BiOS: January 28, 2017; Published: 19 April 2017); https://doi.org/10.1117/12.2253185.5369982356001.
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