Abstract 2559: Reflectance, Fluorescence, and Raman Spectroscopy Identify Features of Vulnerable Atherosclerotic Plaque In Vivo Including a Thin Fibrous Cap, Necrotic Core or Superficial Foam Cells, and Thrombus

Abstract

Early detection and treatment of vulnerable atherosclerotic plaques, the lesions most prone to rupture, is critical to reducing patient mortality associated with cardiovascular disease. The combination of reflectance, fluorescence, and Raman spectroscopy - termed multimodal spectroscopy (MMS) - provides complementary and depth-sensitive information about tissue composition. We assessed the hypothesis that MMS can detect morphological features of vulnerable plaque: thin fibrous cap (TFC), necrotic core (NC), superficial foam cells (SFC), intralesional hemorrhage (IH), and thrombus. Methods. In vivo and ex vivo MMS spectra were collected from 12 patients undergoing peripheral vascular surgeries. The data collection was facilitated by means of a novel MMS probe catheter and a portable clinical instrument developed in our laboratory. During carotid endarterectomies, MMS spectra were collected in vivo from the intimal surface of the plaque with the probe held normal to the artery wall. During femoral bypasses, MMS spectra were collected in vivo either through the proximal anastomosis site from the posterior artery wall or adjacent to the incision. A tissue specimen was excised for additional MMS spectral collection ex vivo. Histopathological analysis was performed by a blinded cardiovascular pathologist to assess the vulnerability of each spectrally evaluated tissue site using a quantitative index based on the dimension or severity of the following: TFC, NC, SFC, IH, and thrombus. Across the total set of 76 evaluated tissue locations, MMS is shown to have the ability to detect vulnerability features including a TFC, NC or SFCs, and thrombus. A TFC is detected by measuring the relative amount of collagen assessed by fluorescence, a large NC or SFCs are detected through the combination of beta-carotene absorption and the Raman spectral signature of lipids, and thrombus is detected through its Raman signature. The results indicate that rupture-prone vulnerable plaques could be detected with a sensitivity of 96% and specificity of 72%. In conclusion, these encouraging results will help bring MMS into the clinical arena as a powerful, catheter-based diagnostic technique for early detection of vulnerable plaques.