Phipps JE, Vela D, Hoyt T, Halaney DL, Mancuso JJ, Buja LM, Asmis R, Milner TE, Feldman MD. Macrophages and intravascular OCT bright spots: a quantitative study.
JACC Cardiovasc Imaging 2014;
8:63-72. [PMID:
25499133 DOI:
10.1016/j.jcmg.2014.07.027]
[Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/13/2014] [Revised: 06/25/2014] [Accepted: 07/16/2014] [Indexed: 12/15/2022]
Abstract
OBJECTIVES
This study hypothesized that bright spots in intravascular optical coherence tomography (IVOCT) images may originate by colocalization of plaque materials of differing indexes of refraction. To quantitatively identify bright spots, we developed an algorithm that accounts for factors including tissue depth, distance from light source, and signal-to-noise ratio. We used this algorithm to perform a bright spot analysis of IVOCT images and compared these results with histological examination of matching tissue sections.
BACKGROUND
Bright spots are thought to represent macrophages in IVOCT images, and studies of alternative etiologies have not been reported.
METHODS
Fresh human coronary arteries (n = 14 from 10 hearts) were imaged with IVOCT in a mock catheterization laboratory and then processed for histological analysis. The quantitative bright spot algorithm was applied to all images.
RESULTS
Results are reported for 1,599 IVOCT images co-registered with histology. Macrophages alone were responsible for only 23% of the bright spot-positive regions, although they were present in 57% of bright spot-positive regions (as determined by histology). Additional etiologies for bright spots included cellular fibrous tissue (8%), interfaces between calcium and fibrous tissue (10%), calcium and lipids (5%), and fibrous cap and lipid pool (3%). Additionally, we showed that large pools of macrophages in CD68(+) histology sections corresponded to dark regions in comparative IVOCT images; this is due to the fact that a pool of lipid-rich macrophages will have the same index of refraction as a pool of lipid and thus will not cause bright spots.
CONCLUSIONS
Bright spots in IVOCT images were correlated with a variety of plaque components that cause sharp changes in the index of refraction. Algorithms that incorporate these correlations may be developed to improve the identification of some types of vulnerable plaque and allow standardization of IVOCT image interpretation.
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