title: Macrophages and intravascular OCT bright spots: a quantitative study.
abstract: OBJECTIVE
  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.
authors.affiliation: University of Texas Health Science Center San Antonio, San Antonio, Texas.
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Phipps
authors.affiliation: Texas Heart Institute, Houston, Texas.
authors.forename: Deborah
authors.initials: D
authors.lastname: Vela
authors.affiliation: University of Texas Health Science Center San Antonio, San Antonio, Texas.
authors.forename: Taylor
authors.initials: T
authors.lastname: Hoyt
authors.affiliation: University of Texas Health Science Center San Antonio, San Antonio, Texas; Department of Veterans Affairs, South Texas Veterans Health Care System, San Antonio, Texas.
authors.forename: David L
authors.initials: DL
authors.lastname: Halaney
authors.affiliation: University of Texas Health Science Center San Antonio, San Antonio, Texas.
authors.forename: J Jacob
authors.initials: JJ
authors.lastname: Mancuso
authors.affiliation: Texas Heart Institute, Houston, Texas.
authors.forename: L Maximilian
authors.initials: LM
authors.lastname: Buja
authors.affiliation: University of Texas Health Science Center San Antonio, San Antonio, Texas.
authors.forename: Reto
authors.initials: R
authors.lastname: Asmis
authors.affiliation: University of Texas at Austin, Austin, Texas.
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Milner
authors.affiliation: University of Texas Health Science Center San Antonio, San Antonio, Texas; Department of Veterans Affairs, South Texas Veterans Health Care System, San Antonio, Texas. Electronic address: feldmanm@uthscsa.edu.
authors.forename: Marc D
authors.initials: MD
authors.lastname: Feldman
mesh_terms: D000465:Algorithms; D003331:Coronary Vessels / Q000473:pathology*; D006801:Humans; D008264:Macrophages / Q000473:pathology*; D041623:Tomography, Optical Coherence
keywords: intravascular optical coherence tomography; macrophages; quantitative analysis bright spots