title: Characterization of atherosclerotic plaques by laser speckle imaging.
abstract: BACKGROUND
  A method capable of determining atherosclerotic plaque composition and measuring plaque viscoelasticity can provide valuable insight into intrinsic features associated with plaque rupture and can enable the identification of high-risk lesions. In this article, we describe a new optical technique, laser speckle imaging (LSI), that measures an index of plaque viscoelasticity. We evaluate the potential of LSI for characterizing atherosclerotic plaque.
  
  
  RESULTS
  Time-varying helium-neon laser speckle images were acquired from 118 aortic plaque specimens from 14 human cadavers under static and deforming conditions (0 to 200 microm/s). Temporal fluctuations in the speckle patterns were quantified by exponential fitting of the normalized cross-correlation of sequential frames in each image series of speckle patterns to obtain the exponential decay time constant, tau. The decorrelation time constants of thin-cap fibroatheromas (TCFA) (tau=47.5+/-19.2 ms) were significantly lower than those of other atherosclerotic lesions (P<0.001), and the sensitivity and specificity of the LSI technique for identifying TCFAs were >90%. Speckle decorrelation time constants demonstrated strong correlation with histological measurements of plaque collagen (R=0.73, P<0.0001), fibrous cap thickness (R=0.87, P<0.0001), and necrotic core area (R=-0.81, P<0.0001). Under deforming conditions (10 to 200 microm/s), tau correlated well with cap thickness in necrotic core fibroatheromas (P>0.05).
  
  
  CONCLUSIONS
  The measurement of speckle decorrelation time constant from laser speckle images provides an index of plaque viscoelasticity and facilitates the characterization of plaque type. Our results demonstrate that LSI is a highly sensitive technique for characterizing plaque and identifying thin-cap fibroatheromas.
authors.affiliation: Department of Dermatology, Harvard Medical School, Wellman Center for Photomedicine, Massachusetts General Hospital, 40 Blossom St, BAR 718, Boston, MA 02114, USA. snadkarni@hms.harvard.edu
authors.forename: Seemantini K
authors.initials: SK
authors.lastname: Nadkarni
authors.forename: Brett E
authors.initials: BE
authors.lastname: Bouma
authors.forename: Tina
authors.initials: T
authors.lastname: Helg
authors.forename: Raymond
authors.initials: R
authors.lastname: Chan
authors.forename: Elkan
authors.initials: E
authors.lastname: Halpern
authors.forename: Alexandra
authors.initials: A
authors.lastname: Chau
authors.forename: Milan Singh
authors.initials: MS
authors.lastname: Minsky
authors.forename: Jason T
authors.initials: JT
authors.lastname: Motz
authors.forename: Stuart L
authors.initials: SL
authors.lastname: Houser
authors.forename: Guillermo J
authors.initials: GJ
authors.lastname: Tearney
mesh_terms: D000704:Analysis of Variance; D001011:Aorta / Q000473:pathology*; D050197:Atherosclerosis / Q000000981:diagnostic imaging / Q000473:pathology*; D002102:Cadaver; D003324:Coronary Artery Disease / Q000000981:diagnostic imaging / Q000473:pathology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007834:Lasers; D011859:Radiography