Published online before print August 1, 2005, doi: 10.1161/CIRCULATIONAHA.104.520098
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(Circulation. 2005;112:885-892.)
© 2005 American Heart Association, Inc.
Vascular Medicine |
Characterization of Atherosclerotic Plaques by Laser Speckle Imaging
From the Department of Dermatology (S.K.N., B.E.B.), Department of Pathology (S.L.H., G.J.T.), and Department of Radiology (R.C., E.H.), Harvard Medical School, and Wellman Center for Photomedicine (S.K.N., B.E.B., T.H., R.C., A.C., M.S.M., J.T.M., G.J.T.), Massachusetts General Hospital, Boston, and Departments of Health Sciences and Technology (B.E.B.) and Mechanical Engineering (A.C.), Massachusetts Institute of Technology, Cambridge.
Correspondence to Seemantini K. Nadkarni, PhD, Harvard Medical School, Massachusetts General Hospital and Wellman Center for Photomedicine, 40 Blossom St, BAR 718, Boston, MA 02114. E-mail snadkarni{at}hms.harvard.edu
Received March 30, 2004; de novo received November 6, 2004; revision received March 30, 2005; accepted April 4, 2005.
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.
Methods and 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 µm/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, 
. The decorrelation time constants of thin-cap fibroatheromas (TCFA) (=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 µm/s), 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.
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