title: Tissue characterization of atherosclerotic plaques by intravascular ultrasound radiofrequency signal analysis: an in vitro study of human coronary arteries.
abstract: BACKGROUND
  Conventional gray-scale images of intravascular ultrasound (IVUS) cannot accurately differentiate histologic subtypes of sonolucent coronary plaques with or without a lipid core.
  
  
  METHODS
  We analyzed radiofrequency signals obtained in vitro from 24 regions of interest (ROI) of noncalcified (sonolucent) plaques in 10 atherosclerotic coronary artery specimens pressure-fixed by formalin. Radiofrequency signals were sampled with a 30-MHz IVUS catheter and digitized at 500 MHz in 8-bit resolution. The ROIs were histologically categorized into 12 plaques with a lipid core and 12 plaques without it. Integrated backscatter and statistical parameters of the radiofrequency envelope (mean/SD ratio [MSR], skewness, and kurtosis) within the ROI were calculated offline, and their ability to detect a lipid core was compared with visual analysis of the IVUS video images. In the group with lipid cores, percent area of a lipid core in each ROI was measured in a digitized histologic image by a computerized planimeter.
  
  
  RESULTS
  Sensitivity and specificity of MSR, skewness, and kurtosis for lipid core detection were substantially greater than visual video image analysis (83.3% and 91.7%, 100% and 91.7%, 100% and 91.7% vs 53.3% and 71.7%). Furthermore, the parameters of integrated backscatter, MSR, skewness, and kurtosis were significantly correlated to percent of core area (r = -0.64, -0.73, 0.78, and 0.63, respectively; P<.05).
  
  
  CONCLUSIONS
  Compared with IVUS video images, the parameters of radiofrequency signal analysis may be used to aid in more accurate detection and quantitative evaluation of a lipid core, which is one of the major factors of a vulnerable coronary plaque.
authors.affiliation: Division of Cardiovascular Medicine andthe Department of Pathology, Stanford University School of Medicine, CA, USA. nkomiyam@aa.mbn.or.jp
authors.forename: N
authors.initials: N
authors.lastname: Komiyama
authors.forename: G J
authors.initials: GJ
authors.lastname: Berry
authors.forename: M L
authors.initials: ML
authors.lastname: Kolz
authors.forename: A
authors.initials: A
authors.lastname: Oshima
authors.forename: J A
authors.initials: JA
authors.lastname: Metz
authors.forename: P
authors.initials: P
authors.lastname: Preuss
authors.forename: A F
authors.initials: AF
authors.lastname: Brisken
authors.forename: M
authors.initials: M
authors.lastname: Pauliina Moore
authors.forename: P G
authors.initials: PG
authors.lastname: Yock
authors.forename: P J
authors.initials: PJ
authors.lastname: Fitzgerald
mesh_terms: D003324:Coronary Artery Disease / Q000000981:diagnostic imaging*; D003331:Coronary Vessels / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D066298:In Vitro Techniques; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D018084:Ultrasonography, Interventional; D014741:Video Recording