title: Validation of automatically classified magnetic resonance images for carotid plaque compositional analysis.
abstract: OBJECTIVE
  MRI may be used for noninvasive assessment of atherosclerotic lesions; however, MRI evaluation of plaque composition requires validation against an accepted reference standard, such as the American Heart Association (AHA) lesion grade, defined by histopathological examination.
  
  
  METHODS
  Forty-eight carotid endarterectomy specimen cross-sections had AHA lesion grade determined histopathologically and were concurrently imaged using combinations of 8 MRI contrast weightings in vitro. A maximum likelihood classification algorithm generated MRI "maps" of plaque components, and an AHA lesion grade was assigned correspondingly. Additional analyses compared classification accuracy obtained with a commonly used set of magnetic resonance contrast weightings [proton density (PDw), T1 (T1w), and partial T2 (T2w)] to accuracy obtained with the combination of PDw, T1w, and diffusion-weighted (Dw) contrast.
  
  
  RESULTS
  For the 8-contrast combination, the sensitivities for fibrous tissue, necrotic core, calcification, and hemorrhage detection were 83%, 67%, 86%, and 77%, respectively. The corresponding specificities were 81%, 78%, 99%, and 97%. Good agreement (79%) between magnetic resonance and histopathology for AHA classification was achieved. For the PDw, T1w, and Dw combination, the overall classification accuracy was insignificantly different at 78%, whereas the overall classification accuracy using PDw, T1w, and partial T2w contrast weightings was significantly lower at 67%.
  
  
  CONCLUSIONS
  This study provides proof-of-principle that the composition of atherosclerotic plaques determined by automated classification of high-resolution ex vivo MRI accurately reflects lesion composition defined by histopathological examination.
authors.affiliation: Imaging Research Laboratories, Robarts Research Institute, PO Box 5015, London, Ontario, Canada.
authors.forename: Sharon E
authors.initials: SE
authors.lastname: Clarke
authors.forename: Vadim
authors.initials: V
authors.lastname: Beletsky
authors.forename: Robert R
authors.initials: RR
authors.lastname: Hammond
authors.forename: Robert A
authors.initials: RA
authors.lastname: Hegele
authors.forename: Brian K
authors.initials: BK
authors.lastname: Rutt
mesh_terms: D050197:Atherosclerosis; D001921:Brain / Q000473:pathology; D002340:Carotid Artery Diseases / Q000473:pathology*; D002343:Carotid Artery, Internal / Q000473:pathology; D016893:Carotid Stenosis; D003287:Contrast Media; D004691:Endarterectomy; D016894:Endarterectomy, Carotid / Q000379:methods; D006801:Humans; D007091:Image Processing, Computer-Assisted; D016013:Likelihood Functions; D050356:Lipid Metabolism; D008279:Magnetic Resonance Imaging / Q000379:methods*; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed
chemical_list: D003287:Contrast Media