title: Computer-aided quantification of focal cartilage lesions using MRI: accuracy and initial arthroscopic comparison.
abstract: OBJECTIVE
  The purpose of the study was to validate a Gradient Peak Method (GPM) by evaluating its accuracy and consistency at different magnetic field strengths. The GPM using magnetic resonance imaging (MRI) was previously proposed to quantitatively assess the morphology of focal cartilage lesions, and its feasibility was demonstrated.
  
  
  METHODS
  GPM quantifies the morphologic properties of cartilage lesions based on their three-dimensional geometry. Twenty-two conical and cylindrical lesions were surgically created on fresh porcine knees, and the results obtained by GPM were compared with manually measured lesion dimensions. Another 15 focal lesions of various shapes were created and scanned, and the quantification results were compared at 1.5 Tesla and 3 Tesla. Additionally, cartilage lesions in three patients were scanned, quantified by GPM, and compared with arthroscopic visualization and measurements.
  
  
  RESULTS
  The average absolute errors of GPM (depth: < or =0.4mm; diameter: < or =1.4mm) were within twice the in-plane resolution in depth estimates and within the slice thickness in diameter estimates. Analysis also suggested that the quantifications of GPM using 1.5 Tesla and 3 Tesla data were not statistically different. Moreover, the GPM results were shown to be consistent with the lesion measurements obtained arthroscopically.
  
  
  CONCLUSIONS
  The GPM using MRI provides estimates of lesion thickness, depth, diameter, and area. With this validation, the method can be potentially used as an auxiliary tool to help radiologists and physicians assess cartilage lesions quantitatively and monitor disease progression.
authors.affiliation: University of California at San Francisco, San Francisco, CA 94143, USA.
authors.forename: Keh-Yang
authors.initials: KY
authors.lastname: Lee
authors.forename: Jeffrey N
authors.initials: JN
authors.lastname: Masi
authors.forename: Christian A
authors.initials: CA
authors.lastname: Sell
authors.forename: Robert
authors.initials: R
authors.lastname: Schier
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Link
authors.forename: Lynne S
authors.initials: LS
authors.lastname: Steinbach
authors.forename: Marc
authors.initials: M
authors.lastname: Safran
authors.forename: Benjamin
authors.initials: B
authors.lastname: Ma
authors.forename: Sharmila
authors.initials: S
authors.lastname: Majumdar
mesh_terms: D000818:Animals; D001182:Arthroscopy / Q000379:methods; D002358:Cartilage, Articular / Q000293:injuries / Q000473:pathology*; D005240:Feasibility Studies; D006614:Hindlimb; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000473:pathology; D013552:Swine