title: MR perfusion index as a quantitative method of evaluating epiphyseal perfusion in Legg-Calve-Perthes disease and correlation with short-term radiographic outcome: a preliminary study.
abstract: BACKGROUND
  Current radiographic prognosticators of the outcome of Perthes disease can only be applied after femoral head deformity has occurred. Quantification of femoral head perfusion using the gadolinium-enhanced subtraction magnetic resonance imaging (MRI) technique may serve as an early prognosticator of outcome. The purposes of this study were 2-fold: (1) to develop a reliable method to quantify femoral head perfusion using this MRI technique; and (2) to determine whether the perfusion at early stages of Perthes disease correlates with radiographic deformity after a 2-year follow-up.
  
  
  METHODS
  A total of 20 patients meeting the following inclusion criteria were studied: radiographs and MRI obtained of femoral heads predeformity, age between 5 and 13 years, and unilateral disease. MR perfusion index, a measure of perfusion in the epiphysis, was obtained using digital image analysis of subtraction gadolinium-enhanced MRI. Intraobserver and interobserver agreement of this index was assessed by 2 independent observers. MR perfusion index was correlated with a radiographic deformity index (a measure of femoral head deformity) obtained after a minimum of 2 years.
  
  
  RESULTS
  The intraobserver agreement assessed by the intraclass correlation coefficient was 0.96 for observer 1 and 0.97 for observer 2. The interobserver agreement of the MR perfusion index was 0.90 for trials 1 and 2. MR perfusion index in the early stages of Perthes disease was highly variable, ranging from 0 to 0.70. After a minimum of 2 years following MRI acquisition, radiographs were obtained and evaluated using the deformity index, a continuous measure of femoral head deformity, by 2 blinded observers. Deformity index at 2-year follow-up showed moderate correlation with predeformity MR perfusion index (r=-0.56, P=0.01, R=0.31). In those patients who were treated nonoperatively, the correlation was stronger (r=-0.79, P=0.006, R=0.63).
  
  
  CONCLUSIONS
  MR perfusion index obtained from gadolinium-enhanced subtraction MR images showed a high interobserver agreement. MR perfusion index is highly variable at early stages of Perthes disease, and a lower MR perfusion index correlated with greater radiographic deformity at the 2-year follow-up. This pilot study shows the promise of predeformity MR perfusion index as a possible early prognosticator of outcome in Perthes disease.
  
  
  METHODS
  Prognostic level II.
authors.affiliation: *Texas Scottish Rite Hospital for Children †Center for Excellence in Hip Disorders, Texas Scottish Rite Hospital for Children, Dallas, TX.
authors.forename: Jerry
authors.initials: J
authors.lastname: Du
authors.forename: Amanda
authors.initials: A
authors.lastname: Lu
authors.forename: Molly
authors.initials: M
authors.lastname: Dempsey
authors.forename: John A
authors.initials: JA
authors.lastname: Herring
authors.forename: Harry K W
authors.initials: HK
authors.lastname: Kim
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D003287:Contrast Media; D004838:Epiphyses; D005270:Femur Head / Q000473:pathology*; D005500:Follow-Up Studies; D005682:Gadolinium; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D007873:Legg-Calve-Perthes Disease / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D015588:Observer Variation; D010865:Pilot Projects; D011379:Prognosis; D011446:Prospective Studies; D011859:Radiography; D015203:Reproducibility of Results
chemical_list: D003287:Contrast Media; D005682:Gadolinium