title: Physician self-referral: frequency of negative findings at MR imaging of the knee as a marker of appropriate utilization.
abstract: OBJECTIVE
  To determine whether ownership of magnetic resonance (MR) imaging equipment by ordering physicians affects the likelihood of positive findings at MR imaging of the knee and to evaluate rates of knee abnormalities seen at MR imaging as a metric for comparison of utilization.
  
  
  METHODS
  The institutional review board approved this retrospective HIPAA-compliant study and waived the need for informed consent. A retrospective review was performed of consecutive diagnostic MR images of the knee interpreted by one radiology practice between January and April 2009 for patients who had been referred by two separate physician groups serving the same geographic community: one with financial interest (FI) in the MR imaging equipment used and one with no FI (NFI) in the MR imaging equipment used. The percentage of examinations with negative results was tabulated for both groups, and the relative frequency of each abnormality subtype was calculated among the studies with positive findings in each group. To examine frequency differences among groups, χ(2) tests were used, and to examine mean differences among groups, t tests were used.
  
  
  RESULTS
  Of 700 examinations, 205 had negative results (117 of 350 in the FI group and 88 of 350 in the NFI group, P = .016). Among the examinations with positive results, the mean total number of positive abnormality subtypes per image did not significantly differ between groups: 1.52 for the FI group and 1.53 for the NFI group (P = .96).
  
  
  CONCLUSIONS
  MR images of the knee among patients referred by the FI group were significantly more likely to be negative than those among patients referred by the NFI group. Frequency of abnormality subtype and distribution among examinations with positive results suggests a highly similar distribution and severity of abnormalities between the two patient groups.
authors.affiliation: From the Interventional Radiology Translational Research Laboratory, Department of Radiology, Duke University Medical Center, Erwin Rd, Box 3808, Durham, NC 27710 (M.P.L., B.E.P., J.D.E., R.K.K.); Department of Radiology (T.J.A.) and Center for Biomedical Imaging (H.R.C.), Medical University of South Carolina, Charleston, SC; and Department of Orthopedic Surgery, University of Michigan, Ann Arbor, Mich (R.C.S.).
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Lungren
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Amrhein
authors.forename: Ben E
authors.initials: BE
authors.lastname: Paxton
authors.forename: Ramesh C
authors.initials: RC
authors.lastname: Srinivasan
authors.forename: Heather R
authors.initials: HR
authors.lastname: Collins
authors.forename: James D
authors.initials: JD
authors.lastname: Eastwood
authors.forename: Ramsey K
authors.initials: RK
authors.lastname: Kilani
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007717:Knee / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000706:statistics & numerical data*; D008297:Male; D010067:Ownership; D018584:Physician Self-Referral; D010818:Practice Patterns, Physicians' / Q000706:statistics & numerical data*; D012189:Retrospective Studies; D014600:Utilization Review