title: Macrophage activity in infected areas of an experimental vertebral osteomyelitis model: USPIO-enhanced MR imaging--feasibility study.
abstract: OBJECTIVE
  To prospectively evaluate ultrasmall superparamagnetic iron oxide (USPIO) magnetic resonance (MR) imaging for the depiction of macrophages in infected areas of an experimental rabbit vertebral osteomyelitis model.
  
  
  METHODS
  Lumbar vertebral osteomyelitis was induced in 10 rabbits with intradiscal injection of bacteria in a vertebral disk (test level) versus saline injection in another disk (control level). After a mean interval of 12 days, rabbits were imaged prior to and 24 hours after administration of USPIO. The MR imaging protocol included T1-weighted spin-echo, T2-weighted fast spin-echo, and T2*-weighted gradient-echo sequences. MR findings were compared with histologic findings (macrophage immunostaining and Perls Prussian blue staining). A Wilcoxon signed rank test was used to compare signal-to-noise ratio (SNR) results before and after USPIO administration.
  
  
  RESULTS
  T1-weighted MR images of infected vertebral test levels obtained 24 hours after USPIO administration showed a significant increase in SNR (P = .005), whereas T2- and T2*-weighted images showed no significant changes in SNR (P = .14 and P = .87, respectively). Histologic examination results of infected areas demonstrated complete replacement of hematopoietic bone marrow by macrophage infiltration. Perls Prussian blue staining showed that some macrophages were iron loaded. T1- (P = .02), T2- (P = .04), and T2*-weighted (P = .04) images of control vertebrae showed a significant decrease in SNR. Histologic examination results confirmed the persistence of normal hematopoietic bone marrow without macrophage infiltration, which was reflected by more intensive Perls Prussian blue staining compared with that in infected areas.
  
  
  CONCLUSIONS
  MR imaging can depict USPIO-loaded macrophage infiltration present in infected areas in an experimental rabbit model of vertebral osteomyelitis.
authors.affiliation: Department of Radiology 2, University Hospital of Strasbourg, Strasbourg, France. guillaume.bierry@chru-strasbourg.fr
authors.forename: Guillaume
authors.initials: G
authors.lastname: Bierry
authors.forename: François
authors.initials: F
authors.lastname: Jehl
authors.forename: Nelly
authors.initials: N
authors.lastname: Boehm
authors.forename: Philippe
authors.initials: P
authors.lastname: Robert
authors.forename: Gilles
authors.initials: G
authors.lastname: Prévost
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Dietemann
authors.forename: Hubert
authors.initials: H
authors.lastname: Desal
authors.forename: Stéphane
authors.initials: S
authors.lastname: Kremer
mesh_terms: D000818:Animals; D003287:Contrast Media; D003911:Dextrans; D004195:Disease Models, Animal; D005240:Feasibility Studies; D052203:Ferrosoferric Oxide; D007089:Image Enhancement / Q000379:methods*; D007501:Iron; D008159:Lumbar Vertebrae / Q000473:pathology; D008264:Macrophages / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D058185:Magnetite Nanoparticles; D008297:Male; D010019:Osteomyelitis / Q000175:diagnosis*; D010087:Oxides; D011817:Rabbits; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013122:Spinal Diseases / Q000175:diagnosis*; D013203:Staphylococcal Infections / Q000175:diagnosis*
chemical_list: D003287:Contrast Media; D003911:Dextrans; D058185:Magnetite Nanoparticles; D010087:Oxides; C097921:ferumoxtran-10; D007501:Iron; D052203:Ferrosoferric Oxide