title: Septic arthritis: monitoring with USPIO-enhanced macrophage MR imaging.
abstract: OBJECTIVE
  To prospectively evaluate in vivo noninvasive monitoring of antibiotic therapy in experimental infectious arthritis by imaging macrophages by using magnetic resonance (MR) imaging enhanced with ultrasmall superparamagnetic iron oxide (USPIO) particles.
  
  
  METHODS
  The institutional review committee on animal care approved the experimental protocol. Unilateral knee infection was induced by intra-articular injection of Staphylococcus aureus in 12 rabbits. Each rabbit underwent MR imaging before and after injection of USPIO particles, as well as before and after injection of gadoterate meglumine. All 12 of the animals were imaged during the acute phase of infection. Half were then sacrificed to obtain histopathologic samples, and the other half were imaged a second time after antibiotic treatment. MR imaging data were analyzed and compared with bacteriologic and histopathologic findings.
  
  
  RESULTS
  In acute infections, intense synovitis with marked signal intensity increase of the synovium on gadoterate dimeglumine-enhanced fat-suppressed T1-weighted images was observed in all animals and was associated with areas of signal intensity loss within the infected synovium on USPIO-enhanced T2*-weighted gradient-echo images, reflecting an intense infiltration of USPIO-loaded macrophages. After antibiotic treatment and histologic evidence of healing infection, less synovial signal intensity loss was seen (P = .03). In contradistinction, the signal intensity increase on gadoterate dimeglumine-enhanced fat-suppressed T1-weighted images remained unchanged.
  
  
  CONCLUSIONS
  In contrast to conventional MR imaging performed by using extracellular contrast agents, USPIO-enhanced macrophage MR imaging can demonstrate resolution of experimental bacterial joint infection.
authors.affiliation: EA 4438, University of Strasbourg, Strasbourg, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Lefevre
authors.forename: David
authors.initials: D
authors.lastname: Ruimy
authors.forename: François
authors.initials: F
authors.lastname: Jehl
authors.forename: Agnès
authors.initials: A
authors.lastname: Neuville
authors.forename: Philippe
authors.initials: P
authors.lastname: Robert
authors.forename: Christelle
authors.initials: C
authors.lastname: Sordet
authors.forename: Matthieu
authors.initials: M
authors.lastname: Ehlinger
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Dietemann
authors.forename: Guillaume
authors.initials: G
authors.lastname: Bierry
mesh_terms: D000818:Animals; D001170:Arthritis, Infectious / Q000473:pathology*; D003287:Contrast Media; D017576:Daptomycin / Q000008:administration & dosage / Q000494:pharmacology; D003911:Dextrans; D004195:Disease Models, Animal; D005260:Female; D007719:Knee Joint / Q000473:pathology*; D008264:Macrophages; D008279:Magnetic Resonance Imaging / Q000379:methods*; D058185:Magnetite Nanoparticles; D010068:Oxacillin / Q000008:administration & dosage / Q000494:pharmacology; D011446:Prospective Studies; D011817:Rabbits
chemical_list: D003287:Contrast Media; D003911:Dextrans; D058185:Magnetite Nanoparticles; C065507:ferumoxides; D017576:Daptomycin; D010068:Oxacillin