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Updated: Jun 4, 2026
In vivo Macrophage Imaging Using MR Targeted Contrast Agent for Longitudinal Evaluation of Septic Arthritis
Published on: October 20, 2013
Septic arthritis: monitoring with USPIO-enhanced macrophage MR imaging
Sophie Lefevre1, David Ruimy, François Jehl
1EA 4438, University of Strasbourg, Strasbourg, France.
Purpose:
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.
Materials And 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.
Conclusion:
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.
Insights
Magnetic resonance imaging with ultrasmall superparamagnetic iron oxide (USPIO) particles can noninvasively monitor antibiotic treatment for infectious arthritis by tracking macrophages. This method shows resolution of bacterial joint infections, unlike conventional MRI contrast agents.
Area of Science:
- Biomedical imaging
- Infectious disease research
- Musculoskeletal imaging
Background:
- Infectious arthritis requires effective monitoring for treatment success.
- Conventional MRI contrast agents do not specifically track cellular responses to infection.
Purpose of the Study:
- To evaluate noninvasive monitoring of antibiotic therapy in experimental infectious arthritis.
- To image macrophages using magnetic resonance (MR) imaging enhanced with ultrasmall superparamagnetic iron oxide (USPIO) particles.
Main Methods:
- Induced Staphylococcus aureus knee infection in 12 rabbits.
- Performed MR imaging before and after USPIO and gadoterate meglumine injection.
- Compared imaging findings with bacteriologic and histopathologic results.
Main Results:
- USPIO-enhanced MR imaging showed intense macrophage infiltration in acute infections.
- Signal intensity loss on USPIO-enhanced images decreased after antibiotic treatment (P = .03).
- Gadoterate meglumine enhancement remained unchanged, indicating USPIO's specificity.
Conclusions:
- USPIO-enhanced macrophage MR imaging can demonstrate resolution of experimental bacterial joint infection.
- This technique offers a novel approach for monitoring antibiotic therapy in infectious arthritis.
