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Updated: May 6, 2026
In vivo Macrophage Imaging Using MR Targeted Contrast Agent for Longitudinal Evaluation of Septic Arthritis
Published on: October 20, 2013
In vivo macrophage imaging using MR targeted contrast agent for longitudinal evaluation of septic arthritis
Guillaume Bierry1, Sophie Lefevre, Jean-Louis Dietemann
1Department of Radiology, University Hospital of Strasbourg.
Abstract:
Macrophages are key-cells in the initiation, the development and the regulation of the inflammatory response to bacterial infection. Macrophages are intensively and increasingly recruited in septic joints from the early phases of infection and the infiltration is supposed to regress once efficient removal of the pathogens is obtained. The ability to identify in vivo macrophage activity in an infected joint can therefore provide two main applications: early detection of acute synovitis and monitoring of therapy. In vivo noninvasive detection of macrophages can be performed with magnetic resonance imaging using iron nanoparticles such as ultrasmall superparamagnetic iron oxide (USPIO). After intravascular or intraarticular administration, USPIO are specifically phagocytized by activated macrophages, and, due to their magnetic properties, induce signal changes in tissues presenting macrophage infiltration. A quantitative evaluation of the infiltrate is feasible, as the area with signal loss (number of dark pixels) observed on gradient echo MR images after particles injection is correlated with the amount of iron within the tissue and therefore reflects the number of USPIO-loaded cells. We present here a protocol to perform macrophage imaging using USPIO-enhanced MR imaging in an animal model of septic arthritis, allowing an initial and longitudinal in vivo noninvasive evaluation of macrophages infiltration and an assessment of therapy action.
Insights
This study demonstrates ultrasmall superparamagnetic iron oxide (USPIO) enhanced MRI for noninvasively detecting macrophage activity in septic arthritis. This method allows for early diagnosis and therapy monitoring in infected joints.
Area of Science:
- Immunology
- Radiology
- Biomedical Engineering
Background:
- Macrophages are crucial in bacterial infection responses, particularly in septic joints.
- Monitoring macrophage infiltration is key for diagnosing synovitis and assessing treatment efficacy.
- Current methods lack noninvasive in vivo assessment of macrophage activity in joint infections.
Purpose of the Study:
- To present a protocol for USPIO-enhanced MRI to image macrophage activity in septic arthritis.
- To enable noninvasive, in vivo evaluation of macrophage infiltration and therapeutic response.
- To establish a quantitative method for assessing macrophage presence in infected joints.
Main Methods:
- Utilized ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles for MRI contrast enhancement.
- Administered USPIO intravascularly or intraarticularly in an animal model of septic arthritis.
- Analyzed gradient echo MR images to quantify macrophage infiltration based on signal loss.
Main Results:
- USPIO were phagocytized by activated macrophages in septic joints.
- USPIO-enhanced MRI detected and quantified macrophage infiltration in vivo.
- The signal loss on MR images correlated with the amount of USPIO-loaded macrophages.
Conclusions:
- USPIO-enhanced MRI provides a noninvasive method for evaluating macrophage infiltration in septic arthritis.
- This technique facilitates early detection of synovitis and monitoring of therapeutic interventions.
- The protocol allows for longitudinal assessment of macrophage activity in infected joints.
