USPIO-enhanced magnetic resonance imaging of the knee in asymptomatic volunteers

Effect of intra-articular administration of superparamagnetic iron oxide nanoparticles (SPIONs) for MRI assessment of the cartilage barrier in a large animal model

Early diagnosis of cartilage disease at a time when changes are limited to depletion of extracellular matrix components represents an important diagnostic target to reduce patient morbidity. This report is to present proof of concept for nanoparticle dependent cartilage barrier imaging in a large animal model including the use of clinical magnetic resonance imaging (MRI). Conditioned (following matrix depletion) and unconditioned porcine metacarpophalangeal cartilage was evaluated on the basis of fluorophore conjugated 30 nm and 80 nm spherical gold nanoparticle permeation and multiphoton laser scanning and bright field microscopy after autometallographic particle enhancement. Consequently, conditioned and unconditioned joints underwent MRI pre- and post-injection with 12 nm superparamagnetic iron oxide nanoparticles (SPIONs) to evaluate particle permeation in the context of matrix depletion and use of a clinical 1.5 Tesla MRI scanner. To gauge the potential pro-inflammatory effect of intra-articular nanoparticle delivery co-cultures of equine synovium and cartilage tissue were exposed to an escalating dose of SPIONs and IL-6, IL-10, IFN-γ and PGE₂ were assessed in culture media. The chemotactic potential of growth media samples was subsequently assessed in transwell migration assays on isolated equine neutrophils. Results demonstrate an increase in MRI signal following conditioning of porcine joints which suggests that nanoparticle dependent compositional cartilage imaging is feasible. Tissue culture and neutrophil migration assays highlight a dose dependent inflammatory response following SPION exposure which at the imaging dose investigated was not different from controls. The preliminary safety and imaging data support the continued investigation of nanoparticle dependent compositional cartilage imaging. To our knowledge, this is the first report in using SPIONs as intra-articular MRI contrast agent for studying cartilage barrier function, which could potentially lead to a new diagnostic technique for early detection of cartilage disease.

Macrophages mediated diagnosis of rheumatoid arthritis using fibrin based magnetic nanoparticles as MRI contrast agents

BACKGROUND

A variety of bioimaging tools assists in the diagnosis and evaluation of rheumatoid arthritis (RA) and other osteoarthritis. However, detection of RA in the early stages by targeting its macrophages with suitable contrast agents will help in arresting the progression of the disease.

METHODS

In the present study, we investigated the effectiveness of using magnetic fibrin nanoparticles (MFNPs) conjugated with folic acid (FA-MFNPs) as a specific contrast agent to target the activated macrophages, which overexpress the folate receptors (FR) in the knee joints of rats with antigen-induced arthritis (AIA).

RESULTS

FA-MFNPs were spherical with an average size of 18.3±1.6nm. In vitro studies have shown effective internalization of FA-MFNPs into the Raw264.7 macrophage cells. In vivo studies were carried out by injecting FA-MFNPs intravenously into the arthritic rats. The results showed enhanced MR imaging in the synovium of arthritic joints. Prussian blue histological staining confirmed uptake of FA-MFNPs by macrophages in the synovial tissue.

CONCLUSION

The animal experiment results indicate that FA-MFNPs can be used as a specific MRI contrast agent in identifying phagocytic active macrophages in the synovial joints.

GENERAL SIGNIFICANCE

Blood is the precursor source for synthesising the fibrin-based iron oxide (magnetic) nanoparticles (MFNPs) with diameters between 12 and 15nm. It has excellent superparamagnetic behaviour, biocompatibility, osteogenic potency, hemocompatibility, and biodegradable properties. MFNPs-based nanocomposites might be a promising contrast agent for bioimaging.

MRI thresholds for discrimination between normal and mild temporomandibular joint involvement in juvenile idiopathic arthritis

BACKGROUND

Currently there is no consensus agreement on the degree of enhancement in normal temporomandibular joints (TMJ) in children, which makes it difficult for clinicians to distinguish between the presence/absence of mild synovitis. Quantitative measurements of synovial and condylar enhancement may be useful additions to current qualitative methods on early MRI diagnosis and follow up of TMJ involvement in JIA. The purpose of the study is to establish thresholds/tendencies for quantitative measures that enable distinction between mild TMJ involvement and normal TMJ appearance based on the degree of synovial and bone marrow enhancement in JIA patients.

METHODS

TMJ MRI examinations in 67 children with JIA and in 24 non-rheumatologic children who underwent MRI for neurologic/orbit indications were retrospectively assessed. As a priori determined TMJs of JIA patients were categorized into three groups by experienced staff radiologists based on the degree of synovial and condylar enhancement: no active disease (rheumatologic control), mild and moderate/severe findings. The signal intensity (SI) of the synovial tissue around each condyle and of the bone marrow was measured to calculate the enhancement ratio (ER) and relative SI change. The ER was calculated using signal to noise ratios, while relative SI change was calculated using signal intensities alone. Quantitative measurements of synovial and condylar enhancement of TMJs with mild or moderate/severe findings were compared with the rheumatologic and non-rheumatologic controls.

RESULTS

Mean ER values were significantly different between the TMJs without active disease and those with mild and moderate/severe synovial enhancement, with highest values in the moderate/severe group (P < 0.0001). Similar findings were seen for condylar enhancement with P < 0.005. Relative SI change was unable to differentiate TMJs with mild synovitis from the two controls (P > 0.10). 27/60 (45%) TMJs without active disease had osteochondral changes. 8/40 (20%) TMJs in the mild group did not demonstrate any synovial thickening.

CONCLUSIONS

Quantitative signal to noise ratios of TMJ synovial and condylar enhancement generate thresholds/tendencies, which offer additional information to differentiate mild synovitis from normal TMJs in JIA patients. Osteochondral changes and synovial thickening may not be reliable indicators of active TMJ involvement and should be differentiated from synovial enhancement.

Efficient labeling in vitro with non-ionic gadolinium magnetic resonance imaging contrast agent and fluorescent transfection agent in bone marrow stromal cells of neonatal rats

Although studies have been undertaken on gadolinium labeling-based molecular imaging in magnetic resonance imaging (MRI), the use of non-ionic gadolinium in the tracking of stem cells remains uncommon. To investigate the efficiency in tracking of stem cells with non-ionic gadolinium as an MRI contrast agent, a rhodamine-conjugated fluorescent reagent was used to label bone marrow stromal cells (BMSCs) of neonatal rats in vitro, and MRI scanning was undertaken. The fluorescent-conjugated cell uptake reagents were able to deliver gadodiamide into BMSCs, and cell uptake was verified using flow cytometry. In addition, the labeled stem cells with paramagnetic contrast medium remained detectable by an MRI monitor for a minimum of 28 days. The present study suggested that this method can be applied efficiently and safely for the labeling and tracking of bone marrow stromal cells in neonatal rats.

A rheumatoid arthritis magnetic resonance imaging contrast agent based on folic acid conjugated PEG-b-PAA@SPION

FA-PEG-b-PAA@SPPION offers a unique contrast ability for MRI of rheumatoid arthritis.

Septic arthritis: monitoring with USPIO-enhanced macrophage MR imaging

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.

Principles and basic concepts of molecular imaging

Advanced knowledge in molecular biology and new technological developments in imaging modalities and contrast agents calls for molecular imaging (MI) to play a major role in the near future in many human diseases (Weissleder and Mahmood Radiology 219:316-333, 2001). Imaging systems are providing higher signal-to-noise ratio and higher spatial and/or temporal resolution. New specific contrast agents offer the opportunity to drive new challenges for obtaining functional and biological information on tissue characteristics and tissue processes. All this information could be relevant for diagnosis, prognosis and treatment follow-up and to drive local therapies, enhancing local drug/gene delivery. The recent explosion of all these developments is a radical change of perspective in our imaging community because they could have a tremendous impact on our clinical practice and on teaching programs and they call for a more prominent multidisciplinary approach in this field of research.