In vivo Macrophage Imaging Using MR Targeted Contrast Agent for Longitudinal Evaluation of Septic Arthritis

The overall goal of this experiment is to longitudinally evaluate the macrophage infiltration within the synovium. In the rabbit model of septic A using MR imaging, this could be performed with the use of iron oxide particle that level macrophages and Reveal their presence. Macrophages are Key cells in the development, amplification and resolution of arthritis, especially in septic arthritis.

The in vivo demonstration of their presence and distribution within an infected joint could be a valuable tool to monitor. Antibiotic therapy has an ill joint, is not supposed to be massively infiltrated by macrophages. Macrophages can be available losing cyte.

He R contrast agents such as US PIOs, ultra-small Super paraman iron oxide. After intravascular administration, they are specifically taken up by activated microphages. U-S-P-I-O are composed of an iron IDE core with a crystal size of about 40 nanometers.

They act as small magnets that generate MR signal changings with macrophages containing tissues. You can see on these two axial Mr.Mags of a rabbit knee that 24 hour after U-S-P-I-O administration, the synovium presence and intense and diffuse scenario loss. Due to the presence of SPI OED macrophages, the number of dark pixels observe on MR.R imaging is correlated to the iron content within the tissue and therefore to the number of macrophages.

The longitudinal follow-up of U-S-P-I-O related R signal changes could therefore give an InVivo evaluation of macrophages presence within the John during therapy. Hello, my name is Guian Bii. I'm an assistant professor of radiology at the University Hospital of Strat, born France.

Today we are going to present you how to perform macrophage imaging using MRI in an animal model of septic arthritis. In the first part with our research fellow, we are gonna explain you how to induce a septic arthritis in a rabbit knee using a direct interarticular administration of staphylococcus. Then in a second part, we will demonstrate you how to perform the MRI examination, how to inject the contrast agent, and finally, how to exploit the results.

Place the animal in a dedicated containment cage, anesthetize the animal by an injection of tine and ketamine, which allows for 30 minutes of surgical anesthesia. Shave the knee and scrub it with povidone. Identify the patal ligament as an anterior elastic stretcher.

Then place a 35 gauge needle through it to enter the joint. Inject one milliliter of the bacterial suspension. The injection must be done without resistance, confirming the right intraarticular oral situation of the needle.

Place the animal back in its cage and administrate antalgic therapy using intramuscular injection of bovine every day. After a meantime, we have two days. The animal has reduced spontaneous sleep movements confirming the presence of joint infection.

The R examination can therefore be Performed. Place the animal in a Dedicated containment cage. Scrub the here with pov.

Insert a 24 gauge catheter within an here vein and secure it with additive. This venous line will serve to administrate the contrast. Agent anesthetize the animal using intramuscular injection of ketamine.

Axi then place the animal prone within the MR knee coil. With the knees in full extension, the legs have to be powered to the MR table and can be taped to maintain the extension. The MRI protocol consists in gradient echo T two weighted sequences.

The sequence is preferred as it allows the most sensitive U-S-P-I-O detection. Here is an example of the MR parameters that we currently use. At the end of this first MR examination, inject slowly the U-S-P-I-O through the venous line and rinse with one milliliter of cell line.

The second MR examination is performed 24 hours after the contrast agent administration using the same procedures as previously described. You can see Here two axial T two weight gradient echo images of the rabbit knee on the left without contrast. Agent on the right 24 hour after USPO administration.

As you can see on the picture on the right, her area with USPI loaded, macrophages would demonstrate signal loss with dark pixels. The number of dark pixels is correlated to the iron content and then to the amount of MicroAge infiltration you USPI loaded macrophages can be histologically demonstrated using ent pulse blue staining that tri reveals iron loaded cells as blue dots. The number of dark pixels observed on one ember image can be count using different softwares.

Here an example, using the M SGA software that provides it count after manual or automatic thresholding of the current zone areas. USPA OS MRI allows an indirect evaluation of macrophage distribution that can be lodged into the followed during therapy. A reduction of macrophage infiltration will be associated to reduction of the number of dark pixels In vivo MRI imaging.

Using specific contrast agent allows you to non-invasively evaluate macrophage population within the knee. During therapy, you can then follow macrophages presence and distribution without the need of tissue sampling and in a native environment, which is of particle interest for longitudinal studies.