Inflammation and infection: imaging properties of 18F-FDG-labeled white blood cells versus 18F-FDG.

Unlabelled: (18)F-FDG and (18)F-FDG-labeled white blood cells ((18)F-FDG-WBCs) are valuable radiopharmaceuticals for imaging focal sites of inflammation and infection. In the present study, the imaging properties of both radiotracers were compared in sterile and septic inflammation models.

Methods: Groups of adult male Sprague-Dawley rats (100-120 g) were injected in the left posterior thigh muscle with saline solution (group 1: controls, n = 15), 0.100 mL of turpentine oil (group 2: sterile inflammation, n = 26), 10(9) viable Escherichia coli bacteria (group 3: E. coli septic inflammation, n = 29), or 10(8) viable Pseudomonas aeruginosa bacteria (group 4: P. aeruginosa septic inflammation, n = 25). Twenty-four hours later, the animals were divided into 2 groups: One received (18)F-FDG intravenously and the other received human white blood cells (WBCs) labeled in vitro with (18)F-FDG injected intravenously. Biodistribution and microPET studies were performed 1 h after radiotracer injection. One hour after injection with cell-associated or free (18)F-FDG, phosphorimaging of abscess and contralateral muscle was performed in specimens collected from animals in groups 1, 2, and 3. The region of interest was selected within the abscess wall and values were converted to kBq/g using a (14)C calibration standard curve. Thin-layer radiochromatography (TLRC) was performed to study the chemical forms of (18)F within the WBCs.

Results: Whole-body biodistribution demonstrated a significantly higher uptake ratio of (18)F-FDG-WBCs compared with (18)F-FDG in all sterile and septic inflammation models (t test: sterile, P = 0.048; E. coli, P = 0.040; P. aeruginosa, P = 0.037). microPET imaging confirmed the greater performance of (18)F-FDG-WBCs versus (18)F-FDG in the sterile inflammation model and in both E. coli and P. aeruginosa septic models. Phosphorimaging analysis showed higher (18)F-FDG-WBC uptake than (18)F-FDG in the sterile inflammation and P. aeruginosa septic models and similar tissue uptake in the E. coli septic model. Time course labeling and TLRC of lysed WBCs demonstrated that (18)F-FDG was retained as (18)F-FDG-6-phosphate inside WBCs for at least 2 h, corresponding to the time frame of analysis.

Conclusion: (18)F-FDG-WBCs gave better results compared with (18)F-FDG in all sterile and septic inflammation models. These data suggest that (18)F-FDG-WBC PET may be a useful technique for tracking focal inflammatory lesions in the body.