Small animal PET for the evaluation of an animal model of genital infection

Summary Background:  [18F]-FDG is a widely used tracer for the non-invasive evaluation of hypermetabolic processes like cancer and inflammation. However, [18F]-FDG is considered inaccurate for the diagnosis of urinary tract and genital infections because of its urinary excretion. Since the 1970s, Gallium scintigraphy is a well established test that has been used for the evaluation of inflammation and infection in human patients. Aim:  The aim of this study was to assess the feasibility of 68Ga-Chloride small animal PET for the analysis of an animal model of genital infection, induced after the vaginal inoculum of Chlamydia muridarum. Material and methods:  Thirty mice were infected by placing 15 μl of sucrose phosphate glutamic acid (SPG) 107 inclusion forming units of C. muridarum into the vaginal vault. As controls of inflammation, three animals were challenged with 15 μl of SPG and one healthy animal was used to assess the tracer biodistribution. Four animals died during the experiment. Eleven animals were evaluated with 68Ga-Chloride small animal PET (GE, eXplore Vista) 3–5, 10–12, 17–19 days after infection, as well as three controls of inflammation and one healthy animal. Infection was monitored by obtaining cervical-vaginal swabs from all the animals on the day of each PET procedure. Moreover, five groups of three animals each were killed at 6, 13, 20, 27 and 34 days after infection were studied. Results: 68Ga-PET turned out positive in all the infected animals, concordantly to data obtained by the cervical swabs and by the ex vivo analysis. The tumour-to-background ratio (TBR) decreased over time as the inflammation tended to naturally extinguish. The controls showed a slightly increased uptake of tracer due to the aseptic inflammation caused by SPG and frequent cervical swabs. The healthy control did not show any pelvic uptake. Conclusion: 68Ga-Chloride is a promising tracer for the assessment of genital infection in a mouse animal model.