Radiolabelling of leucocytes with 18fluoro-désoxy-glucose (FDG) in infectious disease imaging

J. Costes1, M. Meyer2, K. Casagrande1, N. Schaefer2, J. Prior, F2, J. Delage1, F. Sadeghipour3. 1 Pharmacy Department, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland.
2 Nuclear Medicine Department, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland
3 Centre de Recherche et d’Innovation en Sciences Pharmaceutiques cliniques, University of Lausanne, Switzerland.

Introduction
Radiolabelled autologous leukocytes (PN) scintigraphy with 99mTc-HMPAO is the gold standard for the diagnosis of infections to ensure a high specificity. However, the sensitivity of this technique can be low for several localizations. PET (Positron Emission Tomography) allows to achieve higher quality and sensitivity for imaging. Thus, we developed a PN labelling method with a PET tracer, the 18FDG.

Material and methods
Volunteers included in the study were patients who were hospitalized in sceptic surgery and had an acute infectious disease. 100 mL of blood were collected from the patients (n = 2). PN were isolated by sedimentation for 60 minutes then, by centrifugation. The obtained PN were incubated with 300 MBq of 18FDG for 20 minutes at 37°C. The labelled cell suspension was washed by centrifugation to remove the free 18FDG. Then, labelling efficiency and 18FDG uptake ratio were calculated. Finally, cell viability was controlled by microscopy analysis (trypan blue).
A clinical protocol was elaborated with the physicians to define the acquisition times and the inclusion criteria.

Results
The mean labelling efficiency calculated was 78.2% and the 18FDG uptake was 91.6%. Cell viability was 98%. The acquisition times defined are 2h and 3h post-injection. The inclusion criteria chosen were: acute infectious with leukocytes > 10 G/L, VS > 5 mm/h. Patients have to be fasted at least since 6 hours before blood collection and not to take any anti-inflammatory or any antibiotic since the day before.
These results validate the in-vitro feasibility of this labelling. Further studies as stability of 18FDG uptake at 2h and 3h, corresponding to the acquisition times have to be performed. Thanks to this method, the imaging can be done on a single day, contrary to scintigraphy which requires an acquisition 24h post injection.

Conclusion
This initial experience shows the feasibility and the potential value of this technique for the diagnosis of infectious diseases where scintigraphy with 99mTc-HMPAO lacks of sensitivity. Moreover, this method allows a high specificity. A cohort of about 10 patients is expected on the next weeks in order to validate it.
Therefore, this protocol could be extended to other indications such in cardiology to detect infection for example in prosthetic valve, pace maker.

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