Imaging sessions

A second series of five nude mice were engrafted with MM cells as described above. The tumoural growth was monitored by bioluminescence approach which is also described in the previous section. PET/CT imaging was performed with an Inveon microPET/CT scanner (Siemens, USA), with [¹⁸F]fludarabine on the last BLI acquisition day (23) and with [¹⁸F]FDG the day after, on the same mice. The information on the in-house radiosynthesis of [¹⁸F]fludarabine can be found elsewhere (S1 Appendix) [5]; the [¹⁸F]FDG was purchased from Cyclopharma S.A (France). PET acquisition was performed after intravenous (caudal vein) injection of [¹⁸F]fludarabine (10.51 ± 0.70 MBq, n = 5) or [¹⁸F]FDG (11.74 ± 0.18 MBq, n = 4 [1 died]). Time-activity curves (TACs) were obtained for three mice with the dynamic imaging up to 90 min post-injection. The static scans were acquired 40 to 60 min after radiotracer administration; since the tumoural uptake had rapidly reached a relative plateau with both radiotracers in the present animal model. The applied acquisition and reconstruction parameters for the PET scans are available in our former publication [7]. Briefly, the emission scan was acquired with default settings of coincidence timing window of 3.4 ns and an energy window of 350 to 650 keV. PET images were reconstructed with 3-dimensional maximum a posteriori (OSEM3D/MAP) reconstruction algorithm. The data were reconstructed into 128 x 128 x 159 matrix images. Data were normalized and dead-time, random, scatter as well as attenuation correction (based on CT) were applied. At the end of imaging investigations, the tumours were processed for IHC examinations; in addition to above mentioned stainings, F4/80 was used as a marker of inflammatory cells. A simple ranking system (o: no staining, from + to +++) was applied to depict the various degrees of staining intensity.