Inveon multimodality pet ct scanner

The in vivo kinetics of [¹⁸F]exendin-4 were evaluated with the Inveon Multimodality PET/CT scanner (Siemens, Knoxville, TN, USA). Rats were anesthetized with isoflurane/O₂ and injected intravenously (i.v.) with [¹⁸F]exendin-4 (radioactivity 23 ± 5 MBq/kg, mass 2 ± 1 μg/kg). PET scans were acquired for up to 6 h (dynamic 0–60 min; static 210–240 min and 330–360 min; N = 2–5 rats/scan). The data were reconstructed with the ordered subset expectation maximization OSEM2D algorithm. Analyses were performed with Inveon Research Workplace 3 software (Siemens), after defining the volumes of interest (VOIs) on selected tissues.

Titration of dose and longitudinal imaging was performed in CT26 tumor-bearing mice (150-200 mm³) and was only performed for ⁸⁹Zr-DFO-CD8a. Mice were injected with ⁸⁹Zr-DFO-CD8a (1.34 ± 0.1 MBq) without or with 5, 10, 30 or 100 µg unlabelled CD8a-F(ab)'2 intravenously (total volume ~ 200 µL in PBS, N=3/group). Small animal PET/CT imaging was performed 1, 4, 24 and 72 hours after injection on an Inveon Multimodality PET/CT scanner (Siemens, Germany). Mice were anesthetized with sevoflurane (3-4% in 80% N₂, 20% O₂) during PET/CT imaging. Static PET data were acquired in list mode with an acquisition time of 300, 300, 600 and 900 seconds for the 1, 4, 24 and 72 time-point, respectively. Images were reconstructed using a 3D maximum a posteriori algorithm with CT based attenuation correction. Image analysis (Inveon Software, Siemens) was performed by drawing CT based regions of interest (ROIs) over the tumor, whole heart, liver, kidney, muscle, inguinal lymph node (ILN), axillary lymph node (ALN) and cervical lymph node (CLN). ROIs over the spleen were drawn by PET based thresholding. The uptake of ⁸⁹Zr-DFO-CD8a was quantified as % injected dose per gram tissue (%ID/g) assuming a soft tissue density of 1 g/cm³. Blood was withdrawn by cardiac puncture and mice were euthanized after the imaging session, organs resected, weighted and the radioactivity counted in a gamma counter.

The tumors were clearly visible when they were first imaged with [¹⁸F]EF5. Mice were anesthetized with 2.5% isoflurane, and body temperature was maintained using a heating pad. PET/CT scans were performed with the Inveon multimodality PET/CT scanner (Siemens Medical Solutions, Knoxville, TN, USA). Following a transmission scan for attenuation correction using the CT modality, an emission scan was acquired in the 3D list mode with an energy window of 350 to 650 keV. Dynamic 80 min long scans were acquired. Sinograms were framed into 25 frames: 6 × 10 s, 4 × 15 s, 2 × 30 s, 2 × 120 s, 1 × 180 s, 6 × 300 s, and 4 × 600 s and reconstructed with an OSEM two-dimensional iterative algorithm. A second [¹⁸F]EF5 scan and an [¹⁸F]FDG scan were performed on consecutive days after the clear exponential growth period of tumors. Mice were injected with [¹⁸F]EF5 (11.1 ± 1.9 MBq) or [¹⁸F]FDG (10.9 ± 2.8 MBq) (mean ± SD). The mice were sacrificed after the last PET/CT scan and tissue oxygen measurements (see below).