Inveon system

One week after occlusion, DM and non-DM mice (n = 15) were injected with 6.81 ± 0.536 MBq of ⁶⁴Cu-NOTA-PEG4-cRGD₂ via the jugular vein and 60 minutes later in vivo microPET-CT imaging was performed using a small animal dedicated Inveon system (Siemens Healthcare USA). An additional group of non-diabetic mice (n = 4) was injected with 7.21 ± 2.31 MBq of ⁶⁴Cu-acetate to study differential organ biodistribution of ⁶⁴Cu-NOTA-PEG4-cRGD₂. Animals were placed on a polyacrylic bed in the supine position with legs secured in an extended position. Mice underwent X-ray microCT imaging (80kVp, 500 μ A, 100 μ m spatial resolution) followed by 15 min microPET imaging (15% energy window centered at 511 keV). All mice were euthanized immediately after last imaging session was completed and tissue samples were taken for gamma well counting and snap-frozen in liquid nitrogen for immunofluorescence analysis.

Siemens Inveon system (Siemens, Germany) was used for the live animal scanning and three dimension images reconstruction. For CS-siRNA nanoparticles injection model, the heads of P17 mice were separated and scanned with the parameters as 80kV, 500 μA, 500 ms exposure time, and scan angle of 360°. For the tooth germ and kidney subcapsular transplantation, after 2 weeks and 4 weeks of the transplantation, the mice and the kidneys with tooth germs were scanned with the same parameters as above, respectively. The experiment group and the controls were subjected to the same radiation.

Prior to micro PET/CT imaging, the mice were fasted overnight (16 h) to minimize bowel movement and maximize tumor ¹⁸F-FDG uptake. Nude mice were pre-anesthetized with 3% isoflurane in oxygen, injected with 3.7 MBq ¹⁸F-FDG via the tail vein catheter, and maintained with 1–2% isoflurane on a heated (37 °C) pad. After the 50-minute uptake period, mouse was fixed in the center of the scanning bed in the prone position under continuous anesthesia with 1.5% isoflurane. PET/CT imaging was performed on an Inveon system (Siemens Preclinical Solutions). After scanning, the filtered back projection method reconstructed coronal, cross-sectional, and sagittal tomographic images for analysis. Siemens Invenon Research Workplace (IRW3.0) was used to obtain the caecum site and quantitatively analyze the reconstructed image to obtain the SUVmax value.

Inhalation anesthesia with isoflurane was used and the eyes of the animals were protected with dexpanthenol eye ointment. Anesthesia was initiated 15 min ahead of experiments by placing the animal in a cage ventilated with oxygen (3.5 L/min) containing 3% isoflurane. Throughout the experiments, anesthesia was maintained by adjusting the isoflurane content (0.6% to 2%) to ensure a respiratory rate in the range 80 to 100/min. For i.v. injection, we inserted a tailored catheter into the lateral tail vein. Simultaneously with a slow bolus injection of 50 to 200 μL of tracer solution, we started the PET with scan duration of 45 min in 3D list mode on a Siemens Inveon system (axial field-of-view of 12.7 cm with a bore diameter of 12 cm, approximately 1.4 mm full-width-at-half-maximum spatial resolution; Siemens Healthcare, Erlangen, Germany). After tracer injection, we flushed the catheter with 50 to 100 μL of isotonic sodium chloride solution. During the scan, a heating pad prevented hypothermia. The radioactivity in the syringe was measured immediately before and after injection with a Capintec CRC® 15R (Capintec Inc, 6 Arrow Road Ramsey, NJ, USA) dose calibrator.