Micro-PET imaging

Eighteen weeks after the model rats were established, ¹⁸F-FDG, ¹⁸F-FLT, and ¹⁸F-FMISO PET imaging were performed. Micro-PET imaging was performed in the order of ¹⁸F-FDG, ¹⁸F-FLT, and ¹⁸F-FMISO for a specific imaging time point, with an interval of 24 h, in consideration of ¹⁸F attenuation. ¹⁸F-FDG, ¹⁸F-FLT, and ¹⁸F-FMISO were injected at 60 min, 120 min, and 240 min before scanning, respectively. The tail vein was injected with ¹⁸F-FDG (about 3.7 MBq, 100 μCi), ¹⁸F-FLT (about 7.4 MBq, 200 μCi), and ¹⁸F-FMISO (about 14.8 MBq, 400 μCi). Before ¹⁸F-FDG PET imaging, the model rats were starved for 12 h and fasted without water. The body temperature of the mice was maintained by a heat lamp throughout the process. All small animal PET imaging was performed under the protocol approved by the Animal Management and Use Committee of the Jiangsu Institute of Atomic Medicine. 10 min before the scan, anesthetized with isoflurane. Micro-PET images were acquired using a 3D Inveon Micro-PET scanner (Siemens). Image reconstruction based on ordered subset expectation maximization using Inveon Acquisition Workplace workstation (version 2.0, Siemens), matrix: 128 × 128 × 159; pixel size: 0.86 × 0.86 × 0.8 mm; truncation frequency 1.5, uniform resolution. For image analysis, ASIProVM 6.8.6.9 image processing software (Concorde Microsystems, LLC) was used to manually outline the region of interest (ROI) to cover the entire liver metastases on the image. The maximum normalized uptake ratio is defined as the tumor SUVmax divided by the liver SUVmax. The formula for SUVmax is: