Multi pinhole collimator

Two nude mice bearing A431 subcutaneous tumors and two nude mice bearing MIAPaCa-2 subcutaneous tumors were injected intravenously with 1.85 MBq ¹¹¹In-labeled anti-CD73 antibody 067-213. The total injected protein dose was adjusted to 20 µg per mouse by adding unlabeled antibody. A single rat was injected intravenously with 37 kBq/g body weight ¹¹¹In-labeled anti-CD73 antibody. The total injected protein dose was adjusted to 2 µg per g body weight by adding unlabeled antibody. At 6, 24, 48, and 96 h after injection, the mice and the rat were anesthetized by isoflurane inhalation, and SPECT/CT data were acquired using a VECTor/CT SPECT/CT Pre-Clinical Imaging system with a multi-pinhole collimator (MILabs, Utrecht, the Netherlands). Following SPECT imaging, CT data were acquired with an X-ray source set at 60 kVp and 615 µA. SPECT images were reconstructed using a pixel-based ordered-subsets expectation-maximization algorithm with 2 subsets and 8 iterations on a 0.8-mm voxel grid without attenuation correction. The volume of interest was manually drawn over tumors, and tracer uptake was quantified by PMOD data analysis software (version 3.4, PMOD Technology, Zürich, Switzerland). CT images were reconstructed using a filtered back-projection algorithm for cone beam. Merged images of SPECT and CT were obtained using PMOD software.

The model mice enrolled in the SPECT/CT imaging study were determined as described in the fluorescence imaging study and injected with approximately 1.85 MBq of ¹¹¹In-labelled anti-TF 1849 IgG or control IgG via the tail vein. The injected antibody dose was adjusted to 50 µg per mouse by adding the corresponding unlabelled antibody. At 1 and 6 h and 1, 2 and 3 days after the injection, the mice were anaesthetized with isoflurane and imaged with the VECTor/CT SPECT/CT Pre-Clinical Imaging system equipped with a multi-pinhole collimator (MILabs, Utrecht, Netherlands). SPECT data were acquired for 10 min at 1 and 6 h and 1 day; 15 min at 2 days; and 20 min at 3 days after the injection. SPECT images were reconstructed using a pixel-based ordered-subsets expectation maximization algorithm with 8 subsets and 2 iterations on a 0.8-mm voxel grid without attenuation correction. CT data were acquired using the X-ray source set at 60 kVp and 615 µA after SPECT scan, and the images were reconstructed using a filtered back-projection algorithm for cone beam. Merged images were obtained using PMOD software (PMOD Technology, Zürich, Switzerland). ROIs were manually drawn on tumours, and the mean and maximum values of the percentage of injected dose per gram of tissue (% ID/g) of ROIs was measured using PMOD software (PMOD Technology).

SPECT imaging was conducted 40 min after the NIR-PIT. Tumor-bearing mice from each group (¹¹¹In-DTPA, n = 7; ^99mTc-HSA-D, n = 8) were intravenously injected with ¹¹¹In-DTPA (7.4 MBq) and ^99mTc-HSA-D (7.4 MBq), respectively. Dynamic SPECT data acquisition was conducted for 60 min, using a VECTor/CT SPECT/CT Pre-Clinical Imaging system with a multi-pinhole collimator (MILabs, Utrecht, the Netherlands) under 1.5% isoflurane anesthesia. SPECT images were reconstructed using a pixel-based ordered-subsets expectation-maximization algorithm with eight subsets and two iterations on a 0.8-mm voxel grid without attenuation correction. Computed tomography scans were acquired with an X-ray source set at 60 kVp and 615 μA after the SPECT scan, and images were reconstructed using a filtered backprojection algorithm for the cone beam. Merged images were obtained using PMOD software (version 3.5; PMOD Technologies, Zurich, Switzerland). The VOI was drawn over tumors and radioprobe uptake was quantified as the % ID/cc, and AUCs covered up to each time point were also calculated appropriately.