Inveon multimodality

Mouse whole‐body scans were performed using a Siemens Inveon MultiModality micro‐computed tomography system (Siemens Medical Solutions USA, Knoxville, TN). Briefly, mice were imaged in a prone position on the scanner radiolucent bed. Anesthesia was provided with 2% isoflurane carried by oxygen through a nose cone during the scan. The high‐resolution micro‐CT exposure settings were 70 kV voltage, 500 uA current, and 520 steps at 360°‐rotation. No contrast agent was used. To compare the amounts of visceral adipose tissue (VAT) between the groups we examined the cross section at the L5 vertebrae (Figure 5C), using Inveon Research Workplace for quantification. Total area of cross section and the areas of observed VAT inside the cross section were measured. Percentage of VAT was calculated as a ratio of VAT area to the total area of cross section expressed. The segmentation of the adipose tissue was based on natural contrast between VAT and surrounding tissues. VAT deposits were segmented out in semiautomated selection mode.23

A subset of mice (three atherosclerotic and three healthy controls) were imaged using a small-animal PET/computed tomography (CT) scanner (Inveon Multimodality; Siemens Medical Solutions, Knoxville, TN, USA). The mice were anesthetized using 1.5% isoflurane, and their temperature was maintained using a heating pad throughout the imaging. Mice were i.v. injected with 11 ± 0.86 MBq (in 50–100 µL) of [⁶⁸Ga]Ga-DOTA-TCTP-1 via the tail vein. PET data were acquired in a list-mode for 60 min, starting from the time of injection of [⁶⁸Ga]Ga-DOTA-TCTP-1. The images were reconstructed using an ordered-subset expectation maximization 2D algorithm with four iterations into 30 × 3 s, 9 × 10 s, 4 × 30 s, 5 × 60 s, and 10 × 300 s time frames. Immediately after the PET scan, 100 µL of intravascular iodinated contrast agent eXIATM160XL (Binitio Biomedical Inc., Ottawa, ON, Canada) was injected and high-resolution CT was acquired (80 kV, 500 μA). CT images were reconstructed using a Feldkamp-based algorithm, and images were analyzed using Carimas v.2.6 software (Turku PET Centre, Turku, Finland). ROIs were drawn in the aortic arch, blood pool (inside the LV cavity), and several relevant organs, according to the high-resolution CT image. Results are reported as the percentage of injected dose per gram (%ID/g) as a function of the time after injection, i.e., as time-activity curves.

Mice were fasted for 3–4 hours, anesthetized with isoflurane (4–5% induction, 1.5−2.5% maintenance), and placed on a dedicated heating pad in the PET/CT scanner (Inveon Multimodality; Siemens Medical Solutions, Knoxville, TN, USA). The mice received i.v. ¹⁸F-FDG (13.9 ± 0.9 MBq) or ¹⁸F-FGln (14.5 ± 0.8 MBq) via a tail vein cannula for the 60 minute dynamic PET imaging. For anatomical reference, an iodinated intravascular contrast agent (100 µL eXIATM160XL; Binitio Biomedical, Ottawa, ON, Canada) was i.v. injected immediately after PET imaging, and a 10 minute high-resolution CT was performed. PET/CT images were analyzed using Carimas 2.10 software (Turku PET Centre, Turku, Finland; www.turkupetcentre.fi/carimas/). The regions of interest (ROI) in the aortic arch, vena cava (representing blood), and myocardium were defined using contrast-enhanced CT as an anatomical reference, as previously described (18 (link)). The myocardial ROI was consistently defined at the same site for all mice tested. The results were expressed as standardized uptake values (SUVs), which were normalized to the injected radioactivity dose and animal body weight. The maximum target-to-background ratio (TBR) at 40–60 minutes post-injection was calculated as follows: SUV_{max, aortic arch}/SUV_{mean, blood} according to the established method (19 (link)).

Male NOD-SCID mice bearing PC-3 xenografts were intravenously injected with 0.18 nmol (approx. 3 MBq) of ⁵⁵Co-NOTA-PEG₂-RM26 in the tail vein. At 3 h pi the animals (n = 3) were anesthetized using isoflurane and PET/CT scanned using the Siemens Inveon Multimodality preclinical scanner (Siemens Healthcare, Knoxville, USA). At 24 h pi the animals were euthanized by intraperitoneal injection of pentobarbital and PET/CT scanned again. CT parameters were 2 bed positions, 360 projections in 360 degrees' rotation, and bin 4. The PET acquisition times of the static scans were 900 s and 1800 s at 3 h and 24 pi, respectively. The PET data were attenuation corrected using the coregistered CT scan and the sinograms were reconstructed using the OSEM3D-MAP reconstruction algorithm (4 OSEM3D iterations, 16 MAP subsets, and 18 MAP iterations, target resolution 0.8 mm). PET and CT data were analyzed using Inveon Research Workplace (Siemens Healthcare) and presented as MIPs adjusted to display a color scale from 0 to the maximum tumor uptake value.

Mice were anesthetized with isoflurane (4−5% for induction and 1.5−2% for maintenance) and the tail vein was cannulated. A CT scan was performed for anatomical reference and attenuation correction. The mice were scanned using a small-animal PET/CT (Inveon Multimodality, Siemens Medical Solutions) at 9 days post-injection as a baseline measurement, and 3, 5, and 7 days after baseline imaging. The mice were i.v. injected with 9.0 ± 0.94 MBq of [⁶⁸Ga]Ga-DOTA-Siglec-9 via the tail vein and a 30 min dynamic PET was performed. PET data acquired in a listmode were iteratively reconstructed with an ordered-subset expectation maximization 3-dimensional algorithm into 6 × 10 s, 4 × 60 s, and 5 × 300 s time frames.
Quantitative PET analysis was performed using Inveon Research Workplace 4.1 software (Siemens Medical Solutions). PET and CT images were automatically superimposed. The regions of interest were defined in the tumor and skeletal muscle based on CT image. The uptake of [⁶⁸Ga]Ga-DOTA-Siglec-9 was reported as mean standardized uptake value.