Oftagel

The same 9-month-old WT (n = 6) and TG (n = 6) mice were imaged using [¹¹C]PBR28 [¹⁸F]DPA-714 and [¹⁸F]F-DPA within a period of 10 days. The mice, anesthetized with a 2.5% isoflurane/oxygen mixture 30 min prior to tracer injection, were injected via a tail vein with [¹⁸F]F-DPA (injected dose 6.9 ± 0.2 MBq; 43 ± 18 μg/kg), [¹⁸F]DPA-714 (injected dose 6.8 ± 0.3 MBq; 0.8 ± 0.3 μg/kg), or [¹¹C]PBR28 (injected dose 10.3 ± 0.8 MBq; 0.4 ± 0.1 μg/kg) for 60-min dynamic scanning using an Inveon multimodality PET/computed tomography (CT) scanner (Siemens Medical Solutions, Knoxville, TN, USA). A few drops of Oftagel (2.5 mg/g; Santen, Tampere, Finland) were applied to the eyes of the animals to prevent eye dryness. The scanner has an axial 12.7-cm field of view and 10-cm transaxial field of view, generating images from 159 transaxial slices of voxel size of 0.78 × 0.78 × 0.8 mm³. CT preceded the PET modality for attenuation correction and anatomical reference. One of the TG animals imaged with [¹⁸F]F-DPA died during the scan, and hence this animal was excluded from the analysis.

Rats were anesthetized with isoflurane/oxygen gas and injected intravenously with [¹⁸F]F-DPA (31.4 ± 2.1 MBq, n = 4 SA at the time of injection = 4.1 ± 0.4 GBq/μmol) for scanning by an Inveon multimodality PET/CT tomograph (Siemens Medical Solutions, Knoxville, TN, USA). In order to prevent eye dryness, a few drops of Oftagel (25 mg/g; Santen, Tampere, Finland) were applied to the eyes of the animals. The scanner has a 12.7 cm axial field of view (FOV) and 10 cm transaxial FOV generating images from 159 transaxial slices. The spatial resolution of the scanner is 1.4 mm according to the manufacturer’s specifications. The animals were scanned for 10 min with computed tomography (CT) for attenuation correction and anatomical reference, and immediately after that, the radiotracer was injected for a 60-min dynamic PET scan. Frames were taken at the following intervals: 30 × 10, 15 × 60, 4 × 300, and 2 × 600 s. Volume of interests (VOIs) were drawn over the whole brain, heart, lung, liver, and kidneys using Inveon Research Workplace Image Analysis software (Siemens Medical Solutions). From the VOIs, time–activity curves (TACs) were obtained and the uptake of [¹⁸F]F-DPA was expressed as percentage of injected dose per milliliter of tissue (%inj. dose/ml).

Animals were fasted 4 – 10-h prior to imaging and anaesthetised in a chamber 20 min prior to the PET imaging using isoflurane (Baxter Medical AB, Kista, Sweden): 4% induction and 1.2–2.0% for maintenance mixed with air flow 400–500 mL/min. A tail vein cannula was inserted prior to imaging and a blood sample was collected for baseline glucose measurement. Oftagel (2.5 mg/g, Santen, Tampere, Finland) was applied to the eyes to avoid drying during imaging. For anatomical reference, a high-definition CT image was acquired using the Molecubes X-CUBE (Molecubes, Ghent, Belgium). The PET image was acquired with the Molecubes β-CUBE (Molecubes). A bolus of [¹⁸F]FDG (1.92 (±0.2)) MBq was administered and emission scans acquired with framing 30 × 10 s, 15 × 60 s and 5 × 300 s. Images were reconstructed twice with ordered-subsets expectation maximisation algorithm in three dimensions (OSEM3D) and 18× with maximum a posterioiri (MAP).