R4 micropet

All animals were anesthetized with humidified, oxygen-enriched 2-3% isoflurane (inhalation). The animal was secured in a transportable holder with fixed firm padding to eliminate motion between PET and MRI scans while allowing it to breathe 2-3% isoflurane via a nose cone fixed to the animal holder. Fiducial markers made with a diluted [¹⁸F]FTC-146 solution (30 µCi/mL) in longitudinal plastic tubes placed across the bottom of the animal holder were utilized for assistance in PET and MRI image co-registration. The animals underwent sequential PET (microPET R4; Siemens Medical Solutions) and MRI (a self-shielded 30-cm-bore 7-T magnet [Varian] with a 9-cm-bore gradient insert [Resonance Research Inc.] using EXCITE2 electronics and the supporting LX11 platform [GE Healthcare]) using dedicated small animal imaging instruments. For PET imaging, 1000 µCi (37 MBq) [¹⁸F]FTC-146 was injected via tail vein, and a 10 min static scan of the thighs was obtained 30 min post-injection. For MRI, T1 Fast Spin Echo images (TR 800 ms; TE 7.7 ms; slice thickness 1 mm; in-plane resolution 234 µm²) were obtained of the rat thighs. Haloperidol (1.6 mg/kg), a widely used S1R blocker, was given intravenously 30 min prior to tracer administration for the blocking studies.

Mice were divided into imaging and control groups (n = 4 mice). To analyze tumor imageability after intratumoral delivery, mice received an intratumoral injection of 10⁴ PFU per tumor of either CF33-hNIS, CF33-Fluc, or PBS when tumors reached 100 mm³. At 7, 15, and 22 days post-viral infection, mice in each group received 200 μCi of I-124 injected per tail vein. The radioisotope was obtained from the City of Hope Small Animal Imaging Core Radiopharmacy. PET imaging was then obtained 2 h following injection using the small-animal PET scanner (microPET R4; Siemens Corporation), which provides fully three-dimensional PET imaging with spatial resolution of better than 2.0 mm and quantitative accuracy for measurement of tissue activity concentration on the order of 10%. The 8-cm axial field of view is adequate for simultaneous whole-body imaging of mice. Advanced image reconstruction software provides resolution approaching 1.0 mm. Quantitative accuracy is supported by scatter, dead time, and measured attenuation corrections. The system includes a fully developed image analysis package that supports volumetric regions of interest and fusion of PET with co-registered anatomic CT. In order to protect mouse thyroids from radioiodine ablation, all mice received T4 supplementation with 5 mg levothyroxine/L of water beginning 1 week prior to radioiodine administration.