Wizard2 link γ counter

For PET imaging, animal studies were carried out in accordance with the University of Wisconsin-Madison Institutional Animal Care and Use Committee. For tumor PET imaging studies, 1 × 10⁶ 4T1 murine breast cancer cells suspended in 30 μL of PBS were injected in the fourth mammary pad of 5–6 week old female BALB/c mice (Envigo, IN). Tumor sizes were monitored regularly, and mice were used when the tumors reached ~7 mm in diameter, typically 7–10 days post-inoculation. Twenty-five OD of ⁶⁴Cu-labeled Pheo nanoparticles was injected intravenously in 4T1 tumor-bearing mice via the tail vein (n = 3). Static positron emission tomography (PET) images were acquired at different time points postinjection (p.i.) on an Inveon microPET/microCT rodent model scanner (Siemens Medical Solutions USA, Inc.). All PET images were reconstructed using a maximum a posteriori algorithm, without attenuation or scatter correction, and analyzed with Inveon Research Workplace software after decay correction. All data are presented as a percentage injected dose per gram (%ID/g). Mice were euthanized after the final PET scans at 72 h postinjection, and ex vivo biodistribution studies were performed, to validate the in vivo results. Blood, tumor, and major organs were collected and wet-weighed, and radioactivity in each tissue was measured on a WIZARD^{2 (link)}γ counter (PerkinElmer) and presented as %ID/g.