In vivo iodide retention by tumor cells infected with MV-NIS. (A) MM1 tumors infected with MV-NIS concentrate iodide and retain it for at least 24 hours. At 9 days after intravenous injection of MV-NIS, mice were imaged serially at 1 (A), 3 (B), 5 (C), 7 (D), 15, and 24 hours after ¹²³I injection. Images A-D were all acquired over 5 minutes and are adjusted for the same image intensity. (E) Quantification of iodide uptake and retention by MM1 tumors after infection with MV-NIS. MM1 tumors take up 12% to 17% of the isotope injected and retain it for at least 24 hours. Error bars indicate SD. Magnification is 0.55 mm per pixel.