HMSC cells were infected with a lentivirus vector carrying the expression cassette for Gluc under the control of CMV promoter. 4 days after infection, 2 million of these cells were implanted subcutaneously with Matrigel in nude mice. Mice were injected i.v. with 100 µg of coelenterazine, prepared by diluting it in methanol to a concentration of 5 µg/µl, than 20 µL was added to 130 µL of PBS and all was i.v. injected. Mice were imaged at different time points using a CCD camera and photon counts were acquired over five minutes. The sum of photon counts/min is plotted. Images are displayed as a pseudo-color photon count image, superimposed on a grayscale anatomic white light image, allowing assessment of both bioluminescent intensity and its anatomical source.