Intravital image of tumor growth within a dorsal window chamber. HCT116/GFP-expressing tumors were grown within a dorsal window chamber, where its growth was monitored over time. Images were captured following excitation with an Argon laser at 488 nm and emission was collected with a 498–538 nm bandpass filter using an Olympus FV1000 multiphoton microscope. Tumor at day 14 was pseudo-colored red in order to superimpose the tumor image on day 4 (green). Growth was quantified along radial lines from the centroid of the day 4 tumor and compared with registered images of the peritumoral pH to correlate growth and invasion to acidity. For details, see article by Estrella and colleagues on page 1524.