Breathing protocols with increasing oxygen incubation times. A, to analyze the impact of oxygen supply in CT26 carcinomas we used three different breathing protocols: (P0) air; (P1) 100% oxygen 1 h prior injection until 3 h p.i.; (P2) 100% oxygen breathing starting 2 min prior tracer injection until 1 h p.i. and during the PET scans; mice were breathing air between the 2 h and 3 h 10 min static scans. The flow chart indicates the injection time points (Inj.) and the PET scans (PET) relative to the uptake times and oxygen or air breathing protocols. B, custom-made chamber for the microPET scans. Animals were anesthetized with 1.5% isoflurane and 0.6 L/min carrier gas flow during injection and microPET scans (either air or 100% oxygen, depending on the breathing protocol).