Effect of oxygen concentration in the breathing gas to tissue oxygenation

Effect of oxygen concentration in the breathing gas to tissue oxygenation was investigated. Difference of T1 relaxivity (ΔR1), which is depending on the oxygen concentration in the sample, in the normal muscle and the SCC tumor tissues were measured under several gas-challenging conditions using 4.7 T MRI. C3H Hen MTV female mice were used for experiment. Squamous cell carcinoma tumor cells were injected into the right hind leg and allowed to grow for 9 days which resulted in a tumor of approximate size of 0.7 cm3. To perform T1 mapping, spin echo images were obtained using a multi-slice multi-echo (MSME) sequence with 5 TRs (repetition time: 4800, 3200, 1600, 800 and 400 ms). For hyperbaric oxygen (HBO) challenge, pressure in the special chamber was gradually increased to 1.5 atm using 2.5 min. Carbogen and HBO challenges could increase ΔR1 in the tumor tissue significantly. ΔR1 in both normal and the tumor tissues tended to decrease when mouse breathed 10% oxygen. The ΔR1 in the normal tissue tended to decrease during 100% oxygen breathing, while the ΔR1 in the tumor tissue did not change. The pO2 in the healthy tissue during 100% oxygen breathing measured by the EPR method also showed lower value than the air breathing. Breathing 100% oxygen can make normal tissue hypoxic.1st QST International Symposiu