A preliminary study of murine walker-256 tumor hypoxia detected by blood oxygen level dependent-MR

Objective: To establish Walker-256 transplantation tumor model in SD Rats. To study of R₂^* signal changes on murine Walker-256 tumor after inhaling Carbogen by blood oxygen level dependent (BOLD)-MR, and to explore the feasibility of BOLD-MRI on detecting tumor hypoxia. Methods: Walker-256 tumor cell implanted subcutaneously in right lower abdomen of 95 female SD rats. MR was performed on the tumor-forming rats when the maximum diameter of tumor reached 1-3 cm, using a 3.0 T MR scanner equipped with a 3 inch animal surface coil. BOLD-MRI was done by using a multiecho SPGR sequence during inhaling air and at 10 minute after inhaling Carbogen, respectively. All images were transferred to GE ADW 4.3 workstation, then a baseline R₂^* (R₂^* a) and R₂^* (R₂^* b) after inhaling Carbogen of tumor was calculated using R₂ Star analysis software and ΔR₂^* was calculated through ΔR₂^* = R₂^* b -R₂^* a^, meanwhile the volume of tumor were calculated as well. The difference of R₂^* signal pre and post-inhaling of Carbogen was compared with a paired t test, Pearson correlation was calculated between R₂^* a, ΔR₂^* and the volume of tumor, respectively. The correlation between ΔR₂^* and R₂^* a was also assessed by Pearson correlation. Results: Sixty-eight of ninety-five female SD rats formed the tumor (71.6%). The volume of tumor was from 352 to 13 173 mm³. Mean ΔR₂^* decreased significantly (-2.26 ± 3.90) s^-1 from (41.18 ± 22.29) s^-1 during breathing air to (38.91 ± 21.35) s^-1 10 min after inhaling Carbogen (t = 4.01, P < 0.01). ΔR₂^* was inversely correlated with R₂^* (r = -0.32, P < 0.05). The ΔR₂^* was well correlated with volume of tumor (r = 0.35, P < 0.05), but R₂^* a was not correlated with volume of tumor (r = -0.03, P > 0.05). Conclusions: BOLD-MRI can detect the R₂^* signal change of murine Walker-256 tumor pre-and post-inhaling of Carbogen. The R₂^* signal showed significant decrease after inhaling Carbogen, however, the individual variation was remarkable. (authors)