Multimodal imaging reveals gliomas are cooler than normal tissue

Motivation: CBF-CMRO2 uncoupling in tumors suggests that the tumor temperature might be different than normal brain temperature. Goal(s): To determine if a temperature gradient exists between tumor and normal brain tissue. Approach: We measured CMRO2, CMRgly, and CBF in rat brains bearing 9L tumors, and calculated the brain temperature distribution using Pennes bioheat equation. We measured the temperature distribution in 9L, RG2, U87 and U251 gliomas using BIRDS with TmDOTP5- and we confirmed these measurements by 1H-MRS using water-NAA and by BIRDS with TmDOTMA-. Results: Our measurements indicate that the tumor temperature is lower by ~10C compared to normal brain temperature. Impact: Temperature regulates the immune response, and thermal- and immuno-therapy might be combined for improved outcome. While temperature is rarely included into discussions related to tumor microenvironment, our results potentially impact future therapeutic directions because cooler conditions enhance tumor growth.