Hyperthermia induces T1 relaxation and blood flow changes in tumors. A MRI thermometry study in vivo

Abstract

Regional hyperthermia in combination with chemotherapy and/or radiotherapy has proven to be an effective treatment concept for locally advanced deep-seated tumors. Simultaneous MR-imaging could be a promising approach for therapy optimization. Purpose of this study was the in vivo investigation of temperature induced longitudinal relaxation time ( T 1) and blood flow changes in a tumor model. Using a 1.5 Tesla MR system, the T 1 sensitivity on temperature and the onset of tissue changes at temperatures >44°C were investigated in muscle samples. Also, fourteen Syrian Golden Hamsters with amelanotic melanoma A-MEL-3 were examined during heating of the tumors. Temperature induced blood flow and T 1 changes were determined continuously during hyperthermia. Changes of T 1 correlated linearly with temperature over a wide range (27-44°C) in the tissue sample. Tissue changes became notable above 44°C. In the tumor model, relative changes of T 1 (unlike blood flow) showed linear correlation with temperature over the entire range of hyperthermia relevant temperatures (32-44°C). For a low thermal dose, T 1 allows the assessment of temperature changes in tumors in vivo. At higher thermal doses, in addition to temperature changes, T 1 also shows tissue changes. Both temperature and tissue changes supply important information for hyperthermia.