The Visualase Thermal Therapy System will be used in this study to give subjects a type of therapy called Laser Interstitial Thermal Therapy (LITT). LITT uses laser light to heat and destroy the affected tissue; this is sometimes referred to as tissue ablation. In LITT, small fiber-optic applicators are placed directly into the tumor and heating is performed from the inside out, which may lead to the destruction of the tumor. During the heating process, MRTI can be used to watch the temperatures around the applicator to make sure that the tumor receives enough treatment and that the normal tissues around the tumor do not get too hot.