The era of MRI-guided radiation therapy (MR-IGRT) began in January 2014 when the first patient was treated with 60Co under real-time MRI guidance. In 2017, the first FDA-approved MRI-Linac began treating patients. Both systems incorporate a double donut magnet design with a 28 cm gap for the radiation beam. A rotating gantry carries either three shielded 60Co heads or a 6 MV Linac with magnetic and RF shielding. In this study, we compare the MRI subsystem performance between the two systems.