A PET-MRI apparatus includes a patient support assembly having a cradle to accommodate a subject, a carriage assembly to attach to the cradle and cause the cradle to selectively travel, and a rear bridge to receive the cradle and carriage. The patient support assembly also includes a front bridge to receive the cradle and carriage assembly and provide for translation therealong, with the front bridge including a first section and a second section that is spaced apart from the first section to form a gap in the front bridge between the first section and the second section in an area adjacent a PET detector array of the PET-MRI apparatus. The front and rear bridges include an anti-tip rail assembly to interact with the cradle and the carriage assembly so as to prevent tipping thereof when traversing over the gap between the first and second sections of the front bridge.