A medical robot for use inside a magnetic resonance imager includes a horizontal motion assembly, a vertical motion assembly and a controller. The horizontal motion assembly includes a motion joint, an ultrasonic motor operably connected to the motion joint and an encoder operably connected to the ultrasonic motor. The motor and encoder are positioned proximate to the joint of the horizontal motion assembly. The vertical motion assembly is operably connected to the horizontal motion assembly and it includes a motion joint, an ultrasonic motor operably connected to the motion joint and an encoder operably connected to the ultrasonic motor. The motor and encoder are positioned proximate to the joint of the vertical motion assembly. The controller is operably connected thereto and is adapted to be powered off when the magnetic resonance imager is being used to collect images. A medical instrument assembly is connectable to the medical robot.