Although it's not seen directly during the MRI scene, the plot implies that Em never removes the ring. Em would have been unable to wear the ring on her hand during the MRI (magnetic resonance imaging) test. Even if it was non-ferromagnetic (like gold), it could have still interfered with the test and medical staff would have likely removed it prior to bringing her into the room.
The scene where the family is hugging Em on the Hospital floor, the ring that supposedly makes the possession continue, slip out of Em's finger. Then the ring is shown again in her finger while Tzado tries to remove the demon from Clyde and while Em hugs Clyde. Immediately after that, Tzado catches the ring on the floor, making the scene confusing.
The Hebrew writing on the side of box in the opening scene appears upside down in relation to the lid and apparently spells out "Dibbuk" backwards. The writing on the lid apparently is backwards Hebrew for "You shall see the punishment of evil".