(Magnetic Resonance Imaging)
For an MRI scan you are put into a hole through a large magnet for up to an hour. Bursts of radio waves are put into your body, and faint return signals from the hydrogen atoms in your body are detected. These signal is used to map out the tissues, which are then displayed as slices, as if you had been cut up like sliced bread. More details of MRI scanning are given on a page of the Medicine net site.
This method can show up a bony spur on the coccyx if there is one. Note - one patient reported that if you get an MRI scan of the pelvis, the coccyx image isn't big enough to see a spur on the coccyx. So make sure that they are going for a clear image of the coccyx.
You can see a video about coccyx MRI scans for tailbone pain from Dr Patrick Foye, www. tailbonedoctor.com.
Horizontal MRI scanners can be unpleasant if you suffer from claustrophobia. Open MRI scanners are now available that you can stand or sit in. These can be used to see whether the coccyx dislocates when you sit down, like the dynamic sit/stand x-ray. Successful diagnosis of a dislocating coccyx using seated MRI scanning was reported by Fonar news:
"We had a patient who was experiencing pain in her tailbone. Although she had been scanned repeatedly in a traditional recumbent MRI, none of the scan results could explain why she was in pain - that is, until she had a MRI in the seated position in the FONAR Stand-Up MRI. The images, which incidentally were excellent in terms of image quality, showed a dislocation of the distal coccyx. This problem could only be identified because the patient was scanned upright [seated]."
See also Dynamic MRI of the pelvic floor muscles in an upright sitting position.