No, Physical Therapist don't generally order MRI's, it’s usually done by your Primary Care Physician or by a specialist such as a Neurologist or Neurosurgeon. At any rate who every orders it, is probably going to want you to have x-rays done first, MRI's are very expensive, if they see something on the x-ray that concerns them, then they will order an MRI. What they do depends a lot on your symptoms, the severity of your pain and how long you’ve had it.