Q: I know your position on x-rays—you advise avoiding them if they’re not medically necessary—but what about MRIs? I have been having lower back pain, and my doctor has suggested that I get one. — S. Alexander, Burlington, VT. A: Our position on MRIs is the same as it is on x-rays—avoid unless absolutely necessary. The contrasting dyes used in MRIs are quite toxic and can produce mild to serious side effects, including kidney failure. As for the magnetic resonance technology itself, we don’t know yet all that it does to the human body. A competent orthopedist will gain much more insight into what’s causing your back pain by doing a medical history and physical exam than from an MRI. MRIs are an adjunctive diagnostic tool at best. They can reveal abnormalities, but very often these abnormalities are not causing the pain. For example, one review article looked at 5,000 findings from low-back MRI studies. Half of the group with abnormal MRIs had no pain; half of the group with norm…