Postoperative pain is an ideal model for study on acute pain changing into chronic pain. The
functional imaging of magnetic resonance can reflect the extent and character of pain exactly
and the structural imaging of it can be a sign of the change. By analyzing fMRI results of
participants with acute pain and following them up for three months, the investigators expect
to find objective indicators for acute pain changing into chronic pain and give preventive
analgesia for people with high risk of chronic pain.