Chronic pain is a major public health issue, which seriously affects patients' quality of life. Neuroinflammation is an important mechanism resulting in chronic pain. Translocator protein (TSPO) has served as a marker of microglial activation and neuroinflammation. 18F-DPA714, a tracer targeted TSPO, can be used to evaluate the microglial activation and neuroinflammation in vivo by PET imaging.Recent and increasing studies have found changes in TSPO and its ligands in various chronic pain models. Reversing their expressions has been shown to alleviate chronic pain in these models, illustrating the effects of TSPO and its ligands.The investigators aim to explore the clinical feasibility used 18F-DPA714 PET imaging to monitor microglial cells activation of center nervous system in chronic pain patients. This study might reveal significant neuroinflammatory process in the center nervous system of the chronic pain patients. The results of this study might provide a new biomarker of disease pathological progression and indicates that TSPO-based therapy may become an alternative strategy for treating chronic pain.

Inclusion Criteria:

• chronic pain patients
• Written informed consent was provided by the patients and their family

Exclusion Criteria:

• history of head trauma ， epilepsy， claustrophobia, rheumatic or autoimmune diseases, psychiatric disorders, severe somatic diseases (neurological,cardiovascular, etc.),previous heart or brain surgery, substance abuse, inability to refrain from hypnotics, magnetic implants, pregnancy, lactation

Patients with chronic pain