The purpose of this research is to determine if a PET/MRI scan using FDG can accurately identify the source of chronic pain. Identifying the source of pain may help doctors treat chronic pain more effectively. Approximately 128 participants will be enrolled and can expect to be on study for up to 12 months.

The investigators aim to precisely localize sites of increased inflammation and potentially pain generation and improve understanding of nociception and inflammation using a unique, hybrid PET/MRI approach in conjunction with intravenously, administered fluorodeoxyglucose (FDG), which has been shown with PET imaging to be an sensitive surrogate marker of inflammation.

The Primary Objective of this pilot prospective, observational research is to determine whether this approach, which combines PET/MRI and an FDA-approved radiotracer, 18F-Fluorodeoxyglucose (FDG), can accurately localize the sites of painful inflammation in individuals with persistent pain.

• Determine if increased FDG uptake on PET as measured by standard uptake value (SUV) or target-to-background (TTB) measurements is increased in area of pain symptoms when compared to same corresponding areas in healthy, asymptomatic volunteers.
• Determine whether amount of FDG uptake as measured on PET is able to localize to abnormalities when compared to MR imaging (T2 signal intensity, morphologic aberrations)

Secondary Objectives:

• Verify that the standard administered adult dose of FDG (0.14 mCi/kg/patient) used currently in the clinics can also be used to detect peripheral pain generators.
• Verify that FDG uptake in asymptomatic, healthy controls will be significantly less than their chronic pain cohorts at the same anatomic location.
• Determine whether longitudinal FDG PET/MR imaging findings in individual patients directly correlate with symptoms as they evolve over time in joint arthroplasty subjects with PPSP.
• Determine if FDG PET/MR imaging findings spatially differ between different pain types.

Inclusion Criteria: Persistent Post-Surgical Pain Patients

• 18-85 years old
• Presents with persistent pain with pain score of ≥4 on Numerical Rating Scale [0:10] for at least 6 months following joint arthroplasty or arthroscopy.
• Able and willing to provide informed consent
• Willing and able to undergo PET/MRI (arthroplasty and arthroscopy participants) and PET/CT (arthroplasty participants only)

Inclusion Criteria: Asymptomatic controls

• 18-85 years old
• Asymptomatic (pain score of ≤2 on the NRS) for at least 6 months following joint arthroplasty or arthroscopy.
• Able and willing to provide informed consent
• Willing and able to undergo PET/MRI

Exclusion Criteria:

• Inability to understand and communicate with the investigators to complete the study-related questionnaires.
• Any co-morbidity which results in severe systemic disease limiting function as defined by the American Society of Anesthesiology (ASA) physical status classification > 3, such as the presence of current or past (6 months) pulmonary, hepatic, renal disease, arthritis, hematopoietic, and neurological diseases not related to chronic pain.
• Pregnant or breastfeeding. (Individuals with childbearing potential will be asked to verbally confirm they are not pregnant. If they cannot confirm, they will have a urine pregnancy test either at the imaging study visit or within 7 days prior to the imaging study visit.)
• Subject with contraindication(s) to or inability to undergo PET/MRI
• Current diagnosis of malignancy of any kind. Participants in remission for at least two years and not undergoing any treatment may be considered per investigator discretion
• Current enrollment in a scientific interventional or treatment study.
• Subject unable or unwilling to provide informed consent

Participants with persistent post-surgical pain and asymptomatic individuals who have undergone joint arthroplasty (hip or knee) or joint arthroscopy (hip or knee).