Inclusion Criteria:  ALL SUBJECTS  The subject has provided written informed consent with HIPAA (Health Information Portability and Accountability Act) authorization before the initiation of any study-related procedures.  The subject has agreed to not engage in any diet, lifestyle, or medication changes until study completion.  HEALTHY CONTROL SUBJECTS  The subject is 30 years of age or greater at the time of consent. The subject is deemed to be clinically free of any inflammatory disease(s), autoimmune disease(s), or arthropathies and has not experienced joint pain for at least 28 days prior to the consent date. The subject is not currently on anti-inflammatory drugs (including non-steroidal anti-inflammatory drugs [NSAIDs]) and has not taken any anti-inflammatories for at least 28 days prior to the consent date. For all ongoing concomitant medications, the subject has maintained a stable dose for at least 28 days prior to the consent date.  CLINICALLY DIAGNOSED ACTIVE RA SUBJECTS  3. The subject is at least 18 years of age and was ≥ 18 years of age at the time of RA diagnosis.  4. The subject has moderate to severe RA as determined by the 2010 American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) Classification Criteria (score of ≥ 6/10).  5. The subject has a 28-joint disease activity score (DAS28) of ≥ 3.2 (includes the Erythrocyte Sedimentation Rate [ESR] test and Visual Analog Scale [VAS]).  6. Subjects receiving traditional DMARDs must have been on therapy for ≥ 90 days and at a stable dose for ≥ 30 days prior to the imaging visit (Day 0). 7. If the subject is receiving bDMARD or janus kinase (JAK) inhibitor therapy, they have been at a stable dose > 60 days prior to the imaging visit (Day 0). 8. If the subject is receiving NSAIDs or oral corticosteroids, the dose has been stable for ≥ 28 days prior to the imaging visit (Day 0). The corticosteroid dose must be ≤ 10 mg/day of prednisone or an equivalent steroid dose.  Exclusion Criteria:  The subject is pregnant or lactating. The subject size or weight is not compatible with imaging per the investigator. The subject is currently receiving radiation therapy or chemotherapy or has received radiation therapy or chemotherapy in the past six months. The subject has had a finger, hand, and/or wrist amputation or hand or wrist joint arthroplasty. The subject has renal insufficiency as demonstrated by a glomerular filtration rate of < 60 mL/min. The subject has hepatic insufficiency as demonstrated by ALT (alanine aminotransferase [SGPT]) or AST (aspartate aminotransferase [SGOT]) greater than 2 times the upper limit of normal. The subject has any severe, acute, or chronic medical conditions and/or psychiatric conditions and/or laboratory abnormalities that would impart, in the judgment of the investigator, excess risk associated with study participation or study drug administration that would deem the subject inappropriate for study participation or compromise the safety of the subject or the quality of the data. The subject has any unstable medical illnesses, including hepatic, renal, gastroenterologic, cardiovascular (including ischemic heart disease), endocrinologic, neurologic, immunologic, or hematologic disease. The subject has a known allergy to or has had an adverse reaction to dextran exposure. The subject has received an investigational product within 30 days prior to Tc 99m tilmanocept administration (Day 0). The subject has received intra-articular corticosteroid injections ≤ 8 weeks prior to Tc 99m tilmanocept administration (Day 0). The subject has received any radiopharmaceutical within 7 days or 10 half-lives prior to Tc 99m tilmanocept administration (Day 0). Healthy Controls only: The subject has a positive rheumatoid factor and an elevated ESR or CRP.