Inclusion Criteria:  Adults with active systemic sclerosis (SSc). Onset of SSc (defined as first non-Raynaud symptom) not more than 5 years ago. Clinically active disease with proximal nailfold capillary abnormalities detected with videocapillaroscopy and/or raised inflammatory markers (CRP or ESR).  Exclusion Criteria:  Underage, pregnant, breastfeeding, handicapped or prisoner History of or current inflammatory joint disease or autoimmune disease other than SSc. History of treatment with, prior to this study, immunosuppressives or disease-modifying anti-rheumatic drugs (DMARDs) such as methotrexate, leflunomide, azathioprine, mycophenolate, cyclophosphamide or biologic agents such as anti-TNF inhibitors, abatacept, or rituximab. Hydroxychloroquine is allowed in the history (≥3 months prior to PET study). Intra-articular or parenteral corticosteroids ≤4 weeks prior to PET/CT study. Prostanoids or other vasoactive treatments like phosphodiesterase-5 inhibitors or endothelin receptor antagonists ≤4 weeks prior to PET/CT study (the use of calcium channel inhibitors is allowed).