Pulmonary and renal involvement are the most common clinical manifestations of antineutrophil cytoplasmic antibody(ANCA)-associated vasculitis (AAV). Studies have shown that both interstitial lung disease (ILD) and renal dysfunction are closely associated with poor prognosis in patients with AAV. Therefore, early identification of whether AAV patients have concomitant ILD and renal involvement is of great clinical importance for assessing disease severity, stratifying prognostic risk, and developing individualized treatment strategies.

Positron emission tomography (PET) is a noninvasive molecular imaging technique that can provide decision-making support for early and accurate diagnosis, timely intervention, as well as evaluation of treatment response and prognosis. In the same individual, PET enables whole-body localization of disease in a single examination, overcoming the limitation of conventional diagnostic methods that typically assess only one region at a time, thereby facilitating patient benefit.

In recent years, many novel PET tracers have been developed and introduced into clinical practice. 68Ga-Fibroblast Activation Protein Inhibitor (FAPI) has been studied in the diagnosis of various malignant and nonmalignant diseases; it targets fibroblast activation protein (FAP) and thus reflects the distribution of cancer-associated fibroblasts (CAFs). However, its clinical significance in AAV remains to be further investigated. This study aims to use a CAF-targeted novel PET tracer to conveniently and noninvasively detect the real-time distribution of lesions in patients, providing valuable information for personalized diagnosis and treatment.

Inclusion Criteria:

1. Age over 18 years;
2. Meeting the 2022 American College of Rheumatology/European Alliance of Associations for Rheumatology (ACR/EULAR) classification criteria for ANCA-associated vasculitis;
3. Diagnosed with concomitant interstitial lung disease based on High-Resolution Computed Tomography (HRCT) images obtained within one year prior to enrollment, interpreted by two radiologists blinded to clinical information;
4. Complete clinical information available;
5. Signed and dated informed consent form;
6. Willingness to comply with the study procedures and cooperate throughout the entire study process.

Exclusion Criteria:

1. Presence of other rheumatic diseases;
2. Presence of other conditions that may cause interstitial lung disease or renal impairment, such as systemic lupus erythematosus, dermatomyositis, or rheumatoid arthritis;
3. History of, or planned, hematopoietic stem cell transplantation;
4. Presence of severe comorbidities deemed by the investigators to be unsuitable for participation in this clinical study, such as severe cardiopulmonary insufficiency, severe bone marrow suppression, or severe hepatic or renal insufficiency;
5. Acute abdominal emergencies such as intestinal perforation or complete intestinal obstruction;
6. Pregnant or potentially pregnant women, and lactating women;
7. Poor treatment compliance.

Participants in this study will be recruited from Ruijin Hospital, Shanghai Jiao Tong University School of Medicine.

The individual participant data will not be shared because the informed consent obtained from participants did not include permission for public data sharing, and institutional as well as ethical guidelines require strict protection of participant confidentiality.