This single-center pilot study is designed to explore the preliminary utility of the [68Ga] Ga-FAPI imaging agent in positron emission tomography (PET) combined with computed tomography (CT) for a range of chronic inflammatory and fibrosing diseases. The study focuses on the potential of [68Ga] Ga-FAPI, a novel radiotracer targeting Fibroblast Activation Protein (FAP), to improve diagnostic accuracy in various medical conditions. Thirteen distinct clinical situations have been selected for this investigation, including rheumatoid arthritis, liver fibrosis, and systemic lupus, among others. This approach aims to ascertain the value of further clinical development in each area and refine the use of this imaging modality in routine care for both initial evaluation and ongoing monitoring of these diseases.

[68Ga] Ga-FAPI is an innovative radiotracer in positron emission tomography (PET) coupled to scanner (CT: computed tomography). It targets the membrane glycoprotein FAP (Fibroblast Activation Protein), a specific surface marker of activated fibroblasts, these constituting one of the main populations of the tumor microenvironment. This radiotracer is the subject of a major development program in the field of oncology and hematologic malignancies. In many cancers, preliminary data suggest, in terms of diagnostic performance, the superiority of [68Ga] Ga-FAPI over the reference evaluation modality carried out with [18F] F-FDG. These results make it possible to consider, in the medium term, the integration of this imaging modality into routine care, for the initial evaluation and monitoring of certain tumor pathologies.

If oncology and hematology constitute the most obvious areas of application of [68Ga] Ga-FAPI, other areas of potential use were quickly mentioned, due to the involvement of activated fibroblasts in the processes. remodeling of the extracellular matrix and tissue repair in general, beyond tumor pathologies. Non-exhaustively, the potential interest of the radiotracer is thus suggested in the characterization of benign tumor pathologies, in the evaluation of ischemic tissues, in chronic inflammatory diseases and in fibrosing diseases. Numerous preliminary data show that it is relevant to develop knowledge concerning the contribution of [68Ga] Ga-FAPI to the evaluation of numerous benign pathologies.

It is in this general context that this single-center pilot study project falls, the general objective of which is to determine the preliminary interest of this imaging modality in different chronic inflammatory and/or fibrosing diseases. The pathologies included in this project were selected by taking into account the concomitant presence of unmet medical needs in terms of disease assessment and recognized local clinical research expertise in the area concerned. On these bases, 15 distinct clinical situations were selected, intended to enable the production of pilot data. This approach will be able to determine the interest in continuing clinical development in each area and will help to specify the modalities.

The 13 clinical situations selected for this pilot study are:

• Rheumatoid arthritis
• Spondyloarthritis
• Inflammatory enterocolopathies
• Liver fibrosis
• Fibrosing interstitial lung disease
• Systemic sarcoidosis
• Polymyalgia rheumatica and giant cell arteritis
• Primary Sjögren's syndrome
• Systemic scleroderma
• Systemic lupus
• Inflammatory myopathies
• Primary or secondary myelofibrosis
• Other orphan systemic diseases
• Endometriosis
• Chronic thrombo embolic disease

Inclusion Criteria:

• Patient aged 18 or over.
• Affected by one of the pathologies concerned by the study (see Table 4)
• Satisfying the consensus classification criteria for the pathology (Table 3).
• Satisfying the corresponding clinical situation (Table 3).
• Negative urine pregnancy test for women of childbearing age.
• Affiliated with or benefiting from social security.
• Informed consent (personally dated and) signed by the participant or any representatives (impartial witness/trusted person).

Exclusion Criteria:

• Patients unable to consent.
• Incapacitated adults.
• Pregnant or breastfeeding women.
• Patients refusing to participate in research.
• Known active cancer.
• Women of childbearing potential unwilling to use appropriate contraception (definitions given in Annex 1).