This multicenter study aims to evaluate the predictive value of tumor microenvironment PET/CT imaging for treatment response and prognosis in patients with aggressive lymphoma. Eligible patients with histologically confirmed aggressive lymphoma will undergo FAPI PET/CT imaging, and selected patients who are candidates for immunotherapy will undergo Grazytracer PET/CT imaging. These imaging methods are intended to assess fibroblast activation protein expression and granzyme B activity in lymphoma lesions, reflecting cancer-associated fibroblasts and cytotoxic T-cell activity in the tumor microenvironment. The study will explore optimal imaging assessment criteria and develop clinical-pathological-imaging models to predict treatment response, prognosis, and the relationship between tumor heterogeneity and refractory or relapsed disease.

Inclusion Criteria:

• Histologically confirmed aggressive lymphoma.
• Baseline PET/CT showing moderate to high FDG uptake in lymphoma lesions.
• No previous history of malignant tumors.
• No significant cardiac, hepatic, or renal dysfunction.
• Expected survival of at least 6 months and ability to complete follow-up.

Exclusion Criteria:

• Low FDG uptake on baseline PET/CT.
• Lymphoma lesions have been surgically removed, with no positive lesions available for evaluation.
• Active or uncontrolled chronic inflammation or infection.
• Uncontrolled diabetes mellitus.
• Incomplete clinical data or loss to follow-up.
• Refusal to sign the informed consent form.
• Inability to lie supine for 30 minutes.