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.