Objective ·To analyze the imaging characteristics and diagnostic value of ¹⁸F-fluorodeoxyglucose positron emission tomography-computed tomography (¹⁸F-FDG PET/CT) in mantle cell lymphoma (MCL) and explore its application to distinguishing between classic and aggressive variants of MCL. Methods ·A retrospective analysis was conducted on the ¹⁸F-FDG PET/CT images and clinical data of 116 pathologically confirmed, newly diagnosed MCL patients. The imaging features of intra- and extra-nodal lesions were summarized. The accuracy of ¹⁸F-FDG PET/CT in diagnosing bone marrow and gastrointestinal involvement in MCL was evaluated. Furthermore, differences in ¹⁸F-FDG PET/CT findings and clinical characteristics between the classic and aggressive variants of MCL were analyzed. Results ·Among the 116 patients, 100.0% showed positive findings on ¹⁸F-FDG PET/CT, with 99.1% exhibiting abnormal lymph nodes and 85.3% having extra-nodal involvement. The most common extra-nodal sites were the spleen, Waldeyer's ring, bone marrow, and gastrointestinal tract. Compared with bone marrow aspiration results, the sensitivity, specificity, and accuracy of ¹⁸F-FDG PET/CT for detecting bone marrow involvement in MCL were 43.4%, 91.5%, and 66.0%, respectively. When compared with endoscopic biopsy results, the sensitivity of ¹⁸F-FDG PET/CT for detecting gastric and intestinal involvement was 100.0% and 94.1%, respectively, with specificity of 75.0% and 100.0%, and accuracy of 92.9% and 94.7%, respectively. There were significant differences in the highest maximum standardized uptake value (SUV_max) and Ki-67 index between the classic and aggressive variants of MCL, with SUV_max positively correlated with Ki-67 index. By using SUV_max > 10.4 as the diagnostic threshold, the sensitivity and specificity for differentiating between the classic and aggressive variants of MCL were 73.9% and 77.4%, respectively, with an AUC value of 0.797. Conclusion ·¹⁸F-FDG PET/CT demonstrates a high detection rate for both intra- and extra-nodal lesions in MCL patients. It exhibits high specificity in diagnosing bone marrow involvement and high sensitivity and specificity in diagnosing gastrointestinal involvement, providing reliable non-invasive diagnostic information for MCL bone marrow and gastrointestinal involvement. However, it is not a substitute for pathological examination. Additionally, the positive correlation between SUV_max and Ki-67 index allows SUV_max to effectively differentiate between the classic and aggressive variants of MCL, with a higher SUV_max (>10.4) indicating a higher likelihood of the aggressive variant. These findings have clinical implications for treatment planning and prognosis assessment.