[Value of PET/MRI in the diagnosis of malignant pleural effusion in comparison with PET/CT]

Objective: To investigate the diagnostic value of PET/MRI for malignant pleural effusion (MPE), and compare its diagnostic difference with PET/CT. Methods: The data of 57 patients with suspected MPE admitted into Union Hospital of Tongji Medical College of Huazhong University of Science and Technology from October 2017 to January 2020 was analyzed. A total of 53 patients were included in the prospective study, and the whole body PET/CT and thoracic PET/MRI were performed on them respectively. Two physicians used a blind method to evaluate the morphological features of PET/CT and PET/MRI images, delineate the region of interest (ROI), obtain the maximum standard uptake value (SUVmax) of the ROI in the PET/CT and PET/MRI images. The target-to-background ratio (TBR) of the lesion was calculated. The diffusion-weighted imaging (DWI) characteristics of the pleura in PET/MRI images were analyzed. Taking pathological diagnosis as the gold standard, the diagnostic effect of PET/CT and PET/MRI on MPE were evaluated. Results: The 53 patients who were finally included were (62.8±1.7) years old, consisting of 31 males. Pathological results showed that 41 cases were MPE and 12 cases were benign pleural effusion (BPE). There were no statistical differences in age, gender and smoking history between the two groups (P>0.05). Bland-Altman analysis showed that the SUVmax of pleural lesions by PET/MRI was higher than that by PET/CT (6.4±0.6 vs 5.3±0.5, P<0.001). The TBR of PET/MRI was higher than that of PET/CT (2.2±0.2 vs 1.8±0.2, P<0.001). The sensitivity, specificity, and accuracy of PET/MRI in the diagnosis of MPE by combining imaging features such as SUVmax and DWI of pleural lesions were 75.6%, 100%, and 81.1%, respectively. The sensitivity, specificity, and accuracy of PET/CT combined with SUVmax and imaging features of pleural lesions in the diagnosis of MPE were 85.4%, 83.3%, and 77.4%, respectively. There was no statistically significant difference between PET/MRI and PET/CT in the area under the curve (AUC) for diagnosing MPE (0.934 vs 0.873, P>0.05). Conclusions: PET/MRI and PET/CT have the equivalent diagnostic efficiency for MPE. However, PET/MRI shows higher SUVmax and TBR for pleural lesions, and has specific pleural DWI imaging characteristics, which is worthy of further clinical research.