Investigation of imaging characters of bone metastases on 18F-FDG PET/CT

Objective: To investigate the imaging characters of bone metastases on 18F-fluorodeoxyglucose (FDG) PET/CT. Methods: 18F-FDG PET/CT studies in 140 patients had been retrospectively reviewed. The metastatic bone lesions were categorized into four groups: osteoblastic, osteolytic, mixed-type, or no change in bone density based on CT morphological features, to evaluate their relationships with the degree of 18F-FDG metabolism. The correlations of the therapeutic conditions with CT morphological features and with the degree of 18F-FDG metabolism were also respectively analyzed. The Mann-Whitney test and χ2-test were performed by SPSS 10.0. Results: In 140 patients, 78(55.7% ) patients were untreated and 62 (44.3%) patients had been treated by chemotherapy or hormonal therapy before this study. A total of 1658 metastatic bone lesions were found in 140 patients, including 415 osteoblastic lesions (25.0%), 567 osteolytic lesions (34.2%), 177 mixed-type lesions (10.7%) and 499 lesions with normal CT appearance (30.1%). Osteolytic and mixed-type lesions showed much higher 18F-FDG uptake on PET/CT than osteoblastic and normal CT lesions in 1045 lesions of 78 untreated patients in terms of mean standardized uptake value (SUVmean). The median of SUVmean of the mixed-type, osteolytic, osteoblastic and normal CT groups was 5.7, 5.2, 4.8 and 4.6, respectively (Z=-4.680, -6.067, -2.237, -4.635, all P < 0.05). Comparing the treated and untreated groups, there were more osteolytic lesions in untreated group (39.6%) ; while more osteoblastic lesions in treated group (35.9%). The CT morphological features of the two groups showed significant difference (χ2 = 67.8, P < 0.05). The median of SUVmean of the untreated group (4.9) was higher than that (4.6) of the treated group (z=-4.315, P<0.05). Conclusions: There is significant metabolic difference among bone metastases with different CT morphological features. The lesions with osteolytic changes, whether purely osteolytic or mixed-type, have higher SUVmean than osteoblastic or normal CT lesions. Chemotherapy and hormonal therapy could change the metabolic features on PET and the morphologic features on CT. (authors)