Objective To discuss the value of diffusion-weighted MRI (DWI) and 18F-FDG-PET/CT in assessing the early therapeutic effect of radiofrequency ablation (RFA) for VX2 sarcomas in experimental rabbits. Methods VX2 sarcoma was inoculated at bilateral hind limbs in 14 New Zealand white rabbits to establish the animal models. The implanted VX2 tumor on one hind leg was treated with ultrasound-guided percutaneous RFA (study group), while no RFA was given to the VX2 tumor on the contralateral hind leg (control group). DWI-MRI was performed at 2 days after RFA, and 18F-FDG-PET/CT examination was employed at 3 days after RFA. The mean apparent diffusion coefficient (ADC) values and standard uptake value (SUV) of the untreated tumor and the ablated tumor were separately calculated. Taking the pathologic result as the gold standard, the consistency of DWI-MRI, PET/CT as well as the combination of DWI-MRI and PET/CT with the clinical diagnosis was separately evaluated by Kappa test. Results Before RFA, DWI-MRI demonstrated that the VX2 tumor was characterized by hypo-intensity signal on T1 and hyper-intensity signal on T2 with ring-shaped enhancement on T1-weighted image; PET/CT showed that the tumor had nodular or ring-shaped 18F-FDG accumulation. After RFA, DWI-MRI revealed that the VX2 tumor was manifested as hyper-intensity signal on T1 and slight higher density on T1 with slight enhancement on contrast-enhanced T1-weighted image; PET/CT showed lowered accumulation of 18F-FDG. The mean ADC value of the ablated tumor was (1.52 ± 0.24) × 10-3 mm2/s, which was obviously higher than that of the un-ablated tumor, that was (1.09 ± 0.12) × 10-3 mm2/s, the difference was statistically significant(P<0.05). The mean SUV value of the ablated tumor was (0.6 ± 0.3), which was significantly lower than that of the ablated tumor (9.6 ± 3.2, P<0.05). No significant difference in sensitivity, specificity and accuracy existed between DWI-MRI and pathology as well as between PET/CT and pathology, the Kappa value being 0.357 and 0.428 respectively (P>0.05). The Kappa value of the consistency between combination of DWI-MRI with PET/CT and pathology was 0.786, which was significantly different from the result by simple DWI-MRI or simple PET/CT evaluation (P< 0.05). Conclusion Both ADC value of DWI-MRI and SUV value of PET/CT are useful indexes for evaluating the early therapeutic effect of RFA. Both DWI-MRI and PET/CT have their respective advantages, nevertheless, combination use of both can effectively improve the evaluation of curative effect for VX2 tumor after RFA in experimental rabbits.

OBJECTIVE: To assess clinical value of fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) for differentiation of malignant from benign focal thyroid incidentaloma. MATERIALS AND METHODS: This retrospective study included 99 patients with focal thyroid incidentaloma of 5216 non-thyroid cancer patients that had undergone PET/CT. PET/CT semi-quantitative parameters, volume-based functional parameters, metabolic tumor volume (MTV), and total lesion glycolysis (TLG) of thyroid incidentaloma were assessed. Receiver-operating characteristic (ROC) analysis was conducted and areas under the curve (AUC) were compared by Hanley and McNeil test to evaluate usefulness of maximum standardized uptake value (SUVmax), MTV and TLG, as markers for differentiating malignant from benign thyroid incidentalomas. RESULTS: Of 99 thyroid incidentalomas, 64 (64.6%) were malignant and 35 (35.4%) were benign. Malignant thyroid incidentalomas were larger (1.8 cm vs. 1.3 cm, p = 0.006), and had higher SUVmax (11.3 vs. 4.8, p < 0.001), MTV (all p < 0.001) and TLG (all p < 0.001) than benign. TLG 4.0 had the highest performance for differentiation of malignant from benign thyroid incidentaloma in all semi-quantitative parameters with AUC 0.895 by ROC curve analysis. AUC (TLG 4.0) was significantly larger than AUC (SUVmean), AUC (MTV 2.5), AUC (MTV 3.0), AUC (MTV 3.5), AUC (TLG 2.5), and AUC (TLG 3.0), respectively (all, p < 0.05). There was no statistical difference between AUC (TLG 4.0) and AUC (SUVmax) (p > 0.05). A threshold TLG 4.0 of 2.475 had 81.3% sensitivity and 94.3% specificity for identifying malignant thyroid incidentalomas. CONCLUSION: Volume-based PET/CT parameters could potentially have clinical value in differential diagnosis of thyroid incidentaloma along with SUVmax.
Area Under Curve ; Diagnosis, Differential ; Electrons ; Fluorodeoxyglucose F18* ; Glycolysis ; Humans ; Positron-Emission Tomography and Computed Tomography* ; Retrospective Studies ; ROC Curve ; Sensitivity and Specificity ; Thyroid Gland* ; Thyroid Neoplasms ; Tumor Burden