Inter-observer variability between readers in detection of bone metastases comparing different modalities; PET/CT, SPECT/CT and planar bone scintigraphy.

OBJECTIVE: To assess the inter-observer variability between readers in the detection of bone metastases for different modalities [planar bone scintigraphy (BS), single photon emission computed tomography/computed tomography (SPECT/CT), and fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) (F-18 FDG PET/CT)]. METHODS: Patients with known primary tumors referred for metastatic workup either by F-18 FDG PET/CT or conventional planar BS and SPECT/CT were enrolled in this prospective study. The three modalities (BS, SPECT/CT, and PET/CT) were acquired for each patient. Interpretation was done by two independent nuclear medicine physicians separately and blindly; reader 1 (R1) and reader 2 (R2). A three-point subjective scale was used (1 = negative for bone metastases, 2 = equivocal, and 3 = positive). The findings were compared to the final patient status based on clinical and radiological follow-up for at least 6 months. The Kappa test was used to assess the degree of agreement between readers in their interpretation of each modality. RESULTS: A total of 54 patients (39 females and 15 males, ages 26-76; mean: 54.7 ±â€…12) were eligible for this study. Fair agreement 0.372 between R1 and R2 in interpretation of BS was noticed that improved to 0.847 after addition of SPECT/CT. Perfect agreement was achieved between R1 and R2 while interpreting PET/CT images (kappa = 0.964, P < 0.001). CONCLUSION: F-18 FDG PET/CT significantly improved the inter-observer variability between readers, allowing for better diagnosis of bone metastases in known cancer patients. Also, it was superior to BS and SPECT/CT in the detection of bone metastases.

Correlation between metabolic uptake of F-18-FDG-PET/computed tomography and thyroglobulin level in differentiated thyroid cancer patients with suspected recurrence.

OBJECTIVE: Our objective is to determine if there is correlation between serum thyroglobulin and SUVmax of the main lesion detected in F18-FDG-PET/CT scan, in differentiated thyroid cancer (DTC) patients with suspected recurrence. METHODS: All DTC patients enrolled in this prospective study, received at least one dose of radioactive iodine. During follow-up, they are suspected to have a recurrence due to elevated tumor markers although negative iodine whole-body scans. For all patients, F18-FDG-PET/CT scanning was performed. A 3D volume of interest was generated over the liver and main lesion to obtain maximum standardized uptake value (SUVmax). We calculated the lesion/liver ratio. Follow-up and/or histopathological examination were the gold standard. Pearson's correlation coefficient was calculated between thyroglobulin and SUVmax of the main lesion. RESULTS: Sixty-eight patients were recruited in this study. F18-FDG-PET/CT identified suspicious malignant lesions in 42 patients, equivocal in 18 patients, while 8 patients showed no abnormal findings. Fifty-two, 6, 8, and 2 patients were true positive, true negative, false positive, and false negative respectively. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were 72%, 57% 87%, 35%, and 69% respectively. The median SUVmax and lesion/liver ratio were significantly higher in the malignant lesions than that of benign lesions (3.9 vs. 1.3 and 1.45 vs. 0.54 respectively). We found that the main lesion SUVmax and lesion/liver ratio have a positive moderate correlation with thyroglobulin (0.338 and 0.325 respectively). CONCLUSION: In DTC patients with suspected recurrence, SUVmax of F18-FDG-PET/CT lesion showed a moderate positive correlation with serum thyroglobulin.