Objectives To investigate the effect of serum glucose level and other confounding factors on the variability of maximum standardized uptake value (SUVmax) in normal tissues within the same patient on two separate occasions and to suggest an ideal reference tissue. Materials and Methods We retrospectively reviewed 334 18F-FDG PET/CT scans of 167 cancer patients including 38 diabetics. All patients had two studies, on average 152 ± 68 days apart. Ten matched volumes of interest were drawn on the brain, right tonsil, blood pool, heart, lung, liver, spleen, bone marrow, fat, and iliopsoas muscle opposite third lumber vertebra away from any pathological 18F-FDG uptake to calculate SUVmax. Results SUVmax of the lungs and heart were significantly different in the two studies (P = 0.003 and P = 0.024 respectively). Only the brain uptake showed a significant moderate negative correlation with the level of blood glucose in diabetic patients (r = −0.537, P = 0.001) in the first study, while the SUVmax of other tissues showed negligible or weak correlation with the level of blood glucose in both studies. The liver showed significant moderate positive correlation with body mass index (BMI) in both studies (r = .416, P = <0.001 versus r = 0.453, P = <0.001, respectively), and blood pool activity showed significant moderate positive correlation with BMI in the first study only (r = 0.414, P = <0.001). The liver and blood pool activities showed significant moderate negative correlation with 18F-FDG uptake time in first study only (r = −0.405, P-value = <0.001; and r = −0.409, P-value = <0.001, respectively). In the multivariate analysis, the liver showed a consistent effect of the injected 18F-FDG dose and uptake duration on its SUVmax on the two occasions. In comparison, spleen and muscle showed consistent effect only of the injected dose on the two occasions. Conclusion The liver, muscle, and splenic activities showed satisfactory test/retest stability and can be used as reference activities. The spleen and muscle appear to be more optimal reference than the liver, as it is only associated with the injected dose of 18F-FDG.

AimTo evaluate the prognostic value of postoperative Tc-99m pertechnetate scanning in patients with differentiated thyroid cancer (DTC).Method Patients with pathologically proven low or intermediate-risk DTC were enrolled in this study. Postoperative Tc-99m pertechnetate scintigraphy was performed 20 min after IV of 185 MBq of Tc-99m pertechnetate Positive thyroid residual uptake was characterized as higher Tc-99m pertechnetate uptake at the thyroid bed than the surrounding background's activity. A negative residual was considered if there was no definite abnormal radioactivity at the thyroid bed. Follow-up by thyroglobulin, thyroglobulin antibodies (Tg Abs), neck ultrasound (US) and diagnostic I-131 WBS (Dx WBS) were considered the reference standard. Successful ablation outcome was considered if there was free Dx WBS, stimulated serum thyroglobulin < 1 ng/ml with negative Tg Abs, and free US Result Two hundred and two patients, mean age; of 38.8 years were retrospectively recruited in this study.Positive residual uptake at the thyroid scan was detected in 131 patients wherea the remaining 71 patients had no detectable uptake. According to the reference standard we encountered 114 and 88 cases with successful ablation and unsuccessful ablation respectively, Tc-99m pertechnetate scanning successfully detected 63 true positive and 46 true negative cases giving 72% sensitivity, 40% specificity, 48% positive predictive value and 56% negative predictive value. ConclusionIn low-and intermediate-risk DTC patients; despite the relatively high sensitivity of postoperative Tc-99m pertechnetate thyroid scan, it has low specificity and low negative predictive value so it cannot be used to predict the ablation outcome. Nucl Med Commun