The objective of the study was to make a quantitative comparison of 24-h thyroid uptake calculated by γ camera-based and thyroid uptake probe-based methods after administration of a diagnostic 131 I capsule in patients with benign thyroid disorders. Methods: The study group comprised 66 patients, of whom 26 were male (28-67 y old) and 40 female (20-65 y old). These patients had benign thyroid disorders (primarily hyperthyroidism [thyrotoxicosis]), most of whom had been referred for evaluation before radioiodine treatment. 131 I (25 μCi [925 MBq]) was administered, and 24-h thyroid uptake was calculated using a probe-based method and a camera-based method with a medium-energy parallel-hole collimator. The paired t test was used to check the variation in values obtained by these 2 methodologies. Result: Of the 66 patients included in this study, 45 had clinical thyrotoxicosis and 21 had nonthyrotoxic multinodular goiter. In the group with thyrotoxicosis, neck uptake ranged from 40.13% to 97.1% by the probe-based method and 36.89% to 95.9% by the camera-based method. In the group with clinically nonthyrotoxic goiter, neck uptake ranged from 1.4% to 38.4% by the probe-based method and 0.6% to 34.8% by the camera-based method. Paired t testing was performed on both groups of patients, and P values were less than 0.05, showing good agreement within the 2 groups of data. Conclusion: The camera-based method is a good substitute for the probe-based method; though not producing identical results, the former could be used to derive useful quantitative information on thyroid function.
The aim was to estimate the physiological standardized uptake values (SUVs) on 68Ga-DOTATATE PET-computed tomography (CT) in normal organs and metastatic tumor lesions (both standard and delayed), and correlating the uptake values and ratios with Krenning Scores (K-score) in patients with metastatic/advanced neuroendocrine tumors (NETs) undergoing PET-CT studies for their management work-up. A total of 32 patients of metastatic NET with 95 discrete tumor lesions were included in this analysis. These patients underwent standard whole-body PET-CT following injection of 2–3 mCi (74–111 MBq) of 68Ga-DOTATATE at 1–1.5 h. The normal physiological SUVmean of the liver and spleen and SUVmax and SUVmean of tumor lesions were estimated by an in-built automated procedure. These patients also underwent a delayed scan (2.5–3 h) and the same parameters were obtained for the delayed study. The tumorous lesions were further classified on the basis of K-score, and this was correlated with the mean SUVmax on both early and delayed scans. SUVmean ratios (tumor-to-liver and tumor-to-spleen) were also calculated for both time-points and correlated with individual K-scores. In lesions with K-score 4, the mean SUVmax was 32.5 in early and 30.5 in delayed scan, for lesions with K-score of 3 and 2, the mean SUVmax were 17.3, 20, and 9.3, 9.2, respectively, while in K-score 1 (n = 1), the delayed mean SUVmax was found to be more than early mean SUVmax (3.2 to 2.3). Statistical significance was evaluated by paired t test, and the changes in SUVmax was found to be statistically insignificant (P > 0.05) in all 3 K-scores. The paired t test was also performed between early and delayed tumor/liver and tumor/spleen mean SUVmean ratios, and no significant changes were observed across all K scores. The mean SUVmean values of the liver in the standard 1-h scan and delayed scans were 8.05 (range: 3–15) and 8.17 (range: 3.2–16), while for spleen, the values were 18 (range: 8.4–36.7) and 20 (range: 10–38.6), respectively. Statistically significant changes were observed in delayed spleen SUVmean values compared to the early scan (P < 0.05), while for liver SUVmean, the difference was not significant. Thus, in the present study, the SUVmax and SUVmean (range and mean values) for normal liver and spleen, and malignant NET lesions, and tumor-to-liver and tumor-to-spleen SUVmean ratios of different K-scores were generated. As could be theoretically expected in receptor-based PET-CT, there was no significant change in the delayed scan compared to the standard 1–1.5 h values
The objective of this work was to evaluate the necessity of a thyroid phantom in counting a standard capsule during estimation of iodine-131 thyroid uptake using gamma camera methods. For this, camera-based uptake was calculated taking a standard capsule within a thyroid phantom, as well as a standard capsule (without phantom) placed at 5, 10, and 15 cm from the face of the collimator. The values obtained in each setting were compared with the traditional standard thyroid probe-based method. Among these four sets of values, that with the phantom was the closest to the reference probe-based uptake values. Among those without the phantom, the camera-based uptake with the standard at 15 cm from the face of the collimator was closer to the standard probe method. However, as the image at 15 cm would give poor resolution, it would not be feasible to adopt this method for clinical routine. Thus, to conclude, for calculating camera-based uptake, a standard capsule in the phantom gives the best comparable values to the standard probe-based method, indicating the need for the phantom when adopting the gamma camera-based methodology.
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