To investigate the optimal threshold for measuring thyroid volume in patients with Grave's hyperthyroidism (GH) by SPECT/CT. A 53 mL butterfly-shaped hollow container made of two 45-degree transparent elbows was put into a NEMA IEC phantom tank. The butterfly-shaped container and the tank were then filled with Na99mTcO4 of different radioactive concentrations, respectively, which could simulate thyroid gland with GH by different target-to-background ratios (T/B) (200:1, 600:1, 1000:1). The different T/B of planar imaging and SPECT/CT were acquired by a Discovery NM/CT 670 Pro SPECT/CT. With Thyroid software (Version 4.0) of GE-Xeleris workstation, the region of the thyroid gland in planar imaging was delineated. The thyroid area and average long diameter of both lobes were substituted into the Allen formula to calculate the thyroid volume. The calculation error was compared with the actual volume. Q-Metrix software was used to perform CT-based attenuation correction, scatter correction, resolution recovery. Ordered-subsets expectation maximization was used to reconstruct SPECT data. 20%, 25%, 30%, 40%, 50%, 60% thresholds were selected to automatically delineate the volume of interest and compared with the real volume, which determinated the optimal threshold. We measured the thyroid volume of 40 GH patients using the threshold and compared the volumes obtained by planar imaging and ultrasound three-dimensional. The differences of the volumes with different T/B and thresholds were compared by the ANOVA and least significant difference t test. The volumes delineated by SPECT/CT were evaluated using ANOVA, least significant difference t test, correlation analysis and, linear regression and Bland–Altman concordance test plot. The differences and consistency of thyroid volume were compared among the above three methods. There was no significant difference in the results between different T/B models (P > 0.05). The thyroid volume calculated by the planar imaging formula method was higher than the real volume, with an average overestimation of 22.81%. The volumes delineated by SPECT/CT threshold automatically decreased while the threshold increased. There were significant differences between groups with different thresholds (P < 0.001). With an average error of 3.73%, the thyroid volume analyzed by the threshold of 25% was close to the results of ultrasound measurement (P > 0.05). Thyroid volume measured by planar imaging method was significantly higher than ultrasound and SPECT/CT threshold automatic delineation method (P < 0.05). The agreement between the SPECT/CT 25% threshold and ultrasound (r = 0.956, b = 0.961) was better than that between the planar imaging and ultrasound (r = 0.590, b = 0.574). The Bland–Altman plot also showed that the thyroid volume measured by the 25% threshold automatic delineation method was in good agreement with the ultrasound measurement. The T/B has no effect on the measurement of thyroid volume in GH patients; planar imaging method can significantly overestimate thyroid volume in GH patients, and 25% threshold automatic delineation method can obtain more accurate thyroid volume in GH patients.

中文翻译：

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Graves甲亢定量SPECT/CT甲状腺体积测量最佳阈值的确定

探讨 SPECT/CT 测量格雷夫氏甲状腺功能亢进症 (GH) 患者甲状腺体积的最佳阈值。将由两个 45 度透明弯头制成的 53 mL 蝴蝶形中空容器放入 NEMA IEC 模型罐中。然后在蝴蝶形容器和罐中分别填充不同放射性浓度的Na99mTcO4，可以通过不同的靶背景比（T/B）（200:1、600:1、1000）用GH模拟甲状腺。 ：1）。平面成像和 SPECT/CT 的不同 T/B 由 Discovery NM/CT 670 Pro SPECT/CT 采集。利用GE-Xeleris工作站的Thyroid软件（4.0版），在平面成像中勾画出甲状腺区域。将甲状腺面积和两叶平均长径代入Allen公式计算甲状腺体积。将计算误差与实际体积进行比较。使用Q-Metrix软件进行基于CT的衰减校正、散射校正、分辨率恢复。使用有序子集期望最大化来重建 SPECT 数据。选择20%、25%、30%、40%、50%、60%阈值自动勾画感兴趣体积，并与真实体积进行比较，确定最佳阈值。我们使用阈值测量了40名GH患者的甲状腺体积，并比较了平面成像和超声三维获得的体积。通过方差分析和最小显着差异t检验比较不同T/B和阈值的体积差异。SPECT/CT 描绘的体积使用方差分析、最小显着差异 t 检验、相关分析、线性回归和 Bland-Altman 一致性检验图进行评估。比较上述三种方法甲状腺体积的差异和一致性。不同T/B模型结果差异无统计学意义（P>0.05）。平面成像公式法计算的甲状腺体积高于真实体积，平均高估22.81%。当阈值增加时，SPECT/CT 阈值描绘的体积自动减小。不同阈值组之间存在显着差异（P < 0.001）。以25%阈值分析的甲状腺体积与超声测量结果比较接近（P>0.05），平均误差为3.73%。平面成像法测量的甲状腺体积显着高于超声和SPECT/CT阈值自动勾画法（P < 0.05）。SPECT/CT 25%阈值和超声之间的一致性（r = 0.956，b = 0.961）优于平面成像和超声之间的一致性（r = 0.590，b = 0.574）。Bland-Altman图还显示，25%阈值自动勾画法测量的甲状腺体积与超声测量结果吻合较好。T/B对GH患者甲状腺体积的测量没有影响；平面成像方法会显着高估GH患者的甲状腺体积，25%阈值自动勾画法可以获得更准确的GH患者甲状腺体积。