Quantitative Accuracy of Clinical 99mTc SPECT/CT Using Ordered-Subset Expectation Maximization with 3-Dimensional Resolution Recovery, Attenuation, and Scatter Correction
Quantitative Accuracy of Clinical 99mTc SPECT/CT Using Ordered-Subset Expectation Maximization with 3-Dimensional Resolution Recovery, Attenuation, and Scatter Correction
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DOI：
10.2967/jnumed.109.071571
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发表时间：
2010-06-01
影响因子：
9.3
通讯作者：
Kuwert, Torsten
中科院分区：
文献类型：
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作者：
Zeintl, Johannes;Vija, Alexander Hans;Kuwert, Torsten
我们提出了一种用于定量Tc-99m SPECT的临床SPECT/CT设备的校准方法。我们使用市售的重建包，包括有序子集期望最大化（OSEM）与深度相关的三维分辨率恢复（OSEM- 3d），基于ct的衰减校正和散射校正。我们在幻影研究中验证了该方法，并将其应用于注射tc -99m-二磷酸酯的患者的图像。方法：通过3个步骤对SPECT重建图像进行绝对定量计算。在步骤1中，我们使用模拟来表征SPECT/CT系统，并得出各种成像参数设置的发射恢复值。我们模拟了不同直径的球体，重点研究了活度估计误差对结构尺寸和位置、像素大小、计数密度和重建参数的依赖关系。在第2步中，我们使用一个大圆柱体幻影对临床SPECT/CT系统与井计数器进行交叉校准。这一步提供了从图像计数到kBq/mL的映射。在步骤3中，将步骤1和步骤2的校正因子应用于重构图像。我们使用了一个具有可变大小球体的圆柱体模型来验证该方法。为了在体内验证，我们获得了16例骨盆（包括膀胱）接受99mtc -二磷酸盐SPECT/CT检查的患者的SPECT/CT数据集。患者尿液中的放射性浓度作为金标准。计算平均定量准确度和se。结果：模拟实验中，放射性浓度绝对定量的平均准确度在3.6%以内（正确率为8.0%），95%置信区间为-19.4% ~ + 12.2%。在患者研究中，平均准确率在1.1%以内（SE, 8.4%）， 95%置信区间在-15.4%和+ 17.5%之间。结论：目前市售的SPECT/CT技术使用OSEM-3D重建、散射校正和基于CT的衰减校正，可以量化Tc-99m放射性浓度的绝对值，在幻影中为3.6%，在膀胱集中的患者中为1.1%。这为SPECT定量进入常规临床领域提供了机会。尽管如此，由不可避免的测量误差引起的不精确性是临床设置中绝对定量的主要因素。
We present a calibration method of a clinical SPECT/CT device for quantitative Tc-99m SPECT. We use a commercially available reconstruction package including ordered-subset expectation maximization (OSEM) with depth-dependent 3-dimensional resolution recovery (OSEM-3D), CT-based attenuation correction, and scatter correction. We validated the method in phantom studies and applied it to images from patients injected with Tc-99m-diphosponate. Methods: The following 3 steps were performed to derive absolute quantitative values from SPECT reconstructed images. In step 1, we used simulations to characterize the SPECT/CT system and derive emission recovery values for various imaging parameter settings. We simulated spheres of varying diameters and focused on the dependencies of activity estimation errors on structure size and position, pixel size, count density, and reconstruction parameters. In step 2, we cross-calibrated our clinical SPECT/CT system with the well counter using a large cylinder phantom. This step provided the mapping from image counts to kBq/mL. And in step 3, correction factors from steps 1 and 2 were applied to reconstructed images. We used a cylinder phantom with variable-sized spheres for verification of the method. For in vivo validation, SPECT/CT datasets from 16 patients undergoing 99mTc-diphosponate SPECT/CT examinations of the pelvis including the bladder were acquired. The radioactivity concentration in the patients' urine served as the gold standard. Mean quantitative accuracy and SEs were calculated. Results: In the phantom experiments, the mean accuracy in quantifying radioactivity concentration in absolute terms was within 3.6% (SE, 8.0%), with a 95% confidence interval between -19.4% and + 12.2%. In the patient studies, the mean accuracy was within 1.1% (SE, 8.4%), with a 95% confidence interval between -15.4% and + 17.5%. Conclusion: Current commercially available SPECT/CT technology using OSEM-3D reconstruction, scatter correction, and CT-based attenuation correction allows quantification of Tc-99m radioactivity concentration in absolute terms within 3.6% in phantoms and 1.1% in patients with a focus on the bladder. This opens up the opportunity of SPECT quantitation entering the routine clinical arena. Still, the imprecision caused by unavoidable measurement errors is a dominant factor for absolute quantitation in a clinical setup.