Pattern Recognition Laboratory, University of Erlangen-Nuremberg, Erlangen, Germany.
J Nucl Med. 2010 Jun;51(6):921-8. doi: 10.2967/jnumed.109.071571. Epub 2010 May 19.
We present a calibration method of a clinical SPECT/CT device for quantitative (99m)Tc 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 (99m)Tc-diphosponate.
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 (99m)Tc-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.
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%.
Current commercially available SPECT/CT technology using OSEM-3D reconstruction, scatter correction, and CT-based attenuation correction allows quantification of (99m)Tc 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.
我们提出了一种临床 SPECT/CT 设备定量（99m）Tc SPECT 的校准方法。我们使用了一种商用重建软件包，包括有序子集期望最大化（OSEM）与深度相关的 3 维分辨率恢复（OSEM-3D）、基于 CT 的衰减校正和散射校正。我们在体模研究中验证了该方法，并将其应用于注射（99m）Tc-二膦酸盐的患者图像。
为了从 SPECT 重建图像中得出绝对定量值，我们进行了以下 3 个步骤。在步骤 1 中，我们使用模拟来描述 SPECT/CT 系统，并为各种成像参数设置推导发射恢复值。我们模拟了不同直径的球体，并关注活动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性。在步骤 2 中，我们使用大圆柱体体模对我们的临床 SPECT/CT 系统与井计数器进行了交叉校准。这一步提供了从图像计数到 kBq/mL 的映射。在步骤 3 中，应用步骤 1 和 2 的校正因子到重建图像。我们使用具有可变大小球体的圆柱体体模来验证该方法。为了体内验证，对 16 名接受骨盆（99m）Tc-二膦酸盐 SPECT/CT 检查的患者的 SPECT/CT 数据集进行了采集，包括膀胱。患者尿液中的放射性浓度作为金标准。计算了平均定量准确性和 SEs。
在体模实验中，以绝对术语量化放射性浓度的平均准确性在 3.6%（SE，8.0%）范围内，95%置信区间为-19.4%至+12.2%。在患者研究中，平均准确性在 1.1%（SE，8.4%）范围内，95%置信区间为-15.4%至+17.5%。
当前商用的使用 OSEM-3D 重建、散射校正和基于 CT 的衰减校正的 SPECT/CT 技术允许在体模中以绝对术语定量（99m）Tc 放射性浓度，准确性在 3.6%范围内，在患者中以绝对术语定量，准确性在 1.1%范围内，重点是膀胱。这为 SPECT 定量进入常规临床领域提供了机会。然而，在临床环境中进行绝对定量时，由于不可避免的测量误差引起的不准确性是一个主要因素。
