Subtraction of single-photon emission computed tomography (SPECT) images has a number of clinical applications in e.g. foci localization in ictal/inter-ictal SPECT and defect detection in rest/stress cardiac SPECT. In this work, we investigated the technical performance of SPECT subtraction for the purpose of quantifying the effect of a vasoconstricting drug (angiotensin-II, or AT2) on the Tc-99m-MAA liver distribution in hepatic radioembolization using an innovative interventional hybrid C-arm scanner. Given that subtraction of SPECT images is challenging due to high noise levels and poor resolution, we compared four methods to obtain a difference image in terms of image quality and quantitative accuracy. These methods included (i) image subtraction: subtraction of independently reconstructed SPECT images, (ii) projection subtraction: reconstruction of a SPECT image from subtracted projections, (iii) projection addition: reconstruction by addition of projections as a background term during the iterative reconstruction, and (iv) image addition: simultaneous reconstruction of the difference image and the subtracted image. Digital simulations (XCAT) and phantom studies (NEMA-IQ and anthropomorphic torso) showed that all four methods were able to generate difference images but their performance on specific metrics varied substantially. Image subtraction had the best quantitative performance (activity recovery coefficient) but had the worst visual quality (contrast-to-noise ratio) due to high noise levels. Projection subtraction showed a slightly better visual quality than image subtraction, but also a slightly worse quantitative accuracy. Projection addition had a substantial bias in its quantitative accuracy which increased with less counts in the projections. Image addition resulted in the best visual image quality but had a quantitative bias when the two images to subtract contained opposing features. All four investigated methods of SPECT subtraction demonstrated the capacity to generate a feasible difference image from two SPECT images. Image subtraction is recommended when the user is only interested in quantitative values, whereas image addition is recommended when the user requires the best visual image quality. Since quantitative accuracy is most important for the dosimetric investigation of AT2 in radioembolization, we recommend using the image subtraction method for this purpose.

中文翻译：

---

放射栓塞中单光子发射计算机断层扫描 (SPECT) 的减法：四种方法的比较


单光子发射计算机断层扫描 (SPECT) 图像的减法具有许多临床应用，例如发作期/发作间期 SPECT 中的病灶定位以及静息/应激心脏 SPECT 中的缺陷检测。在这项工作中，我们研究了 SPECT 减法的技术性能，目的是使用创新的介入混合 C- 来量化肝脏放射栓塞中血管收缩药物（血管紧张素-II 或 AT2）对 Tc-99m-MAA 肝脏分布的影响。手臂扫描仪。由于噪声水平高和分辨率差，SPECT 图像的减影具有挑战性，我们在图像质量和定量精度方面比较了四种获得差异图像的方法。这些方法包括 (i) 图像减法：独立重建的 SPECT 图像的减法，(ii) 投影减法：从减法投影重建 SPECT 图像，(iii) 投影加法：在迭代重建期间通过添加投影作为背景项来重建，以及（iv）图像相加：差值图像和相减图像的同时重建。数字模拟 (XCAT) 和模型研究（NEMA-IQ 和拟人躯干）表明，所有四种方法都能够生成差异图像，但它们在特定指标上的性能差异很大。图像减法具有最佳的定量性能（活动恢复系数），但由于噪声水平较高，视觉质量（对比度与噪声比）最差。投影减法的视觉质量比图像减法稍好，但定量精度也稍差。投影加法在其定量准确性方面存在很大偏差，该偏差随着预测计数的减少而增加。 图像相加产生了最佳的视觉图像质量，但当要减去的两个图像包含相反的特征时，会产生定量偏差。所有四种研究的 SPECT 减影方法都证明了从两幅 SPECT 图像生成可行的差异图像的能力。当用户只对定量值感兴趣时，建议使用图像减法，而当用户需要最佳视觉图像质量时，建议使用图像添加。由于定量准确性对于放射栓塞中 AT2 的剂量测定研究最为重要，因此我们建议为此目的使用图像减法方法。