Kerckhaert Camiel E M, de Jong Hugo W A M, Meddens Marjolein B M, van Rooij Rob, Smits Maarten L J, Rakvongthai Yothin, Dietze Martijn M A
Radiology and Nuclear Medicine, Utrecht University and University Medical Center Utrecht, P.O. Box 85500, 3508 GA, Utrecht, Netherlands.
Chulalongkorn University Biomedical Imaging Group, Department of Radiology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.
EJNMMI Phys. 2024 Aug 15;11(1):72. doi: 10.1186/s40658-024-00675-7.
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.
单光子发射计算机断层扫描（SPECT）图像相减在多种临床应用中具有重要作用，例如在发作期/发作间期SPECT中定位病灶以及在静息/负荷心肌SPECT中检测缺损。在本研究中，我们使用创新的介入式混合C型臂扫描仪，研究了SPECT相减的技术性能，目的是量化血管收缩药物（血管紧张素II，或AT2）对肝动脉栓塞术中Tc-99m-MAA肝脏分布的影响。鉴于SPECT图像相减因噪声水平高和分辨率差而具有挑战性，我们比较了四种方法在图像质量和定量准确性方面获取差异图像的效果。这些方法包括：（i）图像相减：独立重建的SPECT图像相减；（ii）投影相减：从相减后的投影重建SPECT图像；（iii）投影相加：在迭代重建过程中通过添加投影作为背景项进行重建；（iv）图像相加：同时重建差异图像和相减图像。
数字模拟（XCAT）和体模研究（NEMA-IQ和仿真人体躯干）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表现差异很大。图像相减具有最佳的定量性能（活性恢复系数），但由于噪声水平高，视觉质量最差（对比度噪声比）。投影相减的视觉质量略优于图像相减，但定量准确性也略差。投影相加在定量准确性方面存在较大偏差，且随着投影计数减少而增加。图像相加产生的视觉图像质量最佳，但当要相减的两幅图像包含相反特征时存在定量偏差。
所有四种研究的SPECT相减方法都证明了从两幅SPECT图像生成可行差异图像的能力。当用户仅对定量值感兴趣时，建议使用图像相减；而当用户需要最佳视觉图像质量时，建议使用图像相加。由于定量准确性对于肝动脉栓塞术中AT2的剂量学研究最为重要，因此我们建议为此目的使用图像相减方法。
