Chan Chung, Dey Joyoni, Grobshtein Yariv, Wu Jing, Liu Yi-Hwa, Lampert Rachel, Sinusas Albert J, Liu Chi
Department of Diagnostic Radiology, Yale University, New Haven, Connecticut 06520.
Department of Physics and Astronomy, Medical Physics Program, Louisiana State University, Baton Rouge, Louisiana 70803.
Med Phys. 2016 Jan;43(1):213. doi: 10.1118/1.4938098.
A dedicated cardiac hybrid single photon emission computed tomography (SPECT)/CT scanner that uses cadmium zinc telluride detectors and multiple pinhole collimators for stationary acquisition offers many advantages. However, the impact of the reconstruction system matrix (SM) dimension on the reconstructed image quality from truncated projections and 19 angular samples acquired on this scanner has not been extensively investigated. In this study, the authors aimed to investigate the impact of the dimensions of SM and the use of body contour derived from adjunctive CT imaging as an object support in reconstruction on this scanner, in relation to background extracardiac activity.
The authors first simulated a generic SPECT/CT system to image four NCAT phantoms with various levels of extracardiac activity and compared the reconstructions using SM in different dimensions and with/without body contour as a support for quantitative evaluations. The authors then compared the reconstructions of 18 patient studies, which were acquired on a GE Discovery NM570c scanner following injection of different radiotracers, including (99m)Tc-Tetrofosmin and (123)I-mIBG, comparing the scanner's default SM that incompletely covers the body with a large SM that incorporates a patient specific full body contour.
The simulation studies showed that the reconstructions using a SM that only partially covers the body yielded artifacts on the edge of the field of view (FOV), overestimation of activity and increased nonuniformity in the blood pool for the phantoms with higher relative levels of extracardiac activity. However, the impact on the quantitative accuracy in the high activity region, such as the myocardium, was subtle. On the other hand, an excessively large SM that enclosed the entire body alleviated the artifacts and reduced overestimation in the blood pool, but yielded slight underestimation in myocardium and defect regions. The reconstruction using the larger SM with body contour yielded the most quantitatively accurate results in all the regions of interest for a range of uptake levels in the extracardiac regions. In patient studies, the SM incorporating patient specific body contour minimized extracardiac artifacts, yielded similar myocardial activity, lower blood pool activity, and subsequently improved myocardium-to-blood pool contrast (p < 0.0001) by an average of 7% (range 0%-18%) across all the patients, compared to the reconstructions using the scanner's default SM.
Their results demonstrate that using a large SM that incorporates a CT derived body contour in the reconstruction could improve quantitative accuracy within the FOV for clinical studies with high extracardiac activity.
一种专用的心脏混合单光子发射计算机断层扫描（SPECT）/CT扫描仪，其使用碲化镉锌探测器和多个针孔准直器进行静态采集，具有诸多优势。然而，重建系统矩阵（SM）维度对在此扫描仪上采集的截断投影和19个角度样本所重建图像质量的影响尚未得到广泛研究。在本研究中，作者旨在探讨SM维度以及在重建过程中使用源自辅助CT成像的身体轮廓作为物体支撑对该扫描仪上与心外活动背景相关的影响。
作者首先模拟了一个通用的SPECT/CT系统，对四个具有不同心外活动水平的NCAT体模进行成像，并比较了使用不同维度的SM以及有无身体轮廓作为支撑进行重建以进行定量评估。然后，作者比较了18例患者研究的重建结果，这些研究是在GE Discovery NM570c扫描仪上注射不同放射性示踪剂后进行的，包括（99m）Tc - 替曲膦和（123）I - 间碘苄胍，将扫描仪默认的未完全覆盖身体的SM与纳入患者特定全身轮廓的大SM进行比较。
模拟研究表明，对于心外活动相对水平较高的体模，使用仅部分覆盖身体的SM进行重建会在视野（FOV）边缘产生伪影、高估活性并增加血池中的不均匀性。然而，对高活性区域（如心肌）定量准确性的影响较为细微。另一方面，过大的包围整个身体的SM减轻了伪影并减少了血池中的高估，但在心肌和缺损区域产生了轻微的低估。对于心外区域一系列摄取水平，使用带有身体轮廓的较大SM进行重建在所有感兴趣区域产生了最定量准确的结果。在患者研究中，与使用扫描仪默认SM的重建相比，纳入患者特定身体轮廓的SM使心外伪影最小化，产生了相似的心肌活性、更低的血池活性，并随后平均提高了心肌与血池对比度（p < 0.0001），所有患者的对比度提高幅度为7%（范围0% - 18%）。
他们的结果表明，在重建过程中使用纳入CT衍生身体轮廓的大SM可以提高心外活动较高的临床研究中FOV内的定量准确性。
