Department of Radiation Oncology, Dana-Farber/Brigham & Women’s Cancer Center, Boston, MA, USA.
J Appl Clin Med Phys. 2011 Nov 15;12(4):3502. doi: 10.1120/jacmp.v12i4.3502.
For PET/CT, fast CT acquisition time can lead to errors in attenuation correction, particularly at the lung/diaphragm interface. Gated 4D PET can reduce motion artifacts, though residual artifacts may persist depending on the CT dataset used for attenuation correction. We performed phantom studies to evaluate 4D PET images of targets near a density interface using three different methods for attenuation correction: a single 3D CT (3D CTAC), an averaged 4D CT (CINE CTAC), and a fully phase matched 4D CT (4D CTAC). A phantom was designed with two density regions corresponding to diaphragm and lung. An 8 mL sphere phantom loaded with 18F-FDG was used to represent a lung tumor and background FDG included at an 8:1 ratio. Motion patterns of sin(x) and sin4(x) were used for dynamic studies. Image data was acquired using a GE Discovery DVCT-PET/CT scanner. Attenuation correction methods were compared based on normalized recovery coefficient (NRC), as well as a novel quantity "fixed activity volume" (FAV) introduced in our report. Image metrics were compared to those determined from a 3D PET scan with no motion present (3D STATIC). Values of FAV and NRC showed significant variation over the motion cycle when corrected by 3D CTAC images. 4D CTAC- and CINE CTAC-corrected PET images reduced these motion artifacts. The amount of artifact reduction is greater when the target is surrounded by lower density material and when motion was based on sin4(x). 4D CTAC reduced artifacts more than CINE CTAC for most scenarios. For a target surrounded by water equivalent material, there was no advantage to 4D CTAC over CINE CTAC when using the sin(x) motion pattern. Attenuation correction using both 4D CTAC or CINE CTAC can reduce motion artifacts in regions that include a tissue interface such as the lung/diaphragm border. 4D CTAC is more effective than CINE CTAC at reducing artifacts in some, but not all, scenarios.
对于 PET/CT，快速 CT 采集时间可能导致衰减校正错误，特别是在肺/膈肌界面。门控 4D PET 可以减少运动伪影，但根据用于衰减校正的 CT 数据集，残留伪影可能仍然存在。我们进行了体模研究，使用三种不同的衰减校正方法评估密度界面附近目标的 4D PET 图像：单次 3D CT（3D CTAC）、平均 4D CT（CINE CTAC）和完全相位匹配 4D CT（4D CTAC）。设计了一个具有两个密度区域的体模，分别对应于膈肌和肺。使用装有 18F-FDG 的 8mL 球体体模来代表肺肿瘤，背景 FDG 以 8:1 的比例包含。使用 sin(x) 和 sin4(x) 运动模式进行动态研究。图像数据是使用 GE Discovery DVCT-PET/CT 扫描仪采集的。根据归一化恢复系数（NRC）以及我们报告中引入的新量“固定活性体积”（FAV）比较衰减校正方法。将图像指标与不存在运动的 3D PET 扫描（3D STATIC）确定的指标进行比较。使用 3D CTAC 图像校正时，FAV 和 NRC 的值在运动周期内有很大变化。4D CTAC 和 CINE CTAC 校正的 PET 图像减少了这些运动伪影。当目标周围是密度较低的材料且运动基于 sin4(x)时，减少伪影的量更大。对于大多数情况，4D CTAC 比 CINE CTAC 减少伪影更多。对于被水当量材料包围的目标，使用 sin(x)运动模式时，4D CTAC 相对于 CINE CTAC 没有优势。使用 4D CTAC 或 CINE CTAC 进行衰减校正可以减少包括肺/膈肌边界等组织界面在内的区域的运动伪影。4D CTAC 在某些但不是所有情况下比 CINE CTAC 更有效地减少伪影。
