Departamento de Bioingeniería e Ingeniería Aeroespacial, Universidad Carlos III de Madrid, Madrid, Spain.
Phys Med Biol. 2012 May 7;57(9):2477-90. doi: 10.1088/0031-9155/57/9/2477. Epub 2012 Apr 5.
We evaluate the accuracy of scaling CT images for attenuation correction of PET data measured for bone. While the standard tri-linear approach has been well tested for soft tissues, the impact of CT-based attenuation correction on the accuracy of tracer uptake in bone has not been reported in detail. We measured the accuracy of attenuation coefficients of bovine femur segments and patient data using a tri-linear method applied to CT images obtained at different kVp settings. Attenuation values at 511 keV obtained with a (68)Ga/(68)Ge transmission scan were used as a reference standard. The impact of inaccurate attenuation images on PET standardized uptake values (SUVs) was then evaluated using simulated emission images and emission images from five patients with elevated levels of FDG uptake in bone at disease sites. The CT-based linear attenuation images of the bovine femur segments underestimated the true values by 2.9 ± 0.3% for cancellous bone regardless of kVp. For compact bone the underestimation ranged from 1.3% at 140 kVp to 14.1% at 80 kVp. In the patient scans at 140 kVp the underestimation was approximately 2% averaged over all bony regions. The sensitivity analysis indicated that errors in PET SUVs in bone are approximately proportional to errors in the estimated attenuation coefficients for the same regions. The variability in SUV bias also increased approximately linearly with the error in linear attenuation coefficients. These results suggest that bias in bone uptake SUVs of PET tracers ranges from 2.4% to 5.9% when using CT scans at 140 and 120 kVp for attenuation correction. Lower kVp scans have the potential for considerably more error in dense bone. This bias is present in any PET tracer with bone uptake but may be clinically insignificant for many imaging tasks. However, errors from CT-based attenuation correction methods should be carefully evaluated if quantitation of tracer uptake in bone is important.
我们评估了用于骨 PET 数据衰减校正的 CT 图像缩放的准确性。虽然标准的三线性方法已经在软组织中得到了很好的测试，但 CT 基衰减校正对骨示踪剂摄取准确性的影响尚未详细报道。我们使用应用于不同 kVp 设置下获得的 CT 图像的三线性方法测量了牛股骨段和患者数据的衰减系数的准确性。使用（68）Ga/（68）Ge 透射扫描获得的 511keV 处的衰减值作为参考标准。然后，使用模拟发射图像和来自五个在疾病部位骨中摄取 FDG 水平升高的患者的发射图像评估了不准确的衰减图像对 PET 标准化摄取值（SUV）的影响。牛股骨段的基于 CT 的线性衰减图像无论 kVp 如何都低估了松质骨的真实值 2.9 ± 0.3%。对于皮质骨，低估范围从 140kVp 时的 1.3%到 80kVp 时的 14.1%。在 140kVp 时的患者扫描中，所有骨区域的平均低估约为 2%。敏感性分析表明，骨中 PET SUV 的误差与相同区域估计衰减系数的误差大致成比例。SUV 偏差的可变性也随着线性衰减系数误差的增加大致呈线性增加。这些结果表明，当使用 140kVp 和 120kVp 的 CT 扫描进行衰减校正时，PET 示踪剂在骨中的摄取 SUV 的偏差范围为 2.4%至 5.9%。较低的 kVp 扫描在致密骨中可能存在更大的误差。这种偏差存在于任何具有骨摄取的 PET 示踪剂中，但对于许多成像任务可能并不重要。但是，如果定量测定骨中示踪剂摄取很重要，则应仔细评估基于 CT 的衰减校正方法的误差。
