Nagel C C A, Bosmans G, Dekker A L A J, Ollers M C, De Ruysscher D K M, Lambin P, Minken A W H, Lang N, Schäfers K P
Department of Radiation Oncology(MAASTRO), GROW University Hospital Maastricht, Maastricht, The Netherlands.
Med Phys. 2006 Jun;33(6):1840-7. doi: 10.1118/1.2198170.
The motion of lung tumors with respiration causes difficulties in the imaging with computed tomography (CT) and positronemitted tomography (PET). Since an accurate knowledge of the position of the tumor and the surrounding tissues is needed for radiation treatment planning, it is important to improve CT/PET image acquisition. The purpose of this study was to evaluate the potential to improve image acquisition using phased attenuation correction in respiration correlated CT/PET, where data of both modalities were binned retrospectively. Respiration correlated scans were made on a Siemens Biograph Sensation 16 CT/PET scanner which was modified to make a low pitch CT scan and list mode PET scan possible. A lollipop phantom was used in the experiments. The sphere with a diameter of 3.1 cm was filled with approximately 20 MBq 18F-FDG. Three longitudinal movement amplitudes were tested: 2.5, 3.9, and 4.8 cm. After collection of the raw CT data, list mode PET data, and the respiratory signal CT/PET images were binned to ten phases with the help of in-house-built software. Each PET phase was corrected for attenuation with CT data of the corresponding phase. For comparison, the attenuation correction was also performed with nonrespiration correlated (non-RC) CT data. The volume and the amplitude of the movement were calculated for every phaseof both the CT and PET data (with phased attenuation correction). Maximum and average activity concentrations were compared between the phased and nonphased attenuation corrected PET. With a standard non-RC CT/PET scan, the volume was underestimated by as much as 46% in CT and the PET volume was overestimated to 370%. The volumes found with RC-CT/PET scanning had average deviations of 1.9% (+/- 4.8%) and 1.5% (+/- 3.4%) from the actual volume, for the CT and PET volumes, respectively. Evaluation of the maximum activity concentration showed a clear displacement in the images with non-RC attenuation correction, and activity values were on average14% (+/- 12%) lower than with phased attenuation correction. The standard deviation of the maximum activity values found in the different phases was a factor of 10 smaller when phased attenuation correction was applied. In this phantom study, we have shown that a combination of respiration correlated CT/PET scanning with application of phased attenuation correction can improve the imaging of moving objects and can lead to improved volume estimation and a more precise localization and quantification of the activity.
肺部肿瘤随呼吸的运动给计算机断层扫描（CT）和正电子发射断层扫描（PET）成像带来了困难。由于放射治疗计划需要准确了解肿瘤及周围组织的位置，因此改进CT/PET图像采集很重要。本研究的目的是评估在呼吸相关CT/PET中使用相位衰减校正来改进图像采集的潜力，其中两种模态的数据都是回顾性分箱的。在一台经改装以实现低螺距CT扫描和列表模式PET扫描的西门子Biograph Sensation 16 CT/PET扫描仪上进行呼吸相关扫描。实验中使用了一个棒棒糖体模。直径为3.1 cm的球体填充了约20 MBq的18F-FDG。测试了三个纵向运动幅度：2.5、3.9和4.8 cm。在收集原始CT数据、列表模式PET数据后，借助自制软件将呼吸信号CT/PET图像分箱为十个阶段。每个PET阶段用相应阶段的CT数据进行衰减校正。为作比较，也用非呼吸相关（非RC）CT数据进行衰减校正。计算CT和PET数据每个阶段（采用相位衰减校正）的运动体积和幅度。比较相位校正和未相位校正PET的最大和平均活度浓度。在标准的非RC CT/PET扫描中，CT体积低估多达46%，PET体积高估至370%。RC-CT/PET扫描得到的CT和PET体积与实际体积的平均偏差分别为1.9%（±4.8%）和1.5%（±3.4%）。对最大活度浓度的评估显示，在非RC衰减校正的图像中有明显位移，活度值平均比相位衰减校正时低14%（±12%）。应用相位衰减校正时，不同阶段发现的最大活度值的标准差小10倍。在这个体模研究中，我们表明呼吸相关CT/PET扫描与相位衰减校正相结合可以改善运动物体的成像，并能改进体积估计以及更精确地定位和定量活度。
