Department of Radiation Oncology, University of Arizona Health Science Center, Tucson, AZ 85724, USA.
Radiat Oncol. 2007 Feb 24;2:10. doi: 10.1186/1748-717X-2-10.
To quantify volumetric and positional aliasing during non-gated fast- and slow-scan acquisition CT in the presence of 3D target motion.
Single-slice fast, single-slice slow, and multi-slice fast scan helical CTs were acquired of dynamic spherical targets (1 and 3.15 cm in diameter), embedded in an anthropomorphic phantom. 3D target motions typical of clinically observed tumor motion parameters were investigated. Motion excursions included +/- 5, +/- 10, and +/- 15 mm displacements in the S-I direction synchronized with constant displacements of +/- 5 and +/- 2 mm in the A-P and lateral directions, respectively. For each target, scan technique, and motion excursion, eight different initial motion-to-scan phase relationships were investigated.
An anticipated general trend of target volume overestimation was observed. The mean percentage overestimation of the true physical target volume typically increased with target motion amplitude and decreasing target diameter. Slow-scan percentage overestimations were larger, and better approximated the time-averaged motion envelope, as opposed to fast-scans. Motion induced centroid misrepresentation was greater in the S-I direction for fast-scan techniques, and transaxial direction for the slow-scan technique. Overestimation is fairly uniform for slice widths < 5 mm, beyond which there is gross overestimation.
Non-gated CT imaging of targets describing clinically relevant, 3D motion results in aliased overestimation of the target volume and misrepresentation of centroid location, with little or no correlation between the physical target geometry and the CT-generated target geometry. Slow-scan techniques are a practical method for characterizing time-averaged target position. Fast-scan techniques provide a more reliable, albeit still distorted, target margin.
在存在 3D 目标运动的情况下，量化非门控快速和慢速扫描采集 CT 中的容积和位置混叠。
使用动态球形目标（直径为 1 厘米和 3.15 厘米）对单切片快速、单切片慢速和多切片快速螺旋 CT 进行扫描，这些目标嵌入在人体模型中。研究了与 A-P 和侧向方向上的 +/- 2 毫米恒定位移同步的 +/- 5 和 +/- 10 毫米的 3D 目标运动，这些运动幅度代表了临床上观察到的肿瘤运动参数。对于每个目标、扫描技术和运动幅度，研究了八个不同的初始运动到扫描相位关系。
观察到目标体积高估的预期总体趋势。真实物理目标体积的平均百分比高估通常随着目标运动幅度的增加和目标直径的减小而增加。与快速扫描相比，慢速扫描的百分比高估更大，并且更好地近似于时间平均运动包络。对于快速扫描技术，运动引起的质心表示误差在 S-I 方向上更大，而对于慢速扫描技术，在横断方向上更大。对于宽度小于 5 毫米的切片，高估是相当均匀的，超过这个宽度就会出现严重的高估。
对描述临床相关 3D 运动的目标进行非门控 CT 成像会导致目标体积的混叠高估和质心位置的表示错误，物理目标几何形状与 CT 生成的目标几何形状之间几乎没有相关性或没有相关性。慢速扫描技术是一种描述目标位置的实用方法。快速扫描技术提供了更可靠的（尽管仍然是扭曲的）目标边缘。
