Magnitude and effects of x-ray scatter in a 256-slice CT scanner
Magnitude and effects of x-ray scatter in a 256-slice CT scanner
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DOI：
10.1118/1.2239366
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发表时间：
2006-09-01
期刊：
影响因子：
3.8
通讯作者：
Miyazaki, Hiroaki
中科院分区：
文献类型：
--
作者：
Endo, Masahiro;Mori, Shinichiro;Miyazaki, Hiroaki
我们开发了一款原型 256 层 CT 扫描仪，它采用比传统多探测器 CT (MDCT) 更大锥角的锥束连续旋转，以确保宽视野。然而，较大的锥角可能会因 X 射线散射增加而导致图像劣化。散射辐射导致检测到的信号偏离主 X 射线强度的真实测量结果，并可能导致伪影（例如杯状伪影和条纹伪影）、重建 CT 数的定量不准确以及对比度噪声比 (CNR) 的下降。为了减少散射的影响，256 切片扫描仪配备了防散射准直器。在这里，我们估计了原型 256 层 CT 扫描仪在临床扫描条件下的 X 射线散射幅度，并量化了这种散射对 CT 数精度、图像噪声、均匀性和低对比度可检测性的影响。虽然大多数实验都是使用抗散射准直器进行的，但我们也估计了没有准直器的情况下X射线散射的大小，以评估准直器的散射抑制效率。没有准直器的情况下，散射与一次能量注量比 (SPR) 随着锥角的增加而增加，对于 138 mm 光束宽度、200 mm 直径体模的估计值为 49.7%，对于 320 mm 直径体模的估计值为 78.5%。使用准直器后，估计的 SPR 急剧下降，对于 200 毫米和 320 毫米直径的体模，SPR 降低率（有和没有准直器的 SPR 之比）分别为 12.7% 和 16.8%。准直器减少 X 射线散射导致散射效应显着降低。测量的均匀性良好并且与散射量无关。尽管散射仍然影响 CT 数的准确性，但这可以通过重新缩放来纠正。此外，虽然 CNR 降低了，但至少在理论上，这种变化非常微妙，对低对比度可检测性没有实质性影响。 (c) 2006 年美国医学物理学家协会。
We developed a prototype 256-slice CT scanner that employs continuous rotation of a cone-beam with a larger cone angle than conventional multidetector CTs (MDCT) to ensure a wide field of view. However, a larger cone angle may result in image deterioration due to increased x-ray scatter. Scattered radiation causes the detected signals to deviate from the true measurement of primary x-ray intensity and may result in artifacts (e.g., cupping and streak artifacts), quantitative inaccuracy in reconstructed CT number, and degradation of contrast-to-noise ratio (CNR). To reduce the effects of scatter, the 256-slice scanner incorporates an antiscatter collimator. Here, we estimated the magnitude of x-ray scatter in the prototype 256-slice CT scanner under clinical scan conditions and quantified the effects of this scatter on CT number accuracy, image noise, uniformity, and low contrast detectability. Although most experiments were performed with the antiscatter collimator, we also estimated the magnitude of x-ray scatter without the collimator to evaluate the scatter rejection efficiency of the collimator. The scatter-to-primary energy fluence ratio (SPR) without the collimator increased as cone angle increased, with estimated values of 49.7% for a 138 mm beam width with a phantom of 200 mm diameter, and 78.5% for a 320 mm diameter phantom. Estimated SPR was drastically decreased with the collimator, with an SPR reduction rate (ratio of SPR with and without the collimator) of 12.7% and 16.8% for the 200 and 320 mm diameter phantoms, respectively. The reduction in x-ray scatter by the collimator resulted in a considerable reduction in scatter effects. The measured uniformity was good and was independent of scatter amount. Although scatter still affected CT number accuracy, this could be corrected by rescaling. Further, although the CNR was decreased, in theory at least, the change was so subtle that it had no substantial effect on low-contrast detectability. (c) 2006 American Association of Physicists in Medicine.