Landheer Karl, Johns Paul C
Ottawa Medical Physics Institute and Ottawa-Carleton Institute for Physics, Department of Physics, Carleton University, 1125 Colonel By Drive, Ottawa K1S 5B6, Canada.
Rev Sci Instrum. 2012 Sep;83(9):095114. doi: 10.1063/1.4754124.
Traditional projection x-ray imaging utilizes only the information from the primary photons. Low-angle coherent scatter images can be acquired simultaneous to the primary images and provide additional information. In medical applications scatter imaging can improve x-ray contrast or reduce dose using information that is currently discarded in radiological images to augment the transmitted radiation information. Other applications include non-destructive testing and security. A system at the Canadian Light Source synchrotron was configured which utilizes multiple pencil beams (up to five) to create both primary and coherent scatter projection images, simultaneously. The sample was scanned through the beams using an automated step-and-shoot setup. Pixels were acquired in a hexagonal lattice to maximize packing efficiency. The typical pitch was between 1.0 and 1.6 mm. A Maximum Likelihood-Expectation Maximization-based iterative method was used to disentangle the overlapping information from the flat panel digital x-ray detector. The pixel value of the coherent scatter image was generated by integrating the radial profile (scatter intensity versus scattering angle) over an angular range. Different angular ranges maximize the contrast between different materials of interest. A five-beam primary and scatter image set (which had a pixel beam time of 990 ms and total scan time of 56 min) of a porcine phantom is included. For comparison a single-beam coherent scatter image of the same phantom is included. The muscle-fat contrast was 0.10 ± 0.01 and 1.16 ± 0.03 for the five-beam primary and scatter images, respectively. The air kerma was measured free in air using aluminum oxide optically stimulated luminescent dosimeters. The total area-averaged air kerma for the scan was measured to be 7.2 ± 0.4 cGy although due to difficulties in small-beam dosimetry this number could be inaccurate.
传统的投影X射线成像仅利用来自初级光子的信息。低角度相干散射图像可以与初级图像同时获取，并提供额外信息。在医学应用中，散射成像可以利用目前在放射图像中被丢弃的信息来增强透射辐射信息，从而提高X射线对比度或降低剂量。其他应用包括无损检测和安全领域。加拿大光源同步加速器的一个系统被配置为利用多个笔形束（最多五个）同时创建初级和相干散射投影图像。使用自动步进拍摄装置使样品穿过这些束进行扫描。像素以六边形晶格采集以最大化填充效率。典型间距在1.0至1.6毫米之间。使用基于最大似然期望最大化的迭代方法从平板数字X射线探测器中解缠重叠信息。相干散射图像的像素值通过在一个角度范围内对径向轮廓（散射强度与散射角）进行积分生成。不同的角度范围可最大化不同感兴趣材料之间的对比度。包含了一个猪模型的五束初级和散射图像集（像素束时间为990毫秒，总扫描时间为56分钟）。为作比较，还包含了同一模型的单束相干散射图像。五束初级和散射图像的肌肉-脂肪对比度分别为0.10±0.01和1.16±0.03。使用氧化铝光激励发光剂量计在空气中自由测量空气比释动能。尽管由于小束剂量测量存在困难，该扫描的总面积平均空气比释动能测量值为7.2±0.4厘戈瑞，但这个数字可能不准确。
