BACKGROUND:The time of flight (TOF) cone beam computed tomography (CBCT) was recently shown to reduce the X-ray scattering effects by 95%and improve the image CNR by 110%for large volume objects. The advancements in X-ray sources like in compact Free Electron Lasers (FEL) and advancements in detector technology show potential for the TOF method to be feasible in CBCT when imaging large objects. OBJECTIVE:To investigate feasibility and efficacy of TOF CBCT in imaging smaller objects with different targets such as bones and tumors embedded inside the background. METHODS:The TOF method used in this work was verified using a 24cm phantom. Then, the GATE software was used to simulate the CBCT imaging of an 8 cm diameter cylindrical water phantom with two bone targets using a modeled 20 keV quasi-energetic FEL source and various TOF resolutions ranging from 1 to 1000 ps. An inhomogeneous breast phantom of similar size with tumor targets was also imaged using the same system setup. RESULTS:The same results were obtained in the 24cm phantom, which validated the applied CBCT simulation approach. For the case of 8cm cylindrical phantom and bone target, a TOF resolution of 10 ps improved the image contrast-to-noise ratio (CNR) by 57%and reduced the scatter-to-primary ratio (SPR) by 8.63. For the case of breast phantom and tumor target, image CNR was enhanced by 12%and SPR was reduced by 1.35 at 5 ps temporal resolution. CONCLUSIONS:This study indicates that a TOF resolution below 10 ps is required to observe notable enhancements in the image quality and scatter reduction for small objects around 8cm in diameter. The strong scattering targets such as bone can result in substantial improvements by using TOF CBCT.

中文翻译：

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飞行时间锥形束CT成像的可行性研究

背景：飞行时间（TOF）锥形束计算机断层扫描（CBCT）最近被证明可以将大体积物体的 X 射线散射效应降低 95%，并将图像 CNR 提高 110%。紧凑型自由电子激光器 (FEL) 等 X 射线源的进步和探测器技术的进步表明，TOF 方法在对大型物体进行成像时在 CBCT 中是可行的。目的：探讨 TOF CBCT 在对具有不同目标（例如嵌入背景中的骨骼和肿瘤）的较小物体进行成像时的可行性和有效性。方法：在这项工作中使用的 TOF 方法使用 24 厘米的体模进行了验证。然后，GATE 软件用于使用模拟的 20 keV 准高能 FEL 源和范围从 1 到 1000 ps 的各种 TOF 分辨率来模拟具有两个骨骼目标的 8 cm 直径圆柱形水体模的 CBCT 成像。还使用相同的系统设置对具有类似大小的肿瘤目标的不均匀乳房模型进行成像。结果：在 24cm 体模中获得了相同的结果，验证了所应用的 CBCT 模拟方法。对于 8cm 圆柱体模和骨骼目标，10 ps 的 TOF 分辨率将图像对比度与噪声比 (CNR) 提高了 57%，并将散布原色比 (SPR) 降低了 8.63。对于乳腺模型和肿瘤靶点，在 5 ps 时间分辨率下，图像 CNR 提高了 12%，SPR 降低了 1.35。结论：这项研究表明，对于直径约为 8 厘米的小物体，需要低于 10 ps 的 TOF 分辨率才能观察到图像质量的显着增强和散射减少。使用 TOF CBCT 可以显着改善骨骼等强散射目标。