Department of Radiological Science, College of Health Science, Yonsei University, 1 Yonseidae-gil, Wonju 26493, Republic of Korea.
Phys Med Biol. 2019 May 2;64(9):095029. doi: 10.1088/1361-6560/ab0d50.
Respiratory-correlated cone-beam CT (CBCT) not only inhibits rapid scanning due to the slow speed of the LINAC head gantry rotation, but its implementation for routine patient imaging is impractical because of the high radiation dose delivered during the process. Digital tomosynthesis (DTS) is a potentially faster technique that delivers a much lower radiation dose by reducing the number of projections in a limited angular range. Unfortunately, 4D-DTS introduces strong aliasing artifacts in the reconstructed images due to the sparsely sampled projections in each respiratory phase bin. The authors hereby suggest a novel low-dose 4D-DTS image reconstruction method that achieves a compromise between the occurrence of aliasing artifacts and image smoothing using a brute force-based adaptive weighting parameter searching technique. We used a prototype LINAC system mounted with a flat-panel detector to acquire tomosynthesis projections of respiratory motion in a phantom in the anterior-posterior (AP) and lateral views. Three different 4D-DTS image reconstruction schemes that included conventional filtered back-projection (FBP), adaptive steepest descent projection onto convex sets (ASD-POCS), and the proposed brute force-based adaptive total variation (BF-ATV) were implemented in four different respiratory phase bins for both AP and lateral views. All reconstructions were accelerated using a single GPU card to reduce the computation time. To study the performance of the algorithm under various sparse conditions, we operated the prototype system in three different gantry sweep modes. The results indicate that the proposed BF-ATV method yields the largest structural similarities in the differenced image between the ground-truth dataset acquired using the slow gantry sweep mode and the sparse dataset from both moderate and fast sweep modes. In addition, the proposed method maintained the object sharpness with less streaking lines and small loss of sharpness compared to the conventional FBP and ASD-POCS methods. In conclusion, the proposed low-dose 4D-DTS reconstruction scheme may provide better performance due in part to its rapid scanning. Therefore, it is potentially applicable to practical 4D imaging for radiotherapy.
呼吸相关锥形束 CT（CBCT）不仅由于 LINAC 头架旋转速度较慢而抑制快速扫描，而且由于在该过程中传递的高辐射剂量，其用于常规患者成像的实施是不切实际的。数字断层合成术（DTS）是一种潜在更快的技术，通过在有限的角度范围内减少投影的数量来传递低得多的辐射剂量。不幸的是，由于在每个呼吸相位箱中稀疏采样的投影，4D-DTS 在重建图像中引入了强烈的混叠伪影。作者在此建议一种新颖的低剂量 4D-DTS 图像重建方法，该方法使用基于蛮力的自适应加权参数搜索技术在混叠伪影的发生和图像平滑之间取得折衷。我们使用配备有平板探测器的原型 LINAC 系统在前后（AP）和侧视图中在幻影中获取呼吸运动的断层合成投影。在 AP 和侧视图中，针对四个不同的呼吸相位箱实施了三种不同的 4D-DTS 图像重建方案，包括常规滤波后投影（FBP）、自适应最陡下降投影到凸集（ASD-POCS）和基于蛮力的自适应全变差（BF-ATV）。所有重建都使用单个 GPU 卡加速以减少计算时间。为了研究在各种稀疏条件下算法的性能，我们在三种不同的龙门架扫描模式下操作原型系统。结果表明，在从缓慢龙门架扫描模式获得的真实数据集与从中度和快速扫描模式获得的稀疏数据集之间的差分图像中，所提出的 BF-ATV 方法产生了最大的结构相似性。此外，与常规 FBP 和 ASD-POCS 方法相比，所提出的方法在保持物体锐度方面具有更少的条纹线和较小的锐度损失。总之，所提出的低剂量 4D-DTS 重建方案可能会由于其快速扫描而提供更好的性能。因此，它有可能适用于放射治疗的实际 4D 成像。
