This study introduces and evaluates respiratory-correlated four-dimensional (4D) inverse geometry computed tomography (IGCT). The projection data of the IGCT were acquired in a single gantry rotation over 120 s. Three virtual phantoms—static Defrise, 4D Shepp–Logan, and 4D extended cardiac-torso (XCAT)—were used to obtain projection data for the IGCT and cone-beam computed tomography (CBCT). The projection acquisition parameters were determined to eliminate vacancies in the Radon space for an accurate rebinning process. Phase-based sorting was conducted within 10 phase bins, and the sorted projection data were binned into a cone beam geometry. Finally, Feldkamp–Davis–Kress reconstruction was conducted independently at each phase. The reconstructed images were compared using the structural similarity index measure (SSIM) and root mean square error (RMSE). The vertical profile of the Defrise reconstruction image was uniform, and the cone beam artefact was reduced in the IGCT image. Under an ideal projection acquisition condition, the mean coronal plane SSIMs of the Shepp–Logan and 4D XCAT phantoms were 0.899 and 0.706, respectively, which were higher than those of the CBCT (0.784 and 0.623, respectively). Similarly, the mean RMSEs of the coronal plane IGCT (0.036 and 0.158) exhibited an improvement over those of the CBCT (0.165 and 0.261, respectively). The mean standard deviations of the SSIM and RMSE were lower for IGCT than for CBCT. In particular, the SSIM and RMSE of the sagittal and coronal planes of the Shepp–Logan IGCT images were stable in all phase bins; however, those of the CBCT changed depending on the phase bins. Poor image quality was observed for IGCT under inappropriate conditions. This was caused by a vacancy in the Radon space, owing to an inappropriate scan setting. Overall, the proposed 4D IGCT exhibited better image quality than conventional CBCT.

本研究介绍和评估呼吸相关四维 (4D) 逆几何计算机断层扫描 (IGCT)。IGCT 的投影数据是在超过 120 秒的单个机架旋转中获得的。三个虚拟体模——静态 Defrise、4D Shepp-Logan 和 4D 扩展心脏躯干 (XCAT)——用于获取 IGCT 和锥形束计算机断层扫描 (CBCT) 的投影数据。确定投影采集参数以消除氡空间中的空位，以实现准确的重组过程。在 10 个相位箱内进行基于相位的分类，并将分类的投影数据分箱成锥形束几何形状。最后，Feldkamp-Davis-Kress 重建在每个阶段独立进行。使用结构相似性指数测量（SSIM）和均方根误差（RMSE）比较重建的图像。Defrise重建图像的垂直轮廓均匀，IGCT图像中的锥形束伪影减少。在理想的投影采集条件下，Shepp-Logan 和 4D XCAT 体模的平均冠状面 SSIM 分别为 0.899 和 0.706，高于 CBCT（分别为 0.784 和 0.623）。同样，冠状面 IGCT 的平均 RMSE（0.036 和 0.158）比 CBCT 的平均 RMSE（分别为 0.165 和 0.261）有所改善。IGCT 的 SSIM 和 RMSE 的平均标准差低于 CBCT。特别是，Shepp-Logan IGCT 图像的矢状面和冠状面的 SSIM 和 RMSE 在所有相位区间中都是稳定的；然而，CBCT 的那些变化取决于相位箱。在不适当的条件下观察到 IGCT 的图像质量较差。这是由于扫描设置不当导致氡空间出现空缺所致。总体而言，所提出的 4D IGCT 表现出比传统 CBCT 更好的图像质量。