School of Integrated Technology, Yonsei University, Incheon, Republic Of Korea.
KohYoung Technology, Yongin, Republic Of Korea.
Phys Med Biol. 2021 Aug 5;66(16). doi: 10.1088/1361-6560/ac16c1.
Conventional intraoperative computed tomography (CT) has a long scan time, degrading the image quality. Its large size limits the position of a surgeon during surgery. Therefore, this study proposes a CT system comprising of eight carbon-nanotube (CNT)-based x-ray sources and 16 detector modules to solve these limitations. Gantry only requires 45° of rotation to acquire the whole projection, reducing the scan time to 1/8 compared to the full rotation. Moreover, the volume and scan time of the system can be significantly reduced using CNT sources with a small volume and short pulse width and placing a heavy and large high-voltage generator outside the gantry. We divided the proposed system into eight subsystems and sequentially devised a geometry calibration method for each subsystem. Accordingly, a calibration phantom consisting of four polytetrafluoroethylene beads, each with 15 mm diameter, was designed. The geometry calibration parameters were estimated by minimizing the difference between the measured bead projection and the forward projection of the formulated subsystem. By reflecting the estimated geometry calibration parameters, the projection data were obtained via rebinning to be used in the filtered-backprojection reconstruction. The proposed calibration and reconstruction methods were validated by computer simulations and real experiments. Additionally, the accuracy of the geometry calibration method was examined by computer simulation. Furthermore, we validated the improved quality of the reconstructed image through the mean-squared error (MSE), structure similarity (SSIM), and visual inspections for both the simulated and experimental data. The results show that the calibrated images, reconstructed by reflecting the calibration results, have smaller MSE and higher SSIM values than the uncalibrated images. The calibrated images were observed to have fewer artifacts than the uncalibrated images in visual inspection, demonstrating that the proposed calibration and reconstruction methods effectively reduce artifacts caused by geometry misalignments.
传统的术中计算机断层扫描（CT）具有较长的扫描时间，会降低图像质量。其体积较大，限制了外科医生在手术中的位置。因此，本研究提出了一种由八个基于碳纳米管（CNT）的 X 射线源和 16 个探测器模块组成的 CT 系统，以解决这些限制。机架仅需旋转 45°即可获取整个投影，与全旋转相比，扫描时间缩短至 1/8。此外，使用具有小体积和短脉冲宽度的 CNT 源，并将沉重的大型高压发生器放置在机架外部，可以显著减小系统的体积和扫描时间。我们将提出的系统分为八个子系统，并为每个子系统依次设计了一种几何校准方法。因此，设计了一个由四个聚四氟乙烯珠子组成的校准体模，每个珠子直径为 15 毫米。通过最小化测量珠投影与公式化子系统正向投影之间的差异来估计几何校准参数。通过反射估计的几何校准参数，通过重排获取投影数据，用于滤波反投影重建。通过计算机模拟和实际实验验证了所提出的校准和重建方法。此外，通过计算机模拟检查了几何校准方法的准确性。此外，我们通过均方误差（MSE）、结构相似性（SSIM）和模拟与实验数据的视觉检查，验证了重建图像质量的提高。结果表明，反映校准结果的校准图像的 MSE 和 SSIM 值小于未校准图像。在视觉检查中，校准图像比未校准图像观察到的伪影更少，这表明所提出的校准和重建方法有效地减少了几何对准不良引起的伪影。
