4D 多针孔小动物 SPECT 中的同时呼吸运动校正和图像重建。

Medical Physics Program, Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA, USA.

Department of Medical Physics, Faculty of Medicine, Tarbiat Modares University, Tehran, Iran.

Med Phys. 2019 Nov;46(11):5047-5054. doi: 10.1002/mp.13807. Epub 2019 Sep 21.

PURPOSE

Respiratory motion in the chest region during single photon emission computed tomography (SPECT) is a major degrading factor that reduces the accuracy of image quantification. This effect is more notable when the tumor is very small, or the spatial resolution of the imaging system is less than the respiratory motion amplitude. Small animals imaging systems with sub-millimeter spatial resolution need more attention to the respiratory motion for quantitative studies. We developed a motion-embedded four-dimensional (4D)-multi pinhole SPECT (MPS) reconstruction algorithm for respiratory motion correction. This algorithm makes full use of projection statistics for reconstruction of every individual frame.

METHODS

The ROBY phantom with small tumors in liver was generated in eight different phases during one respiratory cycle. The MPS projections were modeled using a fast ray tracing method simulating an MPS acquisition. Individual frames were reconstructed and used for motion estimation. The Demons non-rigid registration algorithm was used to calculate deformation vector fields (DVFs) for simultaneous motion correction and image reconstruction. A motion-embedded 4D-MPS method was used to reconstruct images using all the projections and corresponding DVFs, simultaneously. The 4D-MPS reconstructed images were compared to the low-count single frame (LCSF) reconstructed image, the three-dimensional (3D)-MPS images reconstructed using individual frames, and post reconstruction registration (PRR) that aligns all individual phases to a reference frame using Demons-derived DVFs. The tumor volume relative error (TVE), tumor contrast relative error (TCE), and dice index (DI) for 2, 3, and 4 mm liver were calculated and compared for different reconstruction methods.

RESULTS

For the 4D-MPS reconstruction method, TVE was reduced and DI was higher compared to PRR, 3D-MPS, and LCSF. The extent of the improvement was higher for the small tumor size (i.e. 2 mm). For the biggest tumor in contrast 3 (i.e. 4 mm) TVE for 4D-MPS, PRR, 3D-MPS and, LCSF were 1.33%, 8%, 8%, and 14.67%, respectively.

CONCLUSIONS

The results suggest that motion-embedded 4D-MPS method is an effective and practical way for respiratory motion correction. It reconstructs high quality gated frames while using all projection data to reconstruct each frame.

目的

在单光子发射计算机断层扫描（SPECT）中，胸部区域的呼吸运动会降低图像定量分析的准确性，尤其是当肿瘤非常小或成像系统的空间分辨率小于呼吸运动幅度时，这种影响更为显著。具有亚毫米空间分辨率的小动物成像系统需要更多关注呼吸运动，以进行定量研究。我们开发了一种运动嵌入的四维（4D）多针孔 SPECT（MPS）重建算法，用于呼吸运动校正。该算法充分利用投影统计信息对每一帧进行重建。

方法

ROBY 肝脏小肿瘤模型在一个呼吸周期的八个不同阶段产生。MPS 投影使用快速射线追踪方法建模，模拟 MPS 采集。对单个帧进行重建并用于运动估计。Demons 非刚性配准算法用于计算变形向量场（DVFs），以进行同步运动校正和图像重建。运动嵌入的 4D-MPS 方法用于同时使用所有投影和相应的 DVFs 重建图像。将 4D-MPS 重建图像与低计数单帧（LCSF）重建图像、使用单个帧重建的三维（3D）-MPS 图像以及使用 Demons 衍生的 DVFs 将所有个体相位对齐到参考帧的后重建配准（PRR）进行比较。计算了 2、3 和 4 毫米肝的肿瘤体积相对误差（TVE）、肿瘤对比相对误差（TCE）和骰子指数（DI），并比较了不同重建方法的结果。

结果

对于 4D-MPS 重建方法，与 PRR、3D-MPS 和 LCSF 相比，TVE 降低，DI 升高。对于小肿瘤尺寸（即 2 毫米），改进程度更高。对于对比度 3 中最大的肿瘤（即 4 毫米），4D-MPS、PRR、3D-MPS 和 LCSF 的 TVE 分别为 1.33%、8%、8%和 14.67%。