Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53706, USA.
Department of Radiology, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53706, USA.
Med Phys. 2019 Jun;46(6):2600-2609. doi: 10.1002/mp.13554. Epub 2019 May 6.
Deformable registration of ultrasound (US) and contrast enhanced computed tomography (CECT) images are essential for quantitative comparison of ablation boundaries and dimensions determined using these modalities. This comparison is essential as stiffness-based imaging using US has become popular and offers a nonionizing and cost-effective imaging modality for monitoring minimally invasive microwave ablation procedures. A sensible manual registration method is presented that performs the required CT-US image registration.
The two-dimensional (2D) virtual CT image plane that corresponds to the clinical US B-mode was obtained by "virtually slicing" the 3D CT volume along the plane containing non-anatomical landmarks, namely points along the microwave ablation antenna. The initial slice plane was generated using the vector acquired by rotating the normal vector of the transverse (i.e., xz) plane along the angle subtended by the antenna. This plane was then further rotated along the ablation antenna and shifted along with the direction of normal vector to obtain similar anatomical structures, such as the liver surface and vasculature that is visualized on both the CT virtual slice and US B-mode images on 20 patients. Finally, an affine transformation was estimated using anatomic and non-anatomic landmarks to account for distortion between the colocated CT virtual slice and US B-mode image resulting in a final registered CT virtual slice. Registration accuracy was measured by estimating the Euclidean distance between corresponding registered points on CT and US B-mode images.
Mean and SD of the affine transformed registration error was 1.85 ± 2.14 (mm), computed from 20 coregistered data sets.
Our results demonstrate the ability to obtain 2D virtual CT slices that are registered to clinical US B-mode images. The use of both anatomical and non-anatomical landmarks result in accurate registration useful for validating ablative margins and comparison to electrode displacement elastography based images.
超声（US）和对比增强计算机断层扫描（CECT）图像的变形配准对于使用这些模式确定的消融边界和尺寸的定量比较至关重要。由于基于刚度的 US 成像变得流行，并且为监测微创微波消融过程提供了一种非电离且具有成本效益的成像方式，因此这种比较至关重要。本文提出了一种合理的手动配准方法，用于执行所需的 CT-US 图像配准。
通过沿着包含非解剖学标志物（即微波消融天线沿线的点）的平面“虚拟切片”3D CT 体积，获得与临床 US B 模式相对应的二维（2D）虚拟 CT 图像平面。初始切片平面是通过旋转与横切（即 xz）平面的法向量成一定角度的向量生成的。然后，该平面沿着消融天线进一步旋转，并沿着法向量的方向移动，以获得类似的解剖结构，例如肝脏表面和血管，这些结构在 20 名患者的 CT 虚拟切片和 US B 模式图像上都可以看到。最后，使用解剖学和非解剖学标志物估计仿射变换，以补偿共定位的 CT 虚拟切片和 US B 模式图像之间的失真，从而获得最终注册的 CT 虚拟切片。通过估计 CT 和 US B 模式图像上对应注册点之间的欧几里得距离来测量配准精度。
从 20 个配准数据集计算得出，仿射变换配准误差的平均值和标准差为 1.85 ± 2.14（mm）。
我们的结果表明能够获得与临床 US B 模式图像配准的 2D 虚拟 CT 切片。使用解剖学和非解剖学标志物可实现准确的配准，这对于验证消融边界以及与基于电极位移弹性成像的图像进行比较非常有用。
