Min Yugang, Neylon John, Shah Amish, Meeks Sanford, Lee Percy, Kupelian Patrick, Santhanam Anand P
Department of Radiation Oncology, University of California, Los Angeles, CA, USA,
Int J Comput Assist Radiol Surg. 2014 Sep;9(5):875-89. doi: 10.1007/s11548-013-0975-7. Epub 2014 Jan 14.
The accuracy of 4D-CT registration is limited by inconsistent Hounsfield unit (HU) values in the 4D-CT data from one respiratory phase to another and lower image contrast for lung substructures. This paper presents an optical flow and thin-plate spline (TPS)-based 4D-CT registration method to account for these limitations.
The use of unified HU values on multiple anatomy levels (e.g., the lung contour, blood vessels, and parenchyma) accounts for registration errors by inconsistent landmark HU value. While 3D multi-resolution optical flow analysis registers each anatomical level, TPS is employed for propagating the results from one anatomical level to another ultimately leading to the 4D-CT registration. 4D-CT registration was validated using target registration error (TRE), inverse consistency error (ICE) metrics, and a statistical image comparison using Gamma criteria of 1 % intensity difference in 2 mm(3) window range.
Validation results showed that the proposed method was able to register CT lung datasets with TRE and ICE values <3 mm. In addition, the average number of voxel that failed the Gamma criteria was <3 %, which supports the clinical applicability of the propose registration mechanism.
The proposed 4D-CT registration computes the volumetric lung deformations within clinically viable accuracy.
4D-CT配准的准确性受到4D-CT数据中从一个呼吸阶段到另一个呼吸阶段Hounsfield单位（HU）值不一致以及肺亚结构图像对比度较低的限制。本文提出一种基于光流和薄板样条（TPS）的4D-CT配准方法来解决这些限制。
在多个解剖层面（如肺轮廓、血管和实质）使用统一的HU值，以解决由于地标HU值不一致导致的配准误差。在通过3D多分辨率光流分析对每个解剖层面进行配准的同时，采用TPS将结果从一个解剖层面传播到另一个解剖层面，最终实现4D-CT配准。使用目标配准误差（TRE）、反向一致性误差（ICE）指标以及在2 mm³窗口范围内强度差异为1%的伽马标准进行统计图像比较来验证4D-CT配准。
验证结果表明，所提出的方法能够对CT肺部数据集进行配准，TRE和ICE值<3 mm。此外，未通过伽马标准的体素平均数量<3%，这支持了所提出配准机制的临床适用性。
所提出的4D-CT配准能够在临床上可行的精度范围内计算肺部体积变形。
