Dang Jun, Luo Ouyang, Gu Xuejun, Wang Jing
Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
J Xray Sci Technol. 2015;23(1):11-23. doi: 10.3233/XST-140466.
High quality 4D-CBCT can be obtained by deforming a planning CT (pCT), where the deformation vector fields (DVF) are estimated by matching the forward projections of pCT and 4D-CBCT projections. The matching metric used in the previous study is the sum of squared intensity differences (SSID). The scatter signal level in CBCT projections is much higher than pCT, the SSID metric may not lead to optimal DVF.
To improve the DVF estimation accuracy, we develop a new matching metric that is less sensitive to the intensity level difference caused by the scatter signal.
The negative logarithm of correlation coefficient (NLCC) is used as the matching metric. A non-linear conjugate gradient optimization algorithm is used to estimate the DVF. A 4D NCAT phantom and an anthropomorphic thoracic phantom were used to evaluate the NLCC-based algorithm.
In the NCAT phantom study, the relative reconstruction error is reduced from 18.0% in SSID to 14.13% in NLCC. In the thoracic phantom study, the root mean square error of the tumor motion is reduced from 1.16 mm in SSID to 0.43 mm in NLCC.
NLCC metric can improve the image reconstruction and motion estimation accuracy of DVF-driven image reconstruction for 4D-CBCT.
高质量的4D - CBCT可以通过对计划CT（pCT）进行变形来获得，其中变形矢量场（DVF）通过匹配pCT的前向投影和4D - CBCT投影来估计。先前研究中使用的匹配度量是强度差平方和（SSID）。CBCT投影中的散射信号水平远高于pCT，SSID度量可能无法得到最优的DVF。
为提高DVF估计精度，我们开发了一种对散射信号引起的强度水平差异不太敏感的新匹配度量。
使用相关系数的负对数（NLCC）作为匹配度量。采用非线性共轭梯度优化算法来估计DVF。使用4D NCAT体模和拟人化胸部体模来评估基于NLCC的算法。
在NCAT体模研究中，相对重建误差从SSID中的18.0%降至NLCC中的14.13%。在胸部体模研究中，肿瘤运动的均方根误差从SSID中的1.16 mm降至NLCC中的0.43 mm。
NLCC度量可以提高4D - CBCT的DVF驱动图像重建的图像重建和运动估计精度。
