放疗中基于超声形变场获取伪计算机断层扫描图像的研究

Research of obtaining pseudo-CT images based on ultrasound deformation fields in radiotherapy

目的提出一种改良的基于超声(US)形变场下获得伪CT图像(CTps)方法。方法选用3例术后宫颈癌患者CT与三维US图像数据,包括模拟定位阶段获取的CT与US图像,以及治疗1周后摆位验证阶段获取的锥形束CT (CBCT)与US图像。制作基于两幅US图像全局成像重叠区域(OROW)的掩模和感兴趣区域重叠部分(OROI)的掩模,并分别应用于US图像间的配准中,得到两种形变场。分别将两种形变场应用于模拟CT图像得到两种CTps,比较不同CTps与CBCT的配准精度。结果基于OROI、OROW及不加任何掩模下所得CTps与CBCT的相关系数(CC)的平均值分别为0.95、0.82及0.64,归一化灰度均方根误差(NMSE)平均值分别为0.12、0.42及0.57。结论基于OROI所得掩模下获取的US形变场应用到CTsim时获得的CTps与CBCT的配准效果最好。

Objective An improved method for obtaining pseudo-computed tomography (CTps) based on ultrasound deformation field. Methods The three-dimensional image data of computed tomography and ultrasound for three postoperative cervical cancer patients were selected, including the CT (CTsim) and ultrasound (USsim) images obtained during the simulated positioning stage, and the cone beam CT (CBCT) and ultrasound images obtained during the positioning verification stage of the treatment one week later. Binary masks of the OROI and OROW were created and applied in ultrasound image registration;thus, the deformation field was obtained. The deformation field was applied to CTsim images and different pseudo-CT images were obtained. Similarities between these pseudo-CT images and those of CBCT were compared, and registration accuracies between pseudo-CT images under different binary masks and CTsim were discussed. Results The averages of the correlation coefficient between pseudo-CT based on OROI, OROW, no binary mask and CBCT were 0.95, 0.82 and 0.64 respectively. The average of the normalized mean square Error were 0.12, 0.42 and 0.57 respectively. Conclusion The pseudo-CT based on OROI binary mask matches the best with CTsim and achieves the highest similarity with CBCT.