从千伏在线成像中校正锥形束 CT 中的治疗床图像伪影。

Correction of image artifacts from treatment couch in cone-beam CT from kV on-board imaging.

机构信息

Department of Radiation Oncology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.

出版信息

J Xray Sci Technol. 2011;19(3):321-32. doi: 10.3233/XST-2011-0296.

DOI:10.3233/XST-2011-0296

PMID:21876282

Abstract

PURPOSE

To investigate image artifacts caused by a standard treatment couch on cone-beam CT (CBCT) images from a kV on-board imager and to develop an algorithm based on spatial domain filtering to remove image artifacts in CBCT induced by the treatment couch.

METHODS

Image artifacts in CBCT induced by the treatment couch were quantified by scanning a phantom used to quantify CT image performance. This was performed by scanning the phantom setup on a regular treatment couch and in air with the kV on-board imager. An algorithm was developed to filter image artifacts from the treatment couch by processing of cone-beam radiographic projections using two scans: one scan of the phantom and treatment couch and a second scan of the treatment couch only. This algorithm is based on a pixel-by-pixel removal of beam attenuation due to the treatment couch from each projection of the phantom and couch scan. The net couch-filtered projections were then used to reconstruct CBCT.

RESULTS

We found that the treatment couch causes considerable image artifacts: CT number uniformity is degraded and varies as much as 15%, and noise in CBCT scans with phantom plus couch (3.5%) is higher than for the phantom in air (1.5%). The spatial domain filtering technique reduces noise by more than 1.5%, improves uniformity by a factor of 2, and removes ringing and streaking artifacts related to the standard treatment couch in CBCT reconstructed from couch-filtered projections. This filtering technique was tested successfully to filter other hardware objects such as a patient immobilization body-fix frame.

CONCLUSIONS

The standard treatment couch causes image artifact in CBCT from kV on-board imaging systems. The spatial domain filtering technique developed in this work improves image quality of CBCT by preprocessing the projections prior to CBCT reconstruction. This technique might be useful to filter other hardware objects from CBCT which may contribute to the degradation of image quality.

摘要

目的

研究千伏在线成像系统锥形束 CT（CBCT）图像中标准治疗床引起的图像伪影，并开发一种基于空域滤波的算法，以去除治疗床引起的 CBCT 图像伪影。

方法

通过扫描用于量化 CT 图像性能的体模来量化 CBCT 中治疗床引起的图像伪影。这是通过在常规治疗床上和使用千伏在线成像器在空气中扫描体模设置来完成的。开发了一种算法，通过使用两次扫描处理锥形束射线照相投影来从治疗床过滤图像伪影：一次是对体模和治疗床进行扫描，另一次仅对治疗床进行扫描。该算法基于从体模和治疗床的每个投影中逐像素去除由于治疗床引起的光束衰减。然后使用净治疗床过滤投影来重建 CBCT。

结果

我们发现治疗床会导致相当大的图像伪影：CT 数均匀性降低，最大可达 15%，并且带有体模和治疗床的 CBCT 扫描中的噪声（3.5%）高于空气体模中的噪声（1.5%）。空域滤波技术可将噪声降低 1.5%以上，均匀性提高 2 倍，并去除与标准治疗床相关的 CBCT 中的振铃和条纹伪影。该过滤技术已成功用于过滤其他硬件物体，如患者固定体架。