与 0.35 T MRgRT 机架位置相关的系统依赖性图像失真：特征描述及相应校正。

System-dependent image distortion related to gantry positions of a 0.35 T MRgRT: Characterization and the corresponding correction.

机构信息

Department of Radiation Oncology, Washington University School of Medicine, St. Louis, Missouri, USA.

Department of the Modus Medical, Modus Medical Devices Inc., London, Ontario, Canada.

出版信息

J Appl Clin Med Phys. 2023 Jan;24(1):e13826. doi: 10.1002/acm2.13826. Epub 2022 Nov 10.

DOI:10.1002/acm2.13826

PMID:36354747

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC9903949/

Abstract

PURPOSE

MR-guided radiotherapy with high accuracy treatment planning requires addressing MR imaging artifacts that originate from system imperfections. This work presents the characterization and corresponding correction of gantry-related imaging distortions including geometric distortion and isocenter shift in a 0.35 T magnetic resonance imaging (MRI)-guided radiotherapy (MRgRT) system using distortion vector fields (DVFs).

METHODS

Two phantoms, the magnetic resonance imaging distortion in 3D (MRID ) phantom and the Fluke phantom, along with a human volunteer were imaged at different gantry angles on a 0.35 T MR-Linac. The geometric distortion and isocenter shift were characterized for both phantom images. DVFs with a field of view extended beyond the physical boundary of the MRID phantom were extracted from images taken at 30° gantry angle increments, with vendor-provided distortion correction turned on and off (DstOff). These extended DVFs were then applied to the relevant phantom images to correct their geometric distortions and isocenter shift at the respective gantry angles. The extended DVFs produced from the MRID phantom were also applied to Fluke phantom and human MR images at their respective gantry angles. The resampled images were evaluated using structural similarity index measure (SSIM) comparison with the vendor corrected images from the MRgRT system.

RESULTS

Geometric distortion with "mean (± SD) distortion" of 3.2 ± 0.02, 2.9 ± 0.02, and 1.8 ± 0.01 mm and isocenter shift (±SD) of 0.49 ± 0.3, 0.05 ± 0.2, and 0.01 ± 0.03 mm were present in the DstOff MRID phantom images in right-left (RL), anterior-posterior (AP), and superior-inferior (SI) directions, respectively. After resampling the originally acquired images by applying extended DVFs, the distortion was corrected to 0.18 ± 0.02, 0.09 ± 0.01, 0.15 ± 0.01 mm, and isocenter shift was corrected to 0.14 ± 0.05, -0.02 ± 0.04, and -0.07 ± 0.05 mm in RL, AP, and SI directions, respectively. The Fluke phantom average geometric distortion with "mean (± SD) distortion" of 2.7 ± 0.1 mm was corrected to 0.2 ± 0. 1 mm and the average isocenter shift (± SD) of 0.51 ± 0.2 mm, and 0.05 ± 0.03 was corrected to -0.08 ± 0.03 mm, and -0.05 ± 0.01 in RL and AP directions, respectively. SSIM (mean ± SD) of the original images to resampled images was increased from 0.49 ± 0.02 to 0.78 ± 0.01, 0.45 ± 0.02 to 0.75 ± 0.01, and 0.86 ± 0.25 to 0.98 ± 0.08 for MRID phantom, Fluke phantom, and human MR images, respectively, for all the gantry angles compared to the vendor corrected images.

CONCLUSION

The gantry-related MR imaging distortion including geometric distortion and isocenter shift was characterized and a corresponding correction was demonstrated using extended DVFs on 0.35 T MRgRT system. The characterized gantry-related isocenter shift can be combined with geometric distortion correction to provide a technique for the correction of the full system-dependent distortion in an MRgRT system.

摘要

目的

具有高精度治疗计划的磁共振引导放射治疗需要解决源自系统不完善的磁共振成像伪影。本工作使用失真矢量场（DVF）对 0.35 T 磁共振引导放射治疗（MRgRT）系统中的与机架相关的成像失真（包括几何失真和等中心移位）进行了特征描述和相应的校正。

方法

在 0.35 T MR-Linac 上，使用两个体模（3D 磁共振成像失真体模（MRID）体模和福禄克体模）和一名志愿者在不同的机架角度进行成像。对这两个体模图像的几何失真和等中心位移进行了特征描述。从 30°机架角度增量拍摄的图像中提取了具有超出 MRID 体模物理边界的视场的 DVF，并开启和关闭了供应商提供的失真校正（DstOff）。将这些扩展的 DVF 应用于相应的体模图像，以校正各自机架角度的几何失真和等中心位移。从 MRID 体模生成的扩展 DVF 也应用于福禄克体模和人体 MR 图像在各自的机架角度。使用结构相似性指数测量（SSIM）与从 MRgRT 系统的供应商校正图像进行比较来评估重采样图像。

结果

在 DstOff MRID 体模图像中，存在“平均（±SD）失真”为 3.2±0.02、2.9±0.02 和 1.8±0.01mm 的几何失真和 0.49±0.3、0.05±0.2 和 0.01±0.03mm 的等中心位移，分别在右-左（RL）、前-后（AP）和上-下（SI）方向。在应用扩展的 DVF 对原始采集的图像进行重采样后，失真校正为 0.18±0.02、0.09±0.01、0.15±0.01mm，等中心位移校正为 0.14±0.05、-0.02±0.04 和-0.07±0.05mm，分别在 RL、AP 和 SI 方向。福禄克体模的平均几何失真为“平均（±SD）失真”2.7±0.1mm，校正为 0.2±0.1mm，平均等中心位移（±SD）为 0.51±0.2mm，校正为-0.08±0.03mm，-0.05±0.01mm，分别在 RL 和 AP 方向。原始图像到重采样图像的 SSIM（平均值±SD）从 0.49±0.02 增加到 0.78±0.01、0.45±0.02 到 0.75±0.01 和 0.86±0.25 到 0.98±0.08，对于所有机架角度，与供应商校正图像相比，MRID 体模、福禄克体模和人体 MR 图像的 SSIM 都有所提高。