Characterization, prediction, and correction of geometric distortion in 3 T MR images
Characterization, prediction, and correction of geometric distortion in 3 T MR images
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DOI：
10.1118/1.2402331
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发表时间：
2007-02-01
期刊：
影响因子：
3.8
通讯作者：
Fallone, B. Gino
中科院分区：
文献类型：
--
作者：
Baldwin, Lesley N.;Wachowicz, Keith;Fallone, B. Gino
本文介绍了我们在3T临床磁共振(MR)扫描仪中预测、测量和校正几何失真的方法和结果，目的是在放射治疗计划中提供图像指导。由于背景场的不均匀和应用的梯度中的非线性，几何不准确很容易在规则结构的三维(3D)网格模型的MR图像上可视化。通过计算机断层扫描，使用基于MatLab的计算机程序在三维上准确地确定了模型内略低于10000个控制点的位置。然后，当使用MR扫描仪对模型进行成像时，通过测量控制点的相应位置来确定MR失真。利用逆梯度方法，分离了背景B-0场中梯度非线性引起的失真和背景B-0场中不均匀引起的失真。由于机器相关失真的各种来源可以单独表征，因此可以预测其他成像序列中存在的失真(对于这些序列，无法使用模型法准确测量3D失真)，从而不需要对各种其他成像序列进行单独的失真计算。失真主要是由梯度非线性引起的，最大图像失真据报道比其他研究人员在1.5T时发现的要小。最后，为了提供几何上准确的体模图像，对图像切片进行了失真校正。(C)2007年美国医学物理学家协会。
The work presented herein describes our methods and results for predicting, measuring and correcting geometric distortions in a 3 T clinical magnetic resonance (MR) scanner for the purpose of image guidance in radiation treatment planning. Geometric inaccuracies due to both inhomogeneities in the background field and nonlinearities in the applied gradients were easily visualized on the MR images of a regularly structured three-dimensional (3D) grid phantom. From a computed tomography scan, the locations of just under 10 000 control points within the phantom were accurately determined in three dimensions using a MATLAB-based computer program. MR distortion was then determined by measuring the corresponding locations of the control points when the phantom was imaged using the MR scanner. Using a reversed gradient method, distortions due to gradient nonlinearities were separated from distortions due to inhomogeneities in the background B-0 field. Because the various sources of machine-related distortions can be individually characterized, distortions present in other imaging sequences (for which 3D distortion cannot accurately be measured using phantom methods) can be predicted negating the need for individual distortion calculation for a variety of other imaging sequences. Distortions were found to be primarily caused by gradient nonlinearities and maximum image distortions were reported to be less than those previously found by other researchers at 1.5 T. Finally, the image slices were corrected for distortion in order to provide geometrically accurate phantom images. (c) 2007 American Association of Physicists in Medicine.