Sato Yoshinobu, Tanaka Hisashi, Nishii Takashi, Nakanishi Katsuyuki, Sugano Nobuhiko, Kubota Tetsuya, Nakamura Hironobu, Yoshikawa Hideki, Ochi Takahiro, Tamura Shinichi
Division of Interdisciplinary Image Analysis, Osaka University Graduate School of Medicine, Suita, Japan.
IEEE Trans Med Imaging. 2003 Sep;22(9):1076-88. doi: 10.1109/TMI.2003.816955.
Measuring the thickness of sheet-like thin anatomical structures, such as articular cartilage and brain cortex, in three-dimensional (3-D) magnetic resonance (MR) images is an important diagnostic procedure. This paper investigates the fundamental limits on the accuracy of thickness determination in MR images. We defined thickness here as the distance between the two sides of boundaries measured at the subvoxel resolution, which are the zero-crossings of the second directional derivatives combined with Gaussian blurring along the normal directions of the sheet surface. Based on MR imaging and computer postprocessing parameters, characteristics for the accuracy of thickness determination were derived by a theoretical simulation. We especially focused on the effects of voxel anisotropy in MR imaging with variable orientation of sheet-like structure. Improved and stable accuracy features were observed when the standard deviation of Gaussian blurring combined with thickness determination processes was around square root of 2/2 times as large as the pixel size. The relation between voxel anisotropy in MR imaging and the range of sheet normal orientation within which acceptable accuracy is attainable was also clarified, based on the dependences of voxel anisotropy and the sheet normal orientation obtained by numerical simulations. Finally, in vitro experiments were conducted using an acrylic plate phantom and a resected femoral head to validate the results of theoretical simulation. The simulated thickness was demonstrated to be well-correlated with the actual in vitro thickness.
在三维（3-D）磁共振（MR）图像中测量片状薄解剖结构（如关节软骨和脑皮质）的厚度是一项重要的诊断程序。本文研究了MR图像中厚度测定精度的基本限制。我们将厚度定义为在亚体素分辨率下测量的边界两侧之间的距离，这些边界是二阶方向导数的零交叉点，并结合沿薄片表面法线方向的高斯模糊。基于MR成像和计算机后处理参数，通过理论模拟得出了厚度测定精度的特征。我们特别关注了具有可变片状结构取向的MR成像中体素各向异性的影响。当高斯模糊的标准差与厚度测定过程相结合时，其值约为像素大小的2/2平方根时，观察到了改进的和稳定的精度特征。基于数值模拟得到的体素各向异性和薄片法线方向的依赖性，还阐明了MR成像中的体素各向异性与可获得可接受精度的薄片法线方向范围之间的关系。最后，使用丙烯酸板模型和切除的股骨头进行了体外实验，以验证理论模拟的结果。结果表明，模拟厚度与实际体外厚度具有良好的相关性。
