Neuroimaging Research Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD 21224, USA.
IEEE Trans Med Imaging. 2011 Mar;30(3):747-58. doi: 10.1109/TMI.2010.2095027. Epub 2010 Dec 3.
Nonrigid registration of diffusion magnetic resonance imaging (MRI) is crucial for group analyses and building white matter and fiber tract atlases. Most current diffusion MRI registration techniques are limited to the alignment of diffusion tensor imaging (DTI) data. We propose a novel diffeomorphic registration method for high angular resolution diffusion images by mapping their orientation distribution functions (ODFs). ODFs can be reconstructed using q-ball imaging (QBI) techniques and represented by spherical harmonics (SHs) to resolve intra-voxel fiber crossings. The registration is based on optimizing a diffeomorphic demons cost function. Unlike scalar images, deforming ODF maps requires ODF reorientation to maintain its consistency with the local fiber orientations. Our method simultaneously reorients the ODFs by computing a Wigner rotation matrix at each voxel, and applies it to the SH coefficients during registration. Rotation of the coefficients avoids the estimation of principal directions, which has no analytical solution and is time consuming. The proposed method was validated on both simulated and real data sets with various metrics, which include the distance between the estimated and simulated transformation fields, the standard deviation of the general fractional anisotropy and the directional consistency of the deformed and reference images. The registration performance using SHs with different maximum orders were compared using these metrics. Results show that the diffeomorphic registration improved the affine alignment, and registration using SHs with higher order SHs further improved the registration accuracy by reducing the shape difference and improving the directional consistency of the registered and reference ODF maps.
扩散磁共振成像（MRI）的非刚性配准对于组分析和构建白质及纤维束图谱至关重要。目前大多数扩散 MRI 配准技术仅限于对扩散张量成像（DTI）数据的配准。我们提出了一种新的基于各向异性分辨率扩散图像的微分同胚配准方法，通过映射其方向分布函数（ODF）实现。ODF 可以使用 q 球成像（QBI）技术重建，并表示为球谐函数（SH）以解决体素内纤维交叉问题。配准基于优化微分同胚 demons 代价函数。与标量图像不同，变形 ODF 图谱需要 ODF 重定向以保持与局部纤维方向的一致性。我们的方法通过在每个体素计算魏格纳旋转矩阵来同时重新定向 ODF，并在配准过程中对 SH 系数进行应用。系数的旋转避免了主方向的估计，而主方向的估计没有解析解且耗时。该方法使用不同的最大阶次的 SH 对模拟和真实数据集进行了验证，评估指标包括估计和模拟变换场之间的距离、平均各向异性分数的标准差以及变形和参考图像的方向一致性。使用这些指标比较了不同最大阶次的 SH 配准的性能。结果表明，微分同胚配准改善了仿射配准，而使用更高阶次 SH 的配准进一步通过减少形状差异和提高参考 ODF 图谱的方向一致性提高了配准精度。
