In this paper, a nonrigid coregistration algorithm based on a viscous fluid model is proposed that has been optimized for diffusion tensor images (DTI), in which image correspondence is measured by the mutual information criterion. Several coregistration strategies are introduced and evaluated both on simulated data and on brain intersubject DTI data. Two tensor reorientation methods have been incorporated and quantitatively evaluated. Simulation as well as experimental results show that the proposed viscous fluid model can provide a high coregistration accuracy, although the tensor reorientation was observed to be highly sensitive to the local deformation field. Nevertheless, this coregistration method has demonstrated to significantly improve spatial alignment compared to affine image matching.

No abstract

Purpose: To compare region of interest (ROI)-based and diffusion tensor tractography (DTT)-based methods for evaluating diffusion properties of the spinal cord as a function of age. Materials and Methods:Commonly, an ROI segmentation is used to delineate the spinal cord. In this work, new segmentation methods are developed based on DTT. In a first, DTT-based, segmentation approach, the diffusion properties are calculated on the tracts. In a second method, the diffusion properties are analyzed in the spinal cord voxels that contain a certain number of tracts. We studied the changes in diffusion properties of the human spinal cord in subjects of different ages. Diffusion tensor imaging (DTI) measurements of the cervical spinal cord were acquired on 42 healthy volunteers (age range ϭ 19 -87 years). The fractional anisotropy (FA), the mean diffusivity (MD), and eigenvalues ( 1 , 2 , and 3 ) were compared for the ROIand DTT-based segmentation methods. Results:Our automatic techniques are shown to be highly reproducible and sensitive for detecting DTI changes. FA decreased (r ϭ -0.38; P Ͻ 0.05), whereas MD and eigenvalues increased (r ϭ Ϯ 0.45; P Ͻ 0.05) with age. These trends were not statistically significant for the ROI-based segmentation (P Ͼ 0.05). IT IS GENERALLY KNOWN that during aging nerve cells die, and that the amount of nerve tissue gradually reduces (1). Other age-related changes in the central nervous system are the swelling of the axons, the subsequent diminishing of myelin, and a decreasing quantity of the cytoskeleton (2). Although conventional MRI can detect morphological white matter (WM) changes, it can not reflect the tissue quality with respect to the WM microstructure coherence (3,4). These microstructural alterations will especially affect the local diffusion and are therefore measurable with diffusion tensor imaging (DTI). This relatively new MRI technique measures the diffusion of water molecules and provides insight into the WM structure of the central nervous system (5). Local quantitative measures can be derived from the diffusion tensor, such as the fractional anisotropy (FA), which is a normalized measure for the degree of anisotropy, and the mean diffusivity (MD), i.e., the averaged diffusion. Recent DTI studies of different pathologies are starting to use these quantitative measurements, demonstrating the potential of this in vivo and noninvasive imaging technique for detecting microstructural pathological alterations (6,7). Conclusion: DTT is a robust andThe spinal cord, a clinically important part of the central nervous system containing motor and sensory pathways, is an interesting anatomical WM structure, because degeneration of its microstructure has been reported in many diseases (8,9). Due to its specific nature of measuring microstructural WM alterations, DTI can be seen as an exquisite diagnostic technique for spinal cord examination. The spinal cord is surrounded by cerebrospinal fluid (CSF) where, in contrast to the brain, the gray matter (GM) is situated on the inside of th...