The aim of this study was to characterize in vivo measurements of diffusion along the length of the entire healthy spinal cord and to compare DTI indices, including fractional anisotropy (FA) and mean diffusivity (MD), between cord regions. The objective is to determine whether or not there are significant differences in DTI indices along the cord that must be considered for future applications of characterizing the effects of injury or disease. A cardiac gated, single-shot EPI sequence was used to acquire diffusion-weighted images of the cervical, thoracic, and lumbar regions of the spinal cord in nine neurologically intact subjects (19 to 22 years). For each cord section, FA versus MD values were plotted, and a k-means clustering method was applied to partition the data according to tissue properties. FA and MD values from both white matter (average , average ？mm2/s) and grey matter (average , average ？mm2/s) were relatively consistent along the length of the cord. 1. Introduction Diffusion tensor imaging (DTI) allows for the in vivo？？examination of the extent of damage to white matter microstructure which may enable the detection and diagnosis of subtle injuries and may provide a means of monitoring the effects of a therapeutic intervention. The applications of this technique for characterizing the structural changes that result from lesions in the brain have become well established [1]. More recently, DTI has also been applied to the spinal cord and has been demonstrated to be a similarly valuable tool for assessing the extent of white matter damage in numerous spinal cord-related conditions including multiple sclerosis [2, 3], amyotrophic lateral sclerosis [4, 5], myelitis [6, 7], and spinal cord injury (SCI) [8, 9]. However, despite its potential as a clinical tool, it is first necessary to establish reference values of fractional anisotropy (FA, which describe the degree to which a single diffusion orientation is dominant) and mean diffusivity (MD, which describes the overall diffusivity) in healthy populations in order to be able to properly interpret DT images acquired in patients. Furthermore, estimating the consistency of DTI indices across different regions in the healthy spinal cord is required for proper group comparisons between heterogeneous patient populations and healthy controls. The aim of the present study was therefore to characterize and compare DTI indices across the cervical, thoracic, and lumbar regions of the healthy spinal cord. Several studies have examined FA and MD values at different levels within the cervical spinal cord
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