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Objectives: This study investigated white matter alterations in the corpus callosum (CC) and centrum semiovale (CSO), using diffusion tensor imaging and magnetization transfer imaging, in participants with severe traumatic brain injury (TBI) and related these changes to processing speed measures. Participants and Methods: Fourteen adult participants with severe TBI underwent neuroimaging and assessment, using the Symbol Digit Modalities Test and Trail-Making Test, Part B, at approximately 6 months postinjury. Thirteen demographically similar, neurologically intact adults were imaged for comparison. Results: The TBI group demonstrated lower fractional anisotropy (FA) for the right CSO and higher apparent diffusion coefficient (ADC) for the CSO bilaterally than the control group. Lower FA and higher ADC were noted in all CC regions. Magnetization transfer imaging revealed smaller magnetization transfer ratios (MTRs) in the right and left CSO and CC genu and splenium. Written Symbol Digit Modalities Test performance was related to right CSO FA, bilateral CSO ADC, CC FA, and right CSO MTR, whereas oral Symbol Digit Modalities Test was related to right CSO FA, ADC, and MTR. Trail-Making Test, Part B, was related to right CSO FA and MTR. Conclusions: Advanced neuroimaging modalities such as diffusion tensor imaging and magnetization transfer imaging demonstrate significant alterations in white matter, which are related to processing speed. These techniques may be useful in quantifying the extent of injury even in normal appearing white matter after TBI. [ABSTRACT FROM AUTHOR]