Different Characteristics of the Corticospinal Tract According to the Cerebral Origin: DTI Study

BACKGROUNDANDPURPOSE: Little is known about differences in corticospinal tract fibers according to cerebral origin. Using diffusion tensor tractography, we attempted to investigate the characteristics of the CST according to the cerebral origin in the human brain. MATERIALS AND METHODS: Thirty-six healthy subjects were recruited for this study. A 1.5T Gyroscan Intera system was used for acquisition of DTI. CSTs were reconstructed by selection of fibers passing through seed and target ROIs: seed ROIs, the area of the CST at the pontomedullary junction; target ROIs, the primary motor cortex, the primary somatosensory cortex, the dorsal premotor cortex, and the supplementary motor area. RESULTS: A significant difference in tract volume was observed in each ROI (P .05): M1 (2373.6, 36.9%), S1 (2037.7, 31.7%), SMA (1588.0, 24.7%), and dPMC (429.8, 6.7%). Regarding fractional anisotropy values, the dPMCor SMA showed higher values than theM1 or S1; however, the opposite occurred in terms of the mean diffusivity value (P .05). In addition, fractional anisotropy andmean diffusivity values of the dPMC differed from those of the SMA (P .05); in contrast, no significant difference was observed between the M1 and S1 (P .05). CONCLUSIONS: Tract volume was found to differ according to cerebral origin and was, in descending order, M1, S1, SMA, and dPMC. In addition, the directionality and diffusivity of CST fibers in the SMA and the dPMC differed from those of the M1 and S1, which showed similar characteristics. ABBREVIATIONS: CST corticospinal tract; dPMC dorsal premotor cortex; M1 primary motor cortex, S1 primary somatosensory cortex; SMA supplementary motor area The corticospinal tract is a major neural tract for motor function in the human brain. The CST is known be involved mainly in movement execution of distal extremities, particularly fine-motor activities of the hand. The CST originates from various cortical areas, such as the secondary motor area, the parietal cortex, and the primary motor cortex. The multiple cerebral origins of the CST appear to be important in terms of multiple functions of CST fibers and motor recovery mechanisms: perilesional reorganization following M1 injury. Many previous studies have reported differences in characteristics of CST fibers, in terms of the amount of CST fibers and function, according to the origin of the cerebral cortex. Most of these studies have used animal brains because only postmortem histologic studies or microelectrode stimulation studies have been used for research on the human brain. By contrast, diffusion tensor tractography, a technique derived from DTI, allows 3D visualization and estimation of the CST. Several diffusion tensor tractography studies have reported the characteristics of the whole CST; however, little is known about differences in CST fibers according to the cerebral origin. In the current study, by using diffusion tensor tractography, we attempted to investigate the characteristics of the CST according to the cerebral origin in the human brain. MATERIALS AND METHODS Subjects We recruited 36 healthy right-handed subjects (mean age, 34.2 years; range, 20 49 years; male, 18 subjects [mean age, 33.5 years; range, 20 48 years]; female, 18 subjects [mean age, 34.9 years; range, 20 49 years]) with no previous history of neurologic, psyReceived July 2, 2012; accepted after revision September 17. From the Department of Physical Medicine and Rehabilitation, College of Medicine, Yeungnam University, Taegu, Republic of Korea. This work was supported by the Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (2012R1A1A4A01001873). Please address correspondence to Sung Ho Jang, MD, Department of Physical Medicine and Rehabilitation, College of Medicine, Yeungnam University 317-1, Daemyungdong, Namku, Taegu, 705–717, Republic of Korea; e-mail: strokerehab@hanmail.net Indicates open access to non-subscribers at www.ajnr. org http://dx.doi. org/10.3174/ajnr.A3389 AJNR Am J Neuroradiol 34:1359–63 Jul 2013 www.ajnr. org 1359 chiatric, or physical illness. All subjects understood the purpose of the study and provided written informed consent before participation. The study protocol was approved by our local institutional research board. Diffusion Tensor Image DTI data were obtained by using a Synergy-L sensitivity encoding head coil on a 1.5T Gyroscan Intera system (Philips, Best, the Netherlands) equipped with single-shot echo-planar imaging. For each of the 32 noncollinear diffusion-sensitizing gradients, we acquired 67 contiguous sections parallel to the anterior/posterior commissure line. Imaging parameters were as follows: acquisition matrix 96 96, reconstructed to matrix 128 128, FOV 221 221 mm, TR 10,726 ms, TE 76 ms, parallel imaging reduction factor (sensitivity encoding factor) 2, EPI factor 49, b 1000 s/mm, NEX 1, and a section thickness of 2.3 mm (acquired isotropic voxel size, 2.3 2.3 2.3 mm). Fiber Tracking The Oxford Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB) Software Library (www.fmrib.ox.ac.uk/fsl) was used for analysis of diffusion-weighted imaging data. Affine multiscale 2D registration was used for correction of head motion effect and image distortion due to eddy currents. A probabilistic tractography method, based on a multifiber model, was used in performance of fiber tracking, which was applied in the present study using tractography routines implemented in FMRIB Diffusion (5000 streamline samples, 0.5-mm step lengths, curvature thresholds 0.2). CSTs for the M1, the primary somatosensory cortex, dorsal premotor cortex, and supplementary motor area were determined by selection of fibers passing through seed and target ROIs. Seed ROIs were placed at the CST portion of the pontomedullary junction on the color map. Placement of target ROIs was as follows: 1) the primary motor cortex (anterior boundary: precentral sulcus; posterior boundary: central sulcus; medial boundary: the midline between the right and left hemispheres; lateral boundary: the line passing through the lateral margin of the precentral knob and horizontal to the midline); 2) the primary somatosensory cortex (anterior boundary: central sulcus; posterior boundary: postcentral sulcus; medial boundary: the midline between the right and left hemispheres; lateral boundary: the line passing through the lateral margin of the precentral knob and horizontal to the midline between the right and left hemispheres); 3) the dorsal premotor cortex (anterior boundary: the line joining the anterior extent of the SMA; posterior boundary: precentral sulcus; medial boundary: the lateral margin of the SMA; lateral boundary: the line passing through the lateral margin of the precentral knob and horizontal to the midline); 4) the supplementary motor area (anterior boundary: the line drawn through the anterior commissure perpendicular to the anterior/posterior commissure line; posterior boundary: anterior margin of M1; medial boundary: midline between the right and left hemispheres; lateral boundary: the line 10.6% lateral from the midline, the ratio of 15 mm to the maximum width of the Montreal Neurological Institute atlas) (Fig 1). Of 5000 samples generated from each seed voxel, results for each contact were visualized thresholds and weightings of tract probability at a minimum of 1 streamline through each voxel for analysis. Values of fractional anisotropy, mean diffusivity, and tract volume of the CSTs were measured. Statistical Analysis The Statistical Package for the Social Sciences software (Version 15.0; SPSS, Chicago, Illinois) was used for data analysis. Using 1-way ANOVA with the least significant difference post hoc test, we determined the differences in values for tract volume, fractional anisotropy, and mean diffusivity among CSTs from the M1, FIG 1. A, The seed ROI was placed on the pontomedullary junction (CST area). Target ROIs were placed on the primary motor cortex (red), the primary somatosensory cortex (green), the dorsal premotor cortex (yellow), and the supplementarymotor area (blue). B, CSTswere reconstructed in both hemispheres. Red indicates CSTs for the primary motor cortex; green, CSTs for the primary somatosensory cortex; yellow, CSTs for the dorsal premotor cortex; blue, CSTs for the supplementary motor area. C, CSTs from each ROI were reconstructed in both hemispheres. 1360 Seo Jul 2013 www.ajnr. org S1, dPMC, and SMA. The independent t test was used for determination of the difference in values of tract volume, fractional anisotropy, and mean diffusivity from each CST between the right and left hemispheres. The significance level for the P value was set