Korean J Radiol.  2008 Jun;9(3):191-195. 10.3348/kjr.2008.9.3.191.

Evaluation of the Somatotopic Organization of Corticospinal Tracts in the Internal Capsule and Cerebral Peduncle: Results of Diffusion-Tensor MR Tractography

• Park JK
• Kim BS
• Choi G
• Kim SH
• Choi JC
• Khang H

• KMID: 1758451
• DOI: http://doi.org/10.3348/kjr.2008.9.3.191

Abstract

OBJECTIVE
We have used diffusion tensor tractography (DTT) for the evaluation of the somatotopic organization of corticospinal tracts (CSTs) in the posterior limb of the internal capsule (PLIC) and cerebral peduncle (CP). MATERIALS AND METHODS: We imaged the brains of nine healthy right-handed subjects. We used a spin-echo echo-planar imaging (EPI) sequence with 12 diffusion-sensitized directions. DTT was calculated with an angular threshold of 35 degrees and a fractional anistropy (FA) threshold of 0.25. We determined the location of the CSTs by using two regions of interest (ROI) at expected areas of the pons and expected areas of the lateral half of the PLIC, in the left hemisphere of the brain. Fiber tracts crossing these two ROIs and the precentral gyrus (PCG) were defined as CSTs. Four new ROIs were then defined for the PCG, from the medial to lateral direction, as ROI 1 (medial) to ROI 4 (lateral). Finally, we defined each fiber tract of the CSTs between the pons and each ROI in the PCG by using two ROIs methods. RESULTS: In all subjects, the CSTs were organized along the long axis of the PLIC, and the hand fibers were located anterior to the foot fibers. The CSTs showed transverse orientation in the CP, and the hand fibers were located usually medial to the foot fibers. CONCLUSION: Corticospinal tracts are organized along the long axis of the PLIC and the horizontal direction of the CP.

Keyword

Brain, MR; MR, technology

MeSH Terms

Adult
Diffusion Magnetic Resonance Imaging/*methods
Female
Humans
Internal Capsule/*anatomy & histology
Male
Pyramidal Tracts/*anatomy & histology
Tegmentum Mesencephali/*anatomy & histology

Figure

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  Fig. 1 Region of interest selection for diffusion tensor tractography at pons, posterior limb of internal capsule and precentral gyrus. A. Region of interest for pons was selected at expected corticopinal tract area on diffusion tensor MR imaging color map. Left side is left. B. Region of interest for corticospinal tract was selecteed at lateral half of posterior limb of internal capsule on diffusion tensor MR imaging color map. C. Precentral gyrus was determined by fibers crossing pons and posterior limb of internal capsule regions of interest, and it was identified by using anatomical landmarks such as posterior knob and superior frontal and precentral sulci on a B0 image. D. Four precentral gyrus regions of interest were drawn from medial (ROI 1) to lateral precentral gyrus (ROI 4) on B0 image. ROI 3 and ROI 4 were drawn near to posterior knob of precentral gyrus.

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  Fig. 2 Fiber tracts from medial half of posterior limb of internal capsule by single region of interest tracking. A-C. Fibers from medial posterior limb of internal capsule (purple color) descended to midbrain, which is posterior to cerebral peduncle. Fibers from medial posterior limb of internal capsule terminated at medial portion of precentral gyrus (medial to precentral gyrus regions of interest for corticospinal tracts), postcentral gyrus, and supplementary motor area.

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  Fig. 3 Typical pattern of somatotopic organization of corticospinal tracts at posterior limb of internal capsule. A. Fiber tracts from lateral two regions of interest were located anterior to fiber tracts from medial two regions of interest at precentral gyrus as seen on B0 image (ROI 1-pink, ROI 2-blue, ROI 3-yellow, ROI 4-red). B. Corticospinal tract fibers were organized mainly along long axis of posterior limb of internal capsule. Medial fibers (ROI 1 and ROI 2, presumed foot fibers) were located more posterior to lateral fibers (ROI 3 and ROI 4, presumed hand fibers).

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  Fig. 4 Typical pattern of somatotopic organization of corticospinal tracts at cerebral peduncle. A, B. Corticospinal tract fibers were organized mainly along horizontal (left-to-right) axis of cerebral peduncle. Medial fibers (ROI 1 and ROI 2, presumed foot fibers) were located more lateral to lateral fibers (ROI 3 and ROI 4, presumed hand fibers).

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  Fig. 5 Intermixing of fibers from lateral regions of interest. A. ROI 3 fibers divided anterior and posterior division at precentral gyrus (B0 image). B, C. ROI 4 fibers were located between anterior and posterior divisions at posterior limb of internal capsule and cerebral peduncle.

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