Diffusion Tensor MR Imaging of the Brain and White Matter Tractography

Diffusion Tensor MR Imaging of the Brain and White Matter Tractography

Elias R. Melhem¹^,2, Susumu Mori¹^,2, Govind Mukundan¹, Michael A. Kraut¹^,2, Martin G. Pomper¹ and Peter C. M. van Zijl¹^,2

^¹ Department of Radiology and Radiological Sciences, The Johns Hopkins Medical Institutions, 600 N. Wolfe St., Baltimore, MD 21287-2182.
^² F. M. Kirby Research Center for Functional Brain Imaging, Kennedy-Krieger Institute, The Johns Hopkins Medical Institutions, 707 N. Broadway, Baltimore, MD 21287.

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Fig. 1. —Diagram shows loss of intensity of MR signal (S, solid line) resulting from inefficient rephasing of dephased spins because of displacement of water molecules (diffusion) between application of bipolar gradients (G). With decreased diffusion (reduced displacement of water molecules), rephasing process is more efficient and signal loss is predominantly caused by T2 decay (dotted line).

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Fig. 2. —Diagram shows Stejskal-Tanner pulsed bipolar gradient scheme [24]. This scheme is commonly implemented on clinical MR scanners for diffusion sensitization. Degree of diffusion sensitization (b value) is determined by duration ( ${delta}$ ) and strength (height) of sensitizing pulsed-gradients (G), and time interval between two pulsed gradients ( ${Delta}$ ). RF = radiofrequency.

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Fig. 3. —Graph of natural logarithm of signal intensity (Ln [S / S₀]) from diffusion-weighted images with different degrees of diffusion weighting (b value) allows determination of apparent diffusion coefficient (ADC) based on linear fit of data points. Absolute value of slope of plotted line, and thus ADC, is greater for cerebrospinal fluid (CSF) than for gray matter (GM).

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Fig. 4A. —Diffusion tensor MR images in 20-year-old healthy man. Reference T2-weighted spin-echo echoplanar MR image (TR/TE, 5000/92; b value, 0).

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Fig. 4B. —Diffusion tensor MR images in 20-year-old healthy man. Diffusion-weighted spin-echo echoplanar MR image (5000/92; b value, 600 sec/mm²).

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Fig. 4C. —Diffusion tensor MR images in 20-year-old healthy man. Apparent diffusion coefficient map can be calculated from A and B.

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Fig. 5A. —Drawings show diffusion of water molecule. Diffusion in environment with strongly aligned white matter fibers (high anisotropy).

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Fig. 5B. —Drawings show diffusion of water molecule. Diffusion ellipsoid in three-dimensional space.

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Fig. 6A. —Diffusion tensor MR images in 30-year-old healthy man. Fractional anisotropy map describes degree of diffusion anisotropy in each voxel. In white matter, where anisotropy is high, bright end of gray scale is assigned; in gray matter, where anisotropy is low, dark end of gray scale is assigned.

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Fig. 6B. —Diffusion tensor MR images in 30-year-old healthy man. Vector map coregistered onto T2-weighted MR image (TR/TE, 5000/92) describes orientation of principal eigenvector in each voxel.

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Fig. 6C. —Diffusion tensor MR images in 30-year-old healthy man. Color-coded white matter fiber maps are generated on basis of fractional anisotropy and vector maps. cc = corpus callosum, slf = superior longitudinal fasciculus, ilf = inferior longitudinal fasciculus, cst = corticospinal tract.

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Fig. 6D. —Diffusion tensor MR images in 30-year-old healthy man. Three-dimensional fiber tracts are generated on basis of fractional anisotropy and vector maps.

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Fig. 7. —Schematic shows white matter tracking used by algorithm. Degree of diffusion anisotropy is indicated by gray scale (white is highest), and direction of principal eigenvector in each image voxel is indicated by an arrow. On basis of defined thresholds, tracking (long curved arrows) is along voxels with similar measures of anisotropy and direction of principal eigenvector. Algorithm can distinguish between tracts A and B because they are separated by voxels with low anisotropy, and between tracts A and C because of differences in direction of principal eigenvectors. Asterisks indicate starting points of tracking.

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Fig. 8A. —Diffusion tensor MR images in 26-year-old healthy man. (Reprinted with permission from [82]) Three-dimensional white matter fiber tracking of frontopontine (FPT, green), corticospinal (CST, red), and temporoparietooccipitopontine (TPOPT, blue) tracts coregistered onto sagittal T2-weighted MR images (TR/TE, 5000/92). Tracking is based on two regions of interest (ROIs). ROI placed at level of midbrain (blue arrow) does not allow separation between tracts traversing cerebral peduncle because of closeness and similarities in direction and anisotropy. Another ROI at level of lower pons, below termination of FPT and TPOPT (purple arrow), allows separation of tracts.

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Fig. 8B. —Diffusion tensor MR images in 26-year-old healthy man. (Reprinted with permission from [82]) Three-dimensional white matter fiber tracking of FPT (green), CST (red), and TPOPT (blue) tracts coregistered onto axial T2-weighted MR images (5000/92).

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Fig. 8C. —Diffusion tensor MR images in 26-year-old healthy man. (Reprinted with permission from [82]) Anatomic drawing at level of midbrain shows good agreement with tracking method (B).

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Fig. 9A. —Schematic shows difference between tracking methods. Maintaining information on intercepts is achieved by performing tracking in a continuous number field, which results in precise white matter fiber tracking. Voxels from which tracking is launched are designated by asterisks, direction of principal eigenvector in each voxel is designated by an arrow, and voxels connected by tracking algorithm are indicated by boxes with shaded arrows. Dark arrows indicate interrupted trajectory of track. (Reprinted with permission from [19]) Tracking (long curved arrows) without (A) and with (B) keeping information on intercepts when tracking leaves voxel.

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Fig. 9B. —Schematic shows difference between tracking methods. Maintaining information on intercepts is achieved by performing tracking in a continuous number field, which results in precise white matter fiber tracking. Voxels from which tracking is launched are designated by asterisks, direction of principal eigenvector in each voxel is designated by an arrow, and voxels connected by tracking algorithm are indicated by boxes with shaded arrows. Dark arrows indicate interrupted trajectory of track. (Reprinted with permission from [19]) Tracking (long curved arrows) without (A) and with (B) keeping information on intercepts when tracking leaves voxel.

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Fig. 10A. —Diffusion tensor MR images in 35-year-old healthy man. Three-dimensional fiber tracking of brainstem with ventral (purple) and medial (turquoise) components of middle cerebellar peduncles, inferior cerebellar peduncle (green), superior cerebellar peduncle (yellow), medial longitudinal fasciculus (orange), and corticopontospinal (red) tracts are superimposed on these two images. (Reprinted with permission from [82]) Mid sagittal T2-weighted MR image (TR/TE, 5000/92) of brainstem and cerebellum.

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Fig. 10B. —Diffusion tensor MR images in 35-year-old healthy man. Three-dimensional fiber tracking of brainstem with ventral (purple) and medial (turquoise) components of middle cerebellar peduncles, inferior cerebellar peduncle (green), superior cerebellar peduncle (yellow), medial longitudinal fasciculus (orange), and corticopontospinal (red) tracts are superimposed on these two images. (Reprinted with permission from [82]) Photograph of anatomic specimen shows postmortem dissection of brainstem and cerebellum.

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Fig. 11A. —9-year-old boy with cerebral X-linked adrenoleukodystrophy who presented with progressive motor and visual deficits. T2-weighted MR image (TR/TE, 5000/92) shows abnormal symmetric hyperintensity involving peritrigonal white matter.

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Fig. 11B. —9-year-old boy with cerebral X-linked adrenoleukodystrophy who presented with progressive motor and visual deficits. Fractional anisotropy map shows central zone (asterisks) of marked hypointensity (marked decrease in anisotropy) and peripheral zone (arrowheads) of mild hypointensity (mild decrease in anisotropy).

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Fig. 12A. —6-year-old boy with anterior form of X-linked adrenoleukodystrophy who presented with personality changes. Diffusion-weighted images show three-dimensional fiber tracking of corpus callosum coregistered onto images of affected boy and of 8-year-old healthy boy. In affected boy, substantial decrease is seen in white matter tracts crossing genu and anterior body of corpus callosum and in both frontal lobes compared with healthy boy. Axial (A) and sagittal (B) T2-weighted MR images (TR/TE, 5000/92) of affected boy.

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Fig. 12B. —6-year-old boy with anterior form of X-linked adrenoleukodystrophy who presented with personality changes. Diffusion-weighted images show three-dimensional fiber tracking of corpus callosum coregistered onto images of affected boy and of 8-year-old healthy boy. In affected boy, substantial decrease is seen in white matter tracts crossing genu and anterior body of corpus callosum and in both frontal lobes compared with healthy boy. Axial (A) and sagittal (B) T2-weighted MR images (TR/TE, 5000/92) of affected boy.

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Fig. 12C. —6-year-old boy with anterior form of X-linked adrenoleukodystrophy who presented with personality changes. Diffusion-weighted images show three-dimensional fiber tracking of corpus callosum coregistered onto images of affected boy and of 8-year-old healthy boy. In affected boy, substantial decrease is seen in white matter tracts crossing genu and anterior body of corpus callosum and in both frontal lobes compared with healthy boy. Axial (C) and sagittal (D) T2-weighted MR images (5000/92) of healthy boy.

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Fig. 12D. —6-year-old boy with anterior form of X-linked adrenoleukodystrophy who presented with personality changes. Diffusion-weighted images show three-dimensional fiber tracking of corpus callosum coregistered onto images of affected boy and of 8-year-old healthy boy. In affected boy, substantial decrease is seen in white matter tracts crossing genu and anterior body of corpus callosum and in both frontal lobes compared with healthy boy. Axial (C) and sagittal (D) T2-weighted MR images (5000/92) of healthy boy.

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Fig. 13A. —6-year-old boy with cerebral palsy resulting from periventricular leukomalacia who presented with asymmetric spastic diplegia affecting left side more than right. Color maps of brainstem white matter tracts show decrease in size of corticopontospinal tracts in affected boy (arrowheads, A and B) compared with those shown on color maps of brainstem white matter tracts in 8-year-old healthy boy (arrowheads, C and D). Furthermore, right corticopontospinal tract is more involved than left in affected boy, which correlates with his neurologic examination.

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Fig. 13B. —6-year-old boy with cerebral palsy resulting from periventricular leukomalacia who presented with asymmetric spastic diplegia affecting left side more than right. Color maps of brainstem white matter tracts show decrease in size of corticopontospinal tracts in affected boy (arrowheads, A and B) compared with those shown on color maps of brainstem white matter tracts in 8-year-old healthy boy (arrowheads, C and D). Furthermore, right corticopontospinal tract is more involved than left in affected boy, which correlates with his neurologic examination.

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Fig. 13C. —6-year-old boy with cerebral palsy resulting from periventricular leukomalacia who presented with asymmetric spastic diplegia affecting left side more than right. Color maps of brainstem white matter tracts show decrease in size of corticopontospinal tracts in affected boy (arrowheads, A and B) compared with those shown on color maps of brainstem white matter tracts in 8-year-old healthy boy (arrowheads, C and D). Furthermore, right corticopontospinal tract is more involved than left in affected boy, which correlates with his neurologic examination.

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Fig. 13D. —6-year-old boy with cerebral palsy resulting from periventricular leukomalacia who presented with asymmetric spastic diplegia affecting left side more than right. Color maps of brainstem white matter tracts show decrease in size of corticopontospinal tracts in affected boy (arrowheads, A and B) compared with those shown on color maps of brainstem white matter tracts in 8-year-old healthy boy (arrowheads, C and D). Furthermore, right corticopontospinal tract is more involved than left in affected boy, which correlates with his neurologic examination.

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Fig. 14A. —1-year-old boy with middle hemispheric variant of holoprosencephaly. Axial T2-weighted MR image (TR/TE, 3000/100) above level of lateral ventricles shows site of noncleavage of cerebral hemispheres. Arrowheads indicate white matter.

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Fig. 14B. —1-year-old boy with middle hemispheric variant of holoprosencephaly. Coronal fast phase-sensitive inversion-recovery MR image (3300/40; inversion time, 200 msec) through frontal horns shows noncleavage of cerebral hemispheres with continuation of anomalous gray and white matter (arrowheads) across midline. Note absence of septum pellucidum.

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Fig. 14C. —1-year-old boy with middle hemispheric variant of holoprosencephaly. Fractional anisotropy map in axial plane, above level of lateral ventricles, helps differentiate between white (high anisotropy, arrowheads) and gray (low anisotropy, asterisks) matter crossing midline.

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Fig. 14D. —1-year-old boy with middle hemispheric variant of holoprosencephaly. White matter color map provides information about direction of white matter tracts, with red assigned to tracts running across midline (x-axis, arrowheads) and blue assigned to tracts running perpendicular to image section (z-axis, asterisks).

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Fig. 15A. —T2-weighted MR images (TR/TE, 5000/92) in 48-year-old woman with left-sided posterior fossa meningioma. (Reprinted with permission from [82]) Mid sagittal image shows levels of axial sections (B, C, and D) and slightly hyperintense (compared with brain) extraaxial mass compressing brainstem.

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Fig. 15B. —T2-weighted MR images (TR/TE, 5000/92) in 48-year-old woman with left-sided posterior fossa meningioma. (Reprinted with permission from [82]) Axial images at level of third ventricle (B), anterior commissure (C), and brainstem (D) show coregistered left (red) and right (yellow) corticopontospinal tracts. Note relationship of extraaxial mass to posteriorly displaced left corticospinal tract.

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Fig. 15C. —T2-weighted MR images (TR/TE, 5000/92) in 48-year-old woman with left-sided posterior fossa meningioma. (Reprinted with permission from [82]) Axial images at level of third ventricle (B), anterior commissure (C), and brainstem (D) show coregistered left (red) and right (yellow) corticopontospinal tracts. Note relationship of extraaxial mass to posteriorly displaced left corticospinal tract.

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Fig. 15D. —T2-weighted MR images (TR/TE, 5000/92) in 48-year-old woman with left-sided posterior fossa meningioma. (Reprinted with permission from [82]) Axial images at level of third ventricle (B), anterior commissure (C), and brainstem (D) show coregistered left (red) and right (yellow) corticopontospinal tracts. Note relationship of extraaxial mass to posteriorly displaced left corticospinal tract.

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Fig. 15E. —T2-weighted MR images (TR/TE, 5000/92) in 48-year-old woman with left-sided posterior fossa meningioma. (Reprinted with permission from [82]) Three-dimensional representation of left corticospinal tract superimposed onto sagittal and coronal images better shows relationship between mass (green) and tract (red).

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