Apparent diffusion tensor measurements in myelin-deficient rat spinal cords

Gulani, Vikas; Webb, Andrew; Duncan, Ian D.; Lauterbur, Paul C.

doi:10.1002/1522-2594(200102)45:2<191::aid-mrm1025>3.0.co;2-9

Cited by 236 publications

(169 citation statements)

References 33 publications

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“…The results in Table 2 show that the thickness of myelin significantly affects the predicted ADCs, in that with increasing myelin fraction the ADC is expected to decrease. The model is in qualitative agreement with the work by Gulani et al (22), who found in myelin-deficient rats the ADC in the spinal cord to be lower than in wildtype rats. These observations corroborate the importance of incorporating myelin in the simulation model.…”

Section: Discussionsupporting

confidence: 91%

“…Most models applicable to biological systems such as axons rely on geometric approximations, such as square prisms (17), cylinders (11,20), and ellipsoids (18), and treated myelin sheaths as infinitesimally thin membranes. Although the MR signal contributed from myelin is minor (low water content and short T 2 relaxation time) and it was shown that the presence of the myelin sheath is not requisite for diffusion anisotropy (21)(22)(23), myelin nevertheless constitutes a significant proportion of white matter and, as mentioned, undergoes morphologic changes during injury and repair (12,13).…”

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confidence: 99%

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An image‐based finite difference model for simulating restricted diffusion

Hwang

Chin

Wehrli

et al. 2003

Magnetic Resonance in Med

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Water diffusion in tissues is generally restricted and often anisotropic. Neural tissue is of particular interest, since it is well known that injury alters diffusion in a characteristic manner. Both Monte Carlo simulations and approximate analytical models have previously been reported in attempts to predict water diffusion behavior in the central nervous system. These methods have relied on axonal models, which assume simple geometries (e.g., ellipsoids, cylinders, and square prisms) and ignore the thickness of the myelin sheath. The current work describes a method for generating models using synthetic images. The computations are based on a 3D finite difference (FD) approximation of the diffusion equation. The method was validated with known analytic solutions for diffusion in a cylindrical pore and in a hexagonal array of cylinders. Therefore, it is envisioned that, by exploiting histologic images of neuronal tissues as input model, current method allows investigating the water diffusion behavior inside biological tissues and potentially as- Diffusion-sensitized MRI provides a means of probing the architectural features of structures that are much smaller than a voxel. In the CNS the degree of diffusion anisotropy is sensitive to local differences in nerve fiber orientation (1-3). Various mechanisms have been proposed to explain changes in the apparent diffusion coefficient (ADC) during pathologic states. For example, in the study of cat brain, cellular swelling in the initial stages of ischemia may account for the decreased ADC since water protons originally in the faster-diffusing extracellular space migrate into the intracellular space (4) In addition, the cellular swelling reduces the extracellular space and, thus, increases the tortuosity of the diffusion paths (5). In the rat spinal cord diffusion was found to be anisotropic (6 -8). Spinal cord injury resulted in reduced diffusion anisotropy (9) which has also been attributed to axonal swelling or loss and inflammation (10,11). Changes in the myelin sheath may also affect the ADC. For example, the demyelination resulting from mechanical trauma (12) and the varying levels of remyelination during recovery (13) may cause changes in the permeability of the barrier between the intracellular and extracellular compartments. Furthermore, regenerating and sprouting axon fibers are typically tortuous, small, and unmyelinated (14). The effect of these tissue parameters on the ADC may potentially be exploited to assess the extent of neural damage and repair in vivo. Reduced diffusion anisotropy in multiple sclerosis lesions have also been attributed to loss of axons and myelin (15,16). Diffusion-weighted imaging may thus potentially provide insight into the pathophysiologic changes in MS lesions if the relationship between morphology and the diffusion-sensitized MR signal are better understood.Previous attempts to predict the effects of morphologic changes have relied on Monte Carlo (MC) simulations (11,17) or approximate analytic expressions (18). Exact solutions...

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Section: Discussionsupporting

confidence: 91%

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confidence: 99%

An image‐based finite difference model for simulating restricted diffusion

Hwang

Chin

Wehrli

et al. 2003

Magnetic Resonance in Med

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“…A decrease in FA may be attributed to disorganized axons and hypomyelination. 33,34 Previous DTI studies of tuberous sclerosis complex also revealed a reduction of FA in the white matter lesions 12,13 and normal-appearing white matter. 14 The lower axial diffusivity in the tuberous sclerosis complex group suggested poor integrity of axons.…”

Section: Discussionmentioning

confidence: 94%

Cerebral Diffusion Tensor MR Tractography in Tuberous Sclerosis Complex: Correlation with Neurologic Severity and Tract-Based Spatial Statistical Analysis

Wong

Wang

Schwartz

et al. 2013

AJNR Am J Neuroradiol

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BACKGROUND AND PURPOSE:The neurologic significance of residual cerebral white matter tracts, identified on diffusion tensor tractography, has not been well studied in tuberous sclerosis complex. We aimed to correlate the quantity of reconstructed white matter tracts with the degree of neurologic impairment of subjects with the use of DTI and determined differences in white matter integrity between patients with tuberous sclerosis complex and controls with the use of voxelwise analysis.

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“…Diffusion anisotropy can be detected in the absence of myelin (Beaulieu, 2002), and the contribution of changes in myelin to altered diffusion measurements in vivo has been determined to be relatively low (Beaulieu, 2002, Beaulieu andAllen, 1994), with one study reporting a decrease of 20% in anisotropy in myelin-deficient animal models (Gulani et al, 2001). Nevertheless, in schizophrenia, myelination abnormalities have been demonstrated using MRI and T2 relaxation; reduced myelin water fraction was detected to a greater extent in the chronic than first episode groups and was localized to the genu of the corpus callosum and frontal WM (range 19-36%) (Flynn et al, 2003).…”

Section: Discussionmentioning

confidence: 99%

Altered Interhemispheric and Temporal Lobe White Matter Microstructural Organization in Severe Chronic Schizophrenia

Holleran

Ahmed

Anderson‐Schmidt

et al. 2013

Neuropsychopharmacol

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Diffusion MRI investigations in schizophrenia provide evidence of abnormal white matter (WM) microstructural organization as indicated by reduced fractional anisotropy (FA) primarily in interhemispheric, left frontal and temporal WM. Using tract-based spatial statistics (TBSS), we examined diffusion parameters in a sample of patients with severe chronic schizophrenia. Diffusion MRI data were acquired on 19 patients with chronic severe schizophrenia and 19 age-and gender-matched healthy controls using a 64 gradient direction sequence, (b ¼ 1300 s/mm 2 ) collected on a Siemens 1.5T MRI scanner. Diagnosis of schizophrenia was determined by Diagnostic and Statistical Manual for Mental Disorders 4th Edition (DSM-IV) Structured Clinical Interview for DSM disorder (SCID). Patients were treatment resistance, having failed to respond to at least two antipsychotic medications, and had prolonged periods of moderate to severe positive or negative symptoms. Analysis of diffusion parameters was carried out using TBSS. Individuals with chronic severe schizophrenia had significantly reduced FA with corresponding increased radial diffusivity in the genu, body, and splenium of the corpus callosum, the right posterior limb of the internal capsule, right external capsule, and the right temporal inferior longitudinal fasciculus. There were no voxels of significantly increased FA in patients compared with controls. A decrease in splenium FA was shown to be related to a longer illness duration. We detected widespread abnormal diffusivity properties in the callosal and temporal lobe WM regions in individuals with severe chronic schizophrenia who have not previously been exposed to clozapine. These deficits can be driven by a number of factors that are indistinguishable using in vivo diffusion-weighted imaging, but may be related to reduced axonal number or packing density, abnormal glial cell arrangement or function, and reduced myelin.

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Apparent diffusion tensor measurements in myelin-deficient rat spinal cords

Cited by 236 publications

References 33 publications

An image‐based finite difference model for simulating restricted diffusion

An image‐based finite difference model for simulating restricted diffusion

Cerebral Diffusion Tensor MR Tractography in Tuberous Sclerosis Complex: Correlation with Neurologic Severity and Tract-Based Spatial Statistical Analysis

Altered Interhemispheric and Temporal Lobe White Matter Microstructural Organization in Severe Chronic Schizophrenia

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