Use of diffusion tensor imaging to evaluate weakness

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Object

Recently, diffusion tensor (DT) imaging was introduced to demonstrate white matter tracts. However, research interest has focused on the anatomical rather than the functional aspects of this imaging modality. The authors undertook a functional analysis of DT imaging to determine the relationship between weakness and changes on DT images.

Methods

Diffusion tensor images were obtained in 23 patients with lesions located adjacent to the pyramidal tract. Patients were classified according to their motor deficit. Axial magnetic resonance image sections through the maximum tumor diameters were selected and the mean apparent diffusion coefficients (ADCs) and mean fractional anisotropies (FAs) were measured. One ovoid region of interest (ovROI) was placed in the center of the pyramidal tract and another was designed to include the whole pyramidal tract at the same axial level (wROI). To determine intraobserver variability, a single neurosurgeon measured mean ADCs and FAs four times by using these two different ROI types without knowledge of any clinical information. To determine interobserver variability, a second neurosurgeon who was also unaware of any clinical information measured the mean ADCs and FAs by using the wROI method.

The five measurements produced the same results. The mean FA at the lesion side of the pyramidal tract was significantly lower in patients with weakness (p < 0.01). Little intraobserver measurement variability occurred using the ovROI method, and no interobserver variability occurred using the wROI method.

Conclusions

Motor weakness was significantly related to a low mean FA in the pyramidal tract on the lesion side. Designing an ROI that includes the whole pyramidal tract is an easier and more reproducible method than using an ovROI method.

Abbreviations used in this paper:ADC = apparent diffusion coefficient; DT = diffusion tensor; FA = fractional anisotropy; L/N = lesion side value/normal side value; MR = magnetic resonance; ovROI = ovoid region of interest; wROI = whole pyramidal tract ROI.

Article Information

Address reprint requests to: Chun-Kee Chung, M.D., Ph.D., Department of Neurosurgery, Seoul National University College of Medicine, 28 Yeongeon-dong, Jongno-gu, Seoul 110-744, South Korea. email: chungc@snu.ac.kr.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Case 1. A: A T2-weighted MR image showing a lesion on the right basal ganglia together with peritumoral edema that encroached on the ipsilateral internal capsule. A signal change in the right internal capsule was obvious (arrow). B: An enhanced T1-weighted MR image revealing a focally enhanced mass. C: An FA map without color coding. An ROI was placed on the posterior limb of the internal capsule. The mean ADC and FA values on the lesion side were 1002 × 10−6 mm2/second and 628 × 10−3, respectively, and on the normal side were 800 × 10−6 mm2/second and 713 × 10−3, respectively. D: Tractography image demonstrating a deviated fiber, which was well preserved in its continuity on the internal capsule. The pathological diagnosis was anaplastic astrocytoma.

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    Case 2. A: A T2-weighted MR image showing a right basal ganglia lesion with peritumoral edema that encroached on the ipsilateral internal capsule (arrow). A signal change in the right internal capsule was obvious. B: An enhanced T1-weighted MR image demonstrating a well-enhancing mass. C: An FA map without color coding. An ROI was placed on the posterior limb of the internal capsule. The mean ADC and FA values on the lesion side were 1005 × 106 mm2/seconds and 462 × 10−3, respectively, and on the normal side were 899 × 10−6 mm2/seconds and 635 × 10−3, respectively. D: Coronal FA map revealing a deviated but well-preserved internal capsule. Its mean FA value was obviously lower than that of the normal side. The pathological diagnosis was anaplastic oligodendroglioma.

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    Case 3. A and B: Axial T2-weighted (A) and T1-weighted (B) MR images showing a ring-enhancing lesion in the left basal ganglia with marked perilesional edema, suggesting a brain abscess. C: An FA map demonstrating that the internal capsule had been broken by the mass (arrow). An ROI was placed on the posterior limb of the internal capsule. The mean ADC and FA on the lesion side were 1237 × 10−6 mm2/second and 304 × 10−3, respectively, and on the normal side were 1008 × 10−6 mm2/second and 534 × 10−3, respectively. Because of the patient’s age and the deep-seated nature of the lesion, medical therapy with antibiotics was prescribed. Although the internal capsule seemed to have been broken by the abscess according to the DT image, the patient’s weakness improved to allow ambulation with antibiotics.

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