Highly diffusion-sensitized tensor imaging of unilateral cerebral arterial occlusive disease

Selective neuronal death is a well-recognized histopathologic sequel to moderate ischemic brain damage. However, radiologic visualization of these changes has not been established, even with diffusion tensor imaging (DTI). We sought to determine whether DTI with b values > or =1900 s/mm(2) reveals occult diffusion abnormalities in patients with cerebral arterial occlusive disease.

Six patients (five men, one woman; mean age +/- standard deviation, 66 +/- 8 years) with unilateral internal carotid or middle cerebral arterial occlusive disease but not parenchymal T2 hyperintensity underwent 3T fast DTI with b < or = 1300 s/mm(2) and slow DTI with b > or = 1900 s/mm(2). We postprocessed mean diffusibility and fractional anisotropy (FA) images from the fast and slow DTI datasets. Standardized asymmetry indices (AIs) were used to identify regional asymmetries. Diagnostic accuracy among the DTI modalities was assessed by means of receiver operating characteristic analysis.

In hemispheres ipsilateral to occluded vessel, AIs were significantly elevated on fast mean-diffusibility images of white matter at the levels of the internal capsule (95% confidence interval [CI]: 1.00, 1.09; P = .045) and corona radiata (95% CI: 1.01, 1.12; P = .034). AIs were significantly decreased on slow FA images at the internal capsule (95% CI: 0.84, 0.98; P = .018) and white matter at the internal capsule level (95% CI: 0.92, 1.00, P = .043). The slow FA map had the highest accuracy (89.8%) for detecting the hemisphere ipsilateral to arterial occlusion.

Slow FA maps acquired by using DTI with high b values are useful for visualizing ischemic brain damage in apparently normal WM.