Diffusion tensor imaging and MR spectroscopy in hypertension and presumed cerebral small vessel disease

Abstract

In patients with cerebral small vessel disease (SVD) diffusion tensor imaging (DTI) is sensitive to white matter damage and correlates better with cognitive function than conventional imaging. It has been proposed as a surrogate marker for treatment trials. However, the pathological changes underlying DTI are not known. The purpose of this study was to use magnetic resonance spectroscopy (MRS) to determine the pathological changes underlying DTI abnormalities in a range of patients from asymptomatic white matter hyperintensities to symptomatic cerebral SVD. 29 SVD patients, 63 hypertensive subjects, and 42 normotensive controls were recruited. The relationship between the DTI and MRS parameters in the centrum semiovale white matter was determined. There was a significant reduction in N-acetylaspartate (NAA; 2.067 ؎ 0.042 vs 2.299 ؎ 0.029 and 2.315 ؎ 0.036, P ‫؍‬ 9 ؋ 10 ؊6 ) and increase in mean diffusivity (mm 2 /s ؋ 10 ؊3 ; 0.942 ؎ 0.123 vs 0.822 ؎ 0.064 and 0.792 ؎ 0.057, P ‫؍‬ 1 ؋ 10 ؊8 ) in symptomatic SVD patients compared with the other two groups. DTI parameters correlated with NAA in all three groups, in a graded manner depending on severity of disease (r ؊SVD ؊0.827, hypertensive subjects ؊0.457, controls ؊0.317). NAA is a marker of axonal loss/dysfunction. These findings are consistent with axonal loss/dysfunction being the principal process causing the DTI changes found in cerebral SVD and ageing. Magn Reson Med 59:528 -534, 2008.

Posterior paralimbic and frontal metabolite impairments in asymptomatic hypertension with different treatment outcomes

“…The increase in PPL mI/Cr in our series agrees with a previous report showing higher mI/Cr values in the peritrigonal white matter of patients with asymptomatic hypertension. 5 Regarding the changes in frontal NAA/Cr ratio, the ratio drop in our resistant hypertensive patients is in agreement with two recent chemical-shift imaging reports involving the white matter of the centrum semiovale 21 and particular areas in the white and gray matters. 22 These studies showed decreasing NAA concentrations associated with increasing severity of disease 21 and NAA/Cr decreases in the gray matter of hypertensive patients.…”

“…5 Regarding the changes in frontal NAA/Cr ratio, the ratio drop in our resistant hypertensive patients is in agreement with two recent chemical-shift imaging reports involving the white matter of the centrum semiovale 21 and particular areas in the white and gray matters. 22 These studies showed decreasing NAA concentrations associated with increasing severity of disease 21 and NAA/Cr decreases in the gray matter of hypertensive patients. 22 Contrary to these results, NAA/Cr was not found to differ between treated and untreated hypertensive patients in a recent related study.…”

“…In the Hannesdottir et al 23 study, NAA/Cr ratio was averaged from the ratio values across all voxels measured within a field of view of 22 cm centered in the centrum ovale, including the white and gray matters. In the other studies, the authors carried out either an absolute quantification of white matter metabolites in a similar field of view 21 or metabolite ratio measurements in very specific brain areas (insular cortex, thalami and parieto-occipital peritrigonal white matter), 22 as we did with our single-voxel analysis of the frontal lobe and the PPL. As sensitivity of metabolite ratios to abnormalities has been reported to be less than absolute quantification, 24 the added effects of different quantification methods and differences in the regions of interest possibly accounted for the conflicting results.…”

“…In addition, the originality of these results also dwells in the sample characteristics. Although, in the other quoted papers, comparisons were carried out between groups of normal vs asymptomatic hypertensive patients, 5,22 symptomatic vs asymptomatic hypertensive patients, 21 or treated vs untreated patients, 23 we focused on the effect of medical treatment by comparing two groups of treated asymptomatic hypertensive patients with opposing outcomes.…”

Consensus statement for diagnosis of subcortical small vessel disease

“…Ischemic changes in the white matter can be seen by either 1 H-MRS or DTI and the results are comparable. 91 Diffusion tensor imaging allows measurements of fractional anisotropy and mean diffusivity. 92 Quantification of DTI may be confounded by the heterogeneity of white-matter regions with crossing fiber tracts, which can often be overcome with appropriate image processing methods.…”