Elizabeth Ann Small MBBS, Presenter: Nothing to Disclose

Julien Poublanc MSc, Abstract Co-Author: Nothing to Disclose

Joseph A. Fisher MD, Abstract Co-Author: Stockholder, Thornhill Research Inc

David John Mikulis MD, Abstract Co-Author: Stockholder, Thornhill Research Inc Research Grant, General Electric Company

We sought to determine whether limited cerebrovascular reactivity (vascular reserve) is associated with reduced neuronal density, or a loss of neuronal integrity, using NAA/Cr as a surrogate measure for neuronal health.

Single voxel MR spectroscopy for NAA/Cr (N-acetylaspartate:creatine) ratio (TR 1500, TE 144 ms) was undertaken in 32 patients undergoing cerebrovascular reactivity (CVR) imaging. Cerebrovascular reactivity was measured using blood oxygen level dependent (BOLD) MR imaging with a carbon dioxide stimulus. Mirror image paired spectroscopy voxels, one voxel per hemisphere, were typically selected for each patient. Voxels were centered over normal appearing cortical parenchyma as seen on conventional imaging, in locations which maximized the CVR difference between voxels of a pair as seen on CVR maps. Mean CVR values within the volume of parenchyma corresponding to each spectroscopy voxel were measured. The correlation between NAA/Cr and CVR was assessed. The NAA/Cr in the voxels with limited CVR was compared to the NAA/Cr in the relatively spared voxels in the opposite hemisphere.

There was a weak but statistically significant correlation between CVR and NAA/Cr (n=32, r=0.322; P=0.010). In patients in whom there was visually obvious unilateral CVR reduction with contralateral sparing (n=13), the mean NAA/Cr ratio was lower in voxels with reduced CVR compared to the spared voxels in the opposite hemisphere (Mean NAA/Cr in voxels with reduced CVR = 1.849, SD 0.312; Mean NAA/Cr in voxels with spared CVR = 1.982, SD 0.282; P=0.027).

These results suggest that there may be reduced neuronal density or neuronal degradation in areas of reduced vascular reactivity. The weak correlation could relate to several factors including limited patient numbers, and the variable fraction of grey and white matter included within voxels.

A reduced vascular response (CVR) may result in damaging effects on the health of grey matter, which is inconspicuous on conventional imaging. This may have clinical implications such as cognitive impairment and dementia.

Small, E, Poublanc, J, Fisher, J, Mikulis, D, Decreased Cerebrovascular Reactivity is Associated with a Reduction in Cortical NAA/Cr: Loss of Neuronal Integrity in Areas of Limited Vascular Reserve.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14008478.html