Reduction of N-acetyl aspartate in bilateral cerebral tissue in relation to compromised cerebrovascular reserve capacity as investigated by proton MR spectroscopy and acetazolamide test

Patients with a symptomatic occlusion of the internal carotid artery or middle cerebral artery are at risk of future stroke. The magnetic resonance spectroscopy (MRS) study in such patients has shown no evidence of the reduced N-acetyl aspartate (NAA) in regions ipsilateral to a carotid stenosis or occlusion. This result may be partially attributed to the location of MRS voxel in areas without the reduced perfusion reserve. We hypothesize that it is possible to observe the abnormal metabolism if MRS voxel can be placed in areas with the reduced cerebrovascular reserve. Perfusion measurements may allow the assessment of cerebral perfusion reserve by challenge such patients with cerebral vasodilation drugs such as acetazolamide. 38 patients with chronic occlusion or severe stenosis of the internal carotid artery or middle cerebral artery with or without infarction have been performed with challenge test and MRS studies. In addition, 12 normal volunteers were performed with MRS but without challenge test. Perfusion reserve was evaluated by ArCBF% and post-challenge mean transient time (MTT). A correlation was observed between ArCBF% and post-challenge MTT (r =-0.67). Patients without acute infarction were divided into two groups as mild and severe, compromised in according to the post-challenge hemodynamic data. The spectra for analysis were recorded from voxels in bilateral temporo-parietal white matter area without MRI visible infarction. Metabolite concentration was normalized to the concentration of creatine (Cr). Between normal and severe group, the NAA/Cr ratios in bilateral cerebral tissue were shown to be significantly differences, so do those between mild and severe group (p <0.01). In this work, we demonstrated that abnormal metabolism can be detected by MRS method. NAA/Cr ratio may also be reduced in the unaffected contralateral brain. A threshold level of NAA/Cr was shown to be sustainable until the irreversible ischemic ictus occurs.