[Evaluation of cerebral metabolism by multi-voxel proton magnetic resonance spectroscopy imaging in chronic unilateral internal carotid artery occlusion].

Proton magnetic resonance spectroscopy(1H-MRS) has less been used to analyze cerebral metabolism in ischemic lesions compared to single photon emission computed tomography or positron emission computed tomography. Recent advances in magnetic resonance imaging apparatus and the related software have made possible obtaining multi-voxel 1H-MRS in a single study. We examined multi-voxel 1H-MRS in patients with unilateral internal carotid artery(ICA) occlusion to study the relationship between cerebral metabolism and cerebral blood flow. Fifteen patients(male 11; female 4, 47-76; average 67.1 year-old) with chronic unilateral ICA occlusion and without any marked infarction were studied. 1H-MRS was obtained using a 1.5 T Siemens Magnetom Vision scanner. Multi-voxel spectra were recorded using a SE-2 D-CSI sequence(TR/TE = 1500/135 ms). The volume of interest was 90 x 90 x 20 mm3, placed axially above the lateral ventricle. The single voxel size was 10 x 10 x 20 mm3. N-acetyl aspartate/creatine ratios(NAA/Cr) were calculated on each voxel and were averaged in view of the cortex and the white matter. The regional cerebral blood flow(CBF) was measured by Xenon-CT method. Eight patients were also examined by acetazolamide challenge to evaluate the cerebrovascular reserve capacity. NAA/Cr ratios in normal subjects were 1.905 +/- 0.090(mean +/- standard deviation) in the cortex and 2.183 +/- 0.258 in the white matter in 40's(n = 6), 2.046 +/- 0.166 in the cortex and 2.039 +/- 0.288 in the white matter in 60's(n = 5). The study revealed 7 patients with normal NAA/Cr ratio and CBF, 5 with reduced NAA/Cr ratio and normal CBF, and 3 with reduced NAA/Cr ratio and CBF in the affected cortex. A low correlation coefficient of 0.46 was noted between NAA/Cr ratio and the cerebrovascular reserve capacity calculated by acetazolamide challenge in the affected cortex. In the range of less than +10%(lower limit) in percentile change of regional CBF after acetazolamide injection, NAA/Cr ratio was distributed between 1.600 and 2.044, which were normal or slightly under the lower limit(mean-2 x standard deviation). Multi-voxel 1H-MRS is useful for the evaluation of cerebral metabolism, because it enables to quantify different chemicals in many fields at one time and to compare its distribution with regional CBF. In patients with unilateral ICA occlusion, NAA/Cr ratio of the affected cortex varies depending on the collateral circulation and the contralateral ICA lesions. The Extracranial-Intracranial Bypass should be considered if the case with unilateral ICA occlusion reveals reduced CBF and normal or slightly decreased NAA/Cr ratio in the affected cortex.