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Evaluation of Brain Metabolism in Steno-Occlusive Carotid Artery Disease by Proton MR Spectroscopy: A Correlative Study with Oxygen Metabolism by PET

Department of Radiology and Biomedical Imaging Research Center, Fukui Medical University, Fukui
Department of Neurosurgery, Fukui Red Cross Hospital, Fukui
Department of Cerebral Research, National Institute for Neurological Sciences, Okazaki, Japan

Correspondence: For correspondence or reprints contact: Norihiro Sadato, MD, PhD, Biomedical Imaging Research Center, Fukui Medical University, 23 Shimoaizuki, Matsuoka-cho, Yoshida-gun, Fukui, 910-11 Japan.

ABSTRACT

Carotid occlusive diseases may cause ischemic changes in both the gray matter and the white matter as a result of hemodynamic compromise. To validate the use of proton magnetic resonance spectroscopy (MRS) in evaluating the carotid occlusive diseases, we compared changes in peaks of choline, in the sum of creatine and phosphocreatine, and in Na-cetyl-aspartate (NAA) of the white matter with cortical oxygen metabolism measured by PET. Methods: Eleven patients with unilateral steno-occlusive carotid artery disease underwent PET and MRS. Ten age-matched healthy volunteers underwent MRS. No subjects had cortical infarction. MRS was performed bilaterally in the centrum semi-ovale. Regional blood flow, regional metabolic rate of oxygen (rCMRO₂), and regional oxygen extraction fraction (rOEF) of the cerebral cortex were measured by the steady-state method with ¹⁵O gas. Results: The asymmetry index of the ratio of NAA to the sum of creatine and phosphocreatine (NAA/Cr) correlated positively with the asymmetry index of rCMRO₂ (r = 0.77; P < 0.01). Because rCMRO₂ is a marker of tissue viability, the NAA/Cr of the centrum semiovale may reflect viable neuronal cells. The asymmetry index of the ratio of choline to the sum of creatine and phosphocreatine (Cho/Cr) showed a significant positive correlation with the asymmetry index of rOEF (r = 0.65; P < 0.05). All but 1 patient with an increased Cho/Cr (>1.03) showed an increase in rOEF of the ipsilateral cortex (>0.56). This finding may indicate membrane damage caused by ischemia, because the centrum semiovale is the deep watershed zone. Conclusion: The metabolic changes in the centrum semiovale detected by proton MRS reflect a hemodynamically compromised state and are useful in evaluating tissue viability.

Key Words: magnetic resonance spectroscopy • emission tomography • carotid artery diseases • cerebral ischemia • oxygen metabolism

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