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Anteroposterior Hippocampal Metabolic Heterogeneity: Three-dimensional Multivoxel Proton ¹H MR Spectroscopic Imaging—Initial Findings¹

¹ From the Departments of Radiology (K.G.K., S.L., J.S.B., O.G.) and Psychiatry (L.G., M.J.d.L.), Center for Brain Health, New York University School of Medicine, 550 First Ave, New York, NY 10016. Received August 23, 2007; revision requested November 13; revision received January 8, 2008; accepted March 11; final version accepted April 17. Supported by National Institutes of Health grants EB01015, NS050520, AG12101, AG08051, AG03051 and RR0096. K.G.K. supported by grant NCRR M01RR00096 from the Mentored Medical Student Clinical Research Program. Address correspondence to O.G. (e-mail: oded.gonen{at}med.nyu.edu).

Purpose: To quantify proton magnetic resonance (MR) spectroscopy–detectable metabolite concentrations along anteroposterior axis of hippocampus in healthy young and elderly subjects.

Materials and Methods: Young (three women, three men; age range, 25–35 years) and elderly (four women, two men; age range, 68–72 years) groups underwent MR imaging and proton MR spectroscopic imaging at 3 T in this HIPAA-compliant prospective study and gave institutional review board–approved written consent. Volume of interest was centered on and tilted parallel to hippocampal anteroposterior plane. Absolute N-acetylaspartate (NAA), choline, and creatine levels were obtained in each voxel, with phantom replacement.

Results: Mean NAA, creatine, and choline concentrations in the young group were higher in posterior hippocampus (12.9 mmol/L ± 2.0 [standard deviation], 7.8 mmol/L ± 1.2, 2.3 mmol/L ± 0.4, respectively) than anterior hippocampus (8.0 mmol/L ± 1.1, 6.0 mmol/L ± 1.4, 1.5 mmol/L ± 0.2; P = .005, .02, and .0002, respectively). In the elderly group, mean concentrations were higher in posterior hippocampus (8.6 mmol/L ± 0.9, 5.6 mmol/L ± 0.6, 1.5 mmol/L ± 0.2, respectively) than anterior hippocampus (7.2 mmol/L ± 1.0, 2.4 mmol/L ± 0.3, 1.0 mmol/L ± 0.2; P = .006, .0001, .04, respectively). Mean concentrations were significantly higher in the young group (13.2 mmol/L ± 1.0, 7.4 mmol/L ± 0.8, 2.1 mmol/L ± 0.3, respectively) than in the elderly group (9.0 mmol/L ± 1.0, 5.8 mmol/L ± 0.8, 1.8 mmol/L ± 0.3; P = .0001, .01, .05, respectively). Posteroanterior metabolic gradients differed: NAA decreased faster in the young group (–1.0 mmol/L · cm^–1) than the elderly group (–0.7 mmol/L · cm^–1); creatine and choline concentrations decreased faster in the elderly group (–0.8 and –0.058 mmol/L · cm^–1, respectively) than the young group (–0.16 and –0.008 mmol/L · cm^–1, respectively). No left-right metabolic differences were found.

Conclusion: Significant metabolic heterogeneity was observed between groups and along anteroposterior axis of healthy hippocampus in both groups. Age matching and consistent voxel placement are important for correct comparisons of both absolute metabolic levels and metabolite ratios in longitudinal intra- and intersubject cross-sectional studies.

© RSNA, 2008