Decreased Glutamate Levels in Patients with Amnestic Mild Cognitive Impairment: An sLASER Proton MR Spectroscopy and PiB‐PET Study

BACKGROUND AND PURPOSE Glutamate levels may be informative about the declining neuronal health in the central nervous system. We used an advanced proton MR spectroscopy ( 1 H‐MRS) protocol composed of semi‐localization by adiabatic selective refocusing (sLASER) localization and FAST(EST)MAP shimming for detection of alterations in brain glutamate concentrations in patients with amnestic mild cognitive impairment. METHODS Participants with amnestic mild cognitive impairment ( n = 14; median age = 80) and age‐ and sex‐matched clinically normal controls ( n = 32; median age = 79) from the population‐based Mayo Clinic Study of Aging were recruited prospectively to the 3T single‐voxel 1 H‐MRS study that examined metabolite changes in the posterior cingulate gyri. To be included, controls had to have low β‐amyloid load on [ 11 C] Pittsburgh Compound B (PiB)‐PET (standard uptake value ratio; SUVr < 1.42) and patients with amnestic mild cognitive impairment had to have high β‐amyloid load (SUVr ≥ 1.42). RESULTS Glutamate concentration and the glutamate/ myo ‐inositol ratio were lower in patients with amnestic mild cognitive impairment than clinically normal controls ( P < .05). Higher global cortical PiB‐PET SUVr correlated with lower glutamate/ myo ‐inositol ( r = –.3, P = .04). CONCLUSIONS The advanced sLASER with FAST(EST)MAP shimming is a promising protocol for identifying glutamate alterations. Advanced 1 H‐MRS protocols may add to the understanding of early Alzheimer's disease pathophysiology through detection of glutamate concentration in posterior cingulate gyri of individuals with amnestic mild cognitive impairment.