Quantitative measurements of regional and tissue specific concentrations of brain metabolites were measured in elderly subjects using multislice proton magnetic resonance spectroscopic imaging ( 1 H MRSI). Selective k-space extrapolation and an inversion-recovery sequence were used to minimize lipid contamination and linear regression was used to account for partial volume problems. The technique was applied to measure the concentrations of N-acetyl aspartate (NAA), and creatine (Cr)-and choline (Cho)-containing compounds in cortical gray and white matter, and white matter lesions of the frontal and the parietal lobe in 40 normal elderly subjects (22 females and 18 males, 56 -89 years old, mean age 74 ؎ 8). NAA was about 15% lower in cortical gray matter and 23% lower in white matter lesions when compared to normal white matter. Cr was 11% higher in cortical gray matter than in white matter, and also about 15% higher in the parietal cortex than in the frontal cortex. Cho was 28% lower in cortical gray matter than in white matter. Furthermore, NAA and Cr changes correlated with age. In conclusion, regional and tissue differences of brain metabolites must be considered in addition to age-related changes Key words: magnetic resonance spectroscopic imaging; quantification; aging; gray and white matter; white matter lesions Most magnetic resonance spectroscopy (MRS) studies of the human brain have used single-volume localization methods that measure concentrations of N-acetyl aspartate (NAA), creatine (Cr)-and choline (Cho)-containing compounds, and other metabolites in one operator-specified location. Although these methods are generally easy to implement, they provide limited information about the regional distribution of the brain metabolites. In contrast, MRS imaging (MRSI) techniques acquire spectra simultaneously over a wide brain region, enabling the generation of maps of metabolite distributions. However, 1 H MRSI is technically more challenging. For brain studies, care must be taken to account for an intense signal from extracranial lipids that may otherwise distort weak metabolite resonances, especially in brain regions close to the skull. To avoid distortion from lipids, many 1 H MRSI studies have incorporated volume preselection with point-resolved spectroscopy (PRESS) (1) or stimulated echo acquisition modes (STEAM) (2) to limit the observed region to within the brain.1 H MRSI without volume preselection enabling full brain coverage was first demonstrated by Dynn et al. (3), using outer-volume suppression (OVS) pulses to reduce the lipid signal within the skull region. However, OVS pulses may also partially saturate brain tissue adjacent to the skull, complicating metabolite quantification from this region. Lipid reduction without OVS pulses was accomplished using inversion recovery methods that null the lipid signal during data acquisition (4,5) or data processing methods using lipid selective k-space extrapolation (6,7). The first goal of this study was therefore to develop a multislice 1 H MRSI method...

Hippocampal atrophy detected by MRI is a prominent feature of early Alzheimer's disease (AD), but it is likely that MRI underestimates the degree of hippocampal neuron loss, because reactive gliosis attenuates atrophy. We tested the hypothesis that hippocampal N-acetyl aspartate (NAA: a neuronal marker) and volume used together provide greater discrimination between AD and normal elderly than does either measure alone. We used proton MR spectroscopic imaging (1H MRSI) and tissue segmented and volumetric MR images to measure atrophy-corrected hippocampal NAA and volumes in 12 AD patients (mild to moderate severity) and 17 control subjects of comparable age. In AD, atrophy-corrected NAA from the hippocampal region was reduced by 15.5% on the right and 16.2% on the left (both p < 0.003), and hippocampal volumes were smaller by 20.1% (p < 0.003) on the right and 21.8% (p < 0.001) on the left when compared with control subjects. The NAA reductions and volume losses made independent contributions to the discrimination of AD patients from control subjects. When used separately, neither hippocampal NAA nor volume achieved to classify correctly AD patients better than 80%. When used together, however, the two measures correctly classified 90% of AD patients and 94% of control subjects. In conclusion, hippocampal NAA measured by 1H MRSI combined with quantitative measurements of hippocampal atrophy by MRI may improve diagnosis of AD.

BACKGROUND & PURPOSE Precision Medicine is an approach to disease diagnosis, treatment and prevention which relies on quantitative biomarkers that minimize the variability of individual patient measurements. The aim of this study is to assess the inter-site variability after harmonization of a high angular resolution 3T diffusion tensor imaging protocol across 13 scanners at the 11 academic medical centers participating in the Transforming Research and Clinical Knowledge in Traumatic Brain Injury (TRACK-TBI) multisite study. MATERIALS AND METHODS Diffusion MRI was acquired from a novel isotropic diffusion phantom developed at the National Institute of Standards and Technology (NIST) and from the brain of a traveling volunteer on thirteen 3T MR scanners representing three major vendors (General Electric, Philips and Siemens). Means of the DTI parameters and their coefficients of variation (CoVs) across scanners were calculated for each DTI metric and white matter tract. RESULTS For the NIST diffusion phantom, the CoV of apparent diffusion coefficient (ADC) across the 13 scanners was < 3.8% for a range of diffusivities from 0.4 to1.1×10−6 mm2/s. For the volunteer, the CoVs across scanners of the 4 primary DTI metrics, each averaged over the entire white matter skeleton, were all < 5%. In individual white matter tracts, large central pathways showed good reproducibility with the CoV consistently below 5%. However, smaller tracts showed more variability with the CoV of some DTI metrics reaching 10%. CONCLUSION The results suggest the feasibility of standardizing DTI across 3T scanners from different MR vendors in a large-scale neuroimaging research study.

Background The objectives were first to compare the effects of subcortical ischemic vascular dementia (SIVD) and Alzheimer's disease (AD) on cerebral blood flow (CBF) and second to analyze the relationship between CBF and subcortical vascular disease, measured as volume of white matter lesions (WML). Methods Eight mildly demented patients with SIVD (77 ± 8 years, 26 ± 3 MMSE) and 14 patients with AD were compared to 18 cognitively normal elderly. All subjects had CBF measured using arterial spin labeling MRI and brain volumes assessed using structural MRI. Results AD and SIVD showed marked CBF reductions in frontal (p = 0.001) and parietal (p = 0.001) cortex. In SIVD, increased subcortical WML were associated with reduced CBF in frontal cortex (p = 0.04) in addition to cortical atrophy (frontal: p = 0.05; parietal: p = 0.03). Conclusions Subcortical vascular disease is associated with reduced CBF in the cortex, irrespective of brain atrophy.