Purpose:To measure 1 H relaxation times of cerebral metabolites at 3 T and to investigate regional variations within the brain. Materials and Methods:Investigations were performed on a 3.0-T clinical whole-body magnetic resonance (MR) system. T2 relaxation times of N-acetyl aspartate (NAA), total creatine (tCr), and choline compounds (Cho) were measured in six brain regions of 42 healthy subjects. T1 relaxation times of these metabolites and of myo-inositol (Ins) were determined in occipital white matter (WM), the frontal lobe, and the motor cortex of 10 subjects.Results: T2 values of all metabolites were markedly reduced with respect to 1.5 T in all investigated regions. T2 of NAA was significantly (P Ͻ 0.001) shorter in the motor cortex (247 Ϯ 13 msec) than in occipital WM (301 Ϯ 18 msec). T2 of the tCr methyl resonance showed a corresponding yet less pronounced decrease (162 Ϯ 16 msec vs. 178 Ϯ 9 msec, P ϭ 0.021). Even lower T2 values for all metabolites were measured in the basal ganglia. Metabolite T1 relaxation times at 3.0 T were not significantly different from the values at 1.5 T. Conclusion:Transverse relaxation times of the investigated cerebral metabolites exhibit an inverse proportionality to magnetic field strength, and especially T2 of NAA shows distinct regional variations at 3 T. These can be attributed to differences in relative WM/gray matter (GM) contents and to local paramagnetism. SEVERAL MAGNETIC RESONANCE (MR) studies performed at magnetic fields of 3 T or higher have shown that longitudinal relaxation times T1 of water protons in human brain tissue are prolonged at increasing field strength, whereas T2 of water is progressively reduced (1-5). However, until now, only a few reports on the measurement of proton T1 and T2 relaxation times of brain metabolites in vivo at magnetic fields beyond the 2 T threshold have been published. Accurate values for 1 H metabolite relaxation times are required for reliable and reproducible determination of absolute metabolite concentrations in cerebral tissue by MR spectroscopy (MRS).Analogous to the observed field dependence of water T2 relaxation times, the high-field MRS studies available up to now indicate a steady decrease of 1 H metabolite T2 values of N-acetyl aspartate (NAA), total creatine (tCr), and choline compounds (Cho) when progressing from 1.5-3 T and up to 7 T (6-10). While these data reveal a consistent trend, detailed information at 3 T, particularly regarding variations of metabolite T2 in different cerebral areas, is still incomplete. The aim of our study was to measure 1 H metabolite T2 in an extended set of brain regions covering a broad range of different mixtures of white matter (WM) and gray matter (GM) and with an adequate number of samples for each localization.High-field measurements of 1 H metabolite T1 have been performed at 3.0 T (6), 4.0 T (8), and 4.1 T (9). In contrast to the pronounced effects on water T1, and on water T2 and metabolite T2, no obvious influence of magnetic field strength on 1 H metabolite T1 values can as...

Magnetic resonance (MR) diffusion measurements of the abdomen were performed in 12 healthy volunteers by using a diffusion-weighted single-shot sequence both without and with pulse triggering for different trigger delays. Pulse triggering to the diastolic heart phase led to reduced motion artifacts on the diffusion-weighted MR images and to significantly improved accuracy and reproducibility of measurements of the apparent diffusion coefficients, or ADCs, of abdominal organs.

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In addition to the information traditionally provided with reconstructed perfusion parameter maps, 3D susceptibility-based perfusion MR images allow the identification of acute MCA thromboembolism with a sensitivity higher than that of CT.

Dual-source parallel RF excitation body MR imaging enables reduced dielectric shading, improved homogeneity of the RF magnetic induction field, and accelerated imaging at 3.0 T.

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Spectroscopic changes in the motor cortices of patients with ALS correspond with a reduction in levels of NAA and an elevation in levels of choline and inositol compounds. Since NAA is exclusively expressed in neurons, the observed decrease of NAA reflects neuronal loss or dysfunction. Inositol and choline are associated with plasma membrane metabolism, so the release of these compounds may be related to membrane disorders.

Assessing the distribution of NAA/creatine reduction guided by the expected neuropathologic change can improve the role of 1H-MRS in the assessment of AD. The disease severity can be monitored by relative reduction of NAA/creatine in the MTL in comparison with an intraindividual unaffected control region.