¹H metabolite relaxation times at 3.0 tesla: Measurements of T1 and T2 values in normal brain and determination of regional differences in transverse relaxation

Abstract

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...

Late Proton Magnetic Resonance Spectroscopy following Traumatic Brain Injury during Early Childhood: Relationship with Neurobehavioral Outcomes

“…The method employs a basic set of concentration-calibrated model spectra of individual metabolites to estimate concentrations of similar brain metabolites from in vivo spectral data correcting for residual eddy current effects and actual coil loading by using the transmitter reference amplitude and water reference spectra (Provencher, 1993). The concentration was corrected for T2 relaxation using reported literature values (Traber et al, 2004). Each concentration is reported with a confidence measurement (SD%) reflecting maximum likelihood estimates and their uncertainties (Cramer-Rao lower bounds) (Provencher, 1991).…”

High field MRI in the diagnosis of multiple sclerosis: high field–high yield?

“…Among those quantitative methods, 1 H-MR spectroscopy benefits the most from the advantages provided by the higher magnetic field strengths [18,19,59,60]. Consequently, the most experience concerning quantitative MRI methods in MS patients has been collected for 1 H-MR spectroscopy so far.…”

Proton MR spectroscopy of the brain at 3 T: an update

“…While the T 1 relaxation time of water protons is significantly longer at 3 T as compared to 1.5 T, metabolite T 1 measurements can be either longer [34] or almost unchanged [35,36]. The discrepancies can be explained by the large interindividual variability at 1.5 T and the possible differences in scanner performance, sequence design and strategies for acquiring and evaluating spectra.…”

“…Another factor that can contribute b Spectra recorded at 1.5 T (red) and 3 T (black), using PRESS sequence with TR 2,000 ms, TE 144 ms, 128 averages, voxel size 2.0×2.0×2.0 cm and acquisition time 4 min 56 s, and overlapped for emphasizing the differences. At 3 T, the signal-to-noise ratio (SNR) is about 25% higher and the spectral distance between the metabolites (in hertz) is doubled to the variability is the T 1 regional differences reported both at 3 T and 1.5 T [34,36]. Ethofer et al [34], for example, reported metabolite T 1 values only slightly longer at 3 T vs. 1.5 T in the occipital lobes and cerebellum, and significantly increased at 3 T in the motor cortex, frontoparietal WM and thalamus (Table 1).…”

“…These region-specific variations and the different T 2 effect on NAA, Cho and Cr have to be taken into account when using T 2 values for absolute quantification. Furthermore, due to the decreased T 2 , MRS protocols with shorter TE values are preferable at 3 T, while TR adjustments appear of minor importance because of controversial T 1 relaxation changes [36].…”