Determination Of T1 Relaxation Times Research Articles

Influence of Sulfur-Curing Conditions on the Dynamics and Crosslinking of Rubber Networks: A Time-Domain NMR Study.

The characterization of the structural and dynamic properties of rubber networks is of fundamental importance in rubber science and technology to design materials with optimized mechanical properties. In this work, natural and isoprene rubber networks obtained by curing at three different temperatures (140, 150, and 170 °C) and three different sulfur contents (1, 2, and 3 phr) in the presence of a 3 phr accelerator were studied using a combination of low-field time-domain NMR (TD-NMR) techniques, including 1H multiple-quantum experiments for the measurement of residual dipolar couplings (Dres), the application of the Carr–Purcell–Meiboom–Gill pulse sequence for the measurement of the transverse magnetization decay and the extraction of 1H T2 relaxation times, and the use of field cycling NMR relaxometry for the determination of T1 relaxation times. The microscopic properties determined by TD-NMR experiments were discussed in comparison with the macroscopic properties obtained using equilibrium swelling, moving die rheometer, and calorimetric techniques. The obtained correlations between NMR observables, crosslink density values, maximum torque values, and glass transition temperatures provided insights into the effects of the vulcanization temperature and accelerator/sulfur ratio on the structure of the polymer networks, as well as on the effects of crosslinking on the segmental dynamics of elastomers. Dres and T2 were found to show linear correlations with the crosslink density determined by equilibrium swelling, while T1 depends on the local dynamics of polymer segments related to the glass transition, which is also affected by chemical modifications of the polymer chains occurring during vulcanization.

Gadolinium-Based Magnetic Resonance Contrast Agents at 7 Tesla

PURPOSE/INTRODUCTION: The aim of this study was to determine the T1 relaxivities (r1) of 8 gadolinium (Gd)-based MR contrast agents in human blood plasma at 7 Tesla, compared with 3 Tesla. Eight commercially available Gd-based MR contrast agents were diluted in human blood plasma to concentrations of 0, 0.25, 0.5, 1, and 2 mmol/L. In vitro measurements were performed at 37 degrees C, on a 7 Tesla and on a 3 Tesla whole-body magnetic resonance imaging scanner. For the determination of T1 relaxation times, Inversion Recovery Sequences with inversion times from 0 to 3500 ms were used. The relaxivities were calculated. The r1 relaxivities of all agents, diluted in human blood plasma at body temperature, were lower at 7 Tesla than at 3 Tesla. The values at 3 Tesla were comparable to those published earlier. Notably, in some agents, a minor negative correlation of r1 with a concentration of up to 2 mmol/L could be observed. This was most pronounced in the agents with the highest protein-binding capacity. At 7 Tesla, the in vitro r1 relaxivities of Gd-based contrast agents in human blood plasma are lower than those at 3 Tesla. This work may serve as a basis for the application of Gd-based MR contrast agents at 7 Tesla. Further studies are required to optimize the contrast agent dose in vivo.

Molecular connectivity model for determination of T1 relaxation times of α-carbons of amino acids and cyclic dipeptides

A molecular connectivity model for the calculation of the relaxation times of amino acids and cyclic dipeptides is presented. A power type regression shows the best fit between experimental and calculated data. The simple molecular connectivity index and the simple sum-delta index are the most appropriate indexes in describing the relaxation times of the investigated compounds. The given computational method shows that it is possible to model tumbling rates of solute molecules in a relatively easy and direct way.

Comparison of Different Pulse Sequences for in Vivo Determination of T1 Relaxation Times in the Human Brain

Quantitative in vivo determination of T1 relaxation times by magnetic resonance imaging (MRI) is hampered by several potential sources of error. This study focused on the influence of the radiofrequency pulse sequences applied with special attention to the significance of the repetition time (TR). T1 measurements were performed on the human brain using a whole body MR scanner operating at 1.5 tesla. Three different pulse sequences were compared including two 6-points inversion recovery (IR) sequences with TR = 2.0 s and 4.0, respectively, and a 12-points partial saturation inversion recovery (PSIR) sequence with TR varying between 0.24 and 8.0 s. The median T1 relaxation times obtained in cortical grey matter and cerebrospinal fluid were significantly shorter in the IR experiments at TR = 2 s than in those carried out at TR = 4 s. Concerning white matter the discrepancy was much less pronounced, but still statistically significant. Supplementary phantom measurements indicated that the higher T1 values are increasingly underestimated when TR is reduced to 2 s. The results suggest that the PSIR sequence or IR sequences with a TR greater than 2 X the T1 level of the tissue type investigated should be employed for accurate T1 determination by MRI in clinical work.

Comparison of different pulse sequences for in vivo determination of T1 relaxation times in the human brain

Comparison of different pulse sequences for in vivo determination of T1 relaxation times in the human brain

4641095 Determination of T1 relaxation times used in automated nuclear magnetic resonance image synthesis

4641095 Determination of T1 relaxation times used in automated nuclear magnetic resonance image synthesis

8606843 Determination of T1 relaxation times used in automated nuclear magnetic resonance image synthesis

A method for providing improved estimates of the spin-lattice relaxation time (T1) of an image in a Nuclear Magnetic Resonance (NMR) technique on a human body which utilizes the application of a multiple spin-echo pulse sequence technique at two different pulse repetition times (TR1 and TR2). The signals for each of the different repetition times are measured by first setting the longitudinal magnetization (T1) to an initial value and then waiting the appropriate repetition time in order to provide the measured signal. The magnetization is "flipped" into the x-y plane and the relationship between the measured values for each of the repetition times is utilized to form an algorithm whereby the calculated ratio of the measured signals allows for an initial estimate of T1. The process also utilizes the plurality of spin-echos in the multiple spin-echo pulse sequence to appropriately measure, at each of the echo times TE(i), the decaying value of the measured first and second magnetization signals, which, in turn, provides further estimates of T1 which are then weight averaged.