Magnetic Relaxation Times T1 Research Articles

Correlation analysis between the complex electrical permittivity and relaxation time of tissue mimicking phantoms in 7 T MRI

Dielectric relaxation theory describes the complex permittivity of a material in an alternating field; in particular, Debye theory relates the time it takes for an applied field to achieve the maximum polarization and the electrical properties of the material. Although, Debye’s equations were proposed for electrical polarization, in this study, we investigate the correlation between the magnetic longitudinal relaxation time T1 and the complex electrical permittivity of tissue-mimicking phantoms using a 7 T magnetic resonance scanner. We created phantoms that mimicked several human tissues with specific electrical properties. The electrical properties of the phantoms were measured using bench-test equipment. T1 values were acquired from phantoms using MRI. The measured values were fitted with functions based on dielectric estimations, using relaxation times of electrical polarization, and the mixture theory for dielectrics. The results show that, T1 and the real permittivity are correlated; therefore, the correlation can be approximated with a rational function in the case of water-based phantoms. The correlation between index loss and T1 was determined using a fitting function based on the Debye equation and mixture theory equation, in which the fraction of the materials was taken into account. This phantom study and analysis provide an insight into the application relaxation times used for estimating dielectric properties. Currently, the measurement of electrical properties based on dielectric relaxation theory is based on an antenna, sometimes invasive, that irradiates an electric field into a small sample; thus, it is not possible to create a map of electrical properties for a complex structure such as the human body. This study could be further used to compute the electrical properties maps of tissues by scanning images and measuring T1 maps.

Motional freedom of dimethylammonium ions in a cyanoelpasolite, [(CH3)2NH2]2KCo(CN)6, which exhibits phase transition associated with a distinct change in dielectric property.

The temperature dependence of the 1H nuclear magnetic resonance spin-lattice relaxation time T1 of [(CH3)2NH2]2KCo(CN)6 and the partially deuterated analogue [(CD3)2NH2]2KCo(CN)6 has been reported. A change in the molecular motion of organic cations through the first-order phase transition at Tc = 246 K has been discussed. Although this first-order transition has been reported as an isosymmetric transition, in which the space group of the crystal does not change, the number of the 14N nuclear quadrupole resonance line changed from three in the high-temperature phase to twelve in the low-temperature phase indicating the lowering of crystal symmetry.

Pore Structure Evaluation of Bioclastic Limestone Using NMR and HPMI Measurements

Pore structure evaluation is a crucial segment of revealing the reservoir characteristics and percolation mechanism. Considering the diversity of origins, types and combinations in reservoir space, the effective evaluation method of bioclastic limestone pore structure had not been built yet, which greatly restricted the comprehension of storage-permeability mechanism, as well as the subsequent development strategies. Therefore, this study systematically analyzed the corresponding relationship between the fractal characteristics of capillary pressure curves and pore connectivity. The T2 relaxation criterion of different pore diameter components were determined reasonably according to the features of nuclear magnetic resonance T2 spectrum. Combined with a fuzzy clustering algorithm, a new logging classification method was established using proportions of different pore components as sensitive parameters. The results showed that the capillary force curves of bioclastic limestone reservoir mainly exhibited two kinds of form: “convex” and “concave”. The former showed better storage-percolation characteristics; while the same characteristics of the latter were closely related to inflection points, degrading by the location of respective point from right to left; In addition, the relationship between the pore throat radius r and nuclear magnetic relaxation time T2 could be classified into four stages obviously. With the pore throat radius of 0.15, 1, 5 μm and T2 relaxation time 30, 90 and 200 ms, the pore structure of bioclastic limestone was effectively divided into four categories. On this basis, the calculation precision of permeability would be significantly improved.

Absence of PO2 change in fetal brain despite PO2 increase in placenta in response to maternal oxygen challenge.

Magnetic resonance imaging allows the noninvasive observation of PO2 changes between air breathing and oxygen breathing through quantification of the magnetic longitudinal relaxation time T1. Changes in PO2 are proportional to changes in the longitudinal relaxation rate ΔR1 (where ΔR1=1/T1oxygen-1/T1air). Knowledge of this response could inform clinical interventions using maternal oxygen administration antenatally to treat fetal growth restriction. We present in vivo measurements of the response of the fetal-placental unit to maternal hyperoxia. Prospective cohort. Large tertiary maternity hospital. Nine women undergoing low-risk pregnancy (21-33 weeks of gestation) and five nonpregnant adults. During imaging the air supply to mothers was changed from medical air (21% oxygen) to medical oxygen (100% oxygen) and T1 was monitored over time in both the placenta and fetal brain using a periodically repeated magnetic resonance imaging sequence. To demonstrate that the method could detect a brain response, brain responses from five normal adult volunteers were measured using a similar imaging protocol. Changes in T1 following oxygen challenge. No significant ΔR1 (P=0.42, paired t-test) was observed in fetal brains. A significant placental ΔR1 (P=0.0002, paired t-test) of 0.02±0.01/s (mean±SD) was simultaneously observed in the same participants. In the brains of the nonpregnant adults, a significant ΔR1 (P=0.01, paired t-test) of 0.005±0.002/s was observed. Short-term maternal oxygen administration does not improve fetal brain oxygenation, in contrast to the response observed in the adult brain.

Low prevalence of cardiac siderosis in heavily iron loaded Egyptian thalassemia major patients

Myocardial siderosis in thalassemia major remains the leading cause of death in developing countries. Once heart failure develops, the outlook is usually poor with precipitous deterioration and death. Cardiovascular magnetic resonance (CMR) can measure cardiac iron deposition directly using the magnetic relaxation time T2*. This allows earlier diagnosis and treatment and helps to reduce mortality from this cardiac affection. This study aims to determine the prevalence of cardiac siderosis in Egyptian patients who are heavily iron loaded and its relation to liver iron concentration, serum ferritin, and left ventricular ejection fraction. Eighty-nine β-thalassemia patients receiving chelation therapy (mean age of 20.8 ± 6.4 years) were recruited in this study. Tissue iron levels were determined by CMR with cardiac T2* and liver R2*. The mean ± standard deviation (range) of cardiac T2* was 28.5 ± 11.7 ms (4.3 to 53.8 ms), the left ventricular ejection fraction (LVEF) was 67.7 ± 4.7 % (55 to 78 %), and the liver iron concentration (LIC) was 26.1 ± 13.4 mg Fe/g dry weight (dw) (1.5 to 56 mg Fe/g dw). The mean serum ferritin was 4,510 ± 2,847 ng/ml (533 to 22,360 ng/ml), and in 83.2 %, the serum ferritin was >2,500 ng/ml. The prevalence of myocardial siderosis (T2* of <20 ms) was 24.7 % (mean age 20.9 ± 7.5 years), with mean T2* of 12.7 ± 4.4 ms, mean LVEF of 68.6 ±5.8 %, mean LIC of 30.9 ± 13 mg Fe/g dw, and median serum ferritin of 4,996 ng/ml. There was no correlation between T2* and age, LVEF, LIC, and serum ferritin (P = 0.65, P = 0.085, P = 0.99, and P = 0.63, respectively). Severe cardiac siderosis (T2* of <10 ms) was present in 7.9 %, with a mean age of 18.4 ± 4.4 years. Although these patients had a mean T2* of 7.8 ± 1.7 ms, the LVEF was 65.1 ± 6.2 %, and only one patient had heart failure (T2* of 4.3 ms and LVEF of 55 %). LIC and serum ferritin results were 29.8 ± 17.0 mg/g and 7,200 ± 6,950 ng/ml, respectively. In this group of severe cardiac siderosis, T2* was also not correlated to age (P = 0.5), LVEF (P = 0.14), LIC (P = 0.97), or serum ferritin (P = 0.82). There was a low prevalence of myocardial siderosis in the Egyptian thalassemia patients in spite of very high serum ferritin and high LIC. T2* is the best test that can identify at-risk patients who can be managed with optimization of their chelation therapy. The possibility of a genetic component for the resistance to cardiac iron loading in our population should be considered.

Low Incidence of Cardiac Siderosis in Heavily Iron Overloaded Egyptian Thalassemics.

Abstract 5110 IntroductionMyocardial siderosis in thalassemia major remains the leading cause of death in developing countries. Once heart failure develops, the outlook is usually poor with precipitous deterioration and death. Cardiovascular magnetic resonance (CMR) technology can measure cardiac iron deposition directly using the magnetic relaxation time T2*. This allows earlier diagnosis and treatment and help to reduce mortality from this cardiac affection. Patients and Methods89 β thalassemia patients (10 to 43 years, mean age of 20.78±6.36) were recruited in this study. All patients were receiving chelation therapy of subcutaneous desferroxamine. Evaluation of hemosiderosis was based on CMR, liver magnetic resonance R2 and serum ferritin. ResultsT2* values ranged between 4.3 to 53.8 ms with a mean of 28.50±11.74 ms among our study group. The left ventricular ejection fraction (LVEF) as measured by CMR ranged between 55 and 78%; mean=67.66±4.69%.and liver iron concentration (LIC) ranged between 1.5 to 56 mg/g dry weight with a mean of 26.13±13.37 mg/g. Serum ferritin varied among our study group from 533 to 22363ng/ml; mean=4514.27±2847.58ng/ml with 83.15% above 2500ng/ml. The prevalence of myocardial siderosis (T2*<20ms) among our patients was 22/89 patients (24.7%) aged 20.86±7.54 years with a mean T2* value of 12.718±4.36ms and LVEF of 68.59 ±5.84%. LIC and serum ferritin results were 30.85±13.48 mg/g and 6122.86±4185.67ng/ml respectively. There was no correlation between T2* results and the age, LVEF, LIC and serum ferritin of this group (P=0.651, P=0.085, P=0.999 and P=0.627 respectively). Those patients with severe cardiac siderosis (T2*<10ms) constituted 7/89 (7.9%) with a mean age of 18.43±4.35 years. Although these patients had a mean T2* of 7.8±1.73 ms, the LVEF value was 65.14±6.20 % and only one patient had clinical cardiac disease (T2*=4.3 ms and LVEF =55%). LIC and serum ferritin results were 29.84±16.99mg/g and 7202.14±6953.79ng/ml respectively. In this group of severe cardiac siderosis, T2* was not correlated to age (P=0.5), LVEF (P=0.144), LIC (P=0.969) and serum ferritin (P=0.818). ConclusionLow prevalence of myocardial siderosis in the Egyptian thalassemic patients in spite of the very high serum ferritin. In severely iron overloaded patients the cardiac function was not affected. T2* is the best test that can identify at risk patients who can be treated with optimization of their chelation protocols. The possibility of a genetic component for the susceptibility of cardiac iron loading in our population should be considered. DisclosuresNo relevant conflicts of interest to declare.

C++ OPPS, a new software for the interpretation of protein dynamics from nuclear magnetic resonance measurements

AbstractNuclear magnetic resonance (NMR) is a powerful tool for elucidating protein dynamics because of the possibility to interpret nuclear spin relaxation properties in terms of microdynamic parameters. Magnetic relaxation times T1, T2, and NOE depend on dipolar and quadrupolar interactions, on chemical shift anisotropy and cross‐correlation effects. Within the framework of given motional model, it is possible to express the NMR relaxation times as functions of spectral densities (Abragam, The Principles of Nuclear Magnetism; Oxford University Press: Clarendon, London, 1961), obtaining the connection between macroscopic observables and microscopic properties. In this context, recently Meirovitch et al. (Shapiro et al., Biochemistry 2002, 41, 6271, Meirovitch et al., J Phys Chem B 2006, 110, 20615, Meirovitch et al., J Phys Chem B 2007, 111, 12865) applied the dynamical model introduced by Polimeno and Freed (Polimeno and Freed, Adv Chem Phys 1993, 83, 89, Polimeno and Freed, J Phys Chem 1995, 99, 10995), known as the slowly relaxing local structure (SRLS) model, to the study of NMR data.The program C++OPPS (http://www.chimica.unipd.it/licc/), developed in our laboratory, implements the SRLS model in an user‐friendly way with a graphical user interface (GUI), introduced to simplify the work to users who do not feel at ease with the complex mathematics of the model and the difficulties of command line based programs. The program is an evolution of the old FORTRAN 77 implementation COPPS (COupled Protein Probe Smoluchowski) and presents a number of new features: the presence of an easy to use GUI written in JAVA; high calculation performance thanks to features of C++ language, employment of BLAS (basic linear algebra subprograms) library (Blackford et al., Trans Math Soft 2002, 28, 135) in handling matrix‐vector operations and parallelization of the code under the MPI (message passing interface) paradigm (Gropp et al., Parallel Comput 1996, 22, 789, Gropp and Lusk, User's Guide for mpich, a Portable Implementation of MPI Mathematics and Computer Science Division; Argonne National Laboratory, 1996); possibility to predict the diffusion tensor of the protein via a hydrodynamic approach (Barone et al., J Comp Chem, in press). A cluster version of C++OPPS was also developed, which can be easily accessed by users via the web. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

Pulse NMR of 3He in aerogel at temperature 1.5 K

Experimental data of 3He pulse NMR in contact with aerogel (95%) in a nuclear Larmor frequency range of 5 to 20 MHz at T=1.5 K are reported. For the first time spin kinetics of 3He (adsorbed, gaseous and liquid) has been studied systematically at temperatures higher than degeneracy temperature of this quantum liquid. It has been shown, that in all cases the nuclear spin-lattice relaxation time T1 is linearly proportional to the Larmor frequency, while the spin-spin relaxation time T2 is frequency independent. The magnetic relaxation times T1 and T2 are linearly proportional to the ratio of the magnetization of whole spin system to magnetization of the adsorbed layer of 3He.

NMR Relaxation Time Simulation for Different Models of Motion in (CH3)3NBH3

Monte Carlo simulations of complex rotation of single −CH3 groups, −(CH3)3 groups and −BH3 groups were performed for trimethylamine borane (CH3)3NBH3. In the course of these simulations the correlation functions for different models of rotation were determined. Knowledge of these functions and of some data extracted from NMR experiments allowed for the calculation of the longitudinal magnetic relaxation time T1 as a function of temperature. The values of relaxation times obtained from Monte Carlo simulations are compared to experimental results published by other authors. There is a clear relation between the assumed model of rotation and the shape of the T1 curve versus temperature.

Specific features of the adsorption and nuclear magnetic relaxation of water molecules in active carbons. 1. Relation between the spin-spin relaxation of adsorbed water molecules and structural parameters of microporous active carbons

Relation between the spin-spin nuclear magnetic relaxation time T2 of adsorbed water molecules and parameters of microporous structure of carbon adsorbents is disclosed. The pattern of dependences of T2 on the relative pressure and the number of water molecules per one primary adsorption site (PAS) is governed by the pore sizes and the number and nature of PASs. At a complete micropore filling, the T2 value depends on the volume density of PASs in active carbons. In the absence of PASs in the micropores, T2 is equal approximately to 21 ms. The larger the volume density of PASs, the smaller the number of water molecules per one PAS at the complete filling of micropores; i.e., the looser the packing of water molecules. The results of studying active carbons by the pulsed 1H NMR method agree well with the data of the adsorption method.

Simulation of the NMR Second Moment as a Function of Temperature in the Presence of Molecular Motion. Application to (CH3)3NBH3

The method for simulating the second moment of the NMR absorption spectrum as a function of temperature is presented. The second moment is first calculated as a function of the number of jumps of rotating molecules or their parts (like methyl groups). This number of jumps is rescaled into the frequency of internal rotation and these frequencies are recalculated into equivalent temperatures. The relation between frequency of rotation, and temperature is established on the basis of the Arrhenius relation υc= υo exp (-Ea/RT). The described method is then applied to the analysis of molecular motion in trimethylamine borane (CH3)3NBH3. The proposed method is especially useful in the case of complex structures, where combined motions are possible, because the NMR second moment is much more sensitive to the geometry of motion than the magnetic relaxation times T1 or T1p usualy used in studies of the internal dynamics of solids.

T1 and T2 of ferritin solutions: Effect of loading factor

Proton magnetic relaxation times T1 and T2 were measured at field strengths from 0.05 T to 1.5 T in solutions of ferritin with loading factors from 90 to 3600 iron atoms per molecule. 1/T2 increased linearly with field strength, as previously observed, and the slope per unit iron was approximately the same in all samples. This latter finding indicates that the field dependence of T2 may be used as a measure of ferritin-bound iron, regardless of loading factor. A possible explanation is presented, based on the presumed antiferromagnetic structure of the ferritin core and the linear dependence of 1/T2 on core magnetization. A nonzero contribution to 1/T2 in the limit of low field and a contribution to 1/T1 were also found, both of which increase linearly with loading factor for constant protein concentration; these effects represent quantum mechanical dipole-dipole relaxation of water protons either by iron atoms on the surface of the core or by the iron core itself. Finally, the extrapolated intercept at LF = 0 for both 1/T1 and 1/T2 indicates a contribution from a small number of iron ions bound to the protein shell. These results may help in the use of MRI to measure brain iron and possibly even ferritin loading factor.

Longitudinal spin relaxation in a dilute, degenerate Fermi gas at arbitrary polarization

We calculate the longitudinal magnetic relaxation timeT1−1 for a dilute, polarized Fermi gas with short range interactions at low temperatures. In the limit of small polarizationsT1−1 is proportional toT−2 in agreement with earlier predictions, while in the opposite caseT1−1 is strongly affected by polarization, and in the limit of large polarizations becomes proportional to the square of the energy separation between the Fermi surfaces for up and down spins. The possibility of measuringT1 in dilute solutions of3He in superfluid4He is investigated.

Analysis of nuclear spin-lattice relaxation in HCP transition metals based on Dirac theory

Symmetry adapted expressions for the magnetic and quadrupolar nuclear spin-lattice relaxation time T1 in HCP metals are derived from Dirac theory. They are applied systematically to 3d, 4d and 5d metals (Sc, Ti, Y, Zr, Tc, Lu, Hf, Re, Os) on the basis of semi-relativistic and full-relativistic self-consistent LMTO calculations. General trends and relativistic effects are discussed. The relaxation rate T-11 in Zr is overestimated theoretically by a factor of two, as already found by Asada and Terakura. There is strong evidence that the reason for this error lies in spin-orbit splitting. Shifts of 3 mRy in the band position explain the experimental T-11 in Zr. The Fermi surface of Ti is discussed in connection with the theoretical relaxation rate. Some quantities that are useful for the evaluation of measurements like hyperfine coupling constants and ratios between magnetic and quadrupole relaxation rates are presented. Comparison with the experimental data shows that the quadrupole scattering is well reproduced by the theory.

T1 and T2 of ferritin at different field strengths: effect on MRI.

Nuclear magnetic relaxation times T1 and T2 were measured in ferritin solutions at field strengths from 0.04 to 1.5 T. T1 was relatively constant, but 1/T2 increased linearly with field strength, in agreement with earlier MRI observations in the monkey brain. This finding supports the theory that ferritin is responsible for T2 shortening in brain nuclei containing iron. The linear dependence of 1/T2 on magnetic field is unique and not explained by present theories of the magnetic properties of ferritin.

Frequency Dependent NMR Spin Relaxation Studies of Deuterons and Protons in Nematic Liquid Crystals

Abstract As first discussed by Pincus and Blinc, order fluctuations of the director in a nematic liquid crystal should lead to a characteristic square-root dependence of the nuclear magnetic relaxation times T1 of the considered atoms on the Larmor frequency v, i.e. T1 - v 1/2. The significance of this process is violently disputed in the literature, essentially because standard NMR spectrometers do not allow a broad frequency variation sufficient to separate different dispersion laws reliably. Using a newly developed field-cycling NMR spectrometer with a fast switchable 1.2 T detection field and fast Fourier transform data processing capabilities, it became possible to extend previous proton relaxation studies to selective frequency dependent deuteron T1 measurements in the range between 500 Hz and 7 MHz for various deuterated nematogens (PAA-d6, PAA-d8, PAA-d14, MBBA-d6). Compared with previous proton results in the same frequency range, the relaxation dispersion of the deuterons at identical sites is r...

Retarded green's-function calculation of magnetic resonance relaxation time T1 for rotating molecules or atomic groups in solids

The two-times Green's-function formalism is applied to the calculation of the NMR relaxation time T, for systems of hindered-rotating molecules or atomic groups in solids or solid surfaces at very low temperature. The rotation of the molecules is quantum-mechanically considered as one-phonon induced transitions between the hindered-rotator levels. The nuclear spin system is assumed to be coupled to the bath of thermal phonons through the phonon-rotation interaction. The longitudinal relaxation rate is determined by taking the lowest order approximation for the pole structure of the retarded Green's function; in this way a multiexponential behavior due to the different nuclear spin species present in the molecule or atomic group is obtained.

Proton NMR Relaxation Study of Thermotropic Copolyesters

p-Hydroxybenzoic acid/poly(ethylene terephtharate) (PHB/PET) and p-hydroxybenzoic acid/6-hydroxy-2-naphthoic acid (PHB/PHN) thermotropic copolyesters were investigated in the temperature range from −120 to 180°C by observing the proton magnetic relaxation times T1, T1ρ, and the line width. In the temperature dependence of T1ρ of PHB/PET two minima of the relaxation times were observed. The one at higher temperature corresponds to the glass transition, and the other at lower temperature (40°C) is considered to result from the phenylene group motion. For PHB/PHN, the transition similar to the low temperature one of PHB/PET was observed. The transition temperature of PHB/PHN is higher by 30–40°C as compared with PHB/PET due to the rigid structure. From analysis of line width, it was found that there are two motional regions for both copolyesters, and the activation energies could be obtained. The T1 minimum associated with the glass transition was observed in the T1 experiment. The mesophase formation seems to narrow the distribution of the correlation times of motion.

The Exchange Narrowing of T1 in Solid 3He

The exchange narrowing of the nuclear magnetic relaxation time T1 of solid 3He is investigated on the basis of the heat bath model. The exchange interactions are supposed to be described by the ring exchange model with two or three parameters. It is found that the three parameter model may explain the observed T1, data, but the two parameter model may not.

Practical Economic Considerations of Clinical Nuclear Magnetic Resonance

Nuclear magnetic resonance (NMR) has generated more excitement and more confusion in the medical community than any other new technology in recent memory. Nuclear magnetic resonance has been applied to certain areas of clinical imaging where it competes favorably with computed tomography (CT) and ultrasound. It has been applied in research laboratories as a spectroscopic technique where it provides in vivo information about tissue metabolism. Where each of these applications of NMR fits into the general framework of medical diagnosis is yet to be determined. Even after such a medical determination has been made, various economic factors will ultimately determine if NMR will gain widespread use. Currently, NMR can image the body in thin tomographic slices in either the axial, sagittal, or coronal planes. The intensity of the NMR signal is determined by tissue hydrogen density and by the two magnetic relaxation times T1 and T2. Submillimeter spatial resolution has