Transverse Magnetization Decay Research Articles

Self-Diffusion in IcosahedralAl72.4Pd20.5Mn7.1and Phason Percolation at Low Temperatures Studied byA27lNMR

Aluminum self-diffusion in a monodomain icosahedral quasicrystal ${\mathrm{Al}}_{72.4}{\mathrm{Pd}}_{20.5}{\mathrm{Mn}}_{7.1}$ has been studied at temperatures between 4 and 400 K by ${}^{27}\mathrm{Al}$ NMR measurements of the decay of transverse nuclear spin magnetization in a spatially inhomogeneous electric field gradient. Temperature dependence of the renormalized diffusion constant can be explained in the framework of the Kalugin-Katz phason-assisted diffusion model where the atomic jumps occur as a result of the presence of matching-rules violation defects. The observed self-diffusion process resembles a percolation transition with the percolation threshold at 72 K.

A TROSY CPMG sequence for characterizing chemical exchange in large proteins.

A new NMR spin relaxation experiment is described for measuring chemical exchange time constants from approximately 0.5 ms to 5 ms in 15N-labeled macromolecules. The pulse sequence is based on the Carr-Purcell-Meiboom-Gill technique [Carr and Purcell (1954) Phys. Rev., 94, 630-638; Meiboom and Gill (1958) Rev. Sci. Instrum., 29, 688-691; Loria et al. (1999) J. Am. Chem. Soc., 121, 2331-2332], but implements TROSY selection [Pervushin et al. (1997) Proc. Natl. Acad. Sci. USA, 94, 12366-12371] to permit measurement of exchange linebroadening contributions to the narrower component of the 1H-15N scalar-coupled doublet. This modification extends the size limitation imposed on relaxation measurements due to the fast decay of transverse magnetization in larger macromolecules. The new TROSY-CPMG experiment is demonstrated on a [U-98% 15N] labeled sample of basic pancreatic trypsin inhibitor and a [U-83% 2H, U-98% 15N] labeled sample of triosephosphate isomerase, a 54 kDa homodimeric protein.

Liquid polyethylene glycol dispersed in a poly(styrene)-b-poly(ethylene/butylene)-b-poly(styrene) elastomer: determination of morphology and molecular mobility by light and electron microscopy as well as nuclear magnetic resonance self-diffusion andT2 measurements

An emulsion of liquid polyethylene glycol (PEG) in a rubbery poly(styrene)-b-poly(ethylene/butylene-b-poly-(styrene) (SEBS) matrix was prepared using a poly-(butadiene-b-poly(ethylene oxide) (PB-b-PEO) diblock copolymer as emulsifier. In addition to its emulsifying effect, it was shown that a block copolymer containing a crystalline PEO sequence has a tendency to form micelles as well as supramolecular structures in form of square platelets when they are solubilized in nonpolar solvent such as methylcyclohexane. The filmification of the emulsion by solvent evaporation and the film morphology were examined by light and electron microscopy and by nuclear magnetic resonance (NMR) T2 and self-diffusion measurements. Microscopic evaluations have shown cavities having an average size, depending on the copolymer content, of a few micrometers and filled with liquid PEG. Additionally, smaller structures typically in the range of 30–50 nm have been observed by transmission electron microscopy and are attributed to crystalline lamellae formed by the copolymer in the matrix. The T2 measurements reveal three contributions to the transverse magnetization decay: one of the SEBS matrix, one of the liquid within the cavities and one of the liquid dissolved in the smaller structures formed by the copolymer in the matrix. In the pulsed field gradient NMR self-diffusion experiments two self-diffusion coefficients were found, one of the liquid in the cavities and one of the liquid dissolved in the matrix within the smaller structures. Generally, a restricted diffusion is observed in that latter case owing to confining structures for the diffusing liquid molecules. © 1998 John Wiley & Sons, Ltd.

T1 andT2 relaxations of the13C nuclei of deuterium-labeled nucleosides

The effect of 2H on 13C longitudinal (T1) and transverse (T2) relaxation parameters was determined for the first time for diastereospecifically deuterium-labeled nucleosides, which are used as the building blocks for non-uniform isotope labeling for the solution NMR structure determination of the large biologically functional oligo-DNA and -RNA (‘NMR window’ approach, ref. 7). It emerged that the T1 and T2 of the deuterated methine carbon in the diastereospecifically deuterium-labeled nucleoside 9 could be used as the correction term to give the monoexponential decay of 13C longitudinal and transverse magnetization of the constituent 1H–13C–2H group. The correlation time derived from this corrected T1 of the methylene carbon corresponds well with the correlation time obtained from deuterium relaxation study. The extreme narrowing limit (ωτc≪1) where dipole–dipole (DD) relaxation of 13C and quadrupole (Q) relaxation of 2H are related by T1DD/T2DD≈1 and T1Q/T2Q≈1 was used to demonstrate the above conclusion. The difference in the observable T1 and T2 in various methylene and methine-type carbons with either fully protonated or diastereospecifically deuterated nucleosides 1–14 allowed the estimation of the contribution of the alternative relaxation pathways other than DD relaxation. It was found by comparison of the T1 relaxation of the quaternary carbon with the methine carbon (13C–2H) or (13C–1H) in compound 2 that the contribution of the intermolecular and intramolecular relaxations of 13C with protons that are two bonds away is larger than DD(13C–2H), and the sum of all these contributions define the T1 of the methine carbon (13C–2H). The observed difference between the experimental T1 and T2 of the methine carbon is attributed to the cross-correlation between DD(13C–2H) and Q(2H) relaxation, which is consistent with recent theoretical predictions. For T2 measurement, the decoupling of deuterium with 0.6–2.5 kHz power during the echo period by WALTZ does not effectively eliminate the DD(13C–2H)–Q(2H) cross-correlation for the methine carbon. The suppression of this DD(13C–2H)–Q(2H) cross-correlation was, however, more effective by applying a 180° deuterium pulse in the middle of the short (0.5 ms) echo period (compare T2 of 3.91s and 0.3s, respectively, at 294 K using these two different decoupling procedures). The comparison of the observed T1 and T2 relaxations of the methylene carbon shows that they are indeed very close. The various contributions of the methine carbon relaxation such as DD(13C–2H), intermolecular and cross-correlation, DD(13C–1H)–Q(2H), to the relaxation of the methylene carbon were ca. 15% in T1 and ca. 25% in T2. © 1998 John Wiley & Sons, Ltd.

Analysis of intramedullary cell density by MRI using the multiple spin-echo technique.

Analysis of the intramedullary cell distribution by magnetic resonance imaging (MRI) using conventional techniques involves subjectively interpreting images and estimating the cell distribution on the basis of signal intensity characteristics. In recent years, attempts have been made to achieve more precise analysis by new techniques, including chemical shift imaging. The multiple spin-echo (MSE) technique offers some advantages over conventional MRI. Since it allows measurement of the transverse magnetization decay curve at 32 or more points, it is capable of separating several tissue components with different relaxation times. In addition, this technique can be used with MRI instruments having a static magnetic field as low as 1.0 Tesla. In the present study, the intramedullary cell density was assessed by MRI using the MSE technique in 4 patients with aplastic anemia (AA), 4 patients with myelodysplastic syndrome (MDS), and 5 normal subjects. The water component of the marrow (with a short relaxation time) and the fat component (with a long relaxation time) were separated from each other by analyzing MR images obtained using the MSE technique, and the signal intensity ratio of the 2 components was calculated. The ratio was significantly higher in the AA group than in the other groups (AA vs. MDS, P = 0.0209, AA vs. normal controls, P = 0.0143). The present technique appears promising for quantitative assessment of the intramedullary cell density.

Analysis of intramedullary cell density by MRI using the multiple spin‐echo technique

Analysis of the intramedullary cell distribution by magnetic resonance imaging (MRI) using conventional techniques involves subjectively interpreting images and estimating the cell distribution on the basis of signal intensity characteristics. In recent years, attempts have been made to achieve more precise analysis by new techniques, including chemical shift imaging. The multiple spin-echo (MSE) technique offers some advantages over conventional MRI. Since it allows measurement of the transverse magnetization decay curve at 32 or more points, it is capable of separating several tissue components with different relaxation times. In addition, this technique can be used with MRI instruments having a static magnetic field as low as 1.0 Tesla. In the present study, the intramedullary cell density was assessed by MRI using the MSE technique in 4 patients with aplastic anemia (AA), 4 patients with myelodysplastic syndrome (MDS), and 5 normal subjects. The water component of the marrow (with a short relaxation time) and the fat component (with a long relaxation time) were separated from each other by analyzing MR images obtained using the MSE technique, and the signal intensity ratio of the 2 components was calculated. The ratio was significantly higher in the AA group than in the other groups (AA vs. MDS, P = 0.0209, AA vs. normal controls, P = 0.0143). The present technique appears promising for quantitative assessment of the intramedullary cell density. Am. J. Hematol. 55:134–138, 1997. © 1997 Wiley-Liss, Inc.

Nuclear Magnetic Relaxation Near the Nematic-to-Isotropic Transition in Micellar Systems

Using the NMR 19F technique, decay of the transverse magnetization (DTM) is studied over the nematic-to-isotropic liquid transition region for aqueous micellar solutions of cesium perfluorononanoate. Transverse magnetization decay appears to be single-component in both nematic and isotropic phases and two-component in the two-phase region. Componental composition of the DTM changes fastly near the low-temperature border of the coexistence region but slowly near the high-temperature border. Long exposition at fixed temperature leads to spatial phase separation of the micellar system: the isotropic phase moves up while the nematic one drowns. It is argued that this fact is due to a difference in micellar concentrations between the two phases.

Basal ganglia iron content in Parkinson's disease measured with magnetic resonance

The possibility of using magnetic resonance (MR) to evaluate the severity of the pathological changes of Parkinson's disease (PD) is suggested by the known accumulation of iron in the basal ganglia in PD and the reduced signal evident from this area with conventional T2-weighted MR imaging. To improve the specificity of MR for the measurement of tissue iron content, we have developed a method that quantifies the effects of paramagnetic centers sequestered inside cellular membranes, based on the echo time dependence of the decay of transverse magnetization caused by the local field inhomogeneities which are due to intracellular iron. This method enables an index of local tissue iron content to be calculated for structures of the basal ganglia. We report here the application of this method to a series of patients with PD (n = 12) and of normal, age-matched controls (n = 13). Our objective was to determine whether this measurement of basal ganglia iron concentration correlates with the presence and severity of PD. We observed a significant increase in iron content in both the putamen and pallidum in PD as well as a correlation with the severity of clinical symptomatology. More severely affected patients had a higher iron content in both of these structures. Our results suggest that this MR measurement may provide a noninvasive method of measuring the severity of the pathological changes underlying PD.

Investigation of laminar appearance of articular cartilage by means of magnetic resonance microscopy.

Magnetic resonance (MR) images and relaxation and diffusion maps of articular cartilage were obtained to explain discrepancies in its MR appearance. Porcine specimens were studied only by MR microscopy. For human specimens a combination of MR microscopy and large-scale MR imaging was used. Common features in the laminar structures of human and porcine samples are described. It was found that the decay of transverse magnetization was nonexponential with a rapidly decaying component which prevented construction of reliable proton-density maps. Dependence of T2 values on the orientation of specimens in the magnetic field as well as magnetization transfer experiments supported the previous suggestions about a significant role of dipolar interaction with protons of collagen in the laminar appearance of articular cartilage. The loss of the laminar structure induced by rotation of the human cartilage specimen around the axis normal to its surface demonstrated nonuniform angular distribution of the collagen fibers within the layer.

In vivo characterization of cytotoxic intracellular edema by multicomponent analysis of transverse magnetization decay curves

We investigated the multicompartmental nature of T2 decay in a specific white matter edema model. Triethyltin (TET) intoxication was produced in six male New Zealand White rabbits. Images were obtained over the 23-day study duration using a 64-echo Carr-Purcell-Meiboom-Gill (CPMG) sequence (repetition time = 3000 msec, echo time = 20 msec). T2 decay curves were extracted from 0.7 x 0.7 x 3.0 mm3 voxels in the corpus callosum and contiguous white matter tracts, cortex, thalamic nuclei, hypothalamic nuclei, and the masseter muscles. The curves were fit with biexponential functions. Increased signal intensity in the corpus callosum was evident 2-3 days after the first TET injection. At this time, a substantial slowly relaxing component appeared in the decay curves of the corpus callosum and, to a lesser extent, in the thalamus and hypothalamus. Changes in the rabbits' body weight, general physical condition, and neurologic state paralleled the growth and regression of the second, slowly relaxing component. The appearance and regression of a slowly decaying second component in the T2 decay curve is consistent with the formation and shrink-age of intracellular vesicles in the intramyelin sheaths of central white matter.

Localized T2 measurements using an OSIRIS-CPMG method. Application to measurements of blood oxygenation and transverse relaxation free of diffusion effect.

This work presents a new method allowing localized T2 measurements, based upon the OSIRIS scheme. A train of 180 degrees pulses is applied after the OSIRIS preparation cycle, recording directly the transverse magnetization decay. The method was verified for two nuclei, 1H and 19F, with phantoms and in vivo on rats. The accuracy of the T2 values is discussed, as well as possible applications of the OSIRIS-CPMG method to proton transverse spin relaxation measurements, free of diffusion effects, and to non-invasive in vivo blood oxygenation measurements, through the use of an emulsion of perfluorooctylbromide, a blood substitute containing fluorine.

Exchange and Cross-Relaxation in Adsorbed Water

Previous investigations concerning the NMR relaxation in adsorbed water show that both the longitudinal and the transverse proton magnetization decay in a multiexponential way. Two or more components can always be distinguished in those decay curves. We propose a model for adsorbed water which can account for these different relaxation components and with the aid of this model we give a quantitative description of the longitudinal relaxation in water adsorbed on two silica gels and two controlled pore glasses. The model assumes three phases:the protons of the OH groups on the adsorbent surface, the protons of the water molecules close to the surface ("bound" water), and the protons in the rest of the water ("free" water). We prove the occurrence of cross relaxation between the OH protons and the protons in the bound water and of exchange between bound and free water. The OH protons have very slow longitudinal relaxation with T1 = 4-5 s and very fast transverse relaxation with a characteristic time of about 40 μs. The amount of OH protons corresponds to six OH groups per 100 Å2 for all adsorbents studied. We show that the influence of the surface on the longitudinal relaxation of the adsorbed water is limited to one adsorbed layer, that the longitudinal relaxation time for the bound water lies between 20 and 60 ms, and that the free water exhibits a longitudinal relaxation time comparable to the value for pure water (3.3 s). Values for the cross-relaxation times and exchange times are deduced.

NMR assessment of water uptake in different Vigna spp. seeds

SummaryWater uptake in seeds of ten wild and cultivated Vigna spp. accessions was investigated by NMR Spectroscopy. Water absorbed by the intact seeds was measured at intervals by changes in unabsorbed water using analysis of transverse magnetization decay of water protons. Widely different hydration kinetics of first and higher orders were found amongst the samples. the time required to reach saturation hydration capacity ranged from 3 to 16 h; total amount of absorbed water varied from 1.06 to 1.39g H2O g−1 sample and kinetic constant from 8.2 to 20.4 10−3 min−1.Accessions with a rough seed coat showed a fast water uptake within the first hour while some accessions smooth seed coat need an activation period of 1–5h.No significant relationships were found between kinetic constant, absorbed water and protein content or some morphological characteristics (100 seed mass, length/width, width/thickness).Wild species did not absorb water for days, an attribute related to biological survival, but after dehulling they absorbed water at similar rates to the cultivated cowpeas.NMR can be a suitable technique to investigate some technological characteristics of legumes related to domestic and industrial processing (cooking, canning). It has potential to give data on the various forms of free and bound water, although this was not fully derived in the present work.

Quantitative cerebral magnetic resonance imaging during ACTH treatment of multiple sclerosis

Serial MR scans were performed with the 2DFT imaging method and the filtered backprojection imaging method on 12 patients with multiple sclerosis in acute phase, 4 in a relapsing/remitting form, and 8 in a progressive form, before, during and after ACTH treatment. Both T 1 and T 2mono relaxation times, obtained by fitting transverse magnetization decay curves with a monoexponential function within the apparently normal white matter and the areas of increased signal, were measured. With the backprojection method it was possible to fit the transverse magnetization decay curve with a biexponential function and obtain T 2long and T 2short relaxation times. The T 2mono and T 1 relaxation times of the apparently normal white matter were significantly different from those obtained for volunteers, but no significant differences were found before, during, or after treatment. The transverse magnetization decay curves of the areas of increased signal were better fitted by a biexponential function. No significant changes in these relaxation times were observed after ACTH treatment. These results argue against an anti-oedematous action of ACTH and may suggest that it has an immunosuppressant effect.

Hydration behavior of heart muscle studied by nuclear magnetic relaxation. Changes with heat treatment in muscle hydration and water distribution in heart muscle

The 1 H nuclear magnetic relaxation behavior of heart muscle from chicken, pork, and beef was investigated in relation to composition and processing conditions. Nonlinear regression analysis of the transverse magnetization decay yielded a best fit with three exponential components thatare likely to correspond to three proton populations of average T 2 values in the range 2 ms-0.7 s in three separate types of compartments in the heart muscle. The long T 2 relaxation component may correspond to the protons of a water population within relatively large spaces between muscle cells

Characterization of spin polarized dilute3He-4He solutions below 500 mK

The authors have prepared a large sample of spin polarized liquid {sup 3}He-{sup 4}He at 500 mK. Polarization is obtained by laser optical pumping, and studied by pulsed NMR. They have observed a nuclear magnetization lifetime T{sub 1} longer than 1 hour, and an anomalously long, nonlinear decay of transverse magnetization. 4 refs., 2 figs.

Characterization of cerebral infarction by multicomponent analysis of transverse magnetization decay curves.

Individual components of the transverse magnetization decay curve (TDC) were assessed for their ability to characterize ischemia in photochemically induced cerebral infarcts. Fifty rats were randomly divided into equal-sized experimental and control groups, which were subdivided into groups studied at five different time points, ranging from 6 hours to 22 days. All the rats received transcalvarial irradiation with 560-nm light. Five rats in each time group also received a sensitizing dye before irradiation. In these latter animals, lesions of uniform size and location developed. Lesions were compared with tissue of similar volume and location from the contralateral cortex of the experimental animals and with tissue from both hemispheres of the control animals. TDCs of all the samples were measured and fit with mono- and bi-exponential functions. Unlike the control tissue, infarcted tissue displayed definitive two-component TDC behavior. The time course of the bi-exponential parameters yielded information unavailable from mono-exponential analyses. Bi-exponential analysis of TDCs may have diagnostic use as a more sensitive indicator of cerebral infarction than mono-exponential analyses.

On the water condition in pork meat

The water condition of cured and uncured pork, having different ageing times, was studied in the process of heating to 80°C, using nuclear-magnetic resonance methods. In the transverse magnetization decay functions five components could be distinguished, differing from each other by their relative weights and relaxation times. The greatest relative weight (60–70%) was characteristic of the component having relaxation time 35–45 ms (‘d’), which could be related to immobilized water. The change of the component's ‘d’ relative weight while heating was significantly dependent on the ageing time of meat and the factor of curing or not curing before heating. It was shown that the greatest amount of immobilized water and its strongest bonding were observed in uncured pork during the first 6–7 h and after 48 h post mortem. Cured meat possesses the highest amount of immobilized water at room temperature after 48–96 h post mortem, however, its bonding at heating is higher in the case of meat which is cured during the first hours and after 96 h post mortem.

Single and Multiple Quantum NMR Relaxation Times of Sodium and Potassium in Red Blood Cells

AbstractThe two components T2f and T2s of the transverse magnetization decay curve of 23Na in dog erythrocytes were measured using the triple quantum filtered spectra. It was shown that this technique, in spite of its inferior sensitivity, may be used for systems where T2f and T2s are not very different. Thus it was possible to measure the effect of 2, 3‐diphosphoglycerate (2, 3 DPG) depletion on the intracellular 23Na relaxation rates. The effect found indicates some contribution of hemoglobin‐2, 3‐DPG complexes to the 23Na relaxation in intact erythrocytes. 39K relaxation times were measured in human and chicken erythrocytes. The results indicate binding similar to that of 23Na. Finally, a decrease of the cellular volume of erythrocytes was found to shorten 23Na relaxation times. The result was interpreted as due to an increase in intracellular concentration of proteins.

Long-time magnetization relaxation of spins diffusing in a random field.

We study the free-induction decay and the spin-echo attenuation at long times for spins diffusing in a random magnetic field. We show that the decay of transverse magnetization in a Gaussian random longitudinal field is asymptotically M(t)\ensuremath{\sim}${\mathit{t}}^{\ensuremath{\gamma}\mathrm{\ensuremath{-}}1}$${\mathit{e}}^{\mathrm{\ensuremath{-}}\mathit{t}/\mathrm{\ensuremath{\tau}}}$, where \ensuremath{\gamma} is the exponent of a self-avoiding walk. The usual result given by a cumulant expansion fails due to correlations arising from multiple self-intersections in d\ensuremath{\le}4. Experimental relevance of our analysis is discussed along with the question of universality and the existence of large fluctuations in finite-size systems.