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Transverse relaxation time (T2*) is related to tissue oxygenation and morphology. We aimed to describe T2* weighted MRI in selected fetal organs in normal pregnancies, and to investigate the correlation between fetal organ T2* and placental T2*, birthweight (BW) deviation, and redistribution of fetal blood flow. T2*-weighted MRI was performed in 126 singleton pregnancies between 23+6- and 41+3-weeks' gestation. The T2* value was obtained from the placenta and fetal organs (brain, lungs, heart, liver, kidneys, and spleen). In normal BW pregnancies (BW > 10th centile), the correlation between the T2* value and gestational age (GA) at MRI was estimated by linear regression. The correlation between fetal organ Z-score and BW group was demonstrated by boxplots and investigated by analysis of variance (ANOVA) for each organ. In normal BW pregnancies fetal organ T2* was negatively correlated with GA. We found a significant correlation between BW group and fetal organ T2* z-score in the fetal heart, kidney, lung and spleen. A positive linear correlation was demonstrated between fetal organ T2* and outcomes related to placental function such as BW deviation and placenta T2* in all investigated fetal organs except for the fetal liver. In the fetal heart, kidneys, and spleen the T2* value showed a significant correlation with fetal redistribution of blood flow (Middle cerebral artery Pulsatility Index) before delivery. Fetal T2* is correlated with BW, placental function, and redistribution of fetal blood flow, suggesting that fetal organ T2* reflects fetal oxygenation and morphological changes related to placental dysfunction. • The transversal relaxation time (T2*) is related to tissue oxygenation. • It is feasible to obtain reliable fetal T2* values from selected fetal organs. • Fetal organ T2* is reduced in low BW pregnancies compared to normal BW pregnancies. • Fetal organ T2* is associated with redistribution of fetal blood flow at delivery. • Fetal organ T2* may depict fetal oxygenation changes related to placental dysfunction. [ABSTRACT FROM AUTHOR]

Water-soluble organic admixtures (WSOAs) are widely used in cementitious materials, and may affect the porosity, but their effects on low-field nuclear magnetic resonance (LF-NMR) measurement are often overlooked. Using viscosity modifying admixture (VMA) as an example, this study demonstrates the presence of WSOAs would lead to an overestimation of porosity and a leftward shift of pore size distribution using LF-NMR. This is attributed to the formation of hydrogen bonds between polymer and water molecules, and the decreased distance between nuclear spins, respectively. A strategy is proposed to improve the accuracy of the porosity characterization by eliminating the additional effects of WSOAs in LF-NMR testing. The results show that the addition of small molecular mass non-ionic VMAs replacing mixing water (within a 20 % replacing rate) does not alter the porosity of the paste. This method can be extended to characterize the porosity of various porous materials containing WSOAs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Isotropically-restricted compartments might bias the axonal T 2 estimated from the spherical mean of the strongly diffusion-weighted signal. • The use of the spherical variance is proposed to enable an unbiased estimation of the axonal T 2. • Our analysis does not allow to discard the detectability of an isotropically-restricted compartment in the brain's white matter. In magnetic resonance imaging, the application of a strong diffusion weighting suppresses the signal contributions from the less diffusion-restricted constituents of the brain's white matter, thus enabling the estimation of the transverse relaxation time T 2 that arises from the more diffusion-restricted constituents such as the axons. However, the presence of cell nuclei and vacuoles can confound the estimation of the axonal T 2 , as diffusion within those structures is also restricted, causing the corresponding signal to survive the strong diffusion weighting. We devise an estimator of the axonal T 2 based on the directional spherical variance of the strongly diffusion-weighted signal. The spherical variance T 2 estimates are insensitive to the presence of isotropic contributions to the signal like those provided by cell nuclei and vacuoles. We show that with a strong diffusion weighting these estimates differ from those obtained using the directional spherical mean of the signal which contains both axonal and isotropically-restricted contributions. Our findings hint at the presence of an MRI-visible isotropically-restricted contribution to the signal in the white matter ex vivo fixed tissue (monkey) at 7T, and do not allow us to discard such a possibility also for in vivo human data collected with a clinical 3T system. [ABSTRACT FROM AUTHOR]

Abstract Low-field Nuclear Magnetic Resonance (NMR) is a non-invasive method widely used in the petroleum industry for the evaluation of reservoirs. Pore structure and fluid properties can be evaluated from transverse relaxation (T 2) distributions, obtained by inverting the raw NMR signal measured at subsurface conditions or in the laboratory. This paper aims to cast some light into the best practices for the T 2 data acquisition and inversion in shales, with a focus on the suitability of different inversion methods. For this purpose, the sensitivity to various signal acquisition parameters was evaluated from T 2 experiments using a real shale core plug. Then, four of the most common inversion methods were tested on synthetic T 2 decays, simulating components often associated with shales, and their performance was evaluated. These inversion algorithms were finally applied to real T 2 data from laboratory NMR measurements in brine-saturated shale samples. Methods using a unique regularization parameter were found to produce solutions with a good balance between the level of misfit and bias, but could not resolve adjacent fast T 2 components. In contrast, methods applying variable regularization – based on the noise level of the data – returned T 2 distributions with better accuracy at short times, in exchange of larger bias in the overall solution. When it comes to reproducing individual T 2 components characteristic of shales, the Butler-Reeds-Dawson (BRD) algorithm was found to have the best performance. In addition, our findings suggest that threshold T 2 cut-offs may be derived analytically, upon visual inspection of the T 2 distributions obtained by two different NMR inversion methods. Highlights • Short echo spacings (TE) can improve signal quality but also enhance early experimental noise. • Inversion methods using fixed smoothing cannot resolve adjacent T 2 components correctly. • Inversion methods based on noise level produce better fits but may bias solutions. • The BRD algorithm can differentiate the contribution from adjacent peaks at short T 2 times. • Threshold T 2 cut-offs are determined analytically by using two different NMR inversion methods. [ABSTRACT FROM AUTHOR]

Summary Nuclear Magnetic Resonance (NMR) log can provide accurate porosity independent of lithology, and NMR logging is more advantageous over conventional logs. In recent decades, it has been broadly applied in reservoir evaluation and pore structure study of sandstone and carbonate formations. But in igneous rocks, NMR porosity is underestimated compared to the actual porosity, which limits the application of NMR measurement in such reservoirs. To tackle this problem, NMR measurements were firstly introduced from DX, XS, and CPZ regions, China, and the effect of different igneous rocks on NMR porosity was analyzed in detail. NMR transvers relaxation time (T 2) of igneous rock is very short and the T 2 distribution is in fast relaxation region, and the amplitude of NMR signals is so low. From NMR measurement analysis, NMR porosity relative error generally increases from acid, middle to mafic igneous rocks. Then, combined with element measurement, some influential factors were summarized from laboratory experiments and the relationships of NMR porosity relative error between different paramagnetic elements and magnetic susceptibility were investigated. The elemental analysis from plasma emission spectrometer showed that, NMR porosity relative error is related to paramagnetic mineral contents, and it generally increases as the iron and manganese contents increase. Moreover, the magnetic susceptibility of igneous rock is usually significantly greater than the sedimentary rocks, and from acid, middle to mafic igneous rocks, the magnetic susceptibility trends to increase. According the above analysis, some NMR porosity correction correlations are constructed. Finally, in case study from CPZ region, NMR logging porosity was correlated by the constructed correction correlation from iron content of element spectrum capture log, the corrected NMR porosity is in good agreement with core porosity, which proves the empirical correction method from the paramagnetic element contents reliable. Therefore, this study provides the foundation for NMR measurement correction and NMR logging interpretation of such complex igneous rocks formation. Highlights • NMR distribution of igneous rock is different from sedimentary rock. • The effect of different igneous rocks on NMR porosity was analyzed. • The paramagnetic elements lead to NMR porosity relative error. • NMR porosity relative error is related to the magnetic susceptibility. • NMR porosity correction correlation is constructed and NMR logging porosity is corrected. [ABSTRACT FROM AUTHOR]

The hydration process of starch significantly affects the quality of starch-based food, especially for samples with medium to low water content. In this paper, rice starch, as a representative of cereal starch, and potato starch were chosen as the samples. The proton distributions and flow status of the hydrated rice starch and potato starch with moisture contents of 20–90% and the causes of the differences between them were investigated by 1 H LF-NMR. The longitudinal and transverse proton relaxation (T 1 and T 2 ) of the two starch systems was obtained using the inversion recovery (IR) sequence, the free induction decay (FID) sequence, and the multi-pulse echo CPMG sequence. Through the detection of longitudinal relaxation, two different populations were found in the two hydrated starch systems, and the changes were linearly related to the moisture content. Through the detection of transverse relaxation, two populations were distinguished in the hydrated rice starch samples with different moisture content, whereas two to four different populations were detected in the hydrated potato starch samples. Because of the differences in particle size and swelling capacity, hydrated potato starch showed greater proton freedom and more observable types of protons than hydrated rice starch. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine whether metrics of brain tissue integrity derived from postmortem magnetic resonance imaging (MRI) are associated with late-life cognitive decline, independent of cerebral vessel disease. Using data from 554 older adults, we used voxelwise regression to identify regions where the postmortem MRI transverse relaxation rate constant R 2 was associated with the rate of decline in global cognition. We then used linear mixed models to investigate the association between a composite R 2 measure and cognitive decline, controlling for neuropathology including 3 indices of vessel disease: atherosclerosis, arteriolosclerosis, and cerebral amyloid angiopathy. This composite R 2 measure was associated with the rate of decline (0.049 unit annually per R 2 unit, p < 0.0001) and accounted for 6.1% of its variance, beyond contributions from vessel disease indices and other prominent age-related neuropathologies. Thus, postmortem brain R 2 reflects disease processes underlying cognitive decline that are not captured by vessel disease indices or other standard neuropathologic indices and may provide a measure of brain tissue integrity that is complementary to histopathologic evaluation. [ABSTRACT FROM AUTHOR]

Tissue-inherent relaxation parameters offer valuable information about the arrangement of capillaries: in an external field, capillaries act as magnetic perturbers to generate local inhomogeneous fields due to the susceptibility difference of deoxygenated blood and the surrounding tissue. These field inhomogeneities influence the free induction decay in a characteristic way, and, conversely, the above tissue parameters can be recovered by multi-parametric fits of adequate theoretical models to experimentally sampled free induction decays. In this work we study the influence of different spatial patterns of capillary positions on the free induction decay. Starting from the standard single capillary approximation (Krogh cylinder) for a symmetric array of capillaries, the free induction decay is analyzed for increasingly random capillary positions, using a previously described Gibbs point field model. The effects of diffusion are implemented with a flexible and fast random walk simulation. We find that the asymmetric form of the obtained frequency distribution is more robust against variations of capillary radii than against shifts of capillary positions, and further that, for an inclusion of diffusion effects, the single capillary approximation models the uniform alignment of capillaries in the hexagonal lattice to great accuracy. An increase in randomization of capillary positions then leads to a significant change in relaxation times. This effect, however, is found less pronounced than that of changes in the off-resonance field strengths which are controlled by the oxygen extraction fraction, thus indicating that observed changes in BOLD imaging are more likely to be attributed to changes in oxygenation than to capillary alignment. [ABSTRACT FROM AUTHOR]

Blood is a physiological substance with multiple water compartments, which contain water-binding proteins such as hemoglobin in erythrocytes and albumin in plasma. Knowing the water transverse ( R 2 ) relaxation rates from these different blood compartments is a prerequisite for quantifying the blood oxygenation level-dependent (BOLD) effect. Here, we report the Carr-Purcell-Meiboom-Gill (CPMG) based transverse ( R 2 CPMG ) relaxation rates of water in bovine blood samples circulated in a perfusion system at physiological temperature in order to mimic blood perfusion in humans. R 2 CPMG values of blood plasma, lysed packed erythrocytes, lysed plasma/erythrocyte mixtures, and whole blood at 3 T, 7 T, 9.4 T, 11.7 T and 16.4 T were measured as a function of hematocrit or hemoglobin concentration, oxygenation, and CPMG inter-echo spacing ( τ cp ). R 2 CPMG in lysed cells showed a small τ cp dependence, attributed to the water exchange rate between free and hemoglobin-bound water to be much faster than τ cp . This was contrary to the tangential dependence in whole blood, where a much slower exchange between cells and blood plasma applies. Whole blood data were fitted as a function of τ cp using a general tangential correlation time model applicable for exchange as well as diffusion contributions to R 2 CPMG , and the intercept R 20 blood at infinitely short τ cp was determined. The R 20 blood values at different hematocrit and the R 2 CPMG values of lysed erythrocyte/plasma mixtures at different hemoglobin concentration were used to determine the relaxivity of hemoglobin inside the erythrocyte ( r 2 Hb ) and albumin ( r 2 Alb ) in plasma. The r 2 Hb values obtained from lysed erythrocytes and whole blood were comparable at full oxygenation. However, while r 2 Hb determined from lysed cells showed a linear dependence on oxygenation, this dependence became quadratic in whole blood. This possibly suggests an additional relaxation effect inside intact cells, perhaps due to hemoglobin proximity to the erythrocyte membrane. However, we cannot exclude that this is a consequence of the simple tangential model used to remove relaxation contributions from exchange and diffusion. The extensive data set presented should be useful for future theory development for the transverse relaxation of blood. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance was used to study water proton transverse relaxation in oat β -glucan aqueous solutions during storage. The molecular weights of the samples ranged from 112 to 494 kDa. The polysaccharide structure was identified by IR, GC–MS, NMR spectroscopy, and high performance anion exchange chromatography. In 1% solutions, 494 kDa β -glucan formed stable solution phase. Aggregates were generated in the solution of low molecular weight polysaccharide. The transverse relaxation time of water associated with the aggregate microphase was about 15 ms. The majority of the solution was bulk water, with a relaxation time of 800–1600 ms. The proton exchange rate was about 10 3 s −1 , calculated from two-site exchange model. The proportion of β -glucan in the aggregate microphase increased from 0 to over 80% of the total β -glucan during storage of 112 kDa samples. In the 4% solutions, the evolution of water proton relaxation associated with the gel network can be explained by the fractal structure theory. The relaxation behavior suggested the growth and syneresis of the gel network during the gelation of the low molecular weight β -glucan solutions. [ABSTRACT FROM AUTHOR]

Objective: Neonates at low birth weight due to placental dysfunction are at high risk of adverse outcomes. These outcomes can be substantially improved by prenatal identification. The Magnetic Resonance Imaging (MRI) constant, placental T2* reflects placental structure and oxygenation and thereby placental function. Therefore, we aimed to evaluate the performance of placental T2* in the prediction of low birth weight using the uterine artery (UtA) pulsatility index (PI) as gold standard.Methods: This was a prospective observational study of 100 singleton pregnancies included at 20-40 weeks' gestation. Placental T2* was obtained using a gradient recalled multi-echo MRI sequence and UtA PI was measured using Doppler ultrasound. Placental pathological examination was performed in 57 of the pregnancies. Low birth weight was defined by a Z-score ≤ -2.0.Results: The incidence of low birth weight was 15%. The median time interval between measurements and birth was 7.3 weeks (interquartile range 3.0, 13.7 weeks). Linear regression revealed significant associations between birth weight Z-score and both placental T2* Z-score (r = 0.68, p < 0.0001) and UtA PI Z-score (r = -0.43, p < 0.0001). Receiver operating characteristic curves demonstrated a significantly higher performance of T2* (AUC of 0.92; 95% CI, 0.85-0.98) than UtA PI (AUC of 0.74; 95% CI, 0.60-0.89) in the prediction of low birth weight (p = 0.010). Placental pathological findings were closely related to the T2* values.Conclusions: In this population, placental T2* was a strong predictor of low birth weight and it performed significantly better than the UtA PI. Thus, placental T2* is a promising marker of placental dysfunction which deserves further investigation. [ABSTRACT FROM AUTHOR]

We analyze a new approach for determining flow permeability using a nuclear magnetic resonance (NMR) measurement in the presence of induced fluid flow. Direct detecting of fluid movement in porous core samples through the Carr–Purcell–Meiboom–Gill (CPMG) pulse sequence is demonstrate and theoretical model and analysis is given. Experiments performed on a set of sandstone samples (Berea, Bentheimer, Castle Gate, Leopard) and with synthetic high-perm samples made of abrasive material. The experiments show that the NMR spin echo measurements permit to fix mean fluid velocity about 0.05 mm/s. The experiments and the theoretical model show that for low fluid velocities the mean relaxation rate is proportional to fluid velocity. The results may serve as the basis for determination of mobility of liquids in porous media and permeability. [ABSTRACT FROM AUTHOR]

This study tested the hypothesis that indices of brain tissue integrity derived from postmortem magnetic resonance imaging (MRI) are associated with late life decline in cognitive function and dementia, over and above contributions from common age-related neuropathologies. Cerebral hemispheres were obtained from 425 deceased older adults who had undergone 2 or more annual cognitive assessments, which included clinical diagnosis of dementia. Specimens underwent MRI to produce maps of transverse relaxation rate, R 2 . Voxelwise regression revealed brain regions where R 2 was associated with cognitive decline. We then used random effects models to quantify the extent to which R 2 accounted for variation in decline, after adjustment for demographics and neuropathologic indices of the 3 most common causes of dementia: Alzheimer's disease, cerebrovascular disease, and Lewy body disease. We additionally tested whether R 2 was tied to greater likelihood of clinical diagnosis of Alzheimer's dementia using logistic regression models. During an average of 8.1 years, the mean rate of decline in global cognitive function was 0.13 unit per year ( p < 0.0001). The tissue alteration most commonly related to decline was R 2 slowing in white matter. Each unit decrease in R 2 was associated with an additional 0.053-unit per year steepening of the rate of global cognitive decline ( p < 0.001). Furthermore, R 2 accounted for 8.4% of the variance in rate of global cognitive decline, above and beyond the 26.5% accounted for by demographics and neuropathologic indices, and 7.1%–11.2% of the variance of the decline rates in episodic, semantic, and working memory and perceptual speed. Alterations in R 2 were also related to an increased odds of clinical diagnosis of Alzheimer's dementia (odds ratio = 2.000, 95% confidence interval 1.600, 2.604). Therefore, postmortem MRI indices of brain tissue integrity, particularly in white matter, are useful for elucidating the basis of late life cognitive impairment in older adults and complement traditional indices of neuropathology derived using histopathologic methods. [ABSTRACT FROM AUTHOR]

Transverse relaxation rates for Carr-Purcell-Meiboom-Gill (CPMG) sequences increase with inter-echo time in presence of microscopic magnetic field inhomogeneities due to nuclear spin diffusion. For a weak field approximation that includes diffusion effects, the CPMG relaxation rate shift for proton diffusion around capillaries in muscle tissue can be expressed in terms of a frequency correlation function and the inter-echo time. The present work provides an analytical expression for the local relaxation rate shift that is dependent on local blood volume fraction, diffusion coefficient, capillary radius, susceptibility difference and inter-echo time. Asymptotic regions of the model are in agreement with previous modeling results of Brooks et al., Luz et al. and Ziener et al. In comparison with simulation data, the model shows an equal or better accuracy than established approximations. Also, model behavior coincides with experimental data for rat heart and skeletal muscle. The present work provides analytical tools to extract sub-voxel information about uniform capillary networks that can be used to study capillary organization or micro-circulatory remodeling. [ABSTRACT FROM AUTHOR]

Polymer gel electrolytes (PGEs) have been prepared using lithium tetrafluoroborate (LiBF 4 ), propylene carbonate (PC) and poly (vinylidene fluoride) (PVDF). Self diffusion coefficients have been measured using pulse field gradient nuclear magnetic resonance (PFG-NMR) for the lithium cation, BF 4 anion and solvent molecules using 7 Li, 19 F and 1 H nuclei, respectively. It was found that lithium ion diffusion was slow compared to the much larger fluorinated BF 4 anion, which is attributed to a large solvation shell around the lithium ions. The 7 Li and 1 H diffusion measurements also exhibited two unique environments for the diffusive species. The measurement of NMR transverse relaxation times has confirmed the presence of lithium ions in multiple phases as shown by the diffusion measurements. [ABSTRACT FROM AUTHOR]

Clinical estimates of brain iron concentration are achievable with quantitative transverse relaxation rate R 2 , via time-consuming multiple spin-echo (SE) sequences. The objective of this study was to investigate whether quantitative iron-sensitive information may be derived from 3.0 T dual-contrast fast-spin-echo (FSE) sequences (typically employed in anatomical non-quantitative evaluations), as a routinely-collected alternative to evaluate iron levels in healthy (HC) and Parkinson's disease (PD) brains. MRI 3.0 T FSE data from the Parkinson's Progression Markers Initiative (PPMI) (12 PD, 12 age- and gender-matched HC subjects) were cross-sectionally and longitudinally evaluated. A new measure, 'effective R 2 ', was calculated for bilateral subcortical grey matter (caudate nucleus, putamen, globus pallidus, red nucleus, substantia nigra). Linear regression analysis was performed to correlate 'effective R 2 ' with models of age-dependent brain iron concentration and striatal dopamine transporter (DaT) receptor binding ratio. Effective R 2 was strongly correlated with estimated brain iron concentration. In PD, putaminal effective R 2 difference was observed between the hemispheres contra-/ipsi-lateral to the predominantly symptomatic side at onset. This hemispheric difference was correlated with the putaminal DaT binding ratios in PD. Effective R 2 , derived from rapid dual-contrast FSE sequences, showed viability as an alternative to R 2 from SE sequences. Linear correlation of effective R 2 with estimated iron concentration was comparable to documented iron-dependent R 2. The effective R 2 correlation coefficient was consistent with theoretical R 2 iron-dependence at 3.0 T. Effective R 2 has clinical potential as a fast quantitative method, as an alternative to R 2 , to aid evaluation of brain iron levels and DaT function. [Display omitted] • Effective R 2 ' transverse relaxation derived from dual-contrast FSE 3 T clinical MRI. • Longitudinal evaluation of Effective R 2 in Parkinson's (PD) patients from PPMI study. • Effective R 2 in healthy adults is proportionate with age-dependent brain iron levels. • Effective R 2 distinguishes hemispheres contra- and ipsilateral to PD symptom onset. • Effective R 2 correlates with putaminal dopamine transporter binding in early-stage PD. [ABSTRACT FROM AUTHOR]

Understanding the microscopic mechanisms of film formation in polymer dispersions is a complex analytical and physical challenge. In this contribution, we present results from parallel gravimetric and NMR profiling experiments along with a semiempiric model approach to establish a systematic relation between both data sets. As a result of the semiempiric model, a critical water content at which rotation dynamics of the polymer particles changes can be determined. Furthermore, it is shown that the addition of film-forming agents to the dispersion shifts the critical water content to higher values. [ABSTRACT FROM AUTHOR]

Highlights: [•] The rule of water mobility of chicken breast dried at different temperatures was obtained. [•] The LF-NMR was able to discriminate the drying degree of chicken jerky by specific indicators. [•] Correlations were found between the LF-NMR parameters and quality indicators. [Copyright &y& Elsevier]

Highlights: [•] Hydrophilic coating of oleate-coated SPIONs by surfactants and triblock copolymers. [•] Self-assembly of surfactants onto oleate layer is more predominant than ligand exchange. [•] Structure of amphiphilic molecules affects clustering of SPIONs within hydrophilic coating. [•] Particular effect of outer zone versus nearest one on relaxivity of hydrophilic SPIONs. [•] Counter-ion interactions with ATP induce changes in relaxivity of surfactant-coated SPIONs. [Copyright &y& Elsevier]

Abstract: We previously derived a simple equation for solving time-dependent Bloch equations by a matrix operation. The purpose of this study was to present a theoretical and numerical consideration of the longitudinal (R 1ρ =1/T 1ρ) and transverse relaxation rates in the rotating frame (R 2ρ =1/T 2ρ), based on this method. First, we derived an equation describing the time evolution of the magnetization vector (M(t)) by expanding the matrix exponential into the eigenvalues and the corresponding eigenvectors using diagonalization. Second, we obtained the longitudinal magnetization vector in the rotating frame (M 1ρ(t)) by taking the inner product of M(t) and the eigenvector with the smallest eigenvalue in modulus, and then we obtained the transverse magnetization vector in the rotating frame (M 2ρ(t)) by subtracting M 1ρ(t) from M(t). For comparison, we also computed the spin-locked magnetization vector. We derived the exact solutions for R 1ρ and R 2ρ from the eigenvalues, and compared them with those obtained numerically from M 1ρ(t) and M 2ρ(t), respectively. There was excellent agreement between them. From the exact solutions for R 1ρ and R 2ρ, R 2ρ was found to be given by R 2ρ =(2R 2 + R 1)/2− R 1ρ /2, where R 1 and R 2 denote the conventional longitudinal and transverse relaxation rates, respectively. We also derived M 1ρ(t) and M 2ρ(t) for bulk water protons, in which the effect of chemical exchange was taken into account using a 2-pool chemical exchange model, and we compared the R 1ρ and R 2ρ values obtained from the eigenvalues and those obtained numerically from M 1ρ(t) and M 2ρ(t). There was also excellent agreement between them. In conclusion, this study will be useful for better understanding of the longitudinal and transverse relaxations in the rotating frame and for analyzing the contrast mechanisms in T 1ρ- and T 2ρ-weighted MRI. [Copyright &y& Elsevier]

Abstract: Among the multiple sequences available for functional magnetic resonance imaging (fMRI), the Steady State Free Precession (SSFP) sequence offers the highest signal-to-noise ratio (SNR) per unit time as well as distortion free images not feasible with the more commonly employed single-shot echo planar imaging (EPI) approaches. Signal changes occurring with activation in SSFP sequences reflect underlying changes in both irreversible and reversible transverse relaxation processes. The latter are characterized by changes in the central frequencies and widths of the inherent frequency distribution present within a voxel. In this work, the well-known frequency response of the SSFP signal intensity is generalized to include the widths and central frequencies of some common frequency distributions on SSFP signal intensities. The approach, using a previously unnoted series expansion, allows for a separation of reversible from irreversible transverse relaxation effects on SSFP signal intensity changes. The formalism described here should prove useful for identifying and modeling mechanisms associated with SSFP signal changes accompanying neural activation. [Copyright &y& Elsevier]

Abstract: Water mobility and distribution in fermented sausages produced with differences in pH development as a result of the use of three different starter cultures (T-SPX, F-1, or F-SC-111) and two fermentation temperatures (24°C, or 32°C) were studied using low-field proton NMR relaxometry. Changes in the distribution and mobility of water in fermented sausages upon fermentation and drying were detectable by NMR T2 relaxation, and the progress in the drying process could be followed as a shift towards faster relaxation times. In addition, the distribution of water in the sausages was significantly affected by the pH decline. The sausages were spiked with Listeria monocytogenes, Salmonella, and Escherichia coli VTEC, and partial least squares regressions revealed that 90% of the variation in reduction of Salmonella and VTEC could be explained by the NMR T2 relaxation decay. Consequently, the study demonstrated that NMR relaxometry is a promising technique for elucidating process parameters and microbial safety in the production of fermented meat products. [Copyright &y& Elsevier]

Abstract: We conducted a laboratory study to measure the effect of magnetite concentration and grain size on proton nuclear magnetic resonance (NMR) relaxation rates of sand mixtures and to determine the dominant mechanism by which relaxation occurs. We measured mixtures of quartz and three different forms of magnetite: a powdered synthetic magnetite; a small-grained, natural magnetite; and a large-grained, natural magnetite. The powdered synthetic magnetite was mixed with quartz in five concentrations ranging from 0.14 to 1.4% magnetite by weight; both sizes of natural magnetite were mixed with quartz in concentrations of 1 and 2% magnetite by weight. The NMR response of the water-saturated samples was measured and used to calculate four averaged relaxation rates for each magnetite concentration: the total mean log, bulk fluid, surface, and diffusion relaxation rates. The results of this study show that: 1) surface relaxation was the dominant relaxation mechanism for all samples except the powdered synthetic magnetite sample containing 1.4% magnetite; 2) the surface relaxivity is a function of the fraction of the surface area in the sample composed of magnetite; 3) there is no clear dependence of the diffusion relaxation rate on the concentration of magnetite. [Copyright &y& Elsevier]

Abstract: We present a new model for describing the diffusion-weighted (DW) proton nuclear magnetic resonance signal obtained from normal grey matter. Our model is analytical and, in some respects, is an extension of earlier model schemes. We model tissue as composed of three separate compartments with individual properties of diffusion and transverse relaxation. Our study assumes slow exchange between compartments. We attempt to take cell morphology into account, along with its effect on water diffusion in tissues. Using this model, we simulate diffusion-sensitive MR signals and compare model output to experimental data from human grey matter. In doing this comparison, we perform a global search for good fits in the parameter space of the model. The characteristic nonmonoexponential behavior of the signal as a function of experimental b value is reproduced quite well, along with established values for tissue-specific parameters such as volume fraction, tortuosity and apparent diffusion coefficient. We believe that the presented approach to modeling diffusion in grey matter adds new aspects to the treatment of a longstanding problem. [Copyright &y& Elsevier]

Abstract: The magnetic properties of maghemite nanoparticles and tin-doped maghemite have been studied by 57Fe and 119Sn Mössbauer spectroscopy at temperatures from 6 to 300K with and without applied magnetic fields. The low-temperature 57Fe spectra of both samples, obtained in a field of 4T, can be described in terms of A-site and B-site components with perfect ferrimagnetic order and a strongly canted component, which seems to have its main contribution from B-site ions. At higher temperatures, the components with strong canting are influenced by transverse relaxation, which results in significant line broadening, a reduction of the magnetic hyperfine splitting and a reduction in the relative areas of lines 2 and 5. The 119Sn spectra show a very broad distribution of magnetic hyperfine fields at low temperatures. When the sample was exposed to applied magnetic fields the distribution became narrower. The spectra show that the direction of the hyperfine field of a large fraction of the tin ions in maghemite is antiparallel to the applied field, but a minor fraction of the tin ions have canted hyperfine fields. [Copyright &y& Elsevier]

Abstract: Dairy cream, as a suspension of lipid droplets in water, is a potentially useful magnetic resonance imaging (MRI) phantom material and an interesting material for studying fundamental relaxation mechanisms. Here we report a strong increase in the transverse relaxation rates with field strength for both the water and lipid protons in dairy cream. Also, studies at 4.7 T reveal a nonlinear response of transverse relaxation rates with increasing concentration of a common gadolinium (Gd)-based contrast agent, including an initial decrease of water relaxation rates as measured with Hahn spin echoes at the lower Gd concentrations. The results are treated within the framework of a model in which the magnetic susceptibility difference between the lipid droplets and the aqueous phase plays the prominent role for transverse relaxation. Second-order polynomial fits of the water proton transverse relaxation rate dependence on field strength and on Gd concentration at 4.7 T provided experimental parameters from which model parameters are extracted and compared with expectations available from the literature. [Copyright &y& Elsevier]

Methods for making rapid and accurate measurements and maps of the transverse relaxation time from a single free induction decay (FID) are proposed. The methods use a multi-echo sequence in combination with B1 insensitive (hyperbolic secant or BIREF2b) refocusing pulses and rapid echo-planar imaging techniques. The results were calibrated against a single spin echo echo-planar imaging sequence using a phantom containing a range of CuSO4 concentrations. The mean percentage absolute difference between the multi-echo and single-echo results was 3% for the multi-echo sequence using the hyperbolic secant refocusing pulse, and 7% for the multi-echo sequence using the BIREF2b refocusing pulse, compared to 13% for a multi-echo sequence using a nonselective sinc refocusing pulse. The use of the sequences in vivo has been demonstrated in studies of gastric function, i.e., the measurement of gastric dilution and monitoring of formation of a raft of alginate polysaccharide within the stomach. [Copyright &y& Elsevier]

Using low-field NMR transverse relaxation measurements, the physico-chemical state of water in meat was followed continuously during cooking of 20 uncured and 20 cured pork samples from RN-carriers (n=20) and non-carriers (n=20). The obtained relaxation data were analysed using (i) distributed exponential fitting, and (ii) principal component analysis (PCA). Distributed exponential fitting revealed transition from a system with relatively well-separated components to a less well-defined system with a wide distribution of relaxation times and merged components during cooking. In addition, distributed exponential fitting analysis implied changes in relaxation characteristics that are tentatively ascribed to denaturation of myosin and subsequent shrinkage of the myofibrillar structures. The results are further suggested to reflect formation of new compartments in the myofibrillar lattice during the shrinkage of the existing structures with a succeeding redistribution of water. Nitrite curing was found to affect the distribution of water as well as the progress in the different water populations during cooking. PCA revealed two major shifts in relaxation characteristics around 43 and 56 °C in uncured samples and around 43 and 63 °C in cured samples, and the shift around 43 °C was found to be significantly affected by RN-genotype. The strong shift in water properties around 43 °C is suggested to be a result of myosin denaturation, and thus the results imply differences in myosin denaturation in meat from RN-carriers compared with meat from non-carriers. The second shift in water properties is suggested to reflect the onset of collagen shrinkage causing longitudinal shrinkage of meat, and accordingly the shift from 56 to 63 °C in the presence of salt points towards an effect of curing on structural alterations during cooking. [Copyright &y& Elsevier]

We compare the focal lengths of porcine lenses measured optically and by using a novel MRI technique. The geometric properties of the lenses were also measured and compared. The MRI technique exploits the dependence of both the lens refractive index and relaxation rates on the local protein concentration. By measuring the refractive index and corresponding values of R2 (=1/T2) for samples of lens homogenates with different protein concentrations, the dependence of refractive index on R2 was determined empirically. R2 maps, constructed from monoexponential fits to multiecho images of a slice through the lens containing the optical axis, were converted to refractive index maps using this relationship. A simulated ray trace through the refractive index map provided an estimate of lens focal length that was compared to a direct optical measurement of focal length using a laser ray-tracing method. It was found that the mean focal lengths estimated from the two techniques agreed within experimental uncertainty. The refractive index profile along the optical axis was found to be well described by a simple function of the form n = n0 + n1 × ra where r is the (normalized) lens radius. [Copyright &y& Elsevier]

Analytical expressions for the magnetic energy and the spin-canting angles in some simple ferrimagnetic bulk and surface structures are presented. It is shown that the energy barriers separating different spin-canted states often will be very small. Therefore, the spin canting may be static only at very low temperatures and dynamic at higher temperatures. The calculations elucidate the field dependence of the canting angles, the high-field susceptibility of complex magnetic materials, the high-frequency susceptibility of diamagnetically substituted ferrites, and the apparently temperature-independent relaxation phenomena at very low temperatures. [Copyright &y& Elsevier]

Ferromagnetic or superparamagnetic particles as MRI contrast agent present many advantages for bringing about soft tissue contrast as compared to single-ion complexes. The classic microscopic outersphere theory that works successfully for small molecules in understanding the transverse relaxation rate 1/T2 is not valid for these larger and stronger magnetic spheres. We categorize the relaxation behavior of the tissue-sphere system for ferromagnetic spherical perturbers in five diffusion regimes. Over the entire range of perturber size a general understanding of the relaxation mechanisms is described in terms of basic physical features of the system, and, through empiric models, the imaging sequences of spin echo and gradient echo. The models are verified with results of our spectroscopic measurements as well as simulations and experiments in the literature. Normalized models, obtained through proper scaling of the sphere radius and the relaxation rate, can be used to quantitatively estimate 1/T2 for various combinations of the variables. Effects of diffusion upon image contrast and effects of sphere size change upon relaxation with their possible applications in microvascular dilatation and other areas are then discussed. [Copyright &y& Elsevier]

The magnetic properties of the ferrite Mn0.25Zn0.75Fe2O4 have been studied by Mo¨ssbauer spectroscopy and magnetisation measurements. Mo¨ssbauer spectra, obtained at low temperatures and large applied magnetic fields, showed that almost all Fe3+ ions are in octahedral (B) sites and only about 2% of the Fe3+ ions are in tetrahedral (A) sites. At 5 K about 16% of the B-site Fe3+ ions have spins parallel to the A-site magnetisation, but when the temperature is raised to about 40 K, these spins are reversed. Some other B-site Fe3+ ions show a large spin canting at 5 K and these ions are significantly affected by transverse relaxation at relatively low temperatures. A third group of B-site ions has negligible canting at low temperatures and these ions are only slightly affected by relaxation below 60 K. At low temperatures the material can be described as a cluster spin glass. Above 60 K part of the sample breaks up into superparamagnetic clusters whereas other parts remain ferrimagnetic. [Copyright &y& Elsevier]

The 1H NMR water signal from spectroscopic voxels localized in gray matter contains contributions from tissue and cerebral spinal fluid (CSF). A typically weak CSF signal at short echo times makes separating the tissue and CSF spin-lattice relaxation times (T1) difficult, often yielding poor precision in a bi-exponential relaxation model. Simulations show that reducing the variables in the T1 model by using known signal intensity values significantly improves the precision of the T1 measurement. The method was validated on studies on eight healthy subjects (four males and four females, mean age 21 ± 2 years) through a total of twenty-four spectroscopic relaxation studies. Each study included both T1 and spin-spin relaxation (T2) experiments. All volumes were localized along the Sylvian fissure using a stimulated echo localization technique with a mixing time of 10 ms. The T2 experiment consisted of 16 stimulated echo acquisitions ranging from a minimum echo time (TE) of 20 ms to a maximum of 1000 ms, with a repetition time of 12 s. All T1 experiments consisted of 16 stimulated echo acquisition, using a homospoil saturation recovery technique with a minimum recovery time of 50 ms and a maximum 12 s. The results of the T2 measurements provided the signal intensity values used in the bi-exponential T1 model. The mean T1 values when the signal intensities were constrained by the T2 results were 1055.4 ms ± 7.4% for tissue and 5393.5 ms ± 59% for CSF. When the signal intensities remained free variables in the model, the mean T1 values were 1085 ms ± 19.4% and 5038.8 ms ± 113.0% for tissue and CSF, respectively. The resulting improvement in precision allows the water tissue T1 value to be included in the spectroscopic characterization of brain tissue. [Copyright &y& Elsevier]

We report results of 1H NMR transverse relaxation experiments on human and porcine eye lenses. Several authors have reported that transverse relaxation is not mono-exponential when observed by the Carr-Purcell-Meiboom-Gill (CPMG) sequence and have interpreted the results by postulating the presence of “pools” of water molecules in different binding environments that do not exchange rapidly on the NMR timescale. We have compared CPMG data for intact lenses with results for lens homogenates and have combined a CPMG spectroscopic pulse train with NMR micro-imaging to study the nature of the transverse relaxation process in human and porcine lenses. Fast exchange of water protons with the lens proteins (crystallins) leads to an enhanced transverse relaxation rate that varies linearly with protein concentration. At the resolution of NMR micro-imaging the transverse relaxation process is mono-exponential. The results show that the multi-exponential CPMG data observed spectroscopically for whole lenses reflect spatial variations in crystallin content through the lens rather than the presence of distinct “bound” and “free” water pools. [Copyright &y& Elsevier]

Nuclear magnetic resonance (NMR), and in particular transverse relaxation (T 2), has been used to characterize meat and seafood products for decades. Despite many years of research, it is still not possible to reproducibly correlate the transverse relaxation of muscle foods to attributes that determine their quality and value. Instead of directly trying to interpret the T 2 spectrum itself, typically chemometrics is used to try to relate the relaxation distributions to other measured properties on the sample. As muscle tissue is a porous medium, it is tempting to use equations developed to analyze other porous systems to provide a more direct, quantitative description of the tissue. However, the standard equations used to characterize porous materials have been developed for predominantly geological systems. This article discusses the foundations of transverse relaxation theory in porous media and the challenges that arise when attempting to adapt the equations to a biological system like tissue. One of the biggest issues that needs to be overcome before porous media theory can be reliably applied to characterize meat and seafood is to determine the source of relaxivity in the tissue. In order to better understand how the NMR signal originates, T 2 , diffusion, T 1 -T 2 correlation and T 2 -T 2 exchange experiments were performed on Atlantic cod (Gadus morhua) tissue in a variety of states (e.g. fresh, thawed, homogenized, etc.). In the literature, typically four T 2 peaks are reported for meat and seafood samples. Results of this study indicate that the fastest relaxation peak is attributable to hydrogen within the protein itself and therefore arises from dipolar coupling. The T 2B peak appears to belong to a type of bound water in protein called "buried water", and its relaxation stems from a combination of restricted motion and interaction with the hydrogen in the protein. For the T 21 peak, attributed to fluid in myofibrils, the main relaxation mechanism is the interaction between water molecules and the hydrogen in myosin/actin matrix. The T 22 peak arises predominantly from the interaction of water with dissolved protein in the sarcoplasm. An important finding from the study is the need to include both surface sinks and volume sinks in the interpretation of T 2 relaxation results. Given these sources of the transverse relaxation in tissue, it is highly likely that changes to the T 2 distribution that have been attributed to microstructural changes in the tissue are in reality due to a combination of changes in microstructure, surface relaxation and fluid properties. These findings aid in better interpreting T 2 measurements in meat and seafood products and present a step towards a systematic approach for using transverse relaxation to quantitatively describe changes in tissue, with the ultimate aim of eventually predicting product quality and value from NMR relaxometry. • Multiple relaxation mechanisms exist for T 2 relaxation in muscle tissue. • Volume sinks play an important role in T 2 relaxation in meat and seafood. • Full T 2 distribution should be used for analysis, not just peak location and area. • T 2 relaxation alone problematic to definitively describe chemical and structural changes. • Advanced NMR sequences needed to properly characterize meat and seafood. [ABSTRACT FROM AUTHOR]

Highlights: [•] Internal gradients influence T 2 relaxation times at any magnetic field strength. [•] A general approach is adopted for separating relaxation and diffusion exponents. [•] Accurate T 2 relaxation time distributions are obtained. [•] The method is demonstrated for water saturated glass bead packs. [•] Our technique is applicable to a wide range of porous materials. [Copyright &y& Elsevier]

• Water proton relaxation was significantly (p < 0.05) fastened in smaller droplets • Presence of globular fat and serum solids further restricted the mobility of water • Influence of cooling on water proton relaxation became minimal in smaller droplets • Water phase gelation enhanced (p < 0.05) the rate of fat crystallization • Variable temperature LF-NMR enabled in-situ monitoring of the relaxation dynamics The effects of water content; 15, 30, and 40% (w/w), water droplet size; d 43 15.0–19.6 µm (larger) and d 43 1.2–2.7 µm (smaller), and sodium alginate (0.5%, w/w) induced water gelation on crystallization kinetics and water and fat proton relaxation were studied in water-in-milk fat emulsions during in situ cooling from 40 °C to 5 °C. Anhydrous milk fat (AMF) and commercial butter were employed as two separate fat sources. Although emulsions were crystallized faster than the bulk fat, the variations in the water fraction and droplet size did not show major influence on crystallization properties. Smaller droplet size induced significant (p < 0.05) reduction in water mobility with a minimal effect of the temperature. In AMF-based emulsions, gelation of water phase not only immobilized the water molecules but also enhanced the rate of fat crystallization. Globular fat and serum solids in butter-based emulsions showed to fasten the water proton relaxation. [ABSTRACT FROM AUTHOR]