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The spin-exchange-pumped nuclear magnetic resonance gyroscope (NMRG) is a pivotal tool in quantum navigation. The transverse relaxation of atoms critically impacts the NMRG's performance parameters and is essential for judging normal operation. Conventional methods for measuring transverse relaxation typically use dual beams, which involves complex optical path and frequency stabilization systems, thereby complicating miniaturization and integration. This paper proposes a method to construct a 133Cs parametric resonance magnetometer using a single-beam vertical-cavity surface-emitting laser (VCSEL) to measure the transverse relaxation of 129Xe and 131Xe. Based on this method, the volume of the gyroscope probe is significantly reduced to 50 cm3. Experimental results demonstrate that the constructed Cs-Xe NMRG can achieve a transverse relaxation time (T2) of 8.1 s under static conditions. Within the cell temperature range of 70 °C to 110 °C, T2 decreases with increasing temperature, while the signal amplitude inversely increases. The research lays the foundation for continuous measurement operations of miniaturized NMRGs. [ABSTRACT FROM AUTHOR]

BACKGROUND: Tomato is an indispensable ingredient of the Mediterranean diet. Reformulation of traditional Mediterranean products to increase the adherence of consumers is becoming popular. In this study, a tomato snack bar enriched with olive powder and pea protein was developed by using microwave‐vacuum drying. Formulations also included tomato powder (TP) and low‐methoxylated pectin (LMP) as a structuring agent. RESULTS: The moisture content of microwave‐vacuum‐dried samples varied in the range 13.6–19.8% and water activity (aw) values were ~0.6. LMP and TP concentrations affected the color of microwave‐vacuum‐dried samples. However, the color mainly changed in conventionally dried samples due to browning. In microwave‐vacuum‐dried samples, lycopene content decreased with increasing LMP, but increased with increasing TP. Textural properties of microwave‐vacuum‐dried snack bars increased with increasing LMP and TP. CONCLUSION: Both texture and Fourier transform infrared spectroscopy results indicated that there was a network formation due to the contribution of protein and pectin; however, the type of interaction was highly dependent on the drying mechanism. Nuclear magnetic resonance relaxometry data showed that microwave‐vacuum‐dried samples had a more uniform water distribution. Besides its time and energy efficiency, microwave‐vacuum drying improved the color and textural properties of tomato snack bars compared to conventionally dried ones. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Nitrogen-vacancy (NV) color centers in diamond serve as a unique platform for various types of quantum sensors, including a nuclear magnetic resonance gyroscope. The fundamental sensitivity limit of a quantum sensor is closely related to the free precession dephasing time of the nuclear spin. The dependence of and transverse relaxation time on the magnetic field at room temperature in the field range from 2 to 8 G is investigated, demonstrating that and are not limited by the longitudinal relaxation time of the electron spin projection. [ABSTRACT FROM AUTHOR]

The robustness of NMR coherence transfer in proximity of a paramagnetic center depends on the relaxation properties of the nuclei involved. In the case of Iron-Sulfur Proteins, different pulse schemes or different parameter sets often provide complementary results. Tailored versions of HCACO and CACO experiments significantly increase the number of observed Cα/C' connectivities in highly paramagnetic systems, by recovering many resonances that were lost due to paramagnetic relaxation. Optimized 13C direct detected experiments can significantly extend the available assignments, improving the overall knowledge of these systems. The different relaxation properties of Cα and C' nuclei are exploited in CACO vs COCA experiments and the complementarity of the two experiments is used to obtain structural information. The two [Fe2S2]+ clusters containing NEET protein CISD3 and the one [Fe4S4]2+ cluster containing HiPIP protein PioC have been taken as model systems. We show that tailored experiments contribute to decrease the blind sphere around the cluster, to extend resonance assignment of cluster bound cysteine residues and to retrieve details on the topology of the iron-bound ligand residues. [ABSTRACT FROM AUTHOR]

Glycogen plays essential roles in glucose metabolism. Imaging glycogen in the liver, the major glycogen reservoir in the body, may shed new light on many metabolic disorders. 13C magnetic resonance spectroscopy (MRS) has become the mainstream method for monitoring glycogen in the body. However, the equipment of special hardware to standard clinical magnetic resonance imaging (MRI) scanners limits its clinical applications. Herein, we utilized endogenous glycogen as a T2-based relaxation contrast agent for imaging glycogen metabolism in the liver in vivo. The in vitro results demonstrated that the transverse relaxation rate of glycogen strongly correlates with the concentration, pH, and field strength. Based on the Swift-Connick theory, we characterized the exchange property of glycogen and measured the exchange rate of glycogen as 31,847 Hz at 37 °C. Besides, the viscosity and echo spacing showed no apparent effect on the transverse relaxation rate. This unique feature enables visualization of glycogen signaling in vivo through T2-weighted MRI. Two hours-post intraperitoneal injection of glucagon, a clinical drug to promote glycogenolysis and gluconeogenesis, the signal intensity of the mice's liver increased by 1.8 times from the T2-weighted imaging experiment due to the decomposition of glycogen. This study provides a convenient imaging strategy to non-invasively investigate glycogen metabolism in the liver, which may find clinical applications in metabolic diseases.

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]

Purpose: This study aims to improve the detection of glutamate (Glu) concentration and T 2 using an enhanced transverse relaxation encoding with narrowband decoupling (TREND) technique., Methods: A new editing pulse was designed to simultaneously invert both Glu H3 spins (2.12 ppm and 2.05 ppm) while minimizing the excitation of Glu H4. Additionally, a frequency band was created to invert the lactate (Lac) H2 spin (4.10 ppm) while saturating the NAA aspartyl H2 spin (4.38 ppm). Numerical simulations compared Glu and Lac signals using the original and new editing pulses. In vivo experiments were conducted on healthy participants at 7 T to validate this enhanced TREND technique., Results: Numerical simulations showed prominently enhanced Glu and Lac resonance signals with the new editing pulse. In vivo spectra showed a 47% ± 14% increase in Glu/Cr peak amplitude ratios with the new editing pulse. Using the enhanced TREND sequence, Glu/Cr concentration ratios in the anterior cingulate cortex were 1.03 ± 0.07 with Cramer-Rao lower bounds (CRLBs) of 1.1% ± 0.1%, and Glu T 2 values were 179 ± 18 ms with CRLBs of 1.2% ± 0.1%. The Lac/Cr concentration ratios in the same voxels were 0.05 ± 0.01 with CRLBs of 26% ± 14%, and Lac T 2 values were 196 ± 23 ms with CRLBs of 22% ± 15%., Conclusion: The new editing pulse significantly enhanced the detection of Glu and enabled the detection of Lac using TREND for measuring both the concentration and T 2 of the markers of oxidative metabolism and glycolysis., (Published 2025. This article is a U.S. Government work and is in the public domain in the USA. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.)

Purpose: With advances in anti-diabetes drugs, increasing numbers of patients have high urinary glucose concentrations, which may alter magnetic resonance (MR) signal intensity. We sought to elucidate the effect of urinary glucose concentration and pH on transverse relaxation and MR signal intensity. Materials and methods: The transverse relaxation rate (R2) was measured in samples with different glucose concentrations (in vitro) and in the urinary bladder of seven patients with diabetes and nine healthy volunteers (in vivo). The glucose concentration and pH in the in vitro samples and urine were measured. The signal intensity ratio of the bladder to adjacent tissues was obtained on T2-weighted imaging (WI), T1WI, and MR urography (in vivo). To clarify the effect of pH further, the urine of two healthy subjects was adjusted with acid and/or base to obtain various pH values (ex vivo). Results: R2 increased significantly with high glucose concentrations in the in vitro study. In the in vivo study, high glucose concentration (p < 0.001) and low pH (p = 0.005) were significantly associated with high R2. R2 was higher (p = 0.002) and the signal in maximum-intensity projection images of MR urography was lower (p = 0.005) in patients with diabetes than in healthy subjects. Ex vivo study revealed that a decrease in pH in acid portion resulted in increased R2. Conclusion: High concentrations of urinary glucose and low pH both enhance transverse relaxation, which, in turn, causes low signal intensity in urinary bladder on long echo time (TE) images, such as MR urography. Radiologists should be aware of this phenomenon when interpreting abnormally low-intensity bladders on long TE images. [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]

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[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]

PurposeTo determine whether Lorentzian or Gaussian intra-voxel frequency distributions are better suited for modeling data acquired with gradient-echo sampling of single spin-echoes for the simultaneous characterization of irreversible and reversible relaxation rates. Clinical studies (e.g., of brain iron deposition) using such acquisition schemes have typically assumed Lorentzian distributions.Theory and methodsTheoretical expressions of the time-domain spin-echo signal for intra-voxel Lorentzian and Gaussian distributions were used to fit data from a human brain scanned at both 1.5 Tesla (T) and 3T, resulting in maps of irreversible and reversible relaxation rates for each model. The relative merits of the Lorentzian versus Gaussian model were compared by means of quality of fit considerations.ResultsLorentzian fits were equivalent to Gaussian fits primarily in regions of the brain where irreversible relaxation dominated. In the multiple brain regions where reversible relaxation effects become prominent, however, Gaussian fits were clearly superior.ConclusionThe widespread assumption that a Lorentzian distribution is suitable for quantitative transverse relaxation studies of the brain should be reconsidered, particularly at 3T and higher field strengths as reversible relaxation effects become more prominent. Gaussian distributions offer alternate fits of experimental data that should prove quite useful in general. Magn Reson Med 74:51-62, 2015. © 2014 Wiley Periodicals, Inc.

Purpose: To compare transverse relaxation rates of brain metabolites estimated from single‐TE PRESS acquisitions with more conventionally derived rates estimated from multiple‐TE PRESS acquisitions. Methods: Single‐voxel (8 mL) PRESS data within white matter from 6 subjects were acquired at five different TEs. Transverse relaxation rates R2 of N‐acetylaspartate, creatine, and choline were estimated from a single TE using full versus right‐side‐only sampling of the echo. These R2 values were compared with R2Hahn values obtained from the multiple‐TE PRESS acquisitions. Results: Following baseline subtraction and RMS weighting, interindividual mean R2 values from TE = 288 ms magnitude spectra for choline, creatine, and N‐acetylaspartate were highly correlated with respective R2Hahn values (r2 = 0.99). Paired individual measurements at this TE showed less correlation (r2 = 0.48), primarily due to the N‐acetylaspartate resonance. Using TE = 360 ms data for N‐acetylaspartate and 288 ms for choline and creatine resulted in an improved correlation coefficient (r2 = 0.80). The average absolute intra‐individual differences in the estimated R2s between single‐TE and Hahn method was 9.6 ± 7.7%. Conclusion: For the major brain metabolite singlets, R2Hahn values showed correlations with more fragile measurements of R2 from a single TE that are worthy of interest. Because the left side of long‐TE spin echoes is available "for free" from an acquisition perspective, and although the single‐TE method for estimating R2 values is associated with lower precision, the reduction in scan time may be clinically helpful. [ABSTRACT FROM AUTHOR]

This study presents a low-field hydrogen-1 nuclear magnetic resonance (1H NMR) method to accurately determine water and oil in oil-contaminated coastal sand. Rapid, efficient separation of water and oil signals in the overlapping transverse relaxation (T2) spectra was achieved using a novel approach combining physical (paramagnetic ions Mn2+) and mathematical separation (deconvolution algorithm). High correlation coefficients of 0.998 and 0.982 were obtained between the prepared and NMR determined contents for water and oil together with the maximum errors of 0.84% and 0.54% for the water and oil content separately, which suggests NMR measurement of water and oil contents in oil-contaminated coastal sand is fairly accurate. [ABSTRACT FROM AUTHOR]

Purpose: Measuring the transverse‐relaxation rate R2′ provides valuable information in quantitative evaluation of tissue microstructure, for example, in terms of oxygenation levels. Here, we propose an alternating unbalanced SSFP pulse sequence for rapid whole‐brain 3D R2′ mapping. Methods: Unlike currently practiced, spin echo–based R2′ measurement techniques, the proposed method alternates between SSFP‐FID and SSFP‐ECHO modes for rapid 3D encoding of transverse relaxation rates expressed as R2 + R2′ and R2‐R2′. Z‐shimming gradients embedded into multi‐echo trains of each SSFP module are designed to achieve relative immunity to large‐scale magnetic‐field variations (ΔB0). Appropriate models for the temporal evolution of the two groups of SSFP signals were constructed with ΔB0‐induced modulations accounted for, leading to ΔB0‐corrected estimation of R2, R2′, and R2∗ (= R2 + R2′). Additionally, relative magnetic susceptibility (Δχ) maps were obtained by quantitative susceptibility mapping of the phase data. Numerical simulations were performed to optimize scan parameters, followed by in vivo studies at 3 T in 7 healthy subjects. Measured parameters were evaluated in six brain regions, and subjected to interparameter correlation analysis. Results: The resultant maps of R2′ and additionally derived R2, R2∗, and Δχ all demonstrated the expected contrast across brain territories (eg, deep brain structures versus cortex), with the measured values in good agreement with previous reports. Furthermore, regression analyses yielded strong linear relationships for the transverse relaxation parameters (R2′, R2, and R2∗) against Δχ. Conclusion: Results suggest feasibility of the proposed method as a practical and reliable means for measuring R2′, R2, R2∗, and Δχ across the entire brain. [ABSTRACT FROM AUTHOR]

Purpose: To develop a postprocessing algorithm that corrects geometric distortions due to spatial variations of the static magnetic field amplitude, B0, and effects from relaxation during signal acquisition in EPI. Theory and Methods: An analytic, complex point‐spread function is deduced for k‐space trajectories of EPI variants and applied to corresponding acquisitions in a resolution phantom and in human volunteers at 3 T. With the analytic point‐spread function and experimental maps of B0 (and, optionally, the effective transverse relaxation time, T2*) as input, a point‐spread function matrix operator is devised for distortion correction by a Thikonov‐regularized deconvolution in image space. The point‐spread function operator provides additional information for an appropriate correction of the signal intensity distribution. A previous image combination algorithm for acquisitions with opposite phase blip polarities is adapted to the proposed method to recover destructively interfering signal contributions. Results: Applications of the proposed deconvolution‐based distortion correction ("DecoDisCo") algorithm demonstrate excellent distortion corrections and superior performance regarding the recovery of an undistorted intensity distribution in comparison to a multifrequency reconstruction. Examples include full and partial Fourier standard EPI scans as well as double‐shot center‐out trajectories. Compared with other distortion‐correction approaches, DecoDisCo permits additional deblurring to obtain sharper images in cases of significant T2* effects. Conclusion: Robust distortion corrections in EPI acquisitions are feasible with high quality by regularized deconvolution with an analytic point‐spread function. The general algorithm, which is publicly released on GitHub, can be straightforwardly adapted for specific EPI variants or other acquisition schemes. [ABSTRACT FROM AUTHOR]

Purpose: The intravoxel distribution of the magnetic field strongly influences signal dephasing after RF excitation and the resulting signal decay in gradient echo–based MRI. In this work, several different field distribution models were applied and tested for analysis of microscopic field characteristics within pixels. Theory: A flexible model for improved pixel‐wise characterization of the underlying field distribution is introduced. The proposed symmetric alpha‐stable (SαS) distribution covers Lorentzian, Gaussian, and intermediate field distributions in a continuous way using a two‐parametric (width and shape) function. Methods: The new model was applied on human brain, potatoes (homogeneous isotropic tissue), and stems of pineapple (anisotropic fibrous tissue). Effects of microscopic structure and background gradients on the shape and the widths of the microscopic field distribution were analyzed using gradient echo sampling of the spin echo and multigradient‐echo sequences. Effects of non‐Lorentzian shapes of microscopic field distributions on the results of common T2∗ measurements with mono‐exponential fitting of signal values were tested. Results: Many pixels of the examined objects showed field characteristics in between Lorentzian and Gaussian shapes. Microscopic field inhomogeneities caused by microscopic susceptibility effects and background gradients sometimes led to rather Gaussian than Lorentzian field distribution. In cases with nearly Gaussian field distribution, mono‐exponential fitting of the signal decay resulted in different T2∗ values, depending on the sampling points. Conclusions: Using the concept of more flexible distributions for characterization of microscopic susceptibility effects in tissue provides better fitting of data and nearly sampling point–independent results than common T2∗ measurements with mono‐exponential fitting. [ABSTRACT FROM AUTHOR]

The enhancement of nuclear relaxation rates due to the interaction with a paramagnetic center (known as Paramagnetic Relaxation Enhancement) is a powerful source of structural and dynamics information, widely used in structural biology. However, many signals affected by the hyperfine interaction relax faster than the evolution periods of common NMR experiments and therefore they are broadened beyond detection. This gives rise to a so-called blind sphere around the paramagnetic center, which is a major limitation in the use of PREs. Reducing the blind sphere is extremely important in paramagnetic metalloproteins. The identification, characterization, and proper structural restraining of the first coordination sphere of the metal ion(s) and its immediate neighboring regions is key to understand their biological function. The novel HSQC scheme we propose here, that we termed R2-weighted, HSQC-AP, achieves this aim by detecting signals that escaped detection in a conventional HSQC experiment and provides fully reliable R2 values in the range of 1H R2 rates ca. 50–400 s−1. Independently on the type of paramagnetic center and on the size of the molecule, this experiment decreases the radius of the blind sphere and increases the number of detectable PREs. Here, we report the validation of this approach for the case of PioC, a small protein containing a high potential 4Fe-4S cluster in the reduced [Fe4S4]2+ form. The blind sphere was contracted to a minimal extent, enabling the measurement of R2 rates for the cluster coordinating residues. [ABSTRACT FROM AUTHOR]

The goal of this study was to test a new formalism for extracting reversible and irreversible transverse relaxation rates from resonances within typical proton muscle spectra using only a single spin echo as acquired with routine single‐voxel, point‐resolved echo spectroscopy (PRESS) acquisitions. Single‐voxel, non‐water‐suppressed PRESS acquisitions within the calf muscles of four healthy subjects were performed at 1.5 T using six echo times ranging from 30 to 576 ms. Novel transverse relaxation analyses of water, choline, creatine, and lipid resonances were performed based upon the disparate relaxation sensitivities of the left versus the right sides of spectroscopically sampled spin echoes. Irreversible and reversible transverse relaxation rates R2 and R2′ were extracted for water, metabolites, and lipids using echo times of 288 ms and longer. The R2 values so obtained were compared with more conventional "gold standard" Hahn values, R2Hahn, evaluated from the echo‐time dependence of spectral peak areas generated from right‐side sampling alone. Water resonances displayed biexponential Hahn signal decays, consistent with observations of decreasing R2 values with increasing echo time via the new approach. Choline and creatine resonances displayed monoexponential echo‐time decays, with R2Hahn values in reasonable agreement with R2 values obtained from the single‐echo analyses at the longer echo times. Lipid methylene and methyl R2 values extracted from the new approach were also in reasonable accord with R2Hahn values. Further validation of the technique was provided through PRESS acquisitions on a water phantom to which various levels of gadolinium were added in order to manipulate transverse relaxation rates, yielding excellent agreement between water‐resonance R2Hahn and single‐echo R2 values. In summary, this work demonstrates the feasibility of measuring reversible and irreversible transverse relaxation rates for individual spectral peaks from single‐echo PRESS acquisitions, enabling a reduction in overall scan time relative to the use of multiple acquisitions with varying echo time. [ABSTRACT FROM AUTHOR]

Conventional diffusion‐weighted (DW) MRI suffers from free water contamination due to the finite voxel size. The most common case of free water contamination occurs with cerebrospinal fluid (CSF) in voxels located at the CSF‐tissue interface, such as at the ventricles in the human brain. Another case refers to intra‐tissue free water as in vasogenic oedema. In order to avoid the bias in diffusion metrics, several multi‐compartment methods have been introduced, which explicitly model the presence of a free water compartment. However, fitting multi‐compartment models in DW MRI represents a well known ill conditioned problem. Although during the last decade great effort has been devoted to mitigating this estimation problem, the research field remains active. The aim of this work is to introduce the design, characterise the NMR properties and demonstrate the use of two dedicated anisotropic diffusion fibre phantoms, useful for the study of free water elimination (FWE) and mapping models. In particular, we investigate the recently proposed FWE diffusion tensor imaging approach, which takes explicit account of differences in the transverse relaxation times between the free water and tissue compartments. [ABSTRACT FROM AUTHOR]

Many of the lanthanide‐based nanoparticles are valuable in magnetic resonance imaging (MRI) because they have excellent magnetic properties that make them suitable for MRI contrast agents, while some of them have additional optical properties and thus can serve as fluorescence imaging (FI) agents as well. Herein, we synthesized d‐glucuronic acid‐coated ultrasmall Ln2O3 (Ln = Tb, Dy, and Ho) nanoparticles with average diameters of ∼ 2 nm. All the nanoparticles showed unsaturated but appreciable magnetization of ∼ 4 emu/g at an applied field of 1.8 T at room temperature, and consequently, high transverse water proton relaxivities (r2) of ∼ 7 s–1 mm–1 at 1.5 T, ∼ 35 s–1 mm–1 at 3.0 T, and ∼ 55 s–1 mm–1 at 9.4 T with negligible longitudinal water proton relaxivities (r1), thus being eligible for use as T2 MRI contrast agents at high MR fields. In addition, d‐glucuronic acid‐coated ultrasmall Tb2O3 nanoparticles exhibited fluorescence in the green region, useful for dual‐modal imaging. [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]

Minhong Jeun,1 Sungwook Park,1,2 Hakho Lee,3 Kwan Hyi Lee1,2 1Center for Biomaterials, Biomedical Research Institute, Korea Institute of Science and Technology, Seoul, 2Department of Biomedical Engineering, Korea University of Science and Technology, Daejeon, Republic of Korea; 3Center for Systems Biology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA Abstract: Magnetic-based biosensors are attractive for on-site detection of biomarkers due to the low magnetic susceptibility of biological samples. Here, we report a highly sensitive magnetic-based biosensing system that is composed of a miniaturized nuclear magnetic resonance (NMR) device and magnetically engineered nanoferrite particles (NFPs). The sensing performance, also identified as the transverse relaxation (R2) rate, of the NMR device is directly related to the magnetic properties of the NFPs. Therefore, we developed magnetically engineered NFPs (MnMg-NFP) and used them as NMR agents to exhibit a significantly improved R2 rate. The magnetization of the MnMg-NFPs was increased by controlling the Mn and Mg cation concentration and distribution during the synthesis process. This modification of the Mn and Mg cation directly contributed to improving the R2 rate. The miniaturized NMR system, combined with the magnetically engineered MnMg-NFPs, successfully detected a small amount of infectious influenza A H1N1 nucleoprotein with high sensitivity and stability. Keywords: biosensor, NMR, nanoferrite particles, transverse relaxation, magnetization, on-site detection

Abstract Biophysical modeling of macroscopic diffusion-weighted MRI signal in terms of microscopic cellular parameters holds the promise of quantifying the integrity of white matter. Unfortunately, even fairly simple multi-compartment models of proton diffusion in the white matter do not provide a unique, biophysically plausible solution. Here we report a nontrivial diffusion MRI signal dependence on echo time (T E) in human white matter in vivo. We demonstrate that such T E dependence originates from compartment-specific T 2 values and that it is a promising "orthogonal measure" able to break the degeneracy in parameter estimation, and to yield important relaxation metrics robustly. We thereby enable the precise estimation of the intra- and extra-axonal water T 2 relaxation times, which is precluded by a limited signal-to-noise ratio when using multi-echo relaxometry alone. Highlights • Empirical evidence for different compartmental T 2 values. • TE dependency of diffusion MRI signals biases the interpretation of diffusion parameters. • Including compartmental diffusivities in the biophysical models improves T 2 relaxometry. • Including compartmental T 2 's in the biophysical models improve diffusion modeling. • Compartmental T 2 's may become valuable parameters for WM microstructure. [ABSTRACT FROM AUTHOR]

Background: Exponential fitting of multiecho spin echo sequences with skipped echoes is still commonly used for quantification of transverse relaxation (T2 ).Purpose: To examine the efficacy of skipped echo methods for T2 quantification against computational modeling of the exact signal decay.Study Type: Prospective comparison of methods.Subjects/phantom: Eight volunteers were imaged at 4.7T, six volunteers at 1.5T, and phantoms ([MnCl2 ] = 68-270 mM).Field Strength/sequence: 1.5T and 4.7T; multiple-echo spin echo.Assessment: Exponential fitting for T2 using all echoes, skipping the first echo or skipping all odd echoes, compared with Bloch simulations. Resulting T2 values were examined over a range of T2 (10-150 msec), refocusing flip angles (90-270°), and echo train lengths (ETL = 6-32).Statistical Tests: Shapiro-Wilk tests and Q-Q plots were used to check for normality of data. Paired sample t-tests and Wilcoxon rank tests were used to compare fitting models using α = 0.05. Multiple comparisons were accounted for with Bonferroni correction.Results: In examined regions of interest, typical incorrect estimation of T2 ranged from 23-39% for exponential fitting of all echoes, or 15-32% for skipped echo methods. In vivo, T2 estimation error was reduced to as little as 10% with skipped echo methods using 180° refocusing and ETL = 8, although error varied due to refocusing angle, T2 , and ETL. In vivo, skipped echo T2 values were significantly different than all echo exponential fitting (P < 0.004), but also were significantly different from reference values (P < 0.002, except frontal white matter). Simulations showed skipping the first echo was the most effective form of exponential fitting, in particular for T2 <50 msec and ETL = 8, with potential to reduce T2 errors to 10%, depending on refocusing angle and T2 .Data Conclusion: Skipping echoes is insufficient for avoiding stimulated echo contamination. Resulting T2 errors depend on a complicated interplay of T2 , refocusing angle, and ETL. Modeling of the multiecho sequence is recommended.Level Of Evidence: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:1432-1440. [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]

Measuring molecular diffusion is based on the spatial encoding of spin-carrying molecules using external Larmor frequency gradients. Intrinsic variations of the Larmor frequency and of the local relaxation rate, commonly present in structurally complex samples, interfere with the external gradients, confounding the NMR-measured diffusion propagator. Here we consider, analytically and numerically, the effects of the mesoscopic magnetic structure (local susceptibility and transverse relaxation rate) on the NMR-measured “apparent” diffusion coefficient (ADC). We show that in the fast diffusion regime, when molecules spread past the correlation length of the magnetic structure, the deviation of ADC from the genuine diffusion coefficient increases as a power law of diffusion time. The effect of mesoscopically varying transverse relaxation rate is sequence-independent and always leads to the decrease of ADC with time, whereas the effect sign for the mesoscopic Larmor frequency variations depends on the presence of refocussing pulses in the diffusion sequence. We connect this unexpectedly diverging with time ADC discrepancy to the spatial statistics of the mesocopic magnetic structure. Our results establish a novel kind of NMR contrast tied to the microstructural complexity, and can be applied to discern the mesoscopic effects of hindrances to molecular diffusion, susceptibility variations, and varying local relaxation rate, on the measured diffusion propagator. In particular, we numerically show that the susceptibility effect of a microvascular network is sufficient to explain the observed ADC decrease due to superparamagnetic iron-oxide contrast injection in monkeys. [ABSTRACT FROM AUTHOR]

Purpose: To derive an expression for the transverse signal time course from systems in the motional narrowing regime, such as water diffusing in blood. This was validated in silico and experimentally with ex vivo blood samples. Methods: A closed‐form solution (CFS) for transverse signal decay under any train of refocusing pulses was derived using the weak field approximation. The CFS was validated via simulations of water molecules diffusing in the presence of spherical perturbers, with a range of sizes and under various pulse sequences. The CFS was compared with more conventional fits assuming monoexponential decay, including chemical exchange, using ex vivo blood Carr‐Purcell‐Meiboom‐Gill data. Results: From simulations, the CFS was shown to be valid in the motional narrowing regime and partially into the intermediate dephasing regime, with increased accuracy with increasing Carr‐Purcell‐Meiboom‐Gill refocusing rate. In theoretical calculations of the CFS, fitting for the transverse relaxation rate (R2) gave excellent agreement with the weak field approximation expression for R2 for Carr‐Purcell‐Meiboom‐Gill sequences, but diverged for free induction decay. These same results were confirmed in the ex vivo analysis. Conclusion: Transverse signal decay in the motional narrowing regime can be accurately described analytically. This theory has applications in areas such as tissue iron imaging, relaxometry of blood, and contrast agent imaging. Magn Reson Med 80:341–350, 2018. © 2017 International Society for Magnetic Resonance in Medicine. [ABSTRACT FROM AUTHOR]

SuperParamagnetic Iron Oxide Nanoparticles (SPIONs) are often used in magnetic resonance imaging experiments to enhance Magnetic Resonance (MR) sensitivity and specificity. While the effect of SPIONs on the longitudinal and transverse relaxation time of 1 H spins has been well characterized, their effect on highly diffusive spins, like those of hyperpolarized gases, has not. For spins diffusing in linear magnetic field gradients, the behavior of the magnetization is characterized by the relative size of three length scales: the diffusion length, the structural length, and the dephasing length. However, for spins diffusing in non-linear gradients, such as those generated by iron oxide nanoparticles, that is no longer the case, particularly if the diffusing spins experience the non-linearity of the gradient. To this end, 3D Monte Carlo simulations are used to simulate the signal decay and the resulting image contrast of hyperpolarized xenon gas near SPIONs. These simulations reveal that signal loss near SPIONs is dominated by transverse relaxation, with little contribution from T 1 relaxation, while simulated image contrast and experiments show that diffusion provides no appreciable sensitivity enhancement to SPIONs. [ABSTRACT FROM AUTHOR]

Drought is the main abiotic stress worldwide affecting harvest quality and quantity of numerous crops. To enable better water management, low field NMR (nuclear magnetic resonance) relaxometry was assessed as a developmental marker and a new method for early detection of water deficiency. The effect of a foliar biostimulant against water stress was also investigated. Two leaves of different ranks (four and eight) were studied. The leaves of different ranks were characterized by different NMR T2 spectra which validated the ability of NMR to describe the developmental stage of tobacco. Results also showed that T2 NMR relaxation spectra allow the detection of mild water stress (80% of the field capacity) through the precise characterization of the leaf water status while other water stress markers (relative water content, photosynthetic related parameters…) were not yet impacted. The agricultural impact of the mild water stress was determined through the nitrogen rate in shoots and amino acids assay six weeks after the beginning of the stress and results shows that foliar application of biostimulant limits the negative consequences of drought. Our results demonstrate the sensitivity of NMR to detect slight changes triggered in the leaf by water stress at the tissue level. [ABSTRACT FROM AUTHOR]

Purpose: To characterize the magnetic susceptibility and relaxation times (T1 and T2) of fetal blood at 3 T as a function of the hematocrit (Hct) and oxygen saturation (sO2). Methods: Susceptibility and relaxometry measurements were performed on cord blood specimens (N = 90, derived from six caesarean deliveries) with a range of hematocrits and oxygen saturations (0.09 < Hct < 0.82, 7 < sO2 < 100%). To obtain simple, analytic relationships between MRI properties and blood properties, data were fit to established two‐compartment (plasma and erythrocytes) models. Results: Two‐compartment models effectively described the cord blood data. The root‐mean‐squared deviation between the model and the data was 6.3, 10.3, and 1.3% for fits to T1, T2, and susceptibility measurements. Relaxometry data and estimated T1 and T2 model parameters were generally consistent with those reported in cord blood at 1.5 T and comparable to published values for adult blood. Notably, the measured value of Δχdeo, the susceptibility difference between fully oxygenated (sO2 = 100%) and deoxygenated (sO2 = 0) cord blood was approximately 20% lower than the established adult blood value (Δχdeo,cord = 2.64 ppm, Δχdeo,adult = 3.4 ppm). Conclusions: The described models and associated parameter values can be used to inform acquisition parameters, and interpret fetal/neonatal blood susceptibility measurements and relaxometry data acquired at 3 T with respect to hematocrit and sO2. Magn Reson Med 79:3194–3206, 2018. © 2017 International Society for Magnetic Resonance in Medicine. [ABSTRACT FROM AUTHOR]

Purpose: This work demonstrates a 3D radial multi-echo acquisition scheme for time-efficient sodium (23Na) MR-signal acquisition and analysis. Echo reconstructions were used to produce signal-to-noise ratio (SNR)-enhanced 23Na-images and parameter maps of the biexponential observed transverse relaxation time ( T2*) decay. Methods: A custom-built sequence for radial multi-echo acquisition was proposed for acquisition of a series of 3D volumetric 23Na-images. Measurements acquired in a phantom and in vivo human brains were analyzed for SNR enhancement and multi-component T2* estimation. Results: Rapid gradient refocused imaging acquired 38 echoes within a repetition time of 160 ms. Signal averaging of multi-echo time (TE) measurements showed an average brain tissue SNR enhancement of 34% compared to single-TE images across subjects. Phantom and in vivo measurements detected distinguishable signal decay characteristics for fluid and solid media. Mapping results were investigated in phantom and in vivo experiments for sequence timing optimization and signal decay analysis. The T2* mapping results were consistent with previously reported values and facilitated fluid-signal discrimination. Conclusion: The proposed method offers an efficient 23Na-imaging scheme that extends existing 23Na-MRI sequences by acquiring signal decay information with no increase in time or specific absorption rate. The resultant SNR-enhanced 23Na-images and estimated T2* signal decay characteristics offer great potential for detailed investigation of tissue compartment characterization and clinical application. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effects of sample movement on T 2 measurement and relaxation times distribution; • Pore size distribution and total porosity of representative rock samples; • NMR Logging-while-drilling (LWD) system simulator; Nuclear Magnetic Resonance (NMR) is one of the primary techniques used in the oil industry for logging operations and in the laboratory environment to study rock formations due to its reliability in offering a reliable estimation of oil well productivity. Two types of well-logging operations exist, Wireline Logging and Logging While Drilling (LWD). Wireline Logging involves NMR measurements taken under static conditions. In contrast, LWD involves measurements taken during the drilling process while the tool is in motion, translating, rotating, and vibrating relative to the formation. To understand the behavior of NMR signals measured under LWD conditions on a laboratory scale, we developed a setup that includes a single-sided magnet, rf probes, and a mechanical system that emulates a relative sinusoidal motion between the sample and the applied magnetic field. Four representative rock samples were selected according to their relaxation times, which were short, intermediate, and long compared to the oscillation period of the LWD simulator: three sandstone, Fontainebleau, Berea Sandstone, and Portland Red, and one carbonate, Indiana Limestone. The results show that even with the modifications observed in the relaxation times distribution, which could lead to misinterpreting the geological formation parameters, the total porosity remains unaffected and independent of the sample motion during the NMR measurements, even under severe conditions and using the standard procedures of the data processing. [ABSTRACT FROM AUTHOR]

[Display omitted] • Transverse relaxation is sensitive to tissue microstructure at the mesoscopic scale. • There are distinct universality classes of mesoscopic magnetic structure. • The time-dependent relaxation rate approaches its long-time limit via power laws. • We experimentally detect the transition into maximally random jammed state. Nuclear magnetic resonance (NMR) has been instrumental in deciphering the structure of proteins. Here we show that transverse NMR relaxation, through its time-dependent relaxation rate, is distinctly sensitive to the structure of complex materials or biological tissues at the mesoscopic scale, from micrometers to tens of micrometers. Based on the ideas of universality, we show analytically and numerically that the time-dependent transverse relaxation rate approaches its long-time limit in a power-law fashion, with the dynamical exponent reflecting the universality class of mesoscopic magnetic structure. The spectral line shape acquires the corresponding non-analytic power law singularity at zero frequency. We experimentally detect the change in the dynamical exponent as a result of the transition into maximally random jammed state characterized by hyperuniform correlations. The relation between relaxational dynamics and magnetic structure opens the way for noninvasive characterization of porous media, complex materials and biological tissues [ABSTRACT FROM AUTHOR]