Relaxation Time Of Water Research Articles

Predicting the impact of hydrocarbon saturation on T2 distribution curve of NMR logs – A case study

The Nuclear Magnetic Resonance (NMR) is a valuable technique that provides estimates of various rock and fluid properties, including porosity, permeability, and pore size distribution. The decay or relaxation time of NMR signals is directly related to the pore size, but altering fluid in the pore spaces would also change the T 2 distribution curve. This change is due to the different relaxation time of hydrocarbon and water. This study focuses on predicting NMR T 2 distribution curves at different water saturations using a single T 2 saturation at any given water saturation. To do so, NMR measurements were performed on 9 plugs each at different saturations. Two general equations were derived. The first equation is related to the water response, while the second equation is related to the oil response. These two equations were calibrated and verified using core data. The coefficient of determination (R 2 ) for the first equation is equal to 0.592, while it is equal to 0.975 for the second equation. T 2 distribution curves depend on the amount and the distribution of the fluids within the pore structure. The findings of this study can help to increase the accuracy of the petrophysical properties derived by NMR logging. • A new model is proposed to predict NMR's T2 distribution curve in the oil bearing rocks. • NMR measurements were investigated in 9 plugs individually in different saturations in an oil field. • Two general equations were derived. To validate the equations, five T2 distribution curves which are equivalent to the T2 distribution curve of 100% water saturated rock were constructed by using 5 experimental T2 distributions.

Zero- to Ultralow-Field NMR Spectroscopy of Small Biomolecules.

Nuclear magnetic resonance (NMR) spectroscopy is a well-established analytical technique used to study chemicals and their transformations. However, high-field NMR spectroscopy necessitates advanced infrastructure, and even cryogen-free benchtop NMR spectrometers cannot be readily assembled from commercially available components. We demonstrate construction of a portable zero-field NMR spectrometer employing a commercially available magnetometer and investigate its applications in analytical chemistry. In particular, J-spectra of small representative biomolecules [13C]-formic acid, [1-13C]-glycine, [2,3-13C]-fumarate, and [1-13C]-d-glucose were acquired, and an approach relying on the presence of a transverse magnetic field during the detection was investigated for relaxometry purposes. We found that the water relaxation time strongly depends on the concentration of dissolved d-glucose in the range of 1-10 mM suggesting opportunities for indirect assessment of glucose concentration in aqueous solutions. Extending analytical capabilities of zero-field NMR to aqueous solutions of simple biomolecules (amino acids, sugars, and metabolites) and relaxation studies of aqueous solutions of glucose highlights the analytical potential of noninvasive and portable ZULF NMR sensors for applications outside of research laboratories.

Study of common quantification methods of amide proton transfer magnetic resonance imaging for ischemic stroke detection

To assess the correlation and differences between common amide proton transfer (APT) quantification methods in the diagnosis of ischemic stroke. Five APT quantification methods, including asymmetry analysis and its variants as well as two Lorentzian model-based methods, were applied to data acquired from six rats that underwent middle cerebral artery occlusion scanned at 9.4T. Diffusion and perfusion-weighted images, and water relaxation time maps were also acquired to study the relationship of these conventional imaging modalities with the different APT quantification methods. The APT ischemic area estimates had varying sizes (Jaccard index: 0.544 ≤ J ≤ 0.971) and had varying correlations in their distributions (Pearson correlation coefficient: 0.104 ≤ r ≤ 0.995), revealing discrepancies in the quantified ischemic areas. The Lorentzian methods produced the highest contrast-to-noise ratios (CNRs; 1.427 ≤ CNR ≤ 2.002), but generated APT ischemic areas that were comparable in size to the cerebral blood flow (CBF) deficit areas; asymmetry analysis and its variants produced APT ischemic areas that were smaller than the CBF deficit areas but larger than the apparent diffusion coefficient deficit areas, though having lower CNRs (0.561 ≤ CNR ≤ 1.083). There is a need to further investigate the accuracy and correlation of each quantification method with the pathophysiology using a larger scale multi-imaging modality and multi-time-point clinical study. Future studies should include the magnetization transfer ratio asymmetry results alongside the findings of the study to facilitate the comparison of results between different centers and also the published literature.

Effects of contrast agents on relaxation properties of 31P metabolites.

Phosphorous MR spectroscopy (31P-MRS) forms a powerful, non-invasive research tool to quantify the energetics of the heart in diverse patient populations. 31P-MRS is frequently applied alongside other radiological examinations, many of which use various contrast agents that shorten relaxation times of water in conventional proton MR, for a better characterisation of cardiac function, or following prior computed tomography (CT). It is, however, unknown whether these agents confound 31P-MRS signals, for example, 2,3-diphosphoglycerate (2,3-DPG). In this work, we quantitatively assess the impact of non-ionic, low osmolar iodinated CT contrast agent (iopamidol/Niopam), gadolinium chelates (linear gadopentetic acid dimeglumine/Magnevist and macrocyclic gadoterate meglumine/Dotarem) and superparamagnetic iron oxide nanoparticles (ferumoxytol/Feraheme) on the nuclear T1 and T2 of 31P metabolites (ie, 2,3-DPG), and 1H in water in live human blood and saline phantoms at 11.7 T. Addition of all contrast agents led to significant shortening of all relaxation times in both 1H and 31P saline phantoms. On the contrary, the T1 relaxation time of 2,3-DPG in blood was significantly shortened only by Magnevist (P = .03). Similarly, the only contrast agent that influenced the T2 relaxation times of 2,3-DPG in blood samples was ferumoxytol (P = .02). Our results show that, unlike conventional proton MR, phosphorus MRS is unconfounded in patients who have had prior CT with contrast, not all gadolinium-based contrast agents influence 31P-MRS data in vivo, and that ferumoxytol is a promising contrast agent for the reduction in 31P-MRS blood-pool signal.

Simple Amphoteric Charge Strategy to Reinforce Superhydrophilic Polyvinylidene Fluoride Membrane for Highly Efficient Separation of Various Surfactant-Stabilized Oil-in-Water Emulsions.

Long-term efficient separation of highly emulsified oily wastewater is challenging. Reported herein is the preparation of a reinforced superhydrophilic, underwater superoleophobic membrane with demulsification properties using active iron nanoparticles in situ generated on a polydopamine (PDA)/polyethylenimine (PEI)-modified polyvinylidene fluoride (PVDF) membrane surface. A stable zwitterionic structure is fabricated on the membrane surface and provides it with an excellent capability of binding a hydration layer, leading to enhanced superhydrophilic/underwater superoleophobic properties. The interaction between the membrane surface and water is quantified using the relaxation time of water. After iron nanoparticles in situ anchoring, the superhydrophilic, underwater superoleophobic PDA/PEI modified PVDF membrane shows more stable flux behaviors, higher oil separation efficiency, demulsification, and excellent antioil-fouling properties for various anionic, nonionic, and cationic surfactant-stabilized oil-in-water emulsions in a crossflow filtration system. The reinforced hydration layer and the amphoteric charged demusification properties of the membrane play important roles in enhancing the membrane separation performance. The reinforced membrane also exhibits excellent cleaning and reusability performance in long-term operations. The outstanding separation performance, as well as the simple and cost-effective fabrication process of the membrane with various favorable properties, highlight its promise in practical emulsified oily water applications.

Effect of Relaxation Times in a Preservative Solution on Protein Deterioration Rate.

In this study, the relationship between the deterioration of the enzymatic activity of the protein in a preservative solution and the molecular mobility of the preservative solution was experimentally investigated by dielectric spectroscopy and a protein deterioration test. Dielectric spectroscopy was used to observe the molecular mobilities in the preservative solutions including various ratios of two protective agents, trehalose and ε-poly-l-lysine, at 40 °C. We also examined the enzymatic activity of l-lactate dehydrogenase (LDH) at 40 °C for 40 days to obtain the deterioration rate of LDH in the same preservative solutions. Our experimental results reveal that (1) three relaxation times of water molecular motion are detected by dielectric spectroscopy that we categorize into bulky water (relaxation time of 10 ps), weakly hydration water (relaxation time of tens to hundreds of picoseconds), and strongly hydration water (relaxation time of hundreds of picoseconds to tens of microseconds) and (2) the deterioration rate of LDH has a power-law relationship with the relaxation times of bulky and hydration water with specific power indices. The results also support the protein stabilization theory of high viscosity and the practical advantage of predicting the shelf life of proteins in the preservative solution by the relaxation time of water measured by dielectric spectroscopy.

Effect of ultrasonic pretreatment on the properties of freeze-dried carrot slices by traditional and infrared freeze-drying technologies

The effect of ultrasound pretreatments at different power levels on drying time and quality parameters of freeze-dried carrot slices was studied. The drying time was significantly reduced (p < 0.05) for both traditional freeze-drying (FD) and infrared freeze-drying (IRFD) with ultrasound pretreatment; the reduction was more evident for IRFD. The drying time was reduced from 698 min to 593 min for FD, whereas it was reduced from 577 min to 459 min for IRFD. The higher ultrasonic power seriously destroyed the cell wall, resulting into more void structure. At ultrasonic power of 150 W, 240 W, and 300 W, the drying time was reduced by 20.7%, 23.7%, and 22.6%, respectively, during IRFD, when compared with FD. The retention of β-carotene was significantly higher (p < 0.05) at 240 W and 300 W; the value was, respectively, 22.7% and 32.0% higher than the control value. The LF-NMR study showed the different states of water and the increase in ultrasound power caused the increase in the relaxation time for free water, indicating more easily drying. However, there was no significant difference (p > 0.05) in color, texture, and sensory properties between FD and IRFD samples.

Potential use of low-field nuclear magnetic resonance to determine the drying characteristics and quality of Arctium lappa L. in hot-blast air

The present study investigated the effect of drying temperature (50, 60, 70, and 80 °C) on the drying kinetics and water properties of burdock slices. The changes in water mobility and water distribution were characterized using 1H low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) techniques. The Page model satisfactorily described the hot-air drying curves of burdock. The drying kinetic curves showed that the second stage of drying corresponded exactly with when the relaxation times of free and immobile water decreased to the equilibrium points. MRI showed that water diffused from the center to the surface during drying. Overall, the LF-NMR, color and HPLC data showed that, at 60 °C, free water in burdock dissipated slowly, its color stability was higher, and its chlorogenic acid content was higher than at 70 and 80 °C. Significant correlations were found between moisture content, color and NMR parameters.

Use of magnetic resonance imaging for evaluation of therapeutic response in breast cancer-related lymphedema: A systematic review.

Breast cancer treatment-related lymphedema (BCRL) is a common comorbidity in breast cancer survivors. Although magnetic resonance imaging (MRI) is widely used to evaluate therapeutic response of patients with various medical conditions, it is not routinely used to evaluate lymphedema patients. We conducted a systematic review of the literature to identify studies on the use of MRI to evaluate therapy for BCRL. We hypothesized that MRI could provide information otherwise not possible through other examinations. On October 21, 2019, we conducted a systematic review on the PubMed/MEDLINE and Scopus databases, without time frame or language limitations, to identify studies on the use of MRI to evaluate therapy for BCRL. We excluded studies that investigated other applications of MRI, such as lymphedema diagnosis and surgical planning. Of 63 potential articles identified with the search, three case series fulfilled the eligibility criteria. In total, 53 patients with BCRL were included and quantitatively evaluated with MRI before and after manual lymphatic drainage. Authors used MRI or MR lymphagiography to investigate factors such as lymphatic vessel cross-sectional area, tissue water relaxation time (T2), and chemical exchange saturation transfer. The only study that compared MRI measurement with standard examinations reported that MRI added information to the therapy evaluation. MRI seems to be a promising tool for quantitative measurement of therapeutic response in patients with BCRL. However, the identified studies focused on only manual lymphatic drainage and were limited by the small numbers of patients. More studies are necessary to shed light on the topic.

Effects of Changes in Biopolymer Composition on Moisture in Acetylated Wood

To investigate the effects of changes in biopolymer composition on moisture in acetylated poplar wood (Populus euramericana Cv.), the acetylation of control wood was compared to the acetylation of wood with reduced hemicellulose or lignin content (about 9% reduction of total specimen dry weight in both cases). Time-domain nuclear magnetic resonance relaxometry of water-saturated wood gave spin–spin relaxation times (T2) of water populations, while deuteration in a sorption balance was used to characterize the hydroxyl accessibility of the wood cell walls. As expected, the acetylation of pyridine-swelled wood reduced hydroxyl accessibility and made the cell wall less accessible to water, resulting in a reduction of cell wall moisture content by about 24% compared with control wood. Hemicellulose loss per se increased the spin–spin relaxation time of cell wall water, while delignification had the opposite effect. The combined effect of hemicellulose removal and acetylation caused more than a 30% decrease of cell wall moisture content when compared with control wood. The acetylated and partially delignified wood cell walls contained higher cell wall moisture content than acetylated wood. An approximate theoretical calculation of hydroxyl accessibility for acetylated wood was in the low range, but it agreed rather well with the measured accessibility, while acetylated and partially hemicellulose-depleted and partially delignified wood for unknown reasons resulted in substantially lower hydroxyl accessibilities than the theoretical estimate.

Water status and dynamics of high-moisture Mozzarella cheese as affected by frozen and refrigerated storage

High-moisture Mozzarella is one of the most exported cheeses worldwide, but affected by short shelf-life. Freezing can help to reduce waste, but its effect on quality needs to be considered. In this study, the physico-chemical changes of Mozzarella occurring during frozen storage and subsequent refrigerated storage (after thawing) were evaluated. Frozen cheeses stored at −18 °C between 1 and 4 months showed microstructural damage and different physical, textural, sensory properties. With NMR relaxometry it was possible to observe freeze-related dehydration of caseins, by measuring the changes in water relaxation times within the matrix. These modifications were confirmed by microstructural observations that showed the formation of larger serum channels in samples subjected to freezing, compared with fresh cheeses. Sensory evaluation showed skin peeling off in frozen samples. By observing the changes at various length scales it was therefore possible to identify the critical points affecting HM Mozzarella cheese quality during frozen storage.

Spatially regularized parametric map reconstruction for fast magnetic resonance fingerprinting.

Magnetic resonance fingerprinting (MRF) provides a unique concept for simultaneous and fast acquisition of multiple quantitative MR parameters. Despite acquisition efficiency, adoption of MRF into the clinics is hindered by its dictionary matching-based reconstruction, which is computationally demanding and lacks scalability. Here, we propose a convolutional neural network-based reconstruction, which enables both accurate and fast reconstruction of parametric maps, and is adaptable based on the needs of spatial regularization and the capacity for the reconstruction. We evaluated the method using MRF T1-FF, an MRF sequence for T1 relaxation time of water (T1H2O) and fat fraction (FF) mapping. We demonstrate the method's performance on a highly heterogeneous dataset consisting of 164 patients with various neuromuscular diseases imaged at thighs and legs. We empirically show the benefit of incorporating spatial regularization during the reconstruction and demonstrate that the method learns meaningful features from MR physics perspective. Further, we investigate the ability of the method to handle highly heterogeneous morphometric variations and its generalization to anatomical regions unseen during training. The obtained results outperform the state-of-the-art in deep learning-based MRF reconstruction. The method achieved normalized root mean squared errors of 0.048 ± 0.011 for T1H2O maps and 0.027 ± 0.004 for FF maps when compared to the dictionary matching in a test set of 50 patients. Coupled with fast MRF sequences, the proposed method has the potential of enabling multiparametric MR imaging in clinically feasible time.

Influence of 7T GRE-MRI Signal Compartment Model Choice on Tissue Parameters.

Quantitative assessment of tissue microstructure is important in studying human brain diseases and disorders. Ultra-high field magnetic resonance imaging (MRI) data obtained using a multi-echo gradient echo sequence have been shown to contain information on myelin, axonal, and extracellular compartments in tissue. Quantitative assessment of water fraction, relaxation time (T2*), and frequency shift using multi-compartment models has been shown to be useful in studying white matter properties via specific tissue parameters. It remains unclear how tissue parameters vary with model selection based on 7T multiple echo time gradient-recalled echo (GRE) MRI data. We applied existing signal compartment models to the corpus callosum and investigated whether a three-compartment model can be reduced to two compartments and still resolve white matter parameters [i.e., myelin water fraction (MWF) and g-ratio]. We show that MWF should be computed using a three-compartment model in the corpus callosum, and the g-ratios obtained using three compartment models are consistent with previous reports. We provide results for other parameters, such as signal compartment frequency shifts.

Direct Quantification of Intervertebral Disc Water Content Using MRI.

Water content is a key parameter for simulating tissue swelling and nutrient diffusion. Accurately measuring water content throughout the intervertebral disc (NP = nucleus pulposus; AF = annulus fibrosus) is important for developing patient-specific models. Water content is measured using destructive techniques, Quantitative MRI has been used to estimate water content and detect early degeneration, but it is dependent on scan parameters, concentration of free water molecules, and fiber architecture. To directly measure disc-tissue water content using quantitative MRI and compare MRI-based measurements with biochemical assays, and to quantify changes in disc geometry due to compression. Basic science, controlled. Twenty bone-disc-bone motion segments from skeletally mature bovines. 7T/3D fast low angle shot (FLASH) pulse sequence and a T2 rapid imaging with refocused echoes (RARE) sequence. Disc volumes, NP and AF volumetric water content, and T2 relaxation times were measured through MRI; NP and AF tissue gravimetric water content, mass density, and glycosaminoglycan content were measured through a biochemical assay. Correlations between MRI-based measurement and biochemical composition were evaluated using Pearson's linear regression. Mechanical dehydration resulted in a decrease in disc volume by up to 20% and a decrease in disc height by up to 35%. Direct water content measurements for the NP was achieved by normalizing MRI-based spin density by NP mass density (1.10 ± 0.03 g/cm3 ). However, the same approach underestimated water content in the AF by ~10%, which may be due to a higher concentration of collagen fibers and bound water molecules. Spin density or spin density normalized by mass density to estimate NP and AF water content was more accurate than correlations between water content and relaxation times. Mechanical dehydration decreased disc volume and disc height, and increased maximum cross-sectional area. TECHNICAL EFFICACY STAGE: J. Magn. Reson. Imaging 2020;52:1152-1162.

Low-field magnetic resonance imaging of roots in intact clayey and silty soils

The development of a robust method to non-invasively visualize root morphology in natural soils has been hampered by the opaque, physical, and structural properties of soils. In this work we describe a novel technology, low field magnetic resonance imaging (LF-MRI), for imaging energy sorghum (Sorghum bicolor (L.) Moench) root morphology and architecture in intact soils. The use of magnetic fields much weaker than those used with traditional MRI experiments reduces the distortion due to magnetic material naturally present in agricultural soils. A laboratory based LF-MRI operating at 47 mT magnetic field strength was evaluated using two sets of soil cores: 1) soil/root cores of Weswood silt loam (Udifluventic Haplustept) and a Belk clay (Entic Hapluderts) from a conventionally tilled field, and 2) soil/root cores from rhizotrons filled with either a Houston Black (Udic Haplusterts) clay or a sandy loam purchased from a turf company. The maximum soil water nuclear magnetic resonance (NMR) relaxation time T2 (4 ms) and the typical root water relaxation time T2 (100 ms) are far enough apart to provide a unique contrast mechanism such that the soil water signal has decayed to the point of no longer being detectable during the data collection time period. 2-D MRI projection images were produced of roots with a diameter range of 1.5–2.0 mm using an image acquisition time of 15 min with a pixel resolution of 1.74 mm in four soil types. Additionally, we demonstrate the use of a data-driven machine learning reconstruction approach, Automated Transform by Manifold Approximation (AUTOMAP) to reconstruct raw data and improve the quality of the final images. The application of AUTOMAP showed a SNR (Signal to Noise Ratio) improvement of two fold on average. The use of low field MRI presented here demonstrates the possibility of applying low field MRI through intact soils to root phenotyping and agronomy to aid in understanding of root morphology and the spatial arrangement of roots in situ.

Coupled magnetic resonance and electrical resistivity tomography: An open-source toolbox for surface nuclear-magnetic resonance

Nuclear-magnetic resonance (NMR) is a powerful tool for groundwater system imaging. Ongoing developments in surface NMR, for example, multichannel devices, allow for investigations of increasingly complex subsurface structures. However, with the growing complexity of field cases, the availability of appropriate software to accomplish the in-depth data analysis becomes limited. The open-source Python toolbox coupled magnetic resonance and electrical resistivity tomography (COMET) provides the community with a software for modeling and inversion of complex surface NMR data. COMET allows the NMR parameters’ water content and relaxation time to vary in one dimension or two dimensions and accounts for arbitrary electrical resistivity distributions. It offers a wide range of classes and functions to use the software via scripts without in-depth programming knowledge. We validated COMET to existing software for a simple 1D example. We discovered the potential of COMET by a complex 2D case, showing 2D inversions using different approximations for the resistivity, including a smooth distribution from electrical resistivity tomography (ERT). The use of ERT-based resistivity results in similar water content and relaxation time images compared with using the original synthetic block resistivity. We find that complex inversion may indicate incorrect resistivity by non-Gaussian data misfits, whereas amplitude inversion shows well-fitted data, but leading to erroneous NMR models.

Numerical Simulation of 2-D Underground Magnetic Resonance Tomography by Using Rotating Antenna and Sector Scanning

Magnetic resonance sounding (MRS) has been applied to underground constructions, such as tunnels and mines, to detect and forewarn groundwater sources hidden in front of the mine face, also named disaster water sources. Disaster water sources are mostly found in 2-D or 3-D structures; as such, their spatial distribution characteristics are difficult to reflect accurately by conventional 1-D MRS results. This letter proposes a method for sector-scanning magnetic resonance tomography (MRT) measurement using rotating antennas for 2-D water-bearing structures, such as water-filling conduits, faults, and goafs to obtain the 2-D distribution image of water content and relaxation time ( $T_{2}^{*}$ ) in front of the face by inversion. Through the numerical simulation of conduits, we analyzed the 2-D sensitivity, resolution, and inversion results of the rotating antennas. The imaging result at a high noise level was improved by increasing the number of antenna rotations. We also determined the effects of 2-D MRT on the faults and goafs and discussed the minimum cross-sectional area and maximum distance for reliable imaging of conduits.

A fast multi-exponential inversion of magnetic resonance sounding using iterative Lanczos bidiagonalization algorithm

Due to multi-exponential decay-time properties of the subsurface volume units or layers, magnetic resonance sounding (MRS) relaxation data exhibit a multi-exponential behavior. MRS inverse problem in a multi-exponential modeling framework brings about a very large size of the parameter space which is computationally costly. In this paper, a fast and memory efficient inversion algorithm to retrieve the aquifer properties in terms of water content and relaxation time is presented. The original nonsymmetric linearized forward matrix is projected onto a Krylov subspace with smaller dimension using an iterative Golub-Kahan-Lanczos bidiagonalization (GKL) method. Because of ill-conditioning of the projected linearized forward matrix a regularized damped least squares equation is applied at each step of the GKL factorization method to extract the best possible approximation of the partial water content. Numerical experiments based on synthetic and field data demonstrate that the proposed inversion method provides a good estimation of the water content and relaxation time compared to the standard algorithm with computationally more efficient functionality.

Effect of low temperature on the aging characteristics of a potato starch gel

In this work, the freezing curve of a potato starch gel with different concentrations was determined. The water migration, texture, microstructure and gelatinization of a potato starch gel with 8% starch concentration were studied during aging. The results showed that the freezing characteristics of the potato starch gel with different starch concentrations were quite different. NMR results showed that the relaxation time and proportion of water with different existing states (T21, T22 and T23) in the potato starch gel varied significantly under different aging temperatures. Under different aging temperatures, the texture characteristics and the gel strength of the starch gel were significantly different. The water retention of the gel was better under aging temperatures of 3 °C and −3 °C than for other gel samples. SEM and C-cell results showed that under aging temperatures of 3 °C and 0 °C, the formation of a gel network structure was accelerated, and the gel was relatively firm, with small and uniform pores and a larger pore area and number. The rapid viscosity analysis results showed that the peak viscosity, breakdown and setback of the vacuum freeze-dried gel powder changed differently under the aging temperatures.

Quantitative theory for the transverse relaxation time of blood water.

An integrative model is proposed to describe the dependence of the transverse relaxation rate of blood water protons (R2blood = 1/T2blood ) on hematocrit fraction and oxygenation fraction (Y). This unified model takes into account (a) the diamagnetic effects of albumin, hemoglobin and the cell membrane; (b) the paramagnetic effect of hemoglobin; (c) the effect of compartmental exchange between plasma and erythrocytes under both fast and slow exchange conditions that vary depending on field strength and compartmental relaxation rates and (d) the effect of diffusion through field gradients near the erythrocyte membrane. To validate the model, whole-blood and lysed-blood R2 data acquired previously using Carr-Purcell-Meiboom-Gill measurements as a function of inter-echo spacing τcp at magnetic fields of 3.0, 7.0, 9.4 and 11.7 T were fitted to determine the lifetimes (field-independent physiological constants) for water diffusion and exchange, as well as several physical constants, some of which are field-independent (magnetic susceptibilities) and some are field-dependent (relaxation rates for water protons in solutions of albumin and oxygenated and deoxygenated hemoglobin, ie, blood plasma and erythrocytes, respectively). This combined exchange-diffusion model allowed excellent fitting of the curve of the τcp -dependent relaxation rate dispersion at all four fields using a single average erythrocyte water lifetime, τery = 9.1 ± 1.4 ms, and an averaged diffusional correlation time, τD = 3.15 ± 0.43 ms. Using this model and the determined physiological time constants and relaxation parameters, blood T2 values published by multiple groups based on measurements at magnetic field strengths of 1.5 T and higher could be predicted correctly within error. Establishment of this theory is a fundamental step for quantitative modeling of the BOLD effect underlying functional MRI.