Determination Of Apparent Diffusion Coefficient Research Articles

A novel model for determination of apparent diffusion coefficient of gaseous solvent mixture-heavy oil system with consideration of swelling effect and density variation

A reliable estimation of the apparent diffusion coefficient (D) of gaseous solvent mixtures (GSMs) in heavy oil (HO) is necessary for the design of GSM-based recovery techniques. In this study, diffusion measurements of GSM-HO systems were carried out at various temperatures (25°C to 54.2°C) and pressures (5 to 10 MPa). Then, a novel mathematical model was proposed to describe the diffusion process of GSMs in HO considering the oil swelling effect and density variation. The oil swelling effect was described with a newly developed density model of GSM-HO systems. Finally, the developed model was solved via a numerical method to determine the D of GSMs in HO and the dynamic processes of HO swelling under varied temperature and pressure conditions. The results indicated that the D values at the measured temperatures and pressures ranged from 3.81-22.62×10−10 m2•s−1. The average D value of the GSMs increased with temperature and pressure. The GSM concentration in HO, the height of the GSM-HO interface, and the swelling velocity of HO rapidly increased at the early stage and then slowly increased over time. The maximum GSM concentration was observed at the GSM-HO interface.

Use of a boron-doped diamond electrode to assess the electrochemical response of the naphthol isomers and to attain their truly simultaneous electroanalytical determination

Naphthol, a chemical classified as an endocrine disruptor and known to show carcinogenic activity, is found in the environment as a mixture of its isomers. For the first time, the truly simultaneous voltammetric determination of these isomeric forms of naphthol was explored in this work using a cathodically pretreated BDD electrode (CPT–BDD). The isomers 1–naphthol (1–NAP) and 2–naphthol (2–NAP) showed an irreversible oxidation process at 0.80V and 0.96V vs. Ag/AgCl (3.0molL−1 KCl), respectively, which allowed the simultaneous determination of these compounds. The electrochemical features of the 1–NAP and 2–NAP electrooxidation on CPT–BDD were investigated, including the determination of apparent diffusion coefficients and adsorption studies. Using differential pulse voltammetry under optimized experimental conditions, the analytical curves simultaneously constructed for 1–NAP and 2–NAP were both linear in the concentration range of 0.200 to 3.85μmolL−1 with limits of detection of 50 and 100nmolL−1, respectively. Because the naphthol isomers do not adsorb on CPT–BDD, an excellent repeatability of measurement was verified and the proposed electroanalytical procedure was successfully applied for a truly simultaneous quantification of 1–NAP and 2–NAP in water and synthetic urine samples.

Intravoxel incoherent motion model-based analysis of diffusion-weighted magnetic resonance imaging with 3 b-values for response assessment in locoregional therapy of hepatocellular carcinoma.

PurposeThe aim of this study was to evaluate an intravoxel incoherent motion (IVIM) model–based analysis of diffusion-weighted imaging (DWI) for assessing the response of hepatocellular carcinoma (HCC) to locoregional therapy.Patients and methodsRespiratory-gated DWI (b=0, 50, and 800 s/mm2) was retrospectively analyzed in 25 patients who underwent magnetic resonance imaging at 1.5 T before and 6 weeks following the first cycle of transarterial chemoembolization therapy, transarterial ethanol-lipiodol embolization therapy, and transarterial radioembolization therapy. In addition to the determination of apparent diffusion coefficient, ADC(0,800), an estimation of the diffusion coefficient, D′, and the perfusion fraction, f′, was performed by using a simplified IVIM approach. Parameters were analyzed voxel-wise. Tumor response was assessed in a central slice by using a region of interest (ROI) covering the whole tumor. HCCs were categorized into two groups, responders and nonresponders, according to tumor size changes on first and second follow ups (if available) and changes of contrast-enhanced region on the first follow up.ResultsIn total, 31 HCCs were analyzed: 17 lesions were assigned to responders and 14 were to nonresponders. In responders, ADC(0,800) and D′ were increased after therapy by ~30% (P=0.00004) and ~42% (P=0.00001), respectively, whereas f′ was decreased by ~37% (P=0.00094). No significant changes were found in nonresponders. Responders and nonresponders were better differentiated by changes in D′ than by changes in ADC(0,800) (area under the curve =0.878 vs 0.819 or 0.714, respectively).ConclusionIn patients with HCCs undergoing embolization therapy, diffusion changes were better reflected by D′ than by conventional ADC(0,800), which is influenced by counteracting perfusion changes as assessed by f′.

Determination of apparent diffusion coefficient in balls made from haddock mince during brining

Salting is one of the main processes of preservation in meat and fish industry. Knowledge of how salt affects the muscle microstructure is needed both to model diffusion and to obtain the desired salt concentration in the product. Diffusion of sodium chloride was studied in a gelled minced fish ball-brine system. Systems with both closed circulation of the brine and static conditions were used to study and compare the salt transport process. Effective diffusion coefficients (De) for diffusion of sodium chloride into fish balls made from fresh and frozen haddock mince were determined. A numerical calibration of an analytical model based on Fick's second law was performed, in which salt diffusion follows a non-steady-state process.Critical experimental parameters for the estimation of diffusion coefficients were: size of balls, initial solute concentration in the bulk of brine, freezing of the material before the treatment, and stirring of the brine.The result of experiment shows that a simple fish ball–brine system can be used to model mixing of salt in brining processes.

Current Staging Procedures in Urinary Bladder Cancer.

Currently computed tomography (CT) represents the most widely used standard imaging modality in muscle-invasive urinary bladder cancer. Visualization of local tumor or depth of invasion as well as lymph node staging, however, is often impaired. Magnetic resonance imaging (MRI) with diffusion-weighted sequences, determination of apparent diffusion coefficient (ADC) values or utilization of superparamagnetic iron nanoparticles potentially exhibits advantages in the assessment of local tumor or lymph node involvement and therefore might play a role in routine staging of urinary bladder cancer in the future. Likewise, positron emission tomography (PET) with the currently utilized tracers 18F-FDG, 11C-choline and 11C-acetate is investigated in bladder cancer patients—mostly in combination with diagnostic CT. Although promising results could be obtained for these PET/CT examinations in smaller series, their true value cannot be determined at present.

Role of diffusion weighted MRI in differentiating typical from atypical meningiomas at 1.5 and 3T MRI

PurposeAtypical and malignant meningiomas are considered to have a higher rate of recurrence and show aggressive behavior compared to benign variety. The purpose of our study was to study the role of diffusion weighted imaging and determination of apparent diffusion coefficient (ADC) values and ADC ratios to differentiate typical meningiomas from atypical/malignant variety at 1.5 and 3T MRI. Materials and methodsA total of 94 adult patients (48 patients at 3T and 46 patients at 1.5T) with pathologically proven meningiomas were retrospectively evaluated on conventional and diffusion weighted MRI. The signal intensity of the lesions on DW imaging was evaluated. ADC values and ADC ratios were calculated from lesion and contralateral normal white matter. Results94 lesions comprising of 66 benign and 28 atypical meningiomas were evaluated. The mean ADC values at 3T MRI were 0.82±0.12×10−3 in benign (typical) meningiomas and 0.68±0.10×10−3 in atypical meningiomas. At 1.5T, the mean ADC values of benign meningiomas were 0.83±0.11×10−3 and 0.70±0.09×10−3 in atypical meningiomas. The mean ADC ratios were 1.08±0.17 and 0.85±0.15 for benign and atypical meningiomas respectively. There was a statistically significant difference between the mean ADC ratios and the mean ADC values of typical and atypical meningiomas (P<0.001) at both 1.5T and 3T MRI. ConclusionDWI with calculation of apparent diffusion coefficient (ADC) values and ADC ratios has a potential role in differentiating benign from atypical meningiomas at both 1.5 and 3T MRI. The differences in mean ADC values between benign and atypical meningiomas were similar at both 1.5 and 3T MRI.

Funktionelle Bildgebung beim Harnblasenkarzinom

Computed tomography (CT) represents the current standard imaging modality in muscle invasive bladder cancer; however, local tumor and lymph node staging is often impaired. Magnetic resonance imaging (MRI) with diffusion-weighted sequences, determination of apparent diffusion coefficient (ADC) values or utilization of supraparamagnetic iron nanoparticles potentially exhibits advantages in the assessment of local tumor and lymph node involvement and therefore might play a role in the staging of bladder tumor in the future. Likewise, positron emission tomography (PET) with the currently used tracers (18)F fluorodeoxyglucose ((18)F-FDG), (11)C-choline and (11)C-acetate is being investigated in bladder cancer patients, mostly in combination with diagnostic CT. Although promising results could be obtained for PET/CT investigations to some extent, the true value cannot be determined at present.

Diffusion-weighted MRI with parallel imaging technique: apparent diffusion coefficient determination in normal kidneys and in nonmalignant renal diseases

The purpose of the study was to assess the capability and the reliability of apparent diffusion coefficient (ADC) measurements in the evaluation of different benign renal abnormalities. Twenty-five healthy volunteers and 31 patients, divided into seven different groups (A–G) according to pathology, underwent diffusion-weighted magnetic resonance imaging (DW MRI) of the kidneys using 1.5-T system. DW images were obtained in the axial plane with a spin-echo echo planar imaging single-shot sequence with three b values (0, 300, and 600 s/mm 2). Before acquisition of DW sequences, we performed in each patient a morphological study of the kidneys. ADC was 2.40±0.20×10 −3 mm 2 s −1 in volunteers. A significant difference was found between Groups A (cysts=3.39±0.51×10 −3 mm 2 s −1) and B (acute/chronic renal failure=1.38±0.40×10 −3 mm 2 s −1) and between Groups A and C (chronic pyelonephritis=1.53±0.21×10 −3 mm 2 s −1) ( P<.05). An important difference was also observed among Group D (hydronephrosis=4.82±0.35×10 −3 mm 2 s −1) and Groups A, B, and C ( P<.05), whereas no differences were found between Groups B and C ( P>.05). A considerable correlation between glomerular filtration rate and ADC was found ( P=.04). In conclusion, significant differences were detected among different patient groups, and this suggests that ADC measurements can be useful in differentiating normal renal parenchyma from most commonly encountered nonmalignant renal lesions.

Determination of aroma compound diffusion in model food systems: Comparison of macroscopic and microscopic methodologies

Diffusion properties at macroscopic and microscopic scales for three aroma compounds (in solution and gel systems) were characterized using three different methodologies: the diffusion cell and the Volatile Air Stripping Kinetic methods for the determination of apparent diffusion coefficients and the pulsed-field-gradient Nuclear Magnetic Resonance method for the determination of self-diffusion coefficients. The accuracy of the methods was established by comparing ethyl hexanoate diffusion coefficient in water or D 2O solution and in 1%-agar gel system at 25 and 30 °C. The robustness of the three methodologies was also investigated in 1%- iota-carrageenan system with different NaCl content leading to gel strengthening. In 1%-agar gel as well as in 1%- iota-carrageenan systems, the apparent or self-diffusion coefficients of aroma compounds had the same order of magnitude regardless of the approach, ranging between 2.3 × 10 −10 and 10.4 × 10 −10 m 2 s −1. Diffusion properties were discussed in terms of the different observation scales (diffusion scales) and of the nature of gel network.

Colorimetric determination of lithium-ion mobility in graphite composite electrodes

Abstract A new method for the determination of apparent diffusion coefficients of lithium ions in graphite electrodes was developed. In situ colorimetry – a technique relating the color of an electrode to its state of charge – was used to measure the distribution of lithium ions in model battery electrodes with good local and temporal resolution. Diffusion kinetics data are obtained from the rate of equilibration of a deliberately induced heterogeneous lithium distribution. An apparent activation energy of ca. 17 kJ/mol was measured for the diffusion of lithium in a porous graphite electrode.

Nasopharyngeal inflammatory pseudotumor: Multimodality imaging characterization

Nasopharyngeal inflammatory pseudotumors are very rare idiopathic infiltrative nasopharyngeal/skull base mass lesions. Imaging findings mimic the local infiltrative and destructive features of nasopharyngeal carcinoma, lymphoma and minor salivary gland tumors however without nodal dissemination. Apparent Diffusion Coefficient determination may aid the discrimination of benign from malignant nasopharyngeal lesions. Confident nasopharyngeal biopsy is required for effective therapeutic management. Failure to recognize this rare inflammatory process contributes to protracted symptomatology including evolving cranial neuropathy.

T2′ Imaging Predicts Infarct Growth beyond the Acute Diffusion-weighted Imaging Lesion in Acute Stroke

To show that measurement of the transverse relaxation time that characterizes signal loss caused by local susceptibilities (T2') is sensitive to an increased deoxyhemoglobin concentration in the brain, indicating tissue at risk for infarction. The study was approved by the local institutional review board; patients or their guardians provided informed consent. Magnetic resonance (MR) imaging was performed within 6 hours of symptom onset and again 1-11 days thereafter in 100 consecutive stroke patients, all of whom received intravenous thrombolytic therapy (mean age, 67 years). The MR imaging protocol included diffusion- and perfusion-weighted imaging for determination of apparent diffusion coefficient (ADC) and time to peak (TTP), along with quantitative T2 and T2* imaging. T2' maps were calculated and visually compared with ADC and TTP lesions by two independent observers. A T2'>ADC mismatch was observed by reader 1 in 73 (73%) of 100 patients, and by reader 2 in 65 (65%) patients. Respective sensitivities of T2'>ADC and of TTP>ADC mismatches for later infarct growth were 0.87 and 0.98 for reader 1 and 0.78 and 0.98 for reader 2, with respective specificities of 0.42 and 0.04 for reader 1 and 0.46 and 0.04 for reader 2. The odds ratios for infarct growth in the presence of a T2'>ADC mismatch were 4.59 (reader 1 P = .002) and 3.10 (reader 2 P = .012), while the odds ratios for TTP>ADC mismatch were 2.22 (reader 1 P = .606) and 1.73 (reader 2 P > .999). The presence of a T2'>ADC mismatch is a more specific predictor of infarct growth than is TTP>ADC mismatch and hence may be of clinical value in patient selection for acute stroke therapies in the future.

Plasma Membrane Cholesterol Content Affects Nitric Oxide Diffusion Dynamics and Signaling

Nitric oxide (NO) signaling is inextricably linked to both its physical and chemical properties. Due to its preferentially hydrophobic solubility, NO molecules tend to partition from the aqueous milieu into biological membranes. We hypothesized that plasma membrane ordering provided by cholesterol further couples the physics of NO diffusion with cellular signaling. Fluorescence lifetime quenching studies with pyrene liposome preparations showed that the presence of cholesterol decreased apparent diffusion coefficients of NO approximately 20-40%, depending on the phospholipid composition. Electrochemical measurements indicated that the diffusion rate of NO across artificial bilayer membranes were inversely related to cholesterol content. Sterol transport-defective Niemann-Pick type C1 (NPC1) fibroblasts exhibited increased plasma membrane cholesterol content but decreased activation of both intracellular soluble guanylyl cyclase and vasodilator-stimulated phosphoprotein (VASP) phosphorylation at Ser(239) induced by exogenous NO exposure relative to their normal human fibroblast (NHF) counterparts. Augmentation of plasma membrane cholesterol in NHF diminished production of both cGMP and VASP phosphorylation elicited by NO to NPC1-comparable levels. Conversely, decreasing membrane cholesterol in NPC1 resulted in the augmentation in both cGMP and VASP phosphorylation to a level similar to those observed in NHF. Increasing plasma membrane cholesterol contents in NHF, platelets, erythrocytes and tumor cells also resulted in an increased level of extracellular diaminofluorescein nitrosation following NO exposure. These findings suggest that the impact of cholesterol on membrane fluidity and microdomain structure contributes to the spatial heterogeneity of NO diffusion and signaling.

EPMA analysis for the determination of apparent diffusion coefficient of chloride ion in concrete

EPMA analysis for the determination of apparent diffusion coefficient of chloride ion in concrete

Bumetanide Reduces Cerebral Edema Formation in Rats With Diabetic Ketoacidosis

The mechanisms responsible for cerebral edema formation in diabetic ketoacidosis (DKA) are not well understood, although evidence suggests ischemia as a contributing factor. Previous studies have shown that the Na-K-Cl cotransporter of cerebral microvascular endothelial cells and astrocytes is a major participant in ischemia-induced cerebral edema in stroke. The present study was conducted to test the hypothesis that the Na-K-Cl cotransporter also contributes to cerebral edema in DKA. Sprague-Dawley rats were administered streptozotocin to induce DKA, and then cerebral edema was assessed by determination of apparent diffusion coefficients (ADC) with magnetic resonance diffusion-weighted imaging. Cerebral ADC values in DKA rats were significantly reduced in both cortex and striatum compared with non-DKA control rats, indicating the presence of cerebral edema. Intravenous administration of bumetanide to DKA rats abolished the drop in cortical ADC values, while having no significant effect in the striatum. Insulin and saline treatment had no effect when given after bumetanide but increased both cortical and striatal ADC values when given before bumetanide. Evidence is also presented here that acetoacetate and beta-hydroxybutyrate stimulate brain microvascular Na-K-Cl cotransporter activity. These findings suggest that the Na-K-Cl cotransporter contributes to brain edema in DKA.

Noise correction for the exact determination of apparent diffusion coefficients at low SNR.

Noise in MR image data increases the mean signal intensity of image regions due to the usually performed magnitude reconstruction. Diffusion-weighted imaging (DWI) is especially affected by high noise levels for several reasons, and a decreasing SNR at increasing diffusion weighting causes systematic errors when calculating apparent diffusion coefficients (ADCs). Two different methods are presented to correct biased signal intensities due to the presence of complex noise: 1) with Gaussian intensity distribution, and 2) with arbitrary intensity distribution. The performance of the correction schemes is demonstrated by numerical simulations and DWI measurements on two different MR systems with different noise characteristics. These experiments show that noise significantly influences the determination of ADCs. Applying the proposed correction schemes reduced the bias of the determined ADC to less than 10% of the bias without correction. Magn Reson Med 45:448-453, 2001.

Kinetics of Dopant Diffusion in Poly(3-alkylthiophene) Films Studied by Chronoabsorptometric Method

The kinetics of dopant diffusion in poly(3-alkylthiophene) films is studied by the determination of apparent diffusion coefficient from chronoabsorptometric curves. The diffusion coefficient during oxidation DOx increases with increasing electrolyte concentration and applied potential. On the other hand, the diffusion coefficient during reduction DRed is not dependent on the electrolyte concentration. Both DOx and DRed decrease with increasing alkyl chain length. From the experimental results, a model of charge-transport in poly(3-alkylthiophene) films during doping and undoping processes is proposed.

Fresh look at transport in perfluorosulfonate ionomers: ultramicroelectrode investigations of Nafion and the Dow ionomers

Abstract : Chronoamperometry at ultramicroelectrodes is a powerful and convenient technique for the determination of apparent diffusion coefficients and concentrations of electroactive cations ion-exchanged into Nafion and Dow perfluorosulfonate films. This technique offers tremendous advantages over the conventional electrochemical methods which employ film coated macro sized electrodes. These advantages stem from the elimination of iR distortion at the ultramicroelectrode and from the ability to determine both the concentration and apparent diffusion coefficient of the electroactive cation from a single experiment. Further improvements over the conventional approach were achieved by eliminating coupled diffusion and migration contributions to the measured current response. Under these conditions, charge is transported via ionic diffusion rather than through electron hopping. Furthermore, the apparent diffusion coefficients decrease with increasing concentration of the electroactive cation in the film.