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At least 1,603 records · Page 89Linked to original sources

PubMed2005

Evaluation of a new Spin-echo diffusion-weighted sequence on a 0.35 T open magnetic resonance imaging (MRI)-system: first experiences within 3 h after acute stroke.

In acute stroke, diffusion-weighted magnetic resonance imaging helps to select patients who are eligible for thrombolysis, but is almost exclusively implemented on closed-bore scanners, which make monitoring of patients difficult. We developed and tested a cardiac gated Spin-echo diffusion-weighted sequence with prescan finetrim and motion correction on an open system with 0.35 T. Nineteen stroke patients appropriate for thrombolytic therapy by clinical criteria were enrolled in a prospective study on an intention-to-treat basis. In all but one patient, computed tomography and magnetic resonance imaging including the new diffusion-weighted sequence were performed within 3 h after symptom onset. Images were evaluated for acute cerebral ischemia and hemorrhage by two radiologists blinded to clinical information. Magnetic resonance imaging required a mean total acquisition time of 26 min. Sensitivity for early infarction was 94% in diffusion-weighted imaging and 73% in computed tomography. Six patients were excluded from thrombolysis due to an infarct size of more than 1/3 of the territory of the middle cerebral artery exclusively diagnosed with diffusion-weighted imaging. Hemorrhage was recognised by both, magnetic resonance imaging and computed tomography. We conclude that in acute stroke, diffusion-weighted imaging with an open system at 0.35 T is practicable. The implemented sequence reliably demonstrated the size of the infarction and improved the selection of patients who are eligible for thrombolysis.

Adult↗

PubMed2001

Cerebral abscesses: investigation using apparent diffusion coefficient maps.

The combination of high signal and reduced apparent diffusion coefficients (ADC) within abscesses on diffusion-weighted MRI (DWI) has been reported as characteristic of abscesses, and useful for distinguishing them from cystic or necrotic neoplasms. To assess whether these are consistent findings in abscesses, we used DWI-derived ADC to investigate changes in water diffusibility in cerebral abscesses. We reviewed the MRI studies and clinical records of five patients with brain abscesses, who underwent DWI. Regions of interest were drawn within the abscesses on ADC maps, to obtain the ADC. The center of all five abscesses gave signal higher than that of white matter on DWI. The three largest also appeared bright on ADC maps, i. e., showed ADC substantially lower than those of normal white matter, consistent with restricted diffusion. However, the two smaller abscesses were not visible on ADC maps because their ADC were essentially the same as that of white matter; they did not show restricted diffusion. The absence of restricted diffusion within small abscesses may be related to intrinsic differences in molecular microenvironment between small and large abscesses, or to greater influence of volume averaging with surrounding edema on the ADC in smaller abscesses.

Brain Abscess↗

PubMed2004

Evaluation of agar diffusion bioassay for nisin quantification.

The agar diffusion bioassay is the most widely used method for the quantification of nisin, due to its high sensitivity, simplicity, and cost-effectiveness. This method is based on the measurement of the inhibition zone produced in nisin-sensitive microorganisms. The size of the zone is affected by many factors, such as nisin-sensitive strain, amount of added agar and surfactant, and pre-diffusion step. This research aims to evaluate the effects of nisin-sensitive strains and pre-diffusion on the accuracy and precision of nisin quantification. Three strains of nisin-sensitive microorganisms (Micrococcus luteus, Lactobacillus sakei, Brochothrix thermosphacta) were tested along with three different incubation processes. The best combination was the method using L. sakei as an indicator strain with pre-diffusion at 4 degrees C for 24 h. Compared with M. luteus and B. thermosphacta, L. sakei gave more accurate and reproducible results. Moreover, the pre-diffusion step resulted in larger inhibition zones and more precise results. Finally, the best combination was validated and compared with the method that is usually used and the result showed that the method using L. sakei with pre-diffusion gave more accurate and precise results.

Agar↗

PubMed2000

In vitro and in vivo spin echo diffusion imaging characteristics of synovial fluid: potential non-invasive differentiation of inflammatory and degenerative arthritis.

OBJECTIVE: This study was undertaken to analyse the diffusion characteristics of synovial fluid in degenerative and inflammatory arthropathies. DESIGN AND PATIENTS: Ten in vitro specimens of synovial fluid from patients with both degenerative and inflammatory arthropathy were studied at body temperature with a navigator-corrected spin echo diffusion sequence (B values 0-512 s/mm2), on a Philips 1.5-T Gyroscan. Subsequently synovial fluid from knee joint effusions of 25 patients (10 patients with osteoarthritis, 10 patients with effusions following trauma and 5 patients with effusions secondary to inflammatory arthritis) was evaluated with the same navigator-corrected spin echo diffusion sequence. RESULTS: Both in vitro and in vivo study demonstrated decreased diffusion in patients with effusions secondary to degenerative joint disease (less than 2.40 x 10(-5) cm2/s) relative to patients with effusions accompanying knee trauma (greater than 2.75 x 10(-5) cm2/s) and inflammatory arthritis (in vitro and in vivo greater than 3.00 x 10(-5) cm2/s). CONCLUSION: Synovial fluid in degenerative arthritis shows less diffusion or free water movement than synovial fluid in inflammatory arthritis. Diffusion characteristics of synovial fluid may be used to predict the nature of the underlying form of arthritis in patients presenting with knee joint effusions.

Diagnosis, Differential↗

PubMed2003

Diffusion MRI findings in phenylketonuria.

Two patients with phenylketonuria were studied who were under dietary control since infancy, and who were mentally normal. Diffusion MRI was obtained using a spin-echo, echo-planar sequence with a gradient strength of 30 mT/m at 1.5 T. A trace sequence (TR=5700 ms, and TE=139 ms) was used, acquired in 22 s. Heavily diffusion-weighted (b=1000 mm(2)/s) images, and the apparent diffusion coefficient (ADC) values from automatically generated ADC maps were studied. There were two different patterns in these two patients, restricted and increased diffusion patterns. Restricted diffusion pattern consisted of high-signal on b=1000 s/mm(2) images with low ADC values ranging from 0.46 to 0.57 x 10(-3 )mm2/s. Increased diffusion pattern consisted of normal b=1000 s/mm(2 )images with high ADC values ranging from 1.37 to 1.63 x 10(-3 )mm2/s. It is likely that these values reflected presence of two different histopathological changes in phenylketonuria or reflected different stages of the same disease.

Brain↗

PubMed2004

Dairy cream as a phantom material for biexponential diffusion decay.

Commercially available aliquots of dairy cream are shown to have diffusion decay curves characterized by biexponential functions when studied over a wide range of b-factors. The fast and slow diffusion components responsible for the biexponential decay are attributed to water and lipid protons, respectively. The fast diffusion coefficient and relative fast and slow diffusion component fractions obtained from biexponential fits of cream phantoms over a wide range of b-factors up to 3,000 s/mm2 are similar to those obtained previously for brain. The slow diffusion coefficient from lipid protons is smaller than that found in the brain. Overall, however, the results suggest that dairy cream can serve as a widely available phantom material for testing software and hardware components designed to perform quantitative, biexponential diffusion decay studies.

Animals↗

PubMed2005

Modelling diffusive O(2) supply to isolated preparations of mammalian skeletal and cardiac muscle.

The purpose of this study was to use A. V. Hill's equation describing diffusion of O(2) into cylindrical muscles to assess the adequacy of O(2) supply for commonly used isolated preparations of mammalian cardiac and skeletal muscles. The diffusion equation was solved numerically to give the maximum, steady state O(2) diffusion distances (i.e. the distance from the surface of the muscle to the radial location where P(O(2)) is 0) for both resting and contracting muscles and for a range of temperatures. Non-steady state solutions for the rest-to-work transition were also determined to estimate how long contractile activity could be continued before anoxia develops at the muscle centre. The influence on muscle oxygenation of myoglobin-facilitated O(2) diffusion was also assessed. The analysis was performed for typical sized, whole muscles from adult rats and mice, for frog sartorius muscle and for a range of temperatures. Muscle O(2) consumption rates were taken from the literature. The results indicated that (1) diffusive O(2) supply would be adequate to support resting metabolism of soleus and EDL muscles of rat and mouse but may not be adequate to support the transient high resting metabolic rate of papillary muscles shortly after dissection, (2) during steady contractile activity of soleus and EDL muscles, particularly those from the rat, over a reasonable range of duty cycles, adequate O(2) supply could only be ensured if the radii of preparations was substantially smaller than those of whole muscles and (3) for cardiac muscles, diffusive O(2) supply could only support steady-state metabolism at twitch frequencies <1 Hz for whole papillary muscles from rat and <3 Hz for those from mouse. Reducing experimental temperature markedly enhances O(2) supply to skeletal, but not cardiac, muscle. O(2) supply from myoglobin had only minimal effects on oxygenation under typical isolated muscle conditions.

Animals↗

PubMed1983

Absence of positional change in pulmonary diffusing capacity in systemic sclerosis.

Patients with systemic sclerosis frequently have pulmonary function abnormalities, and recent evidence suggests that pulmonary vascular involvement is a common manifestation. To test the hypothesis that patients with systemic sclerosis have impaired ability to recruit or distend the pulmonary vascular bed, the postural change in the coefficient of carbon monoxide diffusing capacity was measured in 11 patients with systemic sclerosis, and the results were compared with results from age-, smoking-, and sex-matched control subjects with rheumatoid arthritis and with results from healthy subjects. In normal subjects and patients with rheumatoid arthritis increased, the coefficient of diffusion by 9.4 percent (p less than 0.005) and 8.4 percent (p less than 0.01), respectively, when they moved from the sitting to the supine position. In contrast, patients with systemic sclerosis did not show a significant increase in coefficient of diffusion, even those who had otherwise normal pulmonary function. Regression analyses showed that the change in coefficient of diffusion decreased with increasing age (r = -0.57) in normal subjects, and that the change in coefficient of diffusion was a function of the percent predicted forced vital capacity, both in patients with systemic sclerosis (r = 0.59) and in those with rheumatoid arthritis (r = 0.70). Thus, these findings indicate that patients with systemic sclerosis have a nondistensible pulmonary capillary bed and that the absence of positional change in the coefficient of diffusion in systemic sclerosis is a subtle indicator of pulmonary involvement.

Adult↗

PubMed1983

Ketomethylthiobutyric acid formation from methylthioadenosine: a diffusion assay.

Typical enzyme kinetics were observed when 5'-methylthioadenosine was used as substrate with extracts of malignant murine cells in a diffusion assay. The volatile product was measured after diffusion into a solution of the sulfhydryl reagent, 5,5'-dithiobis(2-nitrobenzoic acid), which it reduced to a yellow chromophore. Cysteine was required in the system. The volatile product was identified as H2S derived from the cysteine. The yield of H2S was similar to the amount of 2-keto-4-methylthiobutyric acid (KMTB) formed from methylthioadenosine when the KMTB was measured simultaneously in an ether extraction assay. KMTB could replace methylthioadenosine as a substrate capable of causing the formation of the diffusible product from cysteine. It is concluded that the following sequence of reactions takes place in the diffusion assay system: (1) 5'-methylthioadenosine + Pi leads to adenine + 5-methylthioribose-1-P, (2) 5-methylthioribose-1-P leads to KMTB, (3) KMTB + cysteine leads to methionine + 3-mercaptopyruvate, (4) 3-mercaptopyruvate + excess R-SH leads to pyruvate + H2S, (5) H2S + 5,5'-dithiobis(2-nitrobenzoic acid) leads to 5-mercapto-2-nitrobenzoic acid. Thus, the diffusion assay measures the amount of KMTB formed. The key enzyme, cysteine aminotransferase, EC 2.6.1.3, was partially purified from malignant cells and from liver and several of its characteristics are described. The diffusion assay using this enzyme is useful in measuring de novo synthesis of alpha-keto acids and it is applicable to crude enzyme preparations. The sensitivity is about 5 nmol of keto acid and the accurate range is 5 to 100 nmol.

Adenosine↗

PubMed1984

Kinetics of carbonic anhydrase catalysis in solvents of increased viscosity: a partially diffusion-controlled reaction.

Steady-state kinetic studies of the bovine carbonic anhydrase B-catalyzed hydration of CO2, dehydration of HCO3-, and hydrolysis of p-nitrophenylacetate were made in glycerol/water solvents of increased viscosity in order that the effect of diffusion-control on the substrate association reactions could be determined. The minimum association rate constants (kmin = V/(Km[E0])) were obtained at low substrate concentrations. The esterase activity did not depend upon the solvent viscosity. However, both the CO2 hydration and HCO3- dehydration reactions depended upon the solvent viscosity consistent with partial diffusion control. Thus both chemical activation and diffusion control processes contribute to the observed kmin. In low-viscosity aqueous solutions both hydration and dehydration are largely controlled by chemical activation. However, at higher viscosities, equal to that found in the interior of the erythrocyte, both reactions are largely diffusion controlled. This result can be interpreted to mean that carbonic anhydrase is a highly evolved enzyme that has approached its maximum efficiency. The extent of diffusion control observed rules out H2CO3 as a significant reactant with the enzyme. Several models that yield minimum steric requirements for access of substrate to the active site are examined. Minimum steric constraints are less for the smaller CO2. The slower esterase reaction is not influenced by diffusion.

Animals↗

PubMed1982

Diffusion of sugars and acids in human dental plaque in vitro.

Using a clearance technique, diffusion coefficients, D, were measured in plaque samples in which metabolic activity was eliminated by fixation with glutaraldehyde. Diffusion coefficients for sucrose, sodium acetate and sodium lactate at 37 degrees C were 3.0, 5.0 and 4.8 x 10(-6) cm2 s-1, respectively. Diffusion rate in plaque was between 2- and 5-fold slower than in water with uncharged species retarded less than charged species. However, diffusion in thin layers of plaque (100 microns) was rapid with clearance-halving times. T1/2, of about 6 s for acetate and lactate and 9 s for sucrose. Acetic and lactic acids diffuse faster than sucrose in plaque. Thus, the prolonged lowering of plaque pH following exposure to dietary carbohydrate is due to continued acid production in the plaque rather than to a restriction of diffusion of acid.

Acetates↗

PubMed1992

Protein and lipid lateral diffusion in normal and Rous sarcoma virus transformed chick embryo fibroblasts.

We measured the lateral diffusion of the fluorescent lipid analogue dioctadecylindocarbocyanine iodide (DiI) and of membrane glycoproteins labeled with tetramethylrhodamine (TRITC) succinyl concanavalin A (SConA) via fluorescence photobleaching recovery (FPR) at selected times during a temperature downshift experiment on transformation-defective temperature-sensitive (td-ts) Rous sarcoma virus (RSV) NY68-transformed chicken embryo fibroblasts (CEF) and on identically treated CEF and RSV-transformed CEF. There were no significant differences in the lateral diffusion in DiI at any of the times measured. The lateral diffusion of TRITC-SConA on the RSV-transformed CEF, (1.32 +/- 0.12).10(-10) cm2 s-1, was approximately two times faster than that observed in normal CEF, (0.61 +/- 0.06).10(-10) cm2 s-1. In the cells undergoing RSV NY68-mediated transformation, TRITC-SConA diffusion increased over a 24-h period from a value comparable to that observed in normal CEF, (0.72 +/- 0.13).10(-10) cm2 s-1 to a value comparable to the RSV-CEF transformed cells, (1.74 +/- 0.20).10(-10) cm2 s-1. All diffusion measurements reported were made at the permissive temperature for RSV-NY68 (35 degrees C) unless stated otherwise. The changes in the lateral diffusion of TRITC-SConA occurred between the fifth and twelfth hour of the downshift course and could be associated with cytoskeletal disruption and/or fibronectin degradation, both known to occur at this time in RSV-transformed cells. To assess the contribution of extracellular matrix (ECM) degradation, SConA mobility was measured in normal and RSV-transformed cells treated with trypsin. This treatment increased SConA mobility approximately 4-fold in the normal cells relative to untreated controls and only 2-fold in the RSV-CEF transformed cells. No significant difference in SConA mobility between trypsinized spherical normal and transformed cells was apparent.

Animals↗

PubMed1987

Surface diffusion in human serum lipoproteins.

From the viscosity dependence of the 31P NMR signals, the diffusion coefficients DT of phospholipid molecules in the surface monolayer of HDL, LDL and VLDL have been determined. DT for HDL3 and HDL2 are found to be 2.3 X 10(-8) cm2/s and 1.8 X 10(-8) cm2/s, respectively. These values are similar to values reported for diffusion of phospholipid molecules in phospholipid bilayers above the gel to liquid crystalline phase transition temperature. Viscosity dependence of [16,16,16-2H3]phosphatidylcholine incorporated into HDL2 yielded a value similar to that determined by 31P (DT = 1.9 X 10(-8) cm2/s). Slower diffusion coefficients were measured for LDL2 and VLDL. VLDL had a value DT = 9.1 X 10(-9) cm2/s. The diffusion coefficient for LDL2 was 1.4 X 10(-9) cm2/s. Thus, diffusion of phospholipids in LDL2 is a full order of magnitude slower at 25 degrees C than diffusion of phospholipids in the HDLs.

Diffusion↗

PubMed1989

Water self-diffusion in the calf lens.

Proton pulsed gradient spin echo (PGSE) nuclear magnetic resonance (NMR) spectroscopy was used to explore the free and restricted non-Brownian nature of lens water self-diffusion in calf lens tissue. At all temperatures investigated the water self-diffusion coefficient (Dw) of the cortical homogenate (25% protein) was 1.6-1.7 times greater than that for the nucleus (42% protein), and 0.3-0.5 times the value of Dw for pure water. The nuclear lens homogenate displayed anomalous temperature dependent water diffusion behavior, i.e. a departure from the smooth monotonic decrease in Dw with decreasing temperature, in the temperature range of 3-5 degrees C. By contrast, no such behavior was observed for cortical homogenate. Analysis of water proton echo attenuation data employing a parallel-plate model of restricted diffusion provided values for the parallel-plate barrier separation and self-diffusion coefficient in the limit of free diffusion. Nuclear material showed a smaller spatially average barrier separation and a significantly stronger barrier separation temperature dependence than cortical material.

Animals↗

PubMed1992

High-resolution MR imaging of water diffusion in the rabbit lens.

Movement of water in the lens, specifically water diffusion, was examined with diffusion imaging and H217O-enhanced proton imaging. Diffusion imaging showed restricted water self-diffusion in the cortex which was not concurrent with the change in proton density; nevertheless it was dependent on the gradient direction and might be related to lens fiber/protein organization. The difference in water diffusion patterns between control and galactosemic cataract was subtle but distinguishable. On the other hand, intracameral H217O injection allowed visualization of water movement across the lens. In galactosemic cataracts, water diffused from the anterior cortex towards posterior cortex and into the vitreous. This pattern was not seen in the normal lens.

Animals↗

PubMedDate not supplied

Diffusion coefficients for protein molecules in blood serum.

A new technique is described for the measurement of the self-diffusion coefficients of protein macromolecules in solution. The method makes use of the phenomenon of Taylor dispersion of a solute introduced into a solvent flowing in the laminar regime through a tube of circular section. Results are reported for the self-diffusion coefficient of cholesterol associated with lipoprotein molecules in dogs' serum at pH 7.4 in the temperature range 18-37 degrees C. The diffusivity of bovine serum albumin in serum has also been studied as a function of temperature at pH 7.4 and 4.7. In the more basic solution, measurements of the diffusivity as a function of protein concentration substantially agree with earlier work. For all the systems studied the diffusivity varies rapidly with temperature. The pH of the solution, in the case of bovine serum albumin, also has a significant effect on the diffusivity of the macromolecule. The latter observation is related to the amount of water bound to the protein molecule in solution.

Animals↗

PubMed1991

Convection of macromolecules is the dominant mode of transport across horizontal 0.4- and 3-microns filters in diffusion chambers: significance for biologic monolayer permeability assessment.

The purpose of the present study was to evaluate the permeability characteristics of fluorescein-labeled hydroxyethyl starch (FITC-HES, 20 less than molecular radius, aE less than 111 A) across large pore (0.4- and 3-microns polycarbonate) filters used in endothelial cell monolayer diffusion studies. Although the apparent permeability (P) of the FITC-HES macromolecules across these filters declined as the molecular radius increased, this decline was less than that associated with each solute's free diffusion (D0). Thus, the P/D0 anomalously increased as aE increased, a pattern not seen for free diffusion (flat P/D0 with increased aE) or restricted diffusion (decline in P/D0 with increased aE). Substantial natural convection across the porous filters produced the anomalous P/D0 curve for the following reasons: (1) this effect was elevated with positive pressure and ameliorated by zero driving pressure, and (2) the effect was much greater across filters with large (3 microns) vs small (0.4 microns) pore sizes. In addition, we estimated that less than half of macromolecular transport above 50 A probe radius at zero transmural pressure arrives by diffusion. The findings suggest that the property of restricted diffusion of biologic layers on these filters will be artifactually exaggerated when the measured resistance of the filter is subtracted from that of the filter plus biologic monolayer. Remedies for this problem may include using smaller pore filters, filters layered with extracellular material, or structural methods to determine true filter permeability.

Cell Membrane Permeability↗

PubMed1975

Diffusion in the gas phase: the effects of ambient pressure and gas composition.

Gas transport across the pores of a hen's egg shell occurs by a process of diffusion in the gas phase and for any particular gas depends upon its diffusion coefficient and the pore geometry. The egg shell is thus a convenient model for measuring the diffusive permeability of the shell to a given gas species when its diffusion coefficient is altered by either a change in ambient pressure or by changing the second gas in the diffusion pathway. In this study the permeability of the shell to water vapor and O2 was inversely proportional to ambient pressures over the range of .06 to 8 atmospheres' absolute (ata). The permeability of the shell to water vapor in a He environment (KH20, He) was 2.4 times KH20, air. If KO2, N2 is taken as unity, the permeabilities of the shell to O2 in He, Ar, CO2 and SF6 are 3.38, 0.95, 0.88, and 0.52, respectively. The results are interpreted in terms of the Chapman-Enskog equation, from which binary diffusion coefficients can be predicted for given gas pairs and ambient pressures. These results also provide explantations for the structural modification of egg shells in altitude-adapted chickens, and for the reduced insensible water loss in man at high ambient pressure.

Animals↗