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PubMed1989

Lateral diffusion as a rate-limiting step in ubiquinone-mediated mitochondrial electron transport.

Data are presented which indicate that the diffusion-based collisions of ubiquinone with its redox partners in the mitochondrial inner membrane are a rate-limiting step for maximum (uncoupled) rates of succinate-linked electron transport. Data were obtained from experimental analysis of a comparison of the apparent activation energies of lateral diffusion rates, collision frequencies, and electron transport rates in native and protein-diluted (phospholipid-enriched) inner membranes. Diffusion coefficients for Complex III (ubiquinol:cytochrome c oxidoreductase) and ubiquinone redox components were determined as a function of temperature using fluorescence recovery after photobleaching, and collision frequencies of appropriate redox partners were subsequently calculated. The data reveal that 1) the apparent activation energies for both diffusion and electron transport were highest in the native inner membrane and decreased with decreasing protein density, 2) the apparent activation energy for the diffusion step of ubiquinone made up the most significant portion of the activation energy for the overall kinetic activity, i.e. electron transport steps plus the diffusion steps, 3) the apparent activation energies for both diffusion and electron transport decreased in a proportionate manner as the membrane protein density was decreased, and 4) Arrhenius plots of the ratio of experimental electron transport productive collisions (turnovers) to calculated theoretically predicted, diffusion-based collisions for ubiquinone with its redox partners had little or no temperature dependence, indicating that as temperature increases, increases in electron transport rate are accounted for by the increases in diffusion-based collisions. These data support the Random Collision Model of mitochondrial electron transport in which the rates of diffusion and appropriate concentrations of redox components limit the maximum rates of electron transport in the inner membrane.

Animals↗

PubMed1999

Diffusion in cell-free and cell immobilising kappa-carrageenan gel beads with and without chemical reaction

Diffusion into and from kappa-carrageenan gel beads was studied, both in the absence and presence of bacterial cells, both with and without biochemical reaction. The solutes were indole, L-serine, and L-tryptophan. The reaction was that of indole and L-serine to give L-tryptophan. Established theory concerning diffusion of a single solute in cell-free gels was found to describe well the effect of the gel on diffusivity. Simultaneous diffusion of the three solutes resulted in lower diffusivities than those for individual solutes, suggesting the need to use multicomponent diffusion theory. The effect of cells on diffusion could only be accounted for by models assuming permeable cells. Diffusion with chemical reaction was reasonably well described by an effectiveness factor calculated using an effective diffusivity estimated from diffusion data without reaction. Copyright 1999 John Wiley & Sons, Inc.

Journal Article↗

PubMed1999

Cardiac diffusion tensor MRI in vivo without strain correction.

Cardiac diffusion MRI with diffusion encoding that spans a cardiac cycle is complicated by myocardial strains. This paper presents a method to obtain accurate diffusion data without strain correction. Owing to the synchrony of normal cardiac motion, there are time points in the cardiac cycle, "sweet spots," when the cardiac configuration approximates its temporal mean. If the diffusion is encoded then, the net effect of strain on the observed diffusion approximates zero. To test this, MRI diffusion and strain-rate movies are performed on cyclically deformed gel phantoms and in five normal subjects. In phantoms, the sweet spots predicted from the strain time curves agree with the times when the observed diffusion equals the true diffusion. In humans, the strain prediction of the sweet spots and the locations determined by the diffusion trace show a high correlation, r = 0.99. In all subjects, diffusion MRI presents a fiber orientation pattern comparable to that obtained from a stationary specimen. Magn Reson Med 42:393-403, 1999.

Adult↗

PubMed1998

Characterization of and correction for eddy current artifacts in echo planar diffusion imaging.

Magnetic resonance diffusion imaging is potentially an important tool for the noninvasive characterization of normal and pathological tissue. The technique, however, is prone to a number of artifacts that can severely affect its ability to provide clinically useful information. In this study, the problem of eddy current-induced geometric distortions that occur in diffusion images acquired with echo planar sequences was addressed. These geometric distortions produce artifacts in computed maps of diffusion parameters and are caused by misalignments in the individual diffusion-weighted images that comprise the diffusion data set. A new approach is presented to characterize and calibrate the eddy current effects, enabling the eddy current distortions to be corrected in sets of interleaved (or snapshot) echo planar diffusion images. Correction is achieved by acquiring one-dimensional field maps in the read and phase encode direction for each slice and each diffusion step. The method is then demonstrated through the correction of distortions in diffusion images of the human brain. It is shown that by using the eddy current correction scheme outlined, the eddy current-induced artifacts in the diffusion-weighted images are almost completely eliminated. In addition, there is a significant improvement in the quality of the resulting diffusion tensor maps.

Artifacts↗

PubMed1991

Ultrastructure of diffuse plaques in senile dementia of the Alzheimer type: comparison with primitive plaques.

We compared the ultrastructure between diffuse and primitive plaques in the brains of senile dementia, using pairs of routine electron microscopic ultrathin sections and adjacent semithin sections, which were immunolabeled for beta protein. In the frontal cortex, amyloid fibrils were rarely seen in a minority of diffuse plaques, suggesting an initial stage of the diffuse plaques. A majority of the diffuse plaques had electron-dense material and/or amyloid fibrils between cell processes in part of but not the entire beta/A4-immunoreactive areas. Small degenerating neurites were often seen with apparent amyloid fibrils in the diffuse plaques, and these were considered to be in an advanced stage. The size and number of degenerating neurites were proportional to the amount of amyloid. Bundles of amyloid fibrils were occasionally surrounded by astroglial processes forming gap junctions. Neurons were found within some diffuse plaques, but capillaries were rarely seen. In contrast, in the temporal cortex, the diffuse plaques were smaller, and even these small ones had apparent amyloid fibrils. The amount of amyloid correlated significantly with plaque size in the temporal cortices, but not in the frontal cortices. Most of the diffuse plaques of the frontal lobe remained as advanced diffuse plaques (apparent amyloid with occasional astroglia and some degenerating neurites) for a long time, and did not transformed into primitive plaques, whereas the temporal diffuse plaques tended to transform into primitive plaques.

Alzheimer Disease↗

PubMed2001

The effects of collimator geometry and self-absorption on in-situ mass diffusion measurements.

We consider a real-time methodology for determining self-diffusion coefficients at several temperatures utilizing a single sample, based on a radiotracer technique put forth by Codastefano, Di Zanza and Russo (Codastefano, P., Di Russo, A., Zanza, V. 1977. A new apparatus for accurate diffusion measurements in fluids. Reviews of Science Instrumentation 48, 1650-1653 (CDZ)) and recently optimized by our group (Jalbert, L.B., Banish, R.M., Rosenberger, F.E. 1997. Real-time diffusivity measurements in liquids at several temperatures with one sample. Physical Review E 57, 1727-1736 (JBR)). In this technique the evolution of the concentration distribution of the radiotracer is followed by shielding the source except for a pair of collimated apertures placed at mathematically advantageous positions along the diffusion axis. Radiation detectors at each collimator measure the intensity of radioactive tracer emission at each aperture, and the counting rate difference versus time leads to a determination of the diffusion coefficient. The effects of self-absorption of radiation in the source were previously treated by us using a one-dimensional approximation, which is a typical procedure. However, in order to obtain meaningful counting statistics in the detectors, the size of the collimator apertures must be large enough that the measured counting rate is actually an integral over a three-dimensional region of the source volume rather than an ideal point measurement. Here we consider, by a ray-tracing algorithm, the effects of this finite extent of the observed volume on the experimentally-determined diffusivity. Self-absorption effects are considered both for photon energies that have essentially no absorption in the sample (so that the entire thickness of the sample is effectively viewed) and for those that suffer sufficient self-absorption that the measured radiation comes from only a surface "skin-depth" (approximately 100 microm in extent). Collimation holes from approximately 1 to approximately 100% of the sample diameter are investigated. We find that neither the effects of self-absorption nor of the intrinsic three-dimensional geometry involved have a significant effect on the experimentally determined value of the diffusivity. In addition, linear concentration gradients along the diffusion axis do not influence the diffusivity measurement. A (quadratic) correction formula to determine the actual diffusion coefficient from the experimentally-obtained value is presented.

Journal Article↗

PubMed1982

Size dependence of the translational diffusion of large integral membrane proteins in liquid-crystalline phase lipid bilayers. A study using fluorescence recovery after photobleaching.

The translational diffusion of bovine rhodopsin, the Ca2+-activated adenosinetriphosphatase of rabbit muscle sarcoplasmic reticulum, and the acetylcholine receptor monomer of Torpedo marmorata has been examined at a high dilution (molar ratios of lipid/protein greater than or equal to 3000/1) in liquid-crystalline phase phospholipid bilayer membranes by using the fluorescence recovery after photobleaching technique. These integral membrane proteins having molecular weights of about 37 000 for rhodopsin, about 100 000 for the adenosinetriphosphatase, and about 250 000 for the acetylcholine receptor were reconstituted into membranes of dimyristoylphosphatidylcholine (rhodopsin and acetylcholine receptor), soybean lipids (acetylcholine receptor), and a total lipid extract of rabbit muscle sarcoplasmic reticulum (adenosinetriphosphatase). The translational diffusion coefficients of all the proteins at 310 K were found to be in the range (1-3) X 10(-8) cm2/s. In consideration of the sizes of the membrane-bound portions of these proteins, this result is in agreement with the weak dependence of the translational diffusion coefficient upon diffusing particle size predicted by continuum fluid hydrodynamic models for the diffusion in membranes [Saffman, P. G., & Delbrück, M. (1975) Proc. Natl. Acad. Sci. U.S.A. 72, 3111-3113]. Lipid diffusion was also examined in th same lipid bilayers with the fluorescent lipid derivative N-(7-nitro-2,1,3-benzoxadiazol-4-yl)dimyristoylphosphatidylethanolamine. The translational diffusion coefficient for this lipid derivative was found to be in the range (9-14) X 10(-8) cm2/s at 310 K. In consideration of the dimensions of the lipid molecule, this value for the lipid diffusion coefficient is in agreement with the continuum fluid hydrodynamic model only if a near-complete slip boundary condition is assumed at the bilayer midplane. Alternatively, kinetic diffusion models [Träuble, H., & Sackmann. E. (1972) J. Am. Chem. Soc. 94, 4499-4510] may have to be invoked to explain the lipid diffusion behavior.

Acetylcholine↗

PubMed2006

Diffusion of HDO in pure and acid-doped ice films.

In these experiments, a few bilayers of D(2)O were vapor-deposited on a pure crystalline H(2)O ice film or an ice film doped with a small amount of HCl. Upon deposition, H/D isotopic exchange quickly converted the D(2)O layer into an HDO-rich mixture layer. Infrared absorption spectroscopy followed the changes of the HDO from the initial HDO mixture layer to HDO isolated in the H(2)O ice film. This was possible because isolated HDO in H(2)O ice has a unique, sharp peak in the O-D stretch region that can be distinguished from the broad peak due to the initial HDO mixture layer. The absorbance of isolated HDO displayed first-order kinetics and was attributed to diffusion of HDO from the HDO-rich mixture layer into the underlying H(2)O ice film. While negligible diffusion was observed for pure ice films and for ice films with HCl concentrations up to 1 x 10(-4) mole fraction, diffusion of HDO occurred for higher concentrations of (2-20) x 10(-4) mole fraction HCl with a concentration-independent rate constant. The diffusion under these conditions followed Arrhenius behavior for T = 135-145 K yielding E(a) = 25 +/- 5 kJ/mol. The mechanism for the HDO diffusion involves either (i) molecular self-diffusion or (ii) long-range H/D diffusion by a series of multiple proton hop and orientational turn steps. While these spectroscopic results compare favorably with recent studies of molecular self-diffusion in low-temperature ice films, the diffusion results from all the ice film studies at low temperatures (ca. T < 170 K) differ from earlier bulk ice studies at higher temperatures (ca. T > 220 K). A comparison and discussion of the various diffusion studies are included in this report.

Journal Article↗

PubMed2004

Diffusion of molecules confined in semipenetrable nanoscale carriers probed by pulsed field gradient NMR.

Diffusion of three low-molecular-weight compounds cyclohexane (CX), benzene (BZ), and chloroform (CL) preferentially confined in the cores of nanoscale carriers was probed by pulsed field gradient (PFG) NMR methods. The carriers were monolayer micelles of sodium dodecyl sulfate (SDS), bilayer micelles of poly(hexyl methacrylate)-block-(acrylic acid) (M2), and trilayer micelles of poly(2-ethylhexyl methacrylate)-block-(methyl methacrylate)-block-(acrylic acid) (M3) in D(2)O at 300 K. Although the radius of the confinement space was 10(-)(8) m or lower, the course of the PFG signal attenuation in pulsed gradient spin-echo or stimulated echo experiments under varied diffusion time corresponds to apparently unrestricted diffusion, which is slowed down compared to that of the compound dissolved in D(2)O. Analysis using approximate relations reveals that the response of the system to PFG NMR consists of three independent components, namely (i) diffusion of the carrier as a whole, (ii) hindered escape of a confined molecule and its diffusion in the medium, and (iii) diffusion of the molecules dissolved in the medium. If process ii is fast enough, exchange of the compound between the carrier and the medium includes the influence of iii as a component of a monoexponential PFG decay; otherwise, two sets of signals are observed with different diffusion responses, or biexponential PFG is observed. According to the results of this study, the only barrier of the diffusion of the inspected compounds CX, BZ, and CL out of their confinement in the carriers SDS or M2 is a thermodynamic one, that is, the resistance of the saturated solution to accept surplus molecules of the solute. In a three-layer micelle M3, the additional polymer sheet around the confinement area forms an additional diffusion barrier for CX, however. The study shows that PFG NMR, though unable to observe directly restricted diffusion on the nanoscale, can be useful in studying systems designed, for example, for a controlled release of low-molecular-weight substances.

Journal Article↗

PubMed2004

Experimental evidence of distance-dependent diffusion coefficients of a globular protein observed in polymer aqueous solution forming a network structure on nanometer scale.

The distance dependence of the diffusion coefficient (DDDC) of a globular protein (cytochrome c) in aqueous hyaluronan (HA) solution, which is a model system for extracellular matrices (ECMs), was measured by a combination of three kinds of spectroscopic measurements of diffusion coefficients, the time and space samplings of which are different. The results of the three methods are plotted against the diffusion distance derived from the consideration of each experimental condition. Due to the characteristic morphology of HA with an effective mesh structure, the proteins showed two extreme diffusion modes: (1) short (<10 nm) diffusion with rare contact with polymer chains; (2) long (>100 nm) diffusion significantly disrupted by polymer chains showing an approximately 30% reduction in diffusion coefficient. The transition from the short diffusion to the long one occurs in a very narrow range (10-100 nm) of diffusion distance and this unique character of HA realizing anomalous diffusion should provide suitable environments for various bioactivities when involved in ECM.

Journal Article↗

PubMed2004

Self-diffusion in dense granular shear flows.

Diffusivity is a key quantity in describing velocity fluctuations in granular materials. These fluctuations are the basis of many thermodynamic and hydrodynamic models which aim to provide a statistical description of granular systems. We present experimental results on diffusivity in dense, granular shear flows in a two-dimensional Couette geometry. We find that self-diffusivities D are proportional to the local shear rate gamma; with diffusivities along the direction of the mean flow approximately twice as large as those in the perpendicular direction. The magnitude of the diffusivity is D approximately gamma;a(2), where a is the particle radius. However, the gradient in shear rate, coupling to the mean flow, and strong drag at the moving boundary lead to particle displacements that can appear subdiffusive or superdiffusive. In particular, diffusion appears to be superdiffusive along the mean flow direction due to Taylor dispersion effects and subdiffusive along the perpendicular direction due to the gradient in shear rate. The anisotropic force network leads to an additional anisotropy in the diffusivity that is a property of dense systems and has no obvious analog in rapid flows. Specifically, the diffusivity is suppressed along the direction of the strong force network. A simple random walk simulation reproduces the key features of the data, such as the apparent superdiffusive and subdiffusive behavior arising from the mean velocity field, confirming the underlying diffusive motion. The additional anisotropy is not observed in the simulation since the strong force network is not included. Examples of correlated motion, such as transient vortices, and Lévy flights are also observed. Although correlated motion creates velocity fields which are qualitatively different from collisional Brownian motion and can introduce nondiffusive effects, on average the system appears simply diffusive.

Journal Article↗

PubMed1998

Osteogenic sarcoma: noninvasive in vivo assessment of tumor necrosis with diffusion-weighted MR imaging.

PURPOSE: To evaluate diffusion-weighted magnetic resonance (MR) imaging for detecting tumor necrosis in an animal model of osteogenic sarcoma. MATERIALS AND METHODS: Twelve rats with osteogenic sarcoma underwent T1-weighted unenhanced and gadolinium-enhanced spin-echo and diffusion-weighted spin-echo MR imaging. Histologic correlation was performed. Signal intensities, T2 relaxation times, normalized apparent diffusion coefficients, and relative signal intensity increases were calculated. RESULTS: On diffusion-weighted images, necrotic tumor showed low signal intensity (mean normalized apparent diffusion coefficient, 0.46 +/- 0.20 [1 standard deviation]), indicating rapid diffusion of water molecules as a result of loss of membrane integrity, while viable tumor showed high signal intensity (mean normalized apparent diffusion coefficient, 0.16 +/- 0.05; P < .0001). Differences in the T2 relaxation times and relative signal intensity increases between viable and necrotic tumor were not statistically significant. CONCLUSION: Normalized apparent diffusion coefficients are more accurate in differentiating between viable and necrotic tumor than are T2 relaxation times or relative signal intensity increases on contrast-enhanced images. Signal intensity overlap between viable and necrotic tumor on gadolinium-enhanced images may be caused by the small molecular size of the agent, which permeates the interstitial space freely, thereby also enhancing necrosis. Diffusion-weighted MR imaging depicts differences in diffusion and, ultimately, in membrane integrity between viable and necrotic tumor and may be used to monitor tumor viability during treatment.

Animals↗

PubMed1999

Diffusion-weighted MR imaging: diagnostic accuracy in patients imaged within 6 hours of stroke symptom onset.

PURPOSE: To evaluate the diagnostic accuracy of diffusion-weighted magnetic resonance (MR) imaging performed within 6 hours of the onset of stroke symptoms. MATERIALS AND METHODS: The authors reviewed the patient records and images from all patients hospitalized in a 10-month period in whom diffusion-weighted imaging was performed within 6 hours of the onset of strokelike symptoms (n = 22). Analyses included comparison of the initial interpretation of the diffusion-weighted images with the final clinical diagnosis; blinded reviews of computed tomographic (CT) scans and conventional and diffusion-weighted images; and determination of lesion contrast-to-noise ratios (CNRs). RESULTS: Diffusion-weighted images indicated stroke in 14 patients, all of whom had a final diagnosis of acute stroke. Diffusion-weighted images were negative in eight patients, all of whom had a final clinical diagnosis other than stroke (100% sensitivity, 100% specificity, chi 2 = 23.00, P < .0001). Blinded reviews yielded 100% sensitivity and 86% specificity for diffusion-weighted MR imaging (chi 2 = 15.43, P < .0005); 18% sensitivity and 100% specificity for conventional MR imaging (chi 2 = 2.85, P > .2); and 45% sensitivity and 100% specificity for CT (chi 2 = 4.40, P > .10). Lesion percentage CNRs were 77% for diffusion-weighted imaging, 5.5% for CT, 9.8% for T2-weighted MR imaging, and 3.1% for proton-density-weighted MR imaging (P < .002 for diffusion-weighted imaging vs others). CONCLUSION: Diffusion-weighted MR imaging is highly accurate for diagnosing stroke within 6 hours of symptom onset and is superior to CT and conventional MR imaging.

Aged↗

PubMed1997

Absolute quantitation of diffusion constants in human stroke.

BACKGROUND AND PURPOSE: Animal studies have shown that MR diffusion imaging can outline acute ischemic regions before irreversible damage (infarction) occurs. To study evolution of ischemic lesions in humans, it is therefore important to quantify absolute diffusion constants (D values), but quantitation has not been reproducible among different clinics. These problems are explained, and a method for reproducible quantitation is suggested. METHODS: Diffusion-weighted and absolute diffusion images were acquired, and the absolute apparent diffusion constants in three orthogonal spatial directions (Dxx, Dyy, and Dzz) were measured. These were combined to calculate images of the orientation-independent apparent diffusion parameter Dav = 1/3 Trace[D] = 1/3(Dxx + Dyy + Dzz). Values of the individual diffusion constants and Dav were evaluated in 6 patients and 6 normal volunteers. RESULTS: Patient data show that comparison of diffusion constants between contralateral and ipsilateral hemispheres after ischemia may give results varying by more than 100% depending on orientation. Findings in normal-appearing regions containing a mixture of gray and white matter in patients (n = 5) and in normal volunteers (n = 6) show that Dav = (0.92+/-0.11) x 10(-3) mm2/s, with a small intersubject variation, whereas Dxx, Dyy, and Dzz vary strongly. Hemispheric ratios (ipsilateral/contralateral [I/C]) in these subjects were (I/C)Dav = 1.00+/-0.05, (I/C)Dxx = 1.02+/-0.15, (I/C)Dyy = 1.07+/-0.24, and (I/C)Dzz = 0.96+/-0.28. The individual subjects in this group all had an (I/C)Dav within 10% of unity, while the other three ratios showed intersubject variations as large as 100%. CONCLUSIONS: (I/C)Dav ratios are a reliable means to quantitate changes in absolute diffusion constants for the study of stroke evolution independent of tissue orientation, gradient orientation, and diffusion time. The use of these ratios will enable reproducible intersubject and interclinic quantitation.

Acute Disease↗

PubMed2004

Investigation of the diffusion processes in a self-processing acrylamide-based photopolymer system.

Results from the investigation of the diffusion processes in a dry acrylamide-based photopolymer system are presented. The investigation is carried out in the context of experimental research on optimization of the high-spatial-frequency response of the photopolymer. Tracing the transmission holographic grating dynamics at short times of exposure is utilized to measure diffusion coefficients. The results reveal that two different diffusion processes contribute with opposite sign to the refractive-index modulation responsible for the diffraction grating buildup. Monomer diffusion from dark to bright fringe areas increases the refractive-index modulation. It is characterized with diffusion constant D0 = 1.6 x 10(-7) cm2/s. A second diffusion process takes place during the recording. It decreases the refractive-index modulation and we ascribe it to diffusion of short-chain polymer molecules or radicals from bright to dark fringe areas. The estimated diffusion coefficient for this process is D0 = 6.35 x 10(-10) cm2/s. The presence of the second process could be responsible for the poor high-spatial-frequency response of the investigated photopolymer system. Comparison with the diffusion in photopolymer systems known for their good response at high spatial frequencies shows that both investigated diffusion processes occur in a much faster time scale.

Journal Article↗

PubMed2006

DNA diffusion in mucus: effect of size, topology of DNAs, and transfection reagents.

DNA represents a promising therapeutic and prophylactic macromolecule in treating genetic diseases, infectious diseases and cancers. The therapeutic potential of DNA is directly related to how DNA transports within the targeted tissue. In this study, fluorescence photobleaching recovery was used to examine the diffusion of plasmid DNAs with various size (2.7-8.3 kb), topology, and in the presence of transfection reagents in mucus. We observed that DNAs diffused slower when size of DNAs increased; supercoiled DNAs diffused faster than linear ones; mucus did not reduce the diffusion of linear DNAs but retarded the diffusion of supercoiled DNAs. Diffusion data were fitted to models of a polymer chain diffusing in gel systems. Diffusion of linear DNAs in mucus were better described by the Zimm model with a scaling factor of -0.8, and supercoiled DNAs showed a reptational behavior with a scaling factor of -1.3. Based on the Zimm model, the pore size of bovine mucus was estimated and agreed well with previous experimental data. In the presence of transfection reagents, e.g., liposomes, the diffusion of DNAs increased by a factor of 2 in mucus. By using bovine mucus as a model system, this work suggests that DNA size, topology, and the presence of transfection reagents may affect the diffusion of DNA in tissues, and thus the therapeutic effects of DNA.

Animals↗

PubMed1995

Restricted diffusion of an 19F-labelled organic acid in human erythrocytes analyzed by 19F pulsed field gradient NMR.

The diffusion coefficient of an 19F-labelled organic acid (3-trifluoromethylhippurate: TFMH) was measured in intact human red blood cells (RBCs) and sealed right-side-out ghosts at 22.5 +/- 0.05 degrees C. Diffusion coefficients were measured using stimulated echo and spin-echo pulsed field gradient sequences. The apparent diffusion coefficient (Da) of TFMH in the intracellular space was much smaller than in the extracellular medium. This was due to restricted diffusion of intracellular TFMH since i) the intracellular Da decreased when the diffusion time was increased, and ii) the smaller Da component disappeared when the membrane was permeabilized with saponin. From the intracellular Da values obtained over a range of diffusion times, from 5 ms to 1 s, the apparent radius of the diffusion barrier was estimated to be 3 +/- 1.1 micron assuming spherical geometry. Despite the high protein concentration in the intracellular space of the intact RBC, the intracellular values of Da were similar to the values obtained in the ghosts at the same diffusion times. We therefore conclude that the small diffusion coefficient of intracellular TFMH is mainly explained by the restricted diffusion due to the cell boundary.

Biological Transport↗

PubMed1999

A comparison of fast spin-echo, fluid-attenuated inversion-recovery, and diffusion-weighted MR imaging in the first 10 days after cerebral infarction.

BACKGROUND AND PURPOSE: Echo-planar diffusion-weighted and fluid-attenuated inversion-recovery (FLAIR) imaging have both proved valuable for detecting acute ischemic infarcts, but little is known about the value of diffusion-weighted imaging beyond the acute infarct period. Furthermore, no direct comparison of the techniques has been published. We compared the diagnostic utility of diffusion-weighted, FLAIR, and T2-weighted fast spin-echo (FSE) imaging for detecting cerebral infarctions up to 10 days old. METHODS: FSE, FLAIR, and diffusion-weighted MR sequences were obtained prospectively over a 6-month period in 212 patients with suspected cerebral infarctions. Seventy patients with nonhemorrhagic ischemic infarcts less than 10 days old whose symptoms lasted longer than 48 hours were identified. The three sequences were compared for detectability and conspicuity of abnormalities that correlated with the neurologic deficit. RESULTS: Seventy-two symptomatic infarcts were found in the 70 patients. Diffusion-weighted imaging detected 70 (97%), FLAIR, 69 (96%), and FSE, 64 (89%) of the 72 lesions. Only the difference between diffusion-weighted and FSE imaging approached statistical significance. There was no difference in the number of lesions detected in the patients imaged 48 hours or more after infarction. Lesion conspicuity on diffusion-weighted images was judged superior to that on FSE and FLAIR images in 55 (77%) and 47 (67%) of the cases, respectively. FLAIR images were judged superior to FSE in 34 (48%) of the cases. CONCLUSION: Diffusion-weighted images showed more infarcts than FLAIR and FSE images, and FLAIR images showed more than FSE images, but the differences were not statistically significant. Lesion conspicuity, however, was consistently better on diffusion-weighted images than on either FLAIR or FSE images throughout the 10-day period. Acquisition of diffusion-weighted images in the late acute and subacute periods after ischemic cerebral infarction appears to be beneficial.

Acute Disease↗