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At least 145 records · Page 8Linked to original sources
PubMed1995

In vivo MR determination of water diffusion coefficients and diffusion anisotropy: correlation with structural alteration in gliomas of the cerebral hemispheres.

PURPOSE: To determine whether a relationship exists between water diffusion coefficients or diffusion anisotropy and MR-defined regions of normal or abnormal brain parenchyma in patients with cerebral gliomas. METHODS: In 40 patients with cerebral gliomas, diffusion was characterized in a single column of interest using a motion-insensitive spin-echo sequence that was applied sequentially at two gradient strength settings in three orthogonal directions. Apparent diffusion coefficients (ADCs) were derived for the three orthogonal axes at 128 points along the column. An average ADC and an index of diffusion anisotropy (IDA = diffusion coefficientmax-min/diffusionmean) was than calculated for any of nine MR-determined regions of interest within the tumor or adjacent parenchyma. RESULTS: In cerebral edema, mean ADC (all ADCs as 10(-7) cm2/s) was 138 +/- 24 (versus 83 +/- 6 for normal white matter) with mean IDA of 0.26 +/- 0.14 (versus 0.45 +/- 0.17 for normal white matter). Solid enhancing central tumor mean ADC was 131 +/- 25 with mean IDA of 0.15 +/- 0.10. Solid enhancing tumor margin mean ADC was 131 +/- 25, with IDA of 0.25 +/- 0.20. Cyst or necrosis mean ADC was 235 +/- 35 with IDA of 0.07 +/- 0.04. CONCLUSION: In cerebral gliomas ADC and IDA determinations provide information not available from routine MR imaging. ADC and IDA determinations allow distinction between normal white matter, areas of necrosis or cyst formation, regions of edema, and solid enhancing tumor. ADCs can be quickly and reliably characterized within a motion-insensitive column of interest with standard MR hardware.

Adolescent↗
PubMedDate not supplied

Measurement of the apparent diffusion coefficient in intraductal mucin-producing tumor of the pancreas by diffusion-weighted echo-planar MR imaging.

BACKGROUND: We investigated whether diffusion-weighted echo-planar magnetic resonance (MR) imaging can help differentiate intraductal mucin-producing tumors of the pancreas from other cystic lesions. METHODS: Diffusion-weighted echo-planar MR imaging was performed in patients with mucin-producing tumors (n = 19), pseudocysts (n = 9), chronic pancreatitis with diffuse main pancreatic dilatation (n = 5), and serous cystadenomas (n = 2). Images were obtained with diffusion sensitizing gradients of 30, 300, and 900 s/mm2. The apparent diffusion coefficient (ADC) was calculated. RESULTS: The mean (+/- standard deviation) ADCs of mucin-producing tumors (2.8 x 10(-3) mm2/s +/- 1.0 x 10(-3)), pseudocysts (2.9 x 10(-3) mm2/s +/- 1.2 x 10(-3)), dilated main pancreatic duct in chronic pancreatitis (3.3 x 10(-3) mm2/s +/- 1.2 x 10(-3)), serous cystadenomas (2.9 x 10(-3) and 2.6 x 10(-3) mm2/s), and cerebrospinal fluid (3.5 x 10A(-3) mm2/s +/- 1.1 x 10(-3)) were not statistically different. CONCLUSION: It is difficult to differentiate between mucin-producing tumors and other cystic lesions by ADC measurements when using diffusion-weighted echo-planar MR imaging.

Adult↗
PubMed2006

Diffusion, cross-diffusion and competitive interaction.

The cross-diffusion competition systems were introduced by Shigesada et al. [J. Theor. Biol. 79, 83-99 (1979)] to describe the population pressure by other species. In this paper, introducing the densities of the active individuals and the less active ones, we show that the cross-diffusion competition system can be approximated by the reaction-diffusion system which only includes the linear diffusion. The linearized stability around the constant equilibrium solution is also studied, which implies that the cross-diffusion induced instability can be regarded as Turing's instability of the corresponding reaction-diffusion system.

Algorithms↗
PubMed2003

MR diffusion tensor imaging: recent advance and new techniques for diffusion tensor visualization.

Recently, diffusion tensor imaging is attracting the biomedical researchers for its application in depiction of fiber tracts based on diffusion anisotropy. In this paper, we briefly describe the basic theory of diffusion tensor MR imaging, the determination process of diffusion tensor, and the basic concepts of diffusion tensor visualization techniques. Several results of clinical application in our institute are also introduced. Finally, the limitations, advantages and disadvantages of the techniques are discussed for further application of diffusion tensor visualization.

Anisotropy↗
PubMed2005

Pair correlation functions and the self-diffusion coefficient of Lennard-Jones liquid in the modified free volume theory of diffusion.

In this paper, we apply the Matteoli-Mansoori empirical formula for the pair correlation function of simple fluids obeying the Lennard-Jones potential to calculate reduced self-diffusion coefficients on the basis of the modified free volume theory. The self-diffusion coefficient thus computed as functions of temperature and density is compared with the molecular dynamics simulation data and the self-diffusion coefficient obtained by the modified free volume theory implemented with the Monte Carlo simulation method for the pair correlation function. We show that the Matteoli-Mansoori empirical formula yields sufficiently accurate self-diffusion coefficients in the supercritical regime, provided that the minimum free volume activating diffusion is estimated with the classical turning point of binary collision at the mean relative kinetic energy 3k(B)T/2, where k(B) is the Boltzmann constant and T is the temperature. In the subcritical regime, the empirical formula yields qualitatively correct, but lower values for the self-diffusion coefficients compared with computer simulation values and those from the modified free volume theory implemented with the Monte Carlo simulations for the pair correlation function. However, with a slightly modified critical free volume, the results can be made quite acceptable.

Journal Article↗
PubMed2005

Self-diffusion and collective diffusion of charged colloids studied by dynamic light scattering.

A microemulsion of decane droplets stabilized by a nonionic surfactant film is progressively charged by substitution of a nonionic surfactant molecule by a cationic surfactant. We check that the microemulsion droplets remain identical within the explored range of volume fraction (0.02-0.18) and of the number of charges per droplet (0-40). We probe the dynamics of these microemulsions by dynamic light scattering. Despite the similar structures of the uncharged and charged microemulsions, the dynamics are very different. In the neutral microemulsion, the fluctuations of polarization relax, as is well-known, via the collective diffusion of the droplets. In the charged microemulsions, two modes of relaxation are observed. The fast one is ascribed classically to the collective diffusion of the charged droplets coupled to the diffusion of the counterions. The slow one has, to our knowledge, not been observed previously neither in similar microemulsions nor in charged spherical colloids. We show that the slow mode is also diffusive and suggest that its possible origin is the relaxation of local charge fluctuations via the local exchange of droplets bearing different numbers of charges. The diffusion coefficient associated with this mode is then the self-diffusion coefficient of the droplets.

Journal Article↗
PubMed2006

Diffusion of interacting Brownian particles: Jamming and anomalous diffusion.

The free self-diffusion of an assembly of interacting particles confined on a quasi-one-dimensional ring is investigated both numerically and analytically. The interparticle pairwise interaction can be either attractive or repulsive and the energy barrier opposing thermal hopping of two particles one past the other is finite. Thus, for sufficiently long times, self-diffusion becomes normal or conventional diffusion. However, depending on the particle density, subdiffusive transients with exponent 12 and suppression of normal diffusion are observed. Above a certain density threshold, a sudden drop to zero of the diffusion coefficient for attractive particles signals the transition to a jammed phase. Furthermore, a Gaussian cluster of attractive particles condenses, by shrinking in size, for densities larger than such density threshold; lower density clusters spread out, regardless of the interaction sign, through a diffusion mechanism that is anomalous at short times, and normal for sufficiently long times. These effects could be observed in systems with colloidal particles, vortices, electrons, among other interacting particle systems.

Journal Article↗
PubMed1999

Value of diffusion-weighted imaging and apparent diffusion coefficient in recent cerebral infarctions: a correlative study with contrast-enhanced T1-weighted imaging.

BACKGROUND AND PURPOSE: The clinical usefulness and the time course of diffusion-weighted imaging and apparent diffusion coefficient (ADC) in acute and subacute cerebral infarction have not yet been established, although it is known that contrast-enhanced T1-weighted spin-echo imaging can detect a subacute infarct. Our aim was to study which imaging technique is useful in detecting recent infarcts, and whether an increase in ADC or a decrease in signal intensity on diffusion-weighted images is correlated with enhancement on T1-weighted spin-echo images. METHODS: Forty-one infarctions with a duration of 9 hours to 27 days were studied in 29 patients. The ADC and signal intensity on diffusion-weighted images were compared with the contrast-enhancement ratio (CER) on T1-weighted spin-echo images (CER = signal intensity after contrast injection/signal intensity before contrast injection). RESULTS: ADC was linearly correlated with CER, and signal intensity on diffusion-weighted images was inversely correlated with CER. The correlation between ADC and age of the infarct in the subacute phase was weak. CONCLUSION: Diffusion-weighted and contrast-enhanced T1-weighted spin-echo images complement each other in detecting subacute infarcts. Neovascularization and disruption of the blood-brain barrier in infarcts can be important in increasing ADC in subacute infarcts.

Aged↗
PubMed2004

Diffusion-weighted MRI of spinal cord infarction--high resolution imaging and time course of diffusion abnormality.

Infarction is a rare cause of spinal cord dysfunction. Whereas diffusion-weighted (DW) MRI has been established as a highly sensitive technique for assessing acute cerebral ischemia, its role in spinal cord infarction remains to be determined. The purpose of this study is to present the signal characteristics of acute spinal cord ischemia using DWMRI within the first two days and after one week. MRI including DW imaging (DWI) was performed in three patients with acute spinal cord dysfunction 8, 12 and 30 hours after the onset of symptoms and repeated after one week in two patients. Two initial scans included EPI DW sequences in transverse and sagittal orientation. The remaining examinations were performed with an optimised high-spatial resolution DWI sequence in the transverse plane. The diagnosis of spinal cord ischemia was established by imaging, clinical history and CSF analysis. T2 signal abnormality and restricted diffusion was demonstrated in all initial examinations. Transverse DW sequences had the highest sensitivity. The spinal infarctions were mainly located in the centre of the spinal cord and the grey matter. Contrast enhancement was absent. After one week, the restricted diffusion had normalised (pseudo normalisation) whereas the T2 signal changes had become more prominent. Restricted diffusion in the course of spinal cord ischemic infarction can be demonstrated using DW-MRI. Whereas a diffusion abnormality can be found after few hours, it does not last for longer than one week. At this time, the establishment of the diagnosis has to rely mainly on T2-weighted images with additional post contrast T1-weighted images being useful.

Adult↗
PubMed2003

Metronidazole-induced encephalopathy and inferior olivary hypertrophy: lesion analysis with diffusion-weighted imaging and apparent diffusion coefficient maps.

BACKGROUND: Although several cases of metronidazole-induced encephalopathy have been reported, to our knowledge, there is no previous report of brain changes in anterior commissure, basal ganglia, cerebellar white matter, and inferior olivary nuclei on magnetic resonance images. The precise mechanisms of action of metronidazole-induced encephalopathy have not been determined. OBJECTIVES: To report a unique case of metronidazole-induced encephalopathy extensively involving multiple lesions and to determine the precise mechanism of action of metronidazole-induced encephalopathy. SETTING: University hospital. Patient A 74-year-old woman hospitalized with complaints of progressive dysarthria, dysphagia, and gait disturbance 3 months after the initiation of metronidazole therapy. Intervention Brain magnetic resonance imaging and discontinuation of metronidazole therapy. Main Outcome Measure We observed changes of multiple lesions found on magnetic resonance imaging and analyzed apparent diffusion coefficient map values. RESULTS: Initial fluid-attenuated inversion recovery brain magnetic resonance images showed high signal intensities in diffuse subcortical white matter, anterior commissure, splenium, basal ganglia, midbrain, cerebellar white matter, and bilateral inferior olivary nuclei. These lesions were resolved after discontinuation of metronidazole therapy. However, the lesions in the inferior olivary nuclei were not resolved; rather they became hypertrophic. Apparent diffusion coefficient map values in the symptom period decreased and were normalized after discontinuation of metronidazole therapy. CONCLUSIONS: We describe a patient with metronidazole-induced encephalopathy involving reversible lesions in the anterior commissure, basal ganglia, and cerebellar white matter, which have not been reported previously. We observed inferior olivary hypertrophy, believed to be the result of lesions in the midbrain and cerebellar white matter rather than the result of lesions induced by metronidazole therapy. By using diffusion-weighted imaging and apparent diffusion coefficient maps, we found that metronidazole-induced encephalopathy might be caused by cytotoxic edema.

Aged↗
PubMed1994

Water diffusion in the giant axon of the squid: implications for diffusion-weighted MRI of the nervous system.

To clarify the result that marked diffusional anisotropy had been found in nomyelinated nerve, and in completion of an evaluation of the role of all longitudinal axonal structures, we report NMR measurements of water diffusion in the giant axon of the squid, where diffusional anisotropy is determined by the neurofilamentary structure. The diffusion coefficients of water parallel and perpendicular to the long axis of the squid giant axon at 20 degrees C are (1.61 +/- 0.06) x 10(-5) cm2 s-1 and (1.33 +/- 0.09) x 10(-5) cm2 s-1, respectively, which yield an anisotropic diffusion ratio of 1.2 +/- 0.1. Water diffusion in the squid giant axon is therefore quite rapid and nearly isotropic, thus eliminating the possibility of a significant role for the longitudinally oriented neurofilaments in producing diffusional anisotropy within the axoplasm. In conjunction with our work on garfish nerves therefore, only membranes, either as numerous axonal membranes or as myelin (if present), remain to fulfill the role of the primary determinant of anisotropic water diffusion in nerve and in white matter.

Animals↗
PubMed1995

Measurement of water diffusion in hormone-treated rat uteri by diffusion-weighted magnetic resonance imaging.

In this study, apparent water diffusion coefficients in hormone-treated rat uteri were measured by diffusion-weighted NMR imaging. Four groups of ovariectomized, mature young rats were treated with estrogen, progesterone, estrogen plus progesterone, or saline (as control). It was found that water diffusion is anisotropic in the myometrium, but not in the endometrium, and that it depends on hormonal conditions in the endometrium, but not in the myometrium. The anisotropy of water diffusion can be exploited to improve image contrast among the various uterine tissue types. The hormonal response suggests that diffusion imaging of human uterus may be useful in detecting endometrial pathology.

Animals↗
PubMed2000

Non-steady-state O(2) diffusion in metmyoglobin solutions studied in a diffusion chamber.

In this study, we studied the "passive" diffusion through myoglobin solutions by determining the oxygen diffusion coefficient (DO(2)) and the oxygen permeability (permeability O(2)) of metmyoglobin (metMb) solutions (3-33 g. 100 mL(-1)) at 25 degrees C. These oxygen diffusion parameters were determined in a diffusion chamber using a non-steady-state method and were also determined of albumin solutions (4-32 g. 100 mL(-1)) and distilled water for comparison. From these parameters, the oxygen solubility (alphaO(2)) could be calculated, because alphaO(2) = permeabilityO(2)/DO(2). Both DO(2) and permeabilityO(2) decreased with increasing metMb and albumin concentration. The values of DO(2), permeabilityO(2) and alphaO(2) of both metMb solutions and albumin solutions were comparable with literature values of methemoglobin (metHb) and serum protein solutions. The values of the metMb solutions can be used in following studies of facilitated oxygen diffusion through myoglobin solutions.

Albumins↗
PubMed1990

Diffusion in immobilized-cell agar layers: influence of bacterial growth on the diffusivity of potassium chloride.

The diffusivity of potassium chloride in composite agar slab/microporous membrane structures loaded with various amounts of Escherichia coli whole cells was determined using both time-lag and steady-state methods. The diffusion coefficient of KCl decreased linearly with the logarithm of the immobilized-cell content. The effect exerted by bacterial growth inside the immobilization matrices on KCl diffusivity was then investigated. The diffusion coefficient of KCl obtained by time-lag analysis decreased during incubation of the immobilized-cell structures, whereas less consistent results arose from the steady-state method. An apparent doubling time for immobilized E. coli, increasing with the initial cell content of the gel, was obtained from the calibration relationship between KCl diffusivity and the number of organisms in agar.

Culture Media↗