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PubMed1997

SPLICE: sub-second diffusion-sensitive MR imaging using a modified fast spin-echo acquisition mode.

Recent human studies for measuring of the apparent diffusion coefficient in tissue by magnetic resonance imaging have been conducted by time-consuming standard spin-echo acquisition sequences and phase correction with navigator echoes. Diffusion-weighted echo-planar sequences have been shown to be rapid alternatives for brain imaging. Both methods show inherent disadvantages in applications on thoracic or abdominal sites. A new approach combining single-shot diffusion-weighted imaging with a modified fast spin-echo acquisition mode is reported here. The modification is necessary, because normal fast spin-echo acquisition requires a particular phase relation between the magnetization and the refocusing pulses. Unfortunately, this phase relation is not provided after diffusion sensitive preparation. Therefore, the split echo acquisition mode was developed and is shown to be insensitive to the phase of the magnetization. The advantages of both fast spin-echo acquisition and diffusion weighting can be combined in the SPLICE sequence (split aqcuisition of fast spin-echo signals for diffusion imaging). The applicability of the new technique is shown by series of sub-second diffusion-weighted images from different parts of the body.

Adult↗

PubMed1999

Ionic Diffusivity, Electrical Conductivity, Membrane and Thermoelectric Potentials in Colloids and Granular Porous Media: A Unified Model.

Ionic diffusivity, electrical conductivity, membrane and thermoelectric potentials in isotropic and homogeneous colloidal suspensions, and granular porous media saturated by a binary symmetric 1:1 electrolyte are four interrelated phenomena. The microstructure and the surface properties of the solid grains-water interface influence directly these properties. The ionic diffusivities (and the electrical conductivity, respectively) in colloids and porous media have contributions from diffusion (and electromigration, respectively) through the bulk solution occupying the pores, together with electromigration occurring at the grains-water interface in the electrical double layer. Surface diffusion in porous materials has no contribution from concentration gradients along the grains-water interface. Instead, surface diffusion is envisioned as a purely electromigration process due to the membrane potential. The tortuosities of the transport of anions and cations are equal to the bulk tortuosity of the pore space only at high ionic strength. As the ionic strength decreases, the dominant paths for transport of the ion corresponding to the counterion of the electrical double layer shift from the pore space to the solid grains-water interface. Because anions and cations do not move independently, the membrane potential created by the charge polarization alters the velocity of the anions and influences the mutual diffusivity coefficient of the salt in the porous material. An electric potential of thermal origin is also produced in nonisothermal conditions. The ionic contributions to the electrical conductivity are based on a differential effective medium approach. These ionic contributions to the electrical conductivity are used to derive the ionic diffusivities and the membrane and thermoelectric potentials. The influence of the temperature and the presence, in the pore space, of a second immiscible and nonwetting phase is also considered in this model. Porosity is shown to affect the membrane potential. Several predictions of the model are checked with success by comparing the model to a set of experimental data previously published. Copyright 1999 Academic Press.

Journal Article↗

PubMed2000

Determination of Bulk and Surface Diffusion Coefficients from Experimental Data for Thin Liquid Film Drainage.

This note presents a method for the determination of the surface diffusion coefficient and surface diffusion flux. The theoretical considerations are based on the Onsager linear theory for the definition of the surface diffusion flux and on the Einstein theorem for the definition of the surface diffusion parameter. In this interpretation the surface diffusion coefficient differs from the one commonly defined in the literature. It does not depend on the surfactant concentration and it is a function only of the type of surfactant and the liquid/liquid interface. The theoretical calculations indicate that the effect of the surface diffusion on the film drainage is stronger than that predicted by previous theoretical studies. The experimental data for thin liquid film drainage in the case of low surfactant concentration in the continuous phase could be used for the calculation of the bulk and surface diffusion coefficients. In the present study we utilized the experimental data for the drainage of nitrobenzene films stabilized by different concentrations of dodecanol. Copyright 2000 Academic Press.

Journal Article↗

PubMed2001

A PFG-NMR Study of Restricted Diffusion in Heterogeneous Polymer Particles.

The diffusion resistance to monomers during heterogeneous polymerization of polyolefin particles may have a significant effect on the observed activity. This diffusivity is, in general, unknown. To gain more information on this diffusion resistance in such systems, PFG-NMR has been used to measure the diffusion of organic solvents in various systems of porous polymer particles. In such systems the complex morphology and geometry demands careful analysis of the PFG-NMR attenuation curve. In this study, effects from restricted diffusion, domains having different diffusivity, and internal magnetic field gradients are expected. Thus, the obtained diffusivities have to be considered carefully, and a way to analyze the data taking these effects into account is presented. Copyright 2001 Academic Press.

Journal Article↗

PubMed1994

Evaluation of restricted diffusion in cylinders. Phosphocreatine in rabbit leg muscle.

Interpretation of NMR diffusion data is complicated in the presence of diffusion barriers. In this study, restricted diffusion in cylinders is evaluated. A method is presented to determine the diameter of the cylinder and the unrestricted diffusion coefficient from the dependence of the trace of the diffusion tensor with diffusion time. This method is valid even if the orientation of the cylinders is unknown and varies within the sample. An example is given for the diffusion of phosphocreatine in the cylindrically shaped fibers of rabbit skeletal muscle.

Animals↗

PubMed1996

Possible Systematic Errors in Single-Shot Measurements of the Trace of the Diffusion Tensor

There have been recent proposals of diffusion-weighting pulse sequences that purport to measure the trace of the diffusion tensor, or to weight an image by that rotationally invariant quantity. Here the effect of a time-dependent diffusion tensor on such sequences is investigated theoretically. It is found that the time dependence of the diffusion tensor both breaks the rotational invariance of the pulse sequence and affects the overall magnitude of the diffusion weighting. These deviations are calculated for two pulse sequences, with parameters relevant to experiments on brain tissue. The departure from rotational invariance is found to be surprisingly small: <1%, for reasonable parameters and approximately5% for the most extreme choice of parameters. The overall magnitude of the diffusion weighting, however, may be significantly altered; 10% is estimated for reasonable parameters. It is proposed that this effect should prove a sensitive probe of time dependence in the diffusion tensor.

Journal Article↗

PubMed1999

Invariant and orthonormal scalar measures derived from magnetic resonance diffusion tensor imaging

A diffusion tensor is a mathematical construct used to describe water diffusion in complicated biological structures. It describes a process which occurs in all directions simultaneously. It is difficult to comprehend or graphically display the information in the diffusion tensor. This paper describes a coordinate system approach for producing scalar measures which characterize key aspects of the diffusion tensor. The eigenvalues of the diffusion tensor are introduced as the three elements of a point in a Cartesian coordinate system. The Cartesian coordinates are then expressed in cylindrical and spherical coordinates. The orthonormal coordinates of the spherical system are particularly useful scalar measures of attributes of the diffusion tensor: One coordinate contains all the information about the overall magnitude of diffusion. Another contains all of the anisotropy information. The third coordinate contains all of the information about skewness. No information is lost when transforming the original eigenvalues to spherical coordinates. Copyright 1999 Academic Press.

Journal Article↗

PubMed2001

Diffusion and relaxation effects in general stray field NMR experiments.

We analyze the evolution of magnetization following any series of radiofrequency pulses in strongly inhomogeneous fields, with particular attention to diffusion and relaxation effects. When the inhomogeneity of the static magnetic field approaches or exceeds the strength of the RF field, the magnetization has contributions from different coherence pathways. The diffusion or relaxation induced decay of the signal amplitude is in general nonexponential, even if the sample has single relaxation times T(1), T(2) and a single diffusion coefficient D. In addition, the shape of the echo depends on diffusion and relaxation. It is possible to separate contributions from different coherence pathways by phase cycling of the RF pulses. The general analysis is tested on stray field measurements using two different pulse sequences. We find excellent agreement between measurements and calculations. The inversion recovery sequence is used to study the relaxation effects. We demonstrate two different approaches of data analysis to extract the relaxation time T(1). Finite pulse width effects on the timing of the echo formation are also studied. Diffusion effects are analyzed using the Carr--Purcell--Meiboom--Gill sequence. In a stray field of a constant gradient g, we find that unrestricted diffusion leads to nonexponential signal decay versus echo number N, but within experimental error the diffusion attenuation is still only a function of g(2)Dt(3)(E)N, where t(E) is the echo spacing.

Journal Article↗

PubMed1988

Diffuse type of senile plaques in the brains of Alzheimer-type dementia.

We studied the nature of diffuse type of senile plaques (SP) in the brains of six autopsied subjects with Alzheimer-type dementia (ATD). The densities of SP in the entorhinal cortex were evaluated using serial sections stained by four different methods. Compared with beta protein immunostaining (100% as a reference), the modified Bielschowsky stain (103%) and the periodic acid-methenamine silver (PAM) stain (109%) labeled similar numbers of SP, whereas the Bodian stain labeled only a minor proportion (42%) of these. The vast majority of Bodian-negative plaques were diffuse plaques, which were seen as ill-defined areas of fine fibrillar material after beta protein immunostain with formic acid pretreatment, modified Bielschowsky stain, and PAM stain. They were not stained by Congo red or periodic acid-Schiff stains. Double staining using Bodian and beta protein methods demonstrated that diffuse plaques were free of swollen neurites. Argyrophilia of the diffuse plaques shown by the modified Bielschowsky and PAM stains, became undetectable when sections were pretreated with formic acid. Such treatment made the diffuse plaques immunoreactive to beta protein antiserum, suggesting that diffuse plaques consisted mainly of amyloid, but not neuritic components. The diffuse plaques were distributed in various cortical areas and in the amygdala, and comprised a considerable population of the SP in the ATD brains.

Aged↗

PubMed1989

Diffuse Lewy body disease: light and electron microscopic immunocytochemistry of senile plaques.

The nature of senile plaques (SP) in 27 cases of diffuse Lewy body disease (LBD) was investigated using immunocytochemistry and antibodies to beta amyloid protein synthetic peptides (BetaSP), ubiquitin (UBQ), paired helical filaments (PHF; Ab39) and a 68-kDa protein in Alzheimer brains (Alz50). Lewy bodies were present in widespread areas of the neocortex of all cases and were more easily detected with ubiquitin immunocytochemistry than with conventional stains. All cases had neocortical SP, but only six cases had neocortical neurofibrillary tangles (NFT). SP were very numerous in most cases and were usually "pale", "diffuse" or "very primitive" plaques with thioflavin S fluorescent microscopy. SP in diffuse LBD were immunostained with BetaSP. Several cases had extensive amyloid angiopathy that was also immunoreactive with BetaSP. SP in diffuse LBD were characterized by amyloid deposits with few or no neuritic elements that could be detected with thioflavin S, Bielschowsky's stain or double staining with BetaSP and Bodian's silver stain. They differed from plaques in Alzheimer's disease by lack of PHF-type neurites that could be stained with Ab39. In diffuse LBD, SP contained PHF-type neurites only in areas coexistent with NFT. Some SP had round, granular neurites that were immunoreactive with UBQ, but weakly argyrophilic with Bodian's stain and nonfluorescent with thioflavin S. Diffuse LBD lacked significant neuritic change in the neuropil that could be detected with UBQ, Ab39 and Alz50. The latter finding is a characteristic feature that distinguishes Alzheimer's disease from diffuse LBD.

Aged↗

PubMed1984

Ultrastructural aspects of the histogenesis of diffuse and localized mesothelioma.

During an ultrastructural review of 30 diffuse and 10 localized mesotheliomas, it was apparent that some micrographs showed various stages in the developmental processes involved in the formation of histological patterns in diffuse mesotheliomas and a histogenetic link between diffuse and localized mesotheliomas. Cells in the stromal or sarcomatous regions of diffuse mesothelioma often show varying degrees of mesothelial differentiation and a gradual transition to cells with typical mesothelial characteristics that organize into structures recapitulating the surface layer of serosal membranes. Tumor cells in localized mesotheliomas had many similarities to the "stromal" cells in the diffuse counterpart including intercellular junctions, rare microvilli and occasional foci of basal lamina. It is postulated that diffuse and localized mesotheliomas share a common histogenetic origin as a result of neoplastic induction of specialized submesothelial cells. In this concept, tumor cells in diffuse mesotheliomas reflect stages in the differentiation and organization of normal serosal membranes and localized mesotheliomas mirror the earliest phases of this process.

Humans↗

PubMed2001

Echo planar magnetic resonance imaging of anisotropic diffusion in asparagus stems.

MR diffusion-weighted imaging (DWI) uses the signal loss associated with the random thermal motion of water molecules in the presence of magnetic field gradients to derive a number of parameters that reflect the translational mobility of the water molecules in tissues. In highly organized but asymmetric structures, this mobility may be affected by the obstacles present and this in a direction-dependent way. Important examples of this are white brain matter and the stem of certain plants, both containing fibrous components where diffusion of water molecules across fibers is much more restricted than along the fibers. Diffusion that exhibits such directional dependence is said to be anisotropic, and diffusion tensor magnetic resonance imaging allows localized characterization of this behavior. Interpretation of the information obtained in terms of the underlying tissue structure is often hampered by the complexity of factors that can produce the observed behavior. A phantom that exhibits well-defined anisotropic diffusion and yields sufficient signal can help the experimental testing of the relevant methods and models. In this paper, we have used a phantom consisting of asparagus stems as a test object for assessing the value of the acquisition and postprocessing techniques commonly used in the clinic for this kind of investigation. Because of its strongly fibrous and cylindrically symmetric morphology, exhibiting a well-defined sub-classification of cells on the basis of size and shape, asparagus allows a relatively simple interpretation of the results obtained in the diffusion experiments. Our experiments show that the known structural information about the main cell types encountered correlates well with the behavior patterns of the diffusion parameters.

Algorithms↗

PubMed1997

Cerebral perfusion changes in traumatic diffuse brain injury; IMP SPECT studies.

Diffuse brain injury (DBI) is characterized by axonal degeneration and neuronal damage which cause diffuse brain atrophy. We have investigated the time course of abnormalities in cerebral perfusion distribution in cases of DBI by using Iodine-123-IMP SPECT, and the relationship to the appearance of diffuse brain atrophy. SPECT scans were performed on eight patients with diffuse brain injury due to closed cranial trauma in acute and chronic stages. All patients showed abnormalities in cerebral perfusion with decreases in perfusion, even in non-depicted regions on MRI, and the affected areas varied throughout the period of observation. Diffuse brain atrophy appeared in all patients. In some patients, diffuse brain atrophy was observed at or just after the time when the maximum number of lesions on SPECT were seen. The abnormalities in cerebral perfusion in cases of DBI might therefore be related to axonal degeneration and neuronal damage which causes diffuse brain atrophy.

Adolescent↗

PubMed2001

Diffusion-weighted imaging of the brain: comparison of stimulated- and spin-echo echo-planar sequences.

We used a rat model of focal cerebral ischaemia to compare stimulated-echo (STE) and spin-echo (SE) echo planar (EPI) diffusion-weighted sequences as regards image quality and accuracy of calculation of apparent diffusion coefficients (ADC). Focal cerebral ischaemia was induced by endovascular occlusion of the middle cerebral artery in five rats. MRI was performed on a 2.35 tesla imager. For diffusion-weighted imaging (DWI) we used STE-EPI and SE-EPI with different diffusion times (delta) of 15, 30, 45, 60, 75 and 90 ms using values of b of 200, 300, 400, 500, 600 and 700 s/mm2. We assessed image quality, the signal-to-noise-ratio (SNR) and the accuracy of the ADC calculated from both sequences. Infarcts were delineated in all cases, independent of sequence type and delta. The image quality and SNR of the SE-EPI images were significantly better, with a higher SNR than STE-EPI images for short and intermediate values of delta. However, when delta reached 75 ms STE-EPI became superior to SE-EPI. ADC calculated from STE-EPI images were smaller than those from SE-EPI images for short and intermediate diffusion times, possibly because of the lower SNR of the former. We suggest that SE-EPI sequences be used for DWI of the brain, particularly on experimental systems and whole-body imagers with enhanced gradient hardware, where it is possible to run highly diffusion-weighted sequences (b > 500 s/mm2) with delta less than 50 ms. However, when using very long values of delta because of hardware restrictions or for measurement of restricted diffusion, STE sequences give better results.

Animals↗

PubMed2001

Tuberous sclerosis: diffusion MRI findings in the brain.

Diffusion MRI has mainly been used for detection of acute ischemia, and for distinction of cytotoxic and vasogenic edema. We applied diffusion MRI in patients with tuberous sclerosis in order to evaluate diffusion imaging characteristics of parenchymal changes. Five children with known tuberous sclerosis were included in this study. The MRI examinations were performed on a 1.5-T MR unit. Diffusion MRI was obtained using the echo-planar imaging sequence. Apparent diffusion coefficient (ADC) values from the abnormal brain parenchyma were calculated directly from automatically generated ADC maps. Seven normal children were available for comparison. In this control group the mean ADC value of the normal white matter was 0.84 +/- 0.12 x 10(-3) mm(2)/s. In tuberous sclerosis patients the mean ADC value of the white matter hamartomas ( n=20) was apparently high (1.52 +/- 0.24 x 10(-3) mm(2)/s) compared with that of normal white matter. The ADC value of calcified hamartomas was "zero". The ADC value within a giant cell tumor was 0.89 x 10(-3) mm(2)/s, similar to that of normal cerebral white matter. The ADC maps were superior to b=1000 s/mm(2) (true diffusion) images with respect to lesion evaluation, and they provided mathematical information on tissue integrity. With respect to detection of the exact numbers and sizes of the parenchymal hamartomas fluid-attenuated inversion recovery images were superior to ADC maps. It is believed that diffusion MRI can be useful in evaluation of various parenchymal changes associated with tuberous sclerosis. Further studies on tuberous sclerosis, and on various brain lesions, would provide increasing data on this relatively new MRI sequence.

Brain↗

PubMed2001

Diffuse (or multinodular) follicular variant of papillary thyroid carcinoma: a clinicopathologic and immunohistochemical analysis of ten cases of an aggressive form of differentiated thyroid carcinoma.

In an attempt to advance and improve the characterization of the so-called diffuse follicular variant of papillary thyroid carcinoma (diffuse FVPTC) we studied a series of 59 thyroid carcinomas consecutively treated in a specialized center. The clinicopathologic and some of the immunohistochemical characteristics (uPA-R, Lewis X, Sialyl Lewis X, and MIB-1) of ten cases of FVPTC displaying a multinodular or diffuse pattern of growth, and histologic features similar to those previously described in diffuse FVPTC, were compared with those of common papillary thyroid carcinoma (PTC, 25 cases) and common FVPTC (8 cases). Cases of diffuse FVPTC differed significantly from common PTC and FVPTC in targeting younger patients and in exhibiting a prevalence of multicentricity, extrathyroid extension, nodal metastasis, and vascular invasion. Immunohistochemically, diffuse FVPTC cases were characterized by the overexpression of uPAR and sialyl Lewis X. No differences were observed regarding MIB 1 immunoreactivity. Regardless of the term used to designate the multicentric, invasive form of FVPTC (diffuse or multinodular FVPTC) it is crucial to acknowledge the existence of cases of FVPTC with a guarded prognosis that should be distinguished from the classic, uninodular form of FVPTC.

Adult↗

PubMed2002

Strictureplasty in diffuse Crohn's jejunoileitis: safe and durable.

PURPOSE: As an alternative to resection, strictureplasty may allow for preservation of intestinal length and avoidance of short-bowel syndrome in patients with diffuse Crohn's jejunoileitis. However, the long-term durability of the procedure and its safety have not been confirmed. The purpose of this study was to report our experience with strictureplasty for diffuse Crohn's jejunoileitis. METHODS: Between 1984 and 1999, 123 patients underwent a laparotomy that included an index strictureplasty for diffuse jejunoileitis. Patient history, operative details, and postoperative morbidities were obtained by chart review. Nineteen patients (15 percent) were receiving total parenteral nutrition for short-bowel syndrome, and 81 (66 percent) were taking chronic steroids. Total number of strictureplasties performed was 701 (median, 5/patient). Seventy percent of patients underwent a synchronous bowel resection. Follow-up information was determined by personal or phone interviews. Recurrence was defined as the need for reoperation, and risk was calculated by the Kaplan-Meier method. Patients with diffuse jejunoileitis were also compared with 219 patients with limited small-bowel Crohn's disease undergoing strictureplasty. RESULTS: The overall morbidity rate was 20 percent, with septic complications occurring in 6 percent. The surgical recurrence rate was 29 percent with a median follow-up period of 6.7 (range, 1-16) years. The recurrence rate in diffuse jejunoileitis patients did not differ from that seen in patients with limited small-bowel Crohn's disease (P = 0.38). Short duration of disease and short interval since last surgery were significant predictors of accelerated recurrence (P = 0.008 and 0.04, respectively). CONCLUSIONS: Strictureplasty is a safe and durable alternative to resection in diffuse Crohn's jejunoileitis. Patients with a short duration of disease and short interval since last surgery are at higher risk for accelerated recurrence. Patients with diffuse jejunoileitis do not appear to be at higher risk for recurrence than patients with more limited Crohn's disease.

Adolescent↗

PubMed1984

Myocardial function and perfusion in the CREST syndrome variant of progressive systemic sclerosis. Exercise radionuclide evaluation and comparison with diffuse scleroderma.

Myocardial function and perfusion were evaluated in 22 patients with progressive systemic sclerosis with the CREST syndrome using exercise and radionuclide techniques, pulmonary function testing, and chest roentgenography. The results were compared with a similar study of 26 patients with progressive systemic sclerosis with diffuse scleroderma. The prevalence of thallium perfusion abnormalities was similar in the groups with CREST syndrome and diffuse scleroderma, (64 percent versus 77 percent), but the defects were significantly smaller in the CREST syndrome (p less than 0.01). Reperfusion thallium defects in the absence of extramural coronary artery disease were seen in 38 percent of patients with diffuse scleroderma. This finding was not seen in any of the patients with the CREST syndrome. In diffuse scleroderma, abnormalities of both right and left ventricular function were related to larger thallium perfusion defects. In the CREST syndrome, abnormalities of left ventricular function were minor, were seen only during exercise, and were unrelated to thallium perfusion defects. Abnormal resting right ventricular function was seen in 36 percent of the patients with the CREST syndrome and was associated with an isolated decrease in diffusing capacity of carbon monoxide. It is concluded that the cardiac manifestations of the CREST syndrome are distinct from those found in diffuse scleroderma. Unlike diffuse scleroderma, abnormalities of left ventricular function in the CREST syndrome are minor and are unrelated to abnormalities of coronary perfusion. Right ventricular dysfunction in the CREST syndrome appears to be primarily related to pulmonary vascular disease.

Adult↗