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PubMed2000

Diffusion magnetic resonance imaging: an early surrogate marker of therapeutic efficacy in brain tumors.

BACKGROUND: A surrogate marker for treatment response that can be observed earlier than comparison of sequential magnetic resonance imaging (MRI) scans, which depends on relatively slow changes in tumor volume, may improve survival of brain tumor patients by providing more time for secondary therapeutic interventions. Previous studies in animals with the use of diffusion MRI revealed rapid changes in tumor water diffusion values after successful therapeutic intervention. METHODS: The present study examined the sensitivity of diffusion MRI measurements in orthotopic rat brain tumors derived from implanted rat 9L glioma cells. The effectiveness of therapy for individual brain cancer patients was evaluated by measuring changes in tumor volume on neuroimaging studies conducted 6--8 weeks after the conclusion of a treatment cycle. RESULTS: Diffusion MRI could detect water diffusion changes in orthotopic 9L gliomas after doses of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU or carmustine) that resulted in as little as 0.2 log cell kill, a measure of tumor cell death. Mean apparent diffusion coefficients in tumors were found to be correlated with and highly sensitive to changes in tumor cellularity (r =.78; two-sided P =.041). The feasibility of serial diffusion MRI in the clinical management of primary brain tumor patients was also demonstrated. Increased diffusion values could be detected in human brain tumors shortly after treatment initiation. The magnitude of the diffusion changes corresponded with clinical outcome. CONCLUSIONS: These results suggest that diffusion MRI will provide an early surrogate marker for quantification of treatment response in patients with brain tumors.

Adolescent↗

PubMed2004

Enhanced macromolecular diffusion in brain extracellular space in mouse models of vasogenic edema measured by cortical surface photobleaching.

Diffusion of solutes and macromolecules in brain extracellular space (ECS) is important for normal brain function and efficient drug delivery, and is thought to be impaired in edematous brain. Here we measured the diffusion of an inert macromolecular fluorescent marker (FITC-dextran, 70 kDa) in the ECS by fluorescence recovery after photobleaching after staining the exposed cerebral cortex in vivo. In a brain tumor model of vasogenic (leaky capillary) edema, FITC-dextran diffusion was reduced more than fourfold in hypercellular tumor and surrounding astrogliotic tissue; however, diffusion in brain away from the tumor was approximately 30% faster than in normal contralateral brain. The increased diffusion was abolished by dexamethasone pretreatment. Enhanced ECS diffusion was also found in uninjured brain near a region of leaky brain vessels produced by focal cortical freeze injury. In contrast, ECS diffusion was slowed more than sixfold in cytotoxic brain edema caused by anoxia. Diffusion results were related semiquantitatively to ECS volume fraction and matrix viscosity from in vitro photobleaching studies in a model system consisting of silica particles in a fluorescent water/glycerol matrix. Our data provide in vivo evidence for enhanced ECS diffusion in vasogenic brain edema, yet greatly slowed diffusion in cytotoxic edema and in and around tumors.

Animals↗

PubMed1995

Diffusion and binding measurements within oral biofilms using fluorescence photobleaching recovery methods.

Numerous studies have postulated that bacteria which reside in a biofilm differ from planktonic bacteria. These differences are thought to affect biofilm permeability and, indirectly, the susceptibility of biofilm bacteria to antibacterial agents. In this study fluorescence recovery after photobleaching (FRAP) was used to monitor the diffusion and binding characteristics of a set of size fractionated fluorescein isothiocyanate (FTTC)-conjugated dextrans over small areas (ca. 10 micron) in bacterial biofilms. From these measurements it was straightforward to calculate apparent diffusion rates. Initial studies on the concentration dependence of dextran interaction with planktonic bacteria showed that no irreversible interaction was occurring, however, anomalous faster than free solution diffusion rates were obtained. This phenomenon was modelled using novel analytical and numerical methods which incorporate reversible binding with associated fluorescence changes. Apparent diffusion rates measured in biofilms were highly dependent on biofilm preparation. Sucrose starved biofilms produced an apparent slow-down of two- to fivefold depending on dextran molecular mass and location within the biofilm, indicating that diffusion within the biofilm is hindered. Sucrose supplemented biofilms produced apparent diffusion rates close to those in free solution, suggesting less hindered diffusion. Ex vivo plaque showed diffusion and binding similar to the sucrose supplemented biofilms. The FRAP approach provides a fast and convenient method for determining diffusion rates over small areas within bacterial biofilms. This study reinforces the importance of considering the influence of reversible binding and associated fluorescence changes, as these may have a marked effect on the measured apparent diffusion rate.

Bacteria↗

PubMed1987

Diffusion of [2-14C]diazepam across hairless mouse skin and human skin.

The objectives of this study were to investigate the absorption of diazepam applied topically to the hairless mouse in vivo and to determine the diffusion of diazepam across isolated hairless mouse skin and human skin. [14C]Diazepam was readily absorbed after topical administration to the intact hairless mouse, a total of 75.8% of the 14C-label applied being recovered in urine and feces. Diazepam was found to diffuse across human and hairless mouse skin unchanged in experiments with twin-chambered diffusion cells. The variation in diffusion rate or the flux for both human and mouse tissues was greater among specimens than between duplicate or triplicate trials for a single specimen. Fluxes for mouse skin (stratum corneum, epidermis, and dermis) were greater than for human skin (stratum corneum and epidermis): 0.35-0.61 microgram/cm2/h for mouse skin vs 0.24-0.42 microgram/cm2/h for human skin. The permeability coefficients for mouse skin ranged from 1.4-2.4 X 10(-2)cm/h compared with 0.8-1.4 X 10(-2)cm/h for human skin. Although human stratum corneum is almost twice the thickness of that of the hairless mouse, the diffusion coefficients for human skin were 3-12 times greater (0.76-3.31 X 10(-6) cm2/h for human skin vs 0.12-0.27 X 10(-6) cm2/h for hairless mouse) because of a shorter lag time for diffusion across human skin. These differences between the diffusion coefficients and diffusion rates (or permeability coefficients) suggest that the presence of the dermis may present some barrier properties. In vitro the dermis may require complete saturation before the diazepam can be detected in the receiving chamber. [14C]Diazepam was not detected in the receiving chamber of the Franz cell apparatus in experiments with human skin. This indicated that the rate of diffusion was less than 0.09 microgram/cm2/h. Since this diffusion technique more closely resembles topical administration to humans, these results appear to indicate that achieving therapeutic concentrations in humans may be difficult. In addition, the hairless mouse may not be a suitable model for predicting percutaneous absorption of diazepam in humans.

Absorption↗

PubMed2005

Scanning microradiographic study on the influence of diffusion in the external liquid on the rate of demineralization in hydroxyapatite aggregates.

Subsurface demineralization in enamel caries is known to entail diffusion of reagents and products both within the lesion and within the plaque biofilm external to the lesion. However, development of a predictive mathematical model for subsurface demineralization is hindered by limited quantitative understanding of the effects of these diffusion processes. The purpose of this quantitative study was to investigate and understand the effect of external diffusion length on the rate of demineralization in a simple model system. Ten, 500-microm thick sections cut from a porous hydroxyapatite (HAP) pellet were inserted in scanning microradiography (SMR) cells. The exposed thin edges of the sections were initially separated by columns of water (diffusion lengths) of 0-0.9 cm from a 1-l reservoir of demineralizing buffer (pH 4). Buffer was found to diffuse from the reservoir through the increasing diffusion lengths to the exposed HAP surface, whilst dissolved product diffused along the reverse path. Rates of HAP loss (from SMR measurements) decreased as the diffusion length increased. Experimental data were fitted to a general diffusion-reaction model. This showed that the solution near the HAP surface was almost completely saturated with HAP, and that the diffusion of dissolution products, rather than of buffer species, was rate limiting.

Acetic Acid↗

PubMed1982

The influence of gel formulation on the diffusion of salicylic acid in polyHEMA hydrogels.

The influence of solute concentration, gel hydration, and crosslinking density on diffusion rates in polyHEMA hydrogels has been investigated using a radio-tracer technique. At hydrations above 31% water, diffusion is by pore flow, and increases in the crosslinking density of gels bring about a decrease in the diffusion coefficient, D. Below 31% hydration, diffusion is predominantly by solution diffusion and changes in crosslinking density have little effect on the diffusion coefficient. The diffusion coefficient is invariant with solute concentration within the range reported, although a very high solute concentration, for the gels of lower hydration, the diffusion coefficient is higher than expected. A high value for D may be due to saturation of the binding sites of the diffusant on the polymer chains, leaving a greater proportion of diffusant available for transport.

Diffusion↗

PubMed2006

Acute ischemic stroke: accuracy of diffusion-weighted MR imaging--effects of b value and cerebrospinal fluid suppression.

PURPOSE: To prospectively determine which diffusion-weighted magnetic resonance (MR) imaging technique (ie, conventional diffusion-weighted MR imaging [b = 1000 or 1500 sec/mm2] or fluid-inversion prepared diffusion [FLIPD] MR imaging [b = 1500 sec/mm2]) is most accurate in depicting acute ischemic stroke at 3 T. MATERIALS AND METHODS: The Health Research Ethics Board approved this study; written informed consent was provided by all participants or their surrogate. Diffusion-weighted MR imaging was performed in 75 consecutive patients (43 men, 32 women; mean age, 64.0 years) with acute ischemic stroke. Two experienced neuroradiologists determined the presence of hyperacute stroke lesions at diffusion-weighted MR imaging by locating areas of hyperintensity that corresponded to regions with a decreased diffusion coefficient. These findings were used as the reference standard. Four raters who were blinded to patient history assessed all images and apparent diffusion coefficient maps for the presence of changes that were consistent with acute ischemic stroke. Accuracy, sensitivity, specificity, negative predictive value, positive predictive value, and inter- and intrarater reliability scores were calculated for each technique. RESULTS: Specificity, positive predictive value, and accuracy were not significantly different among the techniques. FLIPD MR images obtained with a b value of 1500 sec/mm2 had decreased sensitivity for acute ischemic stroke (mean, 61.8%; 95% confidence interval [CI]: 55.4%, 67.9%) compared with conventional diffusion-weighted MR images obtained with a b value of either 1000 sec/mm2 (mean, 82.5%; 95% CI: 77.1%, 87.0%) or 1500 sec/mm2 (mean, 84.5%; 95% CI: 79.3%, 88.9%). FLIPD MR images also had decreased negative predictive value (mean, 96.5%; 95% CI: 95.7%, 97.2%) compared with conventional diffusion-weighted MR images obtained with a b value of either 1000 sec/mm2 (mean, 98.4%; 95% CI: 97.8%, 98.8%) or 1500 sec/mm2 (mean, 98.6%; 95% CI: 98.1%, 99.0%). Intra- and interrater reliability scores were generally excellent for all three techniques. CONCLUSION: FLIPD MR images obtained with a b value of 1500 sec/mm2 are less suitable for the detection of acute ischemic stroke owing to a decreased sensitivity and negative predictive value. The performance of the two conventional diffusion-weighted MR imaging techniques (b = 1000 and 1500 sec/mm2) was equivalent.

Acute Disease↗

PubMed1994

Diffusion-weighted imaging differentiates ischemic tissue from traumatized tissue.

BACKGROUND AND PURPOSE: Diffusion-weighted magnetic resonance imaging (MRI) has been shown to be particularly effective in detecting early (0 to 4 hours) pathophysiological changes in localized brain regions after cerebral ischemia. The present study sought to establish whether diffusion-weighted MRI would be similarly effective in predicting outcome after traumatic brain injury. METHODS: Diffusion-weighted MRI images and T2-weighted MRI images were obtained over 4 hours after either moderate fluid percussion-induced traumatic brain injury or unilateral carotid ligation in rats. RESULTS: Diffusion-weighted MRI images of traumatic brain injury demonstrated focal regions of image hypointensity as early as 1 hour after trauma. The relative diffusion coefficient in these hypointense regions was significantly increased (P < .005) by 4 hours after trauma compared with the noninjured hemisphere, but only in the transverse plane in the x direction. In contrast, induction of diffuse, nonfocal ischemia by unilateral carotid ligation resulted in scattered regions of hyperintensity with a significant (P < .001) decrease in relative diffusion coefficient as early as 1 hour after ligation compared with the noninjured hemisphere. This decrease exhibited no directionality. CONCLUSIONS: We conclude that traumatic brain injury results in an increased water diffusion distance with the directionality indicative of bulk flow of extracellular fluid toward the lateral ventricles (vasogenic edema). In contrast, the decreased water diffusion distance with no apparent directionality observed in ischemia is most likely indicative of cytotoxic edema. Diffusion-weighted MRI therefore has the potential to differentiate cases of traumatic brain injury with no focal ischemia from those instances of traumatic brain injury in which focal ischemia is a complication.

Animals↗

PubMed1999

Clinical severity in CADASIL related to ultrastructural damage in white matter: in vivo study with diffusion tensor MRI.

BACKGROUND AND PURPOSE: CADASIL is a newly recognized cause of subcortical ischemic strokes that progressively leads to dementia associated with pseudobulbar palsy and severe motor disability. This deleterious progression and the severity of clinical presentation are widely variable among affected subjects. The exact role played by MRI white-matter abnormalities, a hallmark of the disease, in the severity of the clinical phenotype remains poorly understood. METHODS: To address this issue, we used diffusion tensor imaging (DTI), a new MRI technique highly sensitive to white-matter microstructural changes, in 16 symptomatic patients and 10 age-matched controls. Mean diffusivity and anisotropy of diffusion were measured within hyperintensities identified on T2-weighted images (T2WI) and outside these lesions on 4 slices at the level of centrum semiovale. RESULTS: We found a 60% increase of water mean diffusivity and a parallel loss of diffusion anisotropy in hyperintensities identified on T2WI. The same pattern of diffusion changes, but of lesser intensity, was found in the normal-appearing white matter on T2WI. Mean diffusivity in regions with increased signal on T2WI was higher in patients with severe clinical disability compared with those with no or mild deficit (1.33+/-0.11 versus 1.13+/-0.11 10(-3) mm(2)/s, P<0.01). Furthermore, diffusion measured within T2 hyperintensities correlated with both the Mini-Mental State Examination and Rankin scale scores. In patients with a severe clinical status, the increase of water diffusion in these regions exceeded 70% in comparison with values obtained in the normal white matter in control subjects. CONCLUSIONS: These results indicate that DTI is able to detect important ultrastructural changes in regions with increased signal on T2WI and within the normal-appearing white matter in CADASIL. The diffusion changes might be related to both neuronal loss and demyelination. The degree of the underlying ultrastructural alterations is related to the severity of the clinical status with a possible threshold level of white-matter damage above which severe neurological impairment may occur in this disease. DTI appears to be a promising technique for monitoring disease progression in CADASIL.

Adult↗

PubMed2006

A reaction-diffusion analysis of energetics in large muscle fibers secondarily evolved for aerobic locomotor function.

The muscles that power swimming in the blue crab, Callinectes sapidus, grow hypertrophically, such that in juvenile crabs the cell diameters are <60 microm, whereas fibers of the adult crabs often exceed 600 microm. Thus, as these animals grow, their muscle fibers greatly exceed the surface area to volume ratio and intracellular diffusion distance limits of most cells. Previous studies have shown that arginine phosphate (AP) recovery in the anaerobic (light) fibers, which demonstrate a fiber size dependence on anaerobic processes following contraction, is too slow to be restricted by intracellular metabolite diffusive flux, in spite of the fiber's large size. By contrast, the aerobic (dark) fibers have evolved an intricate network of intracellular subdivisions that maintain an effectively small ;metabolic diameter' throughout development. In the present study, we examined the impact of intracellular metabolite diffusive flux on the rate of post-contractile AP resynthesis in the dark muscle, which has a much higher aerobic capacity than the light muscle. AP recovery was measured for 60 min in adults and 15 min in juveniles following burst contractile activity in dark fibers, and a mathematical reaction-diffusion model was used to test whether the observed aerobic rates of AP resynthesis were fast enough to be limited by intracellular metabolite diffusion. Despite the short diffusion distances and high mitochondrial density, the AP recovery rates were relatively slow and we found no evidence of diffusion limitation. However, during simulation of steady-state contraction, which is an activity more typical of the dark fibers, there were substantial intracellular metabolite gradients, indicative of diffusion limitation. This suggests that high ATP turnover rates may lead to diffusion limitation in muscle even when diffusion distances are short, as in the subdivided dark fibers.

Adenosine Triphosphate↗

PubMed1998

Rapid modeling of diffuse reflectance of light in turbid slabs.

An efficient and accurate hybrid model of the Monte Carlo technique and the diffusion theory was developed to simulate the diffuse reflectance of light in a turbid slab due to an infinitely narrow light beam. The narrow beam was normally incident on the top surface of the slab. The hybrid model was accurate in modeling the diffuse reflectance near the light source, where the diffusion theory was most inaccurate. The hybrid model was much faster than a pure Monte Carlo method by a factor as great as several hundred, depending on the optical properties, the thickness of the slab, and the settings of the hybrid and the Monte Carlo computations. The computation speed of the hybrid model was insensitive to the optical properties of the medium, in contrast to the pure Monte Carlo technique. The diffusion theory was accurate in modeling both the diffuse reflectance far from the source and the diffuse transmittance. The hybrid model and the diffusion theory should be used in conjunction for efficient and accurate computation of diffuse reflectance and diffuse transmittance.

Diffusion↗

PubMed2004

Pulsed-field gradient-nuclear magnetic resonance (PFG NMR) to measure the diffusion of ions and polymers in cartilage: applications in joint diseases.

Since cartilage contains neither blood nor lymph vessels, diffusion is the most important transport process for the supply of cartilage with nutrients and for the removal of metabolic waste products. Therefore, diffusion measurements are of high interest in cartilage research. Different techniques of diffusion measurements exist. Here we describe methods based on pulsed-field gradient nuclear magnetic resonance (PFG NMR). This technique offers the considerable advantage that neither concentration gradients nor labeling of the diffusing species are required. In addition to the description of the fundamentals and the applicability of PFG NMR studies in cartilage research, emphasis is on the influence of the observation time, Delta, on the diffusion coefficient, D: at short times, diffusion is primarily determined by the water content of the sample, and great care is needed to keep this parameter constant. However, by varying the diffusion time, data on the internal structure of cartilage, e.g., the distance of the collagen fibrils, can also be obtained. In addition to classical water diffusion, the diffusion behavior of selected ions and polymers in cartilage is described. The capabilities, the limitations, and the clinical relevance of diffusion measurements for the assessment of joint diseases are discussed.

Animals↗

PubMed2004

Detection of non-Brownian diffusion in the cell membrane in single molecule tracking.

Molecules undergo non-Brownian diffusion in the plasma membrane, but the mechanism behind this anomalous diffusion is controversial. To characterize the anomalous diffusion in the complex system of the plasma membrane and to understand its underlying mechanism, single-molecule/particle methods that allow researchers to avoid ensemble averaging have turned out to be highly effective. However, the intrinsic problems of time-averaging (resolution) and the frequency of the observations have not been explored. These would not matter for the observations of simple Brownian particles, but they do strongly affect the observation of molecules undergoing anomalous diffusion. We examined these effects on the apparent motion of molecules undergoing simple, totally confined, or hop diffusion, using Monte Carlo simulations of particles undergoing short-term confined diffusion within a compartment and long-term hop diffusion between these compartments, explicitly including the effects of time-averaging during a single frame of the camera (exposure time) and the frequency of observations (frame rate). The intricate relationships of these time-related experimental parameters with the intrinsic diffusion parameters have been clarified, which indicated that by systematically varying the frame time and rate, the anomalous diffusion can be clearly detected and characterized. Based on these results, single-particle tracking of transferrin receptor in the plasma membrane of live PtK2 cells were carried out, varying the frame time between 0.025 and 33 ms (0.03-40 kHz), which revealed the hop diffusion of the receptor between 47-nm (average) compartments with an average residency time of 1.7 ms, with the aid of single fluorescent-molecule video imaging.

Animals↗

PubMed2005

Serial diffusion-weighted magnetic resonance imaging in cases of glioma: distinguishing tumor recurrence from postresection injury.

OBJECT: Diffusion-weighted magnetic resonance (MR) imaging is an invaluable tool in the diagnosis of acute stroke and other types of brain injury. Abnormalities in and around the resection cavity on diffusion-weighted imaging have been observed following surgery for infiltrating glioma. The purpose of this study was to investigate prospectively the incidence, time course, and ultimate outcome of these abnormalities. METHODS: Forty-four consecutive patients with newly diagnosed gliomas were prospectively observed using serial MR imaging including diffusion-weighted sequences. Clinical and surgical data were also collected. Immediately postoperatively neuroimaging identified 28 patients (64%) in whom areas of reduced diffusion appeared in or around the resection cavity (mean volume 8.2 +/- 1.5 cm3). Complete resolution of this reduced diffusion was demonstrated within 90 days in 24 patients (86%). On subsequent neuroimages these areas demonstrated Gd enhancement as early as postoperative Day 15 and as late as Day 198 and ultimately took on the appearance of encephalomalacia in 26 (93%) of 28 cases. Postoperative reduced diffusion was not predicted by the clinical or surgical parameters that were assessed. No clinical deficits were attributable to the reduced diffusion. CONCLUSIONS: An abnormality related to diffusion-weighted sequences on postoperative MR imaging can occur after resection of newly diagnosed gliomas. In this study the abnormality typically resolved and was replaced by contrast enhancement on follow-up imaging, ultimately demonstrating encephalomalacia on long-term follow up. Findings on neuroimaging during the period of enhancement could be confused with recurrent tumor and interpreted as early treatment failure. Based on the findings of this study the authors strongly suggest that the inclusion of diffusion-weighted sequences in postoperative MR imaging is essential, as is MR imaging immediately before radiation therapy to monitor disease progression. A new enhancement observed after glioma surgery should be interpreted in the context of the diffusion-weighted image obtained immediately postoperatively.

Adult↗

PubMed1998

Determination of pollutant diffusion coefficients in naturally formed biofilms using a single tube extractive membrane bioreactor.

A novel technique has been used to determine the effective diffusion coefficients for 1,1,2-trichloroethane (TCE), a nonreacting tracer, in biofilms growing on the external surface of a silicone rubber membrane tube during degradation of 1,2-dichloroethane (DCE) by Xanthobacter autotrophicus GJ10 and monochlorobenzene (MCB) by Pseudomonas JS150. Experiments were carried out in a single tube extractive membrane bioreactor (STEMB), whose configuration makes it possible to measure the transmembrane flux of substrates. A video imaging technique (VIT) was employed for in situ biofilm thickness measurement and recording. Diffusion coefficients of TCE in the biofilms and TCE mass transfer coefficients in the liquid films adjacent to the biofilms were determined simultaneously using a resistances-in-series diffusion model. It was found that the flux and overall mass transfer coefficient of TCE decrease with increasing biofilm thickness, showing the importance of biofilm diffusion on the mass transfer process. Similar fluxes were observed for the nonreacting tracer (TCE) and the reactive substrates (MCB or DCE), suggesting that membrane-attached biofilm systems can be rate controlled primarily by substrate diffusion. The TCE diffusion coefficient in the JS150 biofilm appeared to be dependent on biofilm thickness, decreasing markedly for biofilm thicknesses of >1 mm. The values of the TCE diffusion coefficients in the JS150 biofilms <1-mm thick are approximately twice those in water and fall to around 30% of the water value for biofilms >1-mm thick. The TCE diffusion coefficients in the GJ10 biofilms were apparently constant at about the water value. The change in the diffusion coefficient for the JS150 biofilms is attributed to the influence of eddy diffusion and convective flow on transport in the thinner (<1-mm thick) biofilms.

Biodegradation, Environmental↗

PubMed2003

Temporal evolution of diffusion after spontaneous supratentorial intracranial hemorrhage.

BACKGROUND AND PURPOSE: The evolution of apparent diffusion coefficient abnormalities during supratentorial intracranial hemorrhage in normal appearing brain tissue has not been described. Recent investigations using diffusion imaging have revealed increased apparent diffusion coefficient in perihematomal tissue. We report brain tissue abnormalities beyond the visibly abnormal region ipsilateral and contralateral to the hematoma. This preliminary effort should generate meaningful clinical prognostic indicators for moderate size hemorrhages in large scale studies. METHODS: Using the neurology patient encounter database at a tertiary care hospital, we retrospectively identified patients who presented with acute focal neurologic deficits, had CT scans of the head that confirmed spontaneous intracranial hemorrhage, and had a MR images obtained within the first 6 hr to 30 days postictus. The regions identified as targets of this investigation were the hemorrhage and surrounding T2 signal intensity abnormality and the visibly normal supratentorial cerebral tissue. RESULTS: Ninety-five patients were admitted during a period of 25 months. Fifteen patients met the criteria for the study. Elevated whole brain diffusion was shown as early as 6 hr after intracranial hemorrhage. This increase in diffusion was comparable in both hemispheres. Diffusion values in the lesion (hematoma plus T2 signal intensity abnormality) increased slowly with peak increases noted 2 to 3 days after the ictus. CONCLUSION: Diffuse early cerebral response occurs in normal appearing brain tissue both ipsilateral and contralateral to the visibly abnormal hematoma, manifested by increased apparent diffusion coefficient. This response is present before the local response is fully developed. Supratentorial intracranial hemorrhage results in an early diffuse brain response with increased apparent diffusion coefficient in normal appearing brain.

Adult↗

PubMed2004

Diffusion-weighted and conventional MR imaging findings of neuroaxonal dystrophy.

BACKGROUND AND PURPOSE: Neuroaxonal dystrophy is a rare progressive disorder of childhood characterized by mental deterioration and seizures. The diffusion-weighted and conventional MR imaging findings are reported for six cases. METHODS: Six patients aged 19 months to 9 years with proved neuroaxonal dystrophy (one with the infantile form, five juvenile forms) underwent imaging at 1.5 T. Echo-planar diffusion-weighted images were acquired with a trace imaging sequence in five patients and with a three-gradient protocol (4000/110) in one. Images obtained with a b value of 1000 s/mm2 and corresponding apparent diffusion coefficient (ADC) maps were studied. ADCs from lesion sites and normal regions (pons and temporal and occipital lobes) were evaluated. RESULTS: A hyperintense cerebellum (a characteristic of the disease) was evident on fluid-attenuated inversion recovery images in all cases. Four patients had associated cerebral changes. Diffusion-weighted images, especially ADC maps, showed an elevated diffusion pattern in the cerebellum in the five juvenile cases (normal images at b = 1000 s/mm2, ADCs of 1.30-2.60 x 10(-3) mm2/s). A restricted diffusion pattern was evident in the infantile case (hyperintensity at b = 1000 s/mm2, low ADCs of 0.44-0.55 x 10(-3) mm2/s). ADCs were normal in the pons and temporal and occipital lobes (0.64-1.00 x 10(-3) mm2/s). CONCLUSION: An elevated cerebellar diffusion pattern is a predominant feature of juvenile neuroaxonal dystrophy. Coexistent elevated and restricted diffusion patterns were evident in different brain regions in different forms of the disease. Dystrophic axons likely account the restricted diffusion, whereas spheroid formation (swelling) and abnormal myelination result in elevated diffusion.

Biopsy↗

PubMed1991

[The application of in vivo diffusion weighted magnetic resonance imaging to intracranial disorders].

We have developed a magnetic resonance (MR) spin echo method to obtain diffusion weighted imaging using motion-probing gradient (MPG) pulses in one or three orthogonal directions before and after a 180 degree pulse. Phantom models containing water and acetone, normal volunteers and patients with brain tumors, brain edema and infarction were examined. Experimental models of brain edema including triethyltin intoxication and cold injuries were also examined in Wistar rats. MRI was performed at a 1.0-T clinical machine or a 4.7-T experimental machine using spin echo pulse sequences with or without additional MPGs on one or three orthogonal axes. The one direction method was useful to define diffusion anisotropy of myelinated axonal fibers in white matter. Faster diffusion was detected in the white matter parallel to the direction of MPGs. On the other hand, slower diffusion was detected perpendicular to the direction of MPGs because the myelin sheath restricted water diffusion. The three orthogonal gradients method was useful to demonstrate the difference in the diffusion coefficients in various diseases due to its larger total gradient strength. The clear distinction between the cytotoxic edema, which revealed slower diffusion, and the vasogenic edema, which revealed faster diffusion, was demonstrated in the experimental models using diffusion weighted image. In the clinical cases, faster diffusion was demonstrated in the brain tumor and perifocal vasogenic edema, which was in agreement with the results in the experimental models of rats. Brain tumors such as low grade astrocytoma with microcysts and perifocal vasogenic edema have very wide extracellular space.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗