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PubMed2006

Diffusion tensor magnetic resonance imaging at 3.0 tesla shows subtle cerebral grey matter abnormalities in patients with migraine.

BACKGROUND AND OBJECTIVE: Diffusion tensor (DT) magnetic resonance imaging (MRI) has the potential to disclose subtle abnormalities in the brain of migraine patients. This ability may be increased by the use of high field magnets. A DT MRI on a 3.0 tesla scanner was used to measure the extent of tissue damage of the brain normal appearing white (NAWM) and grey matter in migraine patients with T2 visible abnormalities. METHODS: Dual echo, T1 weighted and DT MRI with diffusion gradients applied in 32 non-collinear directions were acquired from 16 patients with migraine and 15 sex and age matched controls. Lesion load on T2 weighted images was measured using a local thresholding segmentation technique, and brain atrophy assessed on T1 weighted images using SIENAx. Mean diffusivity and fractional anisotropy histograms of the NAWM and mean diffusivity histograms of the grey matter were also derived. RESULTS: Brain atrophy did not differ between controls and patients. Compared with healthy subjects, migraine patients had significantly reduced mean diffusivity histogram peak height of the grey matter (p=0.04). No diffusion changes were detected in patients' NAWM. In migraine patients, no correlation was found between T2 weighted lesion load and brain DT histogram derived metrics, whereas age was significantly correlated with grey matter mean diffusivity histogram peak height (p=0.05, r=-0.52). CONCLUSIONS: DT MRI at high field strength discloses subtle grey matter damage in migraine patients, which might be associated with cognitive changes in these patients.

Adult↗
PubMed2005

Blood-brain barrier alterations in both focal and diffuse abnormalities on postmortem MRI in multiple sclerosis.

Postmortem MRI-guided tissue sampling significantly enhances the yield of MS lesions in autopsy material, but so far it is unknown whether abnormalities concur with blood-brain barrier alterations. Here we sampled MS lesions with focal and diffuse abnormalities (diffusely abnormal white matter; DAWM) on MRI; both were coupled to the presence of MS lesions upon neuropathological examination. Extravascular distribution of fibrinogen, indicating BBB disturbance, was observed in so-called (p)reactive lesions that reflect discrete areas of microglial activation without demyelination within an otherwise normal appearing white matter. Leakage became more extensive in active demyelinating MS lesions to chronic inactive lesions. An enlargement of the perivascular (Virchow-Robin) space containing infiltrated leukocytes was associated with both DAWM and focal abnormalities on postmortem MRI. This study shows for the first time that in MS brain changes in the vasculature take place not only in focal lesions but also in DAWM as detected by postmortem MRI.

Aged↗
PubMedDate not supplied

Diffusion and magnetization transfer MRI of brain infarct, infection, and tumor in children.

The purpose of this study was to determine the efficacy of diffusion-weighted imaging (DWI) and magnetization transfer imaging (MTI) in the differential diagnosis of brain infarct, infection, hamartoma, and tumor in 106 children. The apparent diffusion coefficients (ADCs) and magnetization transfer ratios (MTRs) of the lesions were compared using nonparametric tests. There was an inverse relationship between ADC and MTR in subacute/chronic infarct, infection, hamartoma, arachnoid cyst, and tumor relative to normal brain parenchyma. Both ADC and MTR were reduced in acute infarct. DWI and MTI had a complementary role in the differential diagnosis of acute infarct from infection with lower MTR, from hamartoma with higher ADC, and from low-grade gliomas and benign tumors that had higher ADCs and lower MTRs. ADCs increased and MTRs decreased with the duration of infarct and lower tumor grade.

Adolescent↗
PubMed2005

Chronic cholinergic imbalances promote brain diffusion and transport abnormalities.

Cholinergic imbalances occur after traumatic effects and in the initial stages of neurodegenerative diseases, but their long-lasting effects remained largely unexplained. To address this, we used TgS transgenic mice constitutively overexpressing synaptic acetylcholinesterase (AChE-S) and presenting a complex phenotype of progressive neurodeterioration. T1- and T2-weighted magnetic resonance (MR) brain images appeared similar. However, diffusion-weighted MRI showed decreased baseline water apparent diffusion coefficient in the brains of TgS animals. Furthermore, contrast-enhanced MRI after gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) injection demonstrated slower recovery of normal signals in the TgS brains than with controls. Perfusion MR imaging and difference T1 maps calculated from pre- postcontrast T1-weighted MR images indicated accumulation of more Gd-DTPA molecules in the TgS brains than in the parent strain, reflecting impaired blood-brain barrier (BBB) functioning in these transgenic mice. To explore the molecular mechanism(s) underlying these global phenotypes, we performed microarray analysis in the stress-controlling prefrontal cortex of TgS vs. strain-matched wild-type animals. Profound overexpression of numerous ion channels, transporters, and adhesion genes was confirmed by real time RT-PCR tests. Immunohistochemical and immunoblot analyses revealed corresponding increases in the level and cellular distributions of the chloride channel CLCN3 and the water channel AQP4, both of which contribute to BBB maintenance. Our study attributes to balanced cholinergic neurotransmission, a central role in the brain's maintenance of water diffusion and ion transport, and indicates that chronic impairments in this maintenance facilitate neurodeterioration through interference with BBB function.

Acetylcholine↗
PubMed2003

Reversal of perfusion and diffusion abnormalities after intravenous thrombolysis for a lacunar infarction.

Perfusion and diffusion magnetic resonance imaging (MRI) have been used to guide therapy in patients with large vessel occlusions. In an analogous fashion, the authors used perfusion and diffusion MRI to demonstrate a perfusion deficit and a matching diffusion lesion in a patient with lacunar infarct. Following thrombolytic therapy, the authors observed a reversal of the perfusion deficit, the diffusion lesion, and clinical recovery. This case suggests that perfusion and diffusion MRI may be informative in patients with lacunar infarction who are candidates for thrombolysis.

Aged↗
PubMed2003

Computation of the fractional anisotropy and mean diffusivity maps without tensor decoding and diagonalization: Theoretical analysis and validation.

Diffusion tensor MRI (DT-MRI) is a promising modality for in vivo mapping of the organization of deep tissues. The most commonly used DT-MRI invariant maps are the mean diffusivity, mu(D), relative anisotropy (RA), and fractional anisotropy (FA). Because of the computational burden, anisotropy maps are generally computed offline. The availability of a simple procedure to compute RA, FA, and mu(D) online would make DT-MRI more useful in clinical applications that require immediate feedback. In this study, analytical expressions that relate the commonly used tensor anisotropy measures obtained from the decoded and diagonalized DT with those obtained from the first and second moments of the measured diffusion-weighted (DW) data are derived. Specifically, it is shown that for the principal icosahedron encoding scheme, RA is related to the mean and standard deviation (SD) of the DW measurements that can be computed online. Since FA is commonly used as an anisotropy measure, an analytical expression relating RA and FA was derived from the tensor invariants. These results were validated using both Monte Carlo simulations and high-resolution, normal whole-brain DT-MRI measurements acquired with different b-factors, encoding schemes, and signal-to-noise ratio (SNR) levels. The bias introduced by the rotationally variant encoding schemes into the diffusion measures is also investigated.

Algorithms↗
PubMed2000

Relationship between apparent diffusion coefficient and subsequent hemorrhagic transformation following acute ischemic stroke.

BACKGROUND AND PURPOSE: A method for identifying patients at increased risk for developing secondary hemorrhagic transformation (HT) after acute ischemic stroke could be of significant value, particularly in patients being considered for thrombolytic therapy. We hypothesized that diffusion-weighted MRI might aid in the identification of such patients. METHODS: We retrospectively analyzed 17 patients with ischemic stroke who received diffusion-weighted MRI within 8 hours of symptom onset and who also received follow-up neuroimaging within 1 week of initial scan. The apparent diffusion coefficient (ADC) for each pixel in the whole ischemic area was calculated, generating a histogram of values. Areas subsequently experiencing HT were then compared with areas not experiencing HT to determine the relationship between ADC and subsequent HT. RESULTS: A significantly greater percentage of pixels possessed lower ADCs (</=550x10(-)(6) mm(2)/s) in HT lesions compared with non-HT lesions (47% versus 19%; P:<0.001). Moreover, >40% of the pixels possessed values </=550x10(-)(6) mm(2)/s in all lesions experiencing secondary HT, compared with <31% of the pixels in the non-HT-destined lesions. CONCLUSIONS: HT-destined stroke regions possess a significantly great percentage of low ADC values than non-HT-destined regions. Early measurement of ADC values may be a useful tool for assessing secondary HT risk.

Aged↗
PubMed2005

Diffusion-weighted magnetic resonance imaging in Marchiafava-Bignami disease: follow-up studies.

Marchiafava-Bignami disease (MBD), an acute toxic demyelination of the corpus callosum in alcoholics, is associated with poor evolution in the majority of patients. We report here the early and late diffusion magnetic resonance imaging (MRI) and apparent diffusion coefficient (ADC) studies of two patients suffering from MBD with favourable outcome. Diffusion and anatomical MRI changes were parallel to the clinical evolution, suggesting that MRI studies can be helpful for diagnosis and follow-up. Unlike in stroke, restricted diffusion on ADC maps does not seem to be a sign of irreversibility.

Adult↗
PubMed2005

Precipitation of stroke-like event by chickenpox in a child with MELAS syndrome.

The mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes syndrome (MELAS) is a rare congenital disorder of mitochondrial DNA (mtDNA). Herein we report a case of MELAS, whose second stroke-like episode was provoked by chickenpox. A point mutation at nucleotide (nt) 3243 in mtDNA supported the diagnosis of MELAS in this case. History of myopathy, the presence of lesions that did not conform to accepted distributions of vascular territories on cranial magnetic resonance imaging (MRI), normal result of cranial magnetic resonance angiography, hyperintensity on diffusion weighted MRI and apparent diffusion coefficient mapping indicating the presence of vasogenic edema in the fresh stroke-like lesion, and mitochondrial DNA analysis helped to exclude the diagnosis of ischemic cerebral infarction which can also be induced by chickenpox.

Chickenpox↗
PubMed2002

Functional magnetic resonance of human breast tumors: diffusion and perfusion imaging.

This review is focused on two relatively new developments in magnetic resonance imaging (MRI) and their application to breast lesion characterization: diffusion and perfusion MRI. Diffusion MRI measures the mobility of the water protons and thus provides a window to tissue microstructure. Perfusion MRI measures the rate at which blood is delivered to tissue and thus provides information about microvasculature. Because both tissue structure and vasculature are likely to change in disease states, measurement of diffusion and perfusion may have direct physiologic relevance. This review covers topics related to the imaging sequences, image analysis, and clinical studies for diffusion and perfusion breast MRI. Preliminary studies show that the apparent diffusion coefficient (ADC) is a marker of cell density and can distinguish malignant from benign lesions. Perfusion MR also shows promise for breast tumor characterization: malignant tumors have consistently higher relative tissue blood volumes (rTBV) than normal and benign tumors. Additional research is required with large patient cohorts to establish these two techniques on a clinical footing.

Breast↗
PubMed1997

Time course of the apparent diffusion coefficient (ADC) abnormality in human stroke.

Diffusion-weighted MRI can rapidly detect acute cerebral ischemic injury as hyperintense signal changes, reflecting a decline in the apparent diffusion coefficient (ADC) of water through brain parenchyma, whereas ADC is elevated in the chronic stage because of increased extracellular water content. To determine the time course of these ADC changes, we analyzed 157 diffusion-weighted MRI studies performed at varying time points from the initial ischemic event from 101 patients. Data were expressed as the relative ADC (rADC), the ratio of lesion to control regions of interest. We observed two phases in the time course of rADC changes in acute human stroke: a significant (p < 0.005) reduction in rADC lasting for at least 96 hours from stroke onset (mean, 58.3% of control; SEM, 1.47) and an increasing trend from reduction to pseudonormalization to elevation of rADC values at later subacute to chronic time points (> or = 7 days). We suggest that the persistent reduction of rADC within the first four days may reflect ongoing or progressive cytotoxic edema to a greater degree than extracellular edema and cell lysis.

Adult↗
PubMed2006

Magnetic resonance imaging of tissue and vascular layers in the cat retina.

PURPOSE: To report the visual resolution of multiple cell and vascular "layers" in the cat retina using MRI. MATERIALS AND METHODS: T2- and diffusion-weighted MRI at 4.7 Tesla was performed. Layer-specific thickness, T2, spin density, apparent diffusion coefficient perpendicular (ADC(perpendicular)) and parallel (ADC(parallel)) to the retinal surface were tabulated. T1-weighted MRI was acquired before and after intravenous administration of Gd-DTPA and subtraction images were obtained. Histology was performed for validation. RESULTS: Three distinct "layers" were observed. The inner strip nearest to the vitreous (exhibiting large T2, ADC, spin density with Gd-DTPA enhancement) overlapped the ganglion cell layer, bipolar cell layer, and the embedded retinal vascular layer. The middle strip (exhibiting small T2, ADC, spin density without Gd-DTPA enhancement) overlapped the photoreceptor cell layer and the inner and outer segments. The outer strip (exhibiting large T2, ADC, spin density with Gd-DTPA enhancement) overlapped the tapetum and choroidal vascular layer. T2, spin density, ADC(perpendicular) and ADC(parallel) of different "layers" were tabulated. The inner strip was slightly thicker than the other two strips. The total thickness, including neural and nonneural retina, was 358 +/- 13 microm (N = 6) by MRI and 319 +/- 77 microm (N = 5) by histology. CONCLUSION: MRI provides a noninvasive tool to study the retina with laminar specificity without depth limitation.

Animals↗
PubMed2005

Functional magnetic resonance imaging and diffusion tensor imaging in a case of central poststroke pain.

The role of the lesion location within functional pain systems is not fully understood for central poststroke pain (CPSP) pathogenesis. In a patient with CPSP we used data from both functional magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) for anatomo-functional correlations. Structural MRI showed a small residual cavity confined to the right thalamic ventral posterolateral nucleus and the adjacent posterior arm of the internal capsule. DTI maps showed selective reduction of right sensory thalamocortical fibers. Functional MRI, performed with different thermonociceptive stimuli, showed pain-specific signal changes in the anterior cingulate gyrus (BA 24/32) and in the associative parietal regions (BA 5/7). These findings underline, for CPSP pathogenesis, the role of damage of lateral nociceptive thalamoparietal fibers together with the release of activity of anterior cingulate and posterior parietal regions. In a patient with CPSP, we combined noninvasive neuroimaging techniques (functional and diffusion MRI) to assess the anatomo-functional relationship in CPSP. Our investigations show, for CPSP pathogenesis, the role of damage of lateral nociceptive thalamoparietal fibers together with the release of activity of anterior cingulate and posterior parietal regions.

Aged↗
PubMed2000

Temporal evolution of ischemic injury evaluated with diffusion-, perfusion-, and T2-weighted MRI.

OBJECTIVE: Ischemic lesions seen on diffusion-weighted imaging (DWI) are reversible if reperfusion is performed within minutes after the onset of ischemia. This study was designed to determine whether acute reversibility of DWI abnormalities is transient following brief temporary focal brain ischemia and to characterize the temporal evolution of in vivo ischemic lesions. METHODS: Eight rats were subjected to 30 minutes of temporary middle cerebral artery occlusion and underwent diffusion-, perfusion-, and T2-weighted MRI during occlusion; immediately after reperfusion; 30, 60, and 90 minutes after reperfusion; and 12, 24, 48, and 72 hours after reperfusion. Average apparent diffusion coefficient (ADCav) values and the cerebral blood flow index (CBFi) ratio were calculated in both the lateral caudoputamen and overlying cortex at each time point. The size of the in vivo ischemic abnormalities was calculated from the ADCav and the T2 maps. Postmortem triphenyltetrazolium chloride (TTC) staining was used to verify ischemic injury. RESULTS: Both the CBFi ratio and ADCav values declined significantly in the two regions during occlusion. The CBFi ratio recovered immediately after reperfusion and remained unchanged over 72 hours. However, ADCav values returned to normal at 60 to 90 minutes and secondarily decreased at 12 hours after reperfusion as compared with those in the contralateral hemisphere. The extent of the in vivo ischemic lesions maximized at 48 hours and was highly correlated with TTC-derived lesion size. CONCLUSIONS: Acute recovery of initial ADCav-defined lesions after reperfusion is transient, and secondary ADCav-defined lesions develop in a slow and delayed fashion.

Animals↗
PubMed2003

[Report on the ECR2003 (European Congress of Radiology): comparison of apparent diffusion coefficient (ADC) between different MRI scanners].

PURPOSE: To analyze reproducibility of ADC measurements on different MRI scanners. METHODS AND MATERIALS: Diffusion-weighted imaging (DWI) of a home-made phantom (gelatine of different concentration was enclosed in case of circle pillar shape) was performed with the following protocol; spin-echo type echo planar imaging; TR=7000 msec, TE=minimal, matrix=128 x 128, FOV=220 mm, slice thickness=5mm, NEX=1, b-factor=0, 500, and 1000 sec/mm(2) on four different 1.5T MR scanners [GE Signa Horizon (two of them), GE Signa Horizon Lx, and Siemens Magnetom Symphony]. Image analysis were performed on a workstation (GE Medical Systems) or on an operators console of Symphony (for data of Symphony). We used two-point method. Regions of interest (ROIs) were set on every part of ADC map of home-made phantom and ADCs were measured. A linear approximation graphs were also made with every MRI scanner and b-factor. RESULTS: A linear approximation was performed, formulas were y=-0.08x+2.32, r(2)=0.84(Lx), y=-0.09x+2.58, r(2)=0.89(Horizon-1) y=-0.11x+2.67, r(2)=0.95(Horizon-2), y=-0.08x+2.42, r(2)=0.97(Symphony) at b-factor of 500sec/mm(2). y=-0.08x+2.33, r(2)=0.91(Lx), y=-0.09x+2.43, r(2)=0.93(Horizon-1), y=-0.08x +2.48, r(2)=0.92(Horizon-2), y=-0.07x+2.39, r(2)=0.96(Symphony) at b-factor of 1000 sec/mm(2). CONCLUSIONS: ADC values measured at two MRI scanners (same model and older than the other scanners) are higher than other scanners on b-factor=500 sec/mm(2), but at b-factor=1000 sec/mm(2), a good relationship between every scanners was obtained. This result seems to depend on generation of the MRI scanners; newly scanners have good relations b-factor 500 and 1000 sec/mm(2). Pulse sequence design may be improved and optimized in newly scanners. When ADCs were used as quantitative value, a proper b-factor must be used.

Diffusion Magnetic Resonance Imaging↗
PubMed2000

Brain tissue sodium is a ticking clock telling time after arterial occlusion in rat focal cerebral ischemia.

BACKGROUND AND PURPOSE: Many patients with acute stroke are excluded from receiving thrombolysis agents within the necessary time limit (3 or 6 hours from stroke onset) because they or their family members are unable provide the time of stroke onset. Brain tissue sodium concentration ([Na(+)]) increases gradually and incessantly during the initial hours of experimental focal cerebral ischemia but only in severely damaged brain regions. We propose that this steady increase in [Na(+)] can be used to estimate the time after arterial occlusion in the rat middle cerebral artery occlusion model of ischemic stroke. METHODS: Sixteen anesthetized Sprague-Dawley rats underwent permanent middle cerebral artery occlusion combined with bilateral common artery occlusion. After 100 to 450 minutes, diffusion-weighted MRI was used to generate apparent diffusion coefficient (ADC) maps, cerebral blood flow (CBF) was determined with (14)C-iodoantipyrine (in a subset of 7 animals), and the brain was frozen. Autoradiographic CBF sections and punch samples for Na(+) analysis were obtained from the brain at the same level of the MR image. Severely at risk regions were identified with an ADC of <520 microm(2)/s and, in the subset, with both ADC of <520 microm(2)/s and CBF of <40 mL. 100 g(-1). min(-1). RESULTS: Both CBF and the ADC dropped quickly and remained stable in the initial hours after ischemic onset. Linear regression revealed strong linearity between [Na(+)] and time after onset, with a slope of 0.95 or 1.00 (mEq/kg DW)/min, with both ADC and ADC-plus-CBF criteria, respectively. The 95% CIs at 180 and 360 minutes were between 41 and 52 minutes. CONCLUSIONS: The time after ischemic onset can be estimated with this 2-step process. First, ADC and CBF are used to identify severely endangered regions. Second, the [Na(+)] in these regions is used to estimate time after onset. The favorable 95% CIs at the time limits for thrombolytic therapy and the availability of measurements of ADC, CBF, and [Na(+)] in humans through the use of MRI suggest that this time-estimation scheme could be used to assess the appropriateness of thrombolysis for patients who do not know when the stroke occurred.

Animals↗
PubMed1993

Correlation of MRI and clinical features in meningeal carcinomatosis.

Ten patients with meningeal carcinomatosis associated with nonhaematological neoplasms were examined: six with breast, two with gastrointestinal and one with lung cancer, plus one with a tumour of unknown origin. Cytology was positive in all but one. The patients were classified into four groups according to the gadolinium-enhanced MRI (Gd-MRI) appearances: group 1 had pure leptomeningeal carcinomatosis, group 2 dural carcinomatosis, group 3 spinal leptomeningeal carcinomatosis, and group 4 had normal Gd-MRI except for hydrocephalus. In group 1, Gd-MRI showed diffuse enhancement of the subarachnoid space, including the cisterns around the midbrain, the sylvian fissures, or cerebellar and cerebral sulci. In group 2, Gd-MRI showed diffuse, thick, partially nodular enhancement of the dura mater. No leptomeningeal or subependymal enhancement was evident. In group 3, nodular masses were seen only in the spinal canal. In group 4, no definite evidence of meningeal carcinomatosis was demonstrated on contrast-enhanced CT (CE-CT) or Gd-MRI. The median survival time was 2.0 months in group 1, 1.0 month in group 3, and 4.5 months in group 4, but the two patients in group 2 were alive 10 and 15 months after a definite diagnosis of meningeal carcinomatosis was made. In all patients examined by both CE-CT and Gd-MRI, the latter was superior for identification of meningeal carcinomatosis. Hydrocephalus in an important indirect sign of leptomeningeal carcinomatosis, but was not seen in patients with dural carcinomatosis despite the presence of increased intracranial pressure.

Aged↗
PubMed1997

Neuroprotection with NBQX in rat focal cerebral ischemia. Effects on ADC probability distribution functions and diffusion-perfusion relationships.

BACKGROUND AND PURPOSE: We have previously shown that treatment with glutamate receptor antagonists after focal ischemia can partially reverse acute lesions measured with diffusion-weighted MRI. The goal of this study was to examine the quantitative nature of these effects of neuroprotection. METHODS: Rats were subjected to permanent occlusion of the middle cerebral artery under halothane anesthesia and treated with 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX) (30 mg/kg IP; two doses given immediately after ischemia and 1 hour after ischemia) or given injections of saline. Diffusion-weighted MRI scans were performed to map the changes in water diffusivity during the first 3 hours after ischemia. Apparent diffusion coefficients (ADCs) within the ischemic hemisphere were calculated, and ischemic changes were expressed as absolute reductions and as a percentage of contralateral mean values. Relative perfusion deficits in the ischemic hemisphere were assessed with dynamic MRI of transient changes in transverse relaxation rates (delta R2*). RESULTS: Analysis with ADC probability distribution functions showed that focal ischemia was present with gradients in ADC reductions emanating from the center to the periphery of the lesion. Ischemic evolution in control rats was manifested as a progressive shift of the probability distribution functions over time. NBQX treatment resulted in a reverse shift of these probability functions. By 3 hours after occlusion, probability distribution functions were significantly improved in treated rats (P < .05). Because of the temporal evolution of the probability distribution functions, ADC thresholds that correlated with histological outcomes of infarction changed over time. NBQX did not alter the cerebral perfusion index, measured as delta R2* peak values. CONCLUSIONS: The results indicate that ADC probability distribution functions can be used to quantitatively evaluate the effects of neuroprotective treatment on the gradients of injury in focal cerebral ischemia. The probability functions also allow for intrasubject comparisons and may therefore be useful for exploring therapeutic windows.

Animals↗