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Query: UMLS:C0038454 (stroke)
 147,016 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Diffusion-weighted MR imaging (DWI) is capable of imaging ischemia-induced changes in water protons in either animal or man. Technical developments are described that allow the routine clinical utility of DWI in a stroke setting to provide objective criteria beyond the neurological exam by which the pathophysiology of stroke can be evaluated. To date, DWI has provided unique information concerning detection and evaluation of acute, symptomatic lesions from older, chronic strokes, detection and localization of small deep infarcts and reversible ischemic neurologic deficits and transient ischemia. Clinical DWI studies suggest that the temporal behaviour of ADC can critically improve the evaluation of clinical ischemia.
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PMID:Clinical aspects of DWI. 873 75

An interleaved echo-planar imaging (EPI) technique is presented for the rapid acquisition of isotropic diffusion-weighted images of stroke patients. Sixteen isotropic diffusion-weighted images at three b values are acquired in less than 3 min. A spiral navigator echo is used to measure the constant and linear phase shifts across the head in both the x and y directions which result from motion during the isotropic diffusion- sensitizing gradients. The measured k-space errors are corrected during a gridding reconstruction. The gridding kernel has a constant width in kx and a variable width in ky which eliminates variable data-density ghosts. The resulting isotropic diffusion-weighted images have excellent lesion-to-normal brain contrast, very good spatial resolution, and little sensitivity to susceptibility effects in the base of the brain. Examples of diffusion-weighted images and ADC maps from several stroke patients are shown.
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PMID:Isotropic diffusion-weighted and spiral-navigated interleaved EPI for routine imaging of acute stroke. 935 48

We studied the effects of rt-PA (recombinant tissue type-plasminogen activator) treatment on the blood-brain barrier (BBB) after thromboembolic stroke in rat. New MRI methods of diffusion and perfusion imaging to observe the hemodynamic and biophysical effects of thrombolysis were combined with methods for assessment of BBB disturbances. In untreated animals clot embolism produced a rapid drop in MRI perfusion values and the ADC (apparent diffusion coefficient), with subsequent infarction. BBB disturbances, visualised as extravasation of serum proteins on cryostat sections, were manifest in nearly all animals in the borderzone of infarcts. In animals treated with rt-PA 15 min after clot embolism thrombolysis resulted in reperfusion of affected brain regions with subsequent improvement of ADC values. Final lesion size on ADC maps was reduced by 36% relative to untreated animals. However, BBB disturbances were not improved after treatment. To the contrary, rt-PA treated animals showed further regions with serum protein extravasation in the infarcted territories and in distant non-ischemic brain regions. MR imaging with the BBB tracer GdDTPA showed more pronounced and widespread contrast enhancement in the rt-PA treated than in the untreated group. Increased blood-brain barrier disturbances have to be taken into account even when thrombolytic therapy is started very early after the onset of stroke.
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PMID:Blood-brain barrier disturbances after rt-PA treatment of thromboembolic stroke in the rat. 941 23

Multispectral (MS) analysis was used to determine the ischemic lesion volume in the rat brain after permanent middle cerebral arterial occlusion. MS analysis used a four-dimensional MS model consisting of an estimate of the average apparent diffusion coefficient of water (ADC(av)), T2, proton density, and perfusion. Four classification methods were investigated: (a) multivariate gaussian (MVG); (b) k-nearest neighbor (k-NN); (c) k-means (KM); and (d) fuzzy c-means (FCM). MVG and k-NN classifiers are supervised methods requiring labeled training data to characterize the stroke lesion. Unsupervised classifiers (KM, FCM) do not require previous statistics or labeled training data, resulting in potentially greater clinical usefulness. All MS methods provided significant correlation with postmortem findings beyond the use of ADC(av) alone (partial correlation given the ADC(av) estimate: MVG, .66; k-NN, .75; KM, .68; FCM, .70). This study demonstrates that MS analysis provides an improved estimate of ischemic lesion volume over that obtained from ADC alone.
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PMID:Determination of focal ischemic lesion volume in the rat brain using multispectral analysis. 984 39

We report an 84-year-old woman with medial medullary syndrome diagnosed by diffusion-weighted magnetic resonance imaging (MRI). She was admitted because of left hemiparesis and hypesthesia. T2-weighted and diffusion-weighted MRI showed a high signal lesion at the right medial medulla oblongata 10 days after the onset. It is well known that diffusion-weighted MRI is useful for detecting supratentrial cerebral ischemic lesions in the extremely acute stage. However, to our knowledge, there have been only a few reports of diffusion-weighted MRI in patients with ischemic stroke of the medulla oblongata. Normal nerve fibers in the direction perpendicular to the motion-probing gradient (MPG) shows a high signal by diffusion-weighted MRI (anisotropy of apparent diffusion cofficient [ADC]). Normal nerve fibers in the pyramidal tract of medulla oblongata also shows a high signal when the MPG pulse is applied in the x and y directions. We solved this problem by using isotropic diffusion-weighted imaging and were able to detect ischemic lesion of medial medullary infarction in the acute phase.
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PMID:[A case of medial medullary syndrome detected by diffusion-weighted magnetic resonance imaging]. 1019 3

Diffusion-weighted MRI (DWI) is becoming important for assessment of acute stroke. Until recently single-shot DWI required expensive technology such as echoplanar imaging (EPI) available only at some research sites. A new medium-field (1.0 T) short-bore MR imager has been developed with which DWI data sets can be acquired. We prospectively studied 169 patients on this 1.0 T commercial system. After conventional imaging, DWI was performed with a single-shot multi-slice sequence with b values 0 an 900 s/mm2, and with the gradients switched in three directions. The apparent diffusion coefficients were calculated with online calculation software. There were 50 patients with totally normal MRI, and 17 had strokes, these strokes were detected as areas of high signal on the images at a maximal b value. There was a drop in the ADC in ischaemic regions: in sub-acute infarcts, the values were between 0.41 and 0.531 x 10(-3) mm2/s. In old infarcts the ADC was 1.15 x 10(-3) mm2/s. Cerebrospinal fluid (CSF) gave low signal whereas areas in the brain had more intermediate intensities (CSF: 3.00; deep white matter: 0.75, cortical grey matter: 0.80, basal ganglia (thalamus): 0.70 and cerebellar white matter: 0.65 x 10(-3) mm2/s. Anisotropy was detected as areas of restricted diffusion along the tracts. These preliminary data show that DWI can be acquired successfully on a medium-field short-bore system. This should allow the technique to be implemented at more sites, therefore facilitating the diagnosis of acute stroke and rendering early intervention feasible.
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PMID:Clinical single-shot diffusion-weighted MRI of the human brain on a short-bore medium-field imager. 1063 62

Stroke in children is thought to be a rare phenomenon, but in a pediatric hospital, it is much more common than is expected. The development of rapid MRI imaging with diffusion techniques and MR spectroscopy has brought to the attention of both the neuroradiologists and clinicians that pediatric infarction, in both detection and management, are challenges for the future. Since 1995, cerebral diffusion has been performed at The Children's Hospital of Philadelphia in the evaluation of patients with acute cerebral compromise. Diffusion imaging looks at the motion of water molecules both intra- and extracellular, and the manner in which they become restricted in their motion when higher gradient strength is applied during the imaging sequence. Restricted diffusion is seen in cytotoxic edema, an early acute manifestation of ischemia/infarction. Diffusion studies are often positive when routine MRI and CT are as yet negative. Confirmation of the death of tissue is provided on proton spectroscopy by a rise in lactate from anaerobic glycolysis and a loss of N-acetylaspartate from neuronal death. Confirmation of the diffusion image findings, by mapping the apparent co-efficient (ADC), is also valuable. Application of these techniques, together with magnetic resonance angiography and magnetic resonance venography, is the substance of this paper.
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PMID:Pediatric cerebrovascular disease. 1120 40

Functional recovery in cytoprotected somatosensory cortex in a rat stroke model was studied using functional MRI (fMRI). Calcium antagonist treatment (isradipine) following permanent middle cerebral artery occlusion (pMCAO) reduced the infarct volume by 33 +/- 9%. The somatosensory cortex representing the forepaws was spared from infarction; however, cerebral blood flow (CBF) was significantly reduced in this area 24 hr following pMCAO. Neural function was assessed at days 1, 2, 5, and 12 following pMCAO by fMRI using electrical stimulation of both forepaws. Vehicle-treated rats did not show fMRI responses in the infarcted somatosensory cortex throughout the study. Several of the isradipine-treated animals displayed functional recovery in the cytoprotected cortex at days 5 (3/5 rats) and 12 (5/10). Correlations with fMRI signals showed that normal T2 and ADC values in the respective brain areas are necessary, but not sufficient prerequisites for functionality. Recovery of neural function is associated with normalization of CBF in the cytoprotected brain area.
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PMID:Recovery of function in cytoprotected cerebral cortex in rat stroke model assessed by functional MRI. 1194 38

Heterogeneous pathology in Alzheimer's Disease (AD) is due to variability in the nature and severity of lesions, overlap with other neurodegenerative diseases such as Parkinson's disease, or the co-existence of cerebrovascular disease. In the MGH-ADRC autopsy archives, remote cerebral infarcts (CVA) were reported in 30% of the otherwise uncomplicated AD cases. To determine the potential significance of cerebrovascular lesions in relation to AD, the relative densities (CERAD grading criteria) of Bielschowsky-stained AD lesions and Ab-amyloid immunoreactive plaques were compared among cases of AD+CVA (N=52), AD (N=48), aged controls (NC; N=9), and aged controls with AD lesions (ADC; N=8). The prevalence of the ApoE varepsilon 4 allele was also determined for each group. This study demonstrated: 1) higher densities of Bielschowsky-stained plaques in AD, AD+CVA, and ADC than in NC (P<0.0001); 2) more abundant neurofibrillary tangles in AD relative to all other groups (P<0.0005), and in AD+CVA and ADC relative to NC (P<0.05); and 3) increased densities of Ab-amyloid-immunoreactive plaques in AD relative to AD+CVA (P=0.0003). In AD+CVA, cerebral vascular lesions consisting of remote microscopic cortical and subcortical white matter infarcts, ischemic lesions, and leukoaraiosis were consistently distributed in structures typically damaged by AD neurodegeneration, as well as in the basal ganglia. The ApoE varepsilon 4 allele was more prevalent in the AD+CVA (70%) than in the AD (58%) group (P=0.05). Since the AD and AD+CVA groups had similar degrees of dementia, the results suggest that cerebral vascular lesions in regions typically destroyed by AD may contribute to the clinical manifestations of AD.
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PMID:Cerebrovascular Pathology Contributes to the Heterogeneity of Alzheimer's Disease. 1221 8

Diffusion-weighted MR imaging (DWI) is particularly sensitive for the detection of acute stoke. Until recently, DWI was performed with EPI technology. We compared 18 patients with clinical suspicion of acute stroke on a standard 1.5T unit and an open low-field MR scanner. Eighteen patients with 20 lesions of acute stroke were studied retrospectively with DWI and ADC mapping on both systems. The technique used was a rotating fast-spin echo T2 at low-field and an EPI sequence at 1.5T. Both examinations were performed within 24 hours and analyzed by two neuroradiologists. We obtained the same results on DWI sequences on both systems, regarding high intensity lesions on DWI. Interpretation of the ADC maps proved to be difficult on low-field MR near the lateral ventricles (3/18). We experienced the same difficulty of interpretation at low and high field in the cerebellum, in the temporal fossa and in cortex situated near bone, due to susceptibility artifacts. Chronic lesions were better visualized at low than at high field. In our opinion, DWI on a low-field open MR scanner is a good technique to evaluate subacute stroke and was as reliable as when performed on a 1.5T MR system.
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PMID:Diffusion weighted MR imaging on a low-field open magnet. Comparison with findings at 1.5T in 18 patients with cerebral ischemia. 1262 88


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