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

We investigated microvascular damage in areas with magnetic resonance imaging (MRI)-defined apparent diffusion coefficient reduction (ADC-R) in a rat model of thromboembolic occlusion of the middle cerebral artery. Rats received either intracarotid recombinant tissue plasminogen activator (rt-PA) or saline. Microvascular basal lamina damage was quantified by immunohistochemical staining of collagen type IV and by videoimaging analysis. ADC-R positive basal ganglia (cortical) areas showed a significant reduction of stained microvascular area by 15+/-6% (8+/-7%) and the microvascular density by 13+/-5% (8+/-6%) of that on the non-ischemic control side (P<0.001). There were no significant microvascular differences between rats given rt-PA or saline, or between those with or without angiographically proven recanalization. This study reports for the first time that microvascular basal lamina damage in experimental thromboembolic stroke is confined to regions with ADC-R in MRI.
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PMID:Microvascular basal lamina damage in thromboembolic stroke in a rat model. 1466 20

Diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) can rapidly detect lesions in acute ischemic stroke patients. The PWI volume is typically substantially larger than the DWI volume shortly after onset, that is, a diffusion/ perfusion mismatch. The aims of this study were to follow the evolution of the diffusion/ perfusion mismatch in permanent and 60- minute temporary focal experimental ischemia models in Sprague-Dawley rats using the intraluminal middle cerebral artery occlusion (MCAO) method. DWI and arterial spin-labeled PWI were performed at 30, 60, 90, 120, and 180 minutes after occlusion and lesion volumes (mm(3)) calculated At 24 hours after MCAO, and infarct volume was determined using triphenyltetrazolium chloride staining. In the permanent MCAO group, the lesion volume on the ADC maps was significantly smaller than that on the cerebral blood flow maps through the first 60 minutes after MCAO; but not after 90 minutes of occlusion. With 60 minutes of transient ischemia, the diffusion/perfusion mismatch was similar, but after reperfusion, the lesion volumes on ADC and cerebral blood flow maps became much smaller. There was a significant difference in 24- hour infarct volumes between the permanent and temporary occlusion groups.
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PMID:Characterizing the diffusion/perfusion mismatch in experimental focal cerebral ischemia. 1475 24

The purpose of this study was to determine the diffusion sensitivity factor b that optimizes the contrast-to-noise ratio (CNR) for both diffusion-weighted signal intensity and the apparent diffusion coefficient (ADCNR) when evaluating ischemic stroke by diffusion-weighted MRI. The relative contrast, noise levels, CNR, and ADCNR were calculated for typical ADC values in human brain, 780 microm(2)/s in adults and 1200 microm(2)/s in neonates in normal tissue, 20-40% less in acute and subacute stroke, and 50% more in chronic stroke. The optimum b factor depends strongly on the ADC, whether TE is fixed or varies with the b factor, whether CNR or ADCNR is measured, and anisotropy. The optimum b factor in adults is 1000 s/mm(2) in acute and chronic stroke, and 1200 s/mm(2) in subacute stroke. The optimum values are about 200 s/mm(2) lower in neonates than in adults. The CNR and ADCNR are within 10% of the optimum over at least a 2-fold range of b factors, from 68-136% of the optimum b factor. If a single b factor is to be used for all situations, a diffusion b factor of 1000 s/mm(2) is recommended.
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PMID:Selection of the optimum b factor for diffusion-weighted magnetic resonance imaging assessment of ischemic stroke. 1512 82

We sought to identify magnetic resonance imaging (MRI) parameters that can identify as well as predict disruption of the blood-brain barrier (BBB) after embolic stroke in the rat. Rats subjected to embolic stroke with (n=13) and without (n=13) rt-PA treatment were followed with MRI using quantitative permeability-related parameters, consisting of: transfer constant (K(i)) of Gd- DTPA, the distribution volume (V(p)) of the mobile protons, and the inverse of the apparent forward transfer rate for magnetization transfer (k(inv)), as well as the apparent diffusion coefficient of water (ADC(w)), T2, and cerebral cerebral blood flow (CBF). Tissue progressing to fibrin leakage resulting from BBB disruption and adjacent tissue were then analyzed to identify MRI markers that characterize BBB disruption. Animals were killed after final MRI measurements at 24 h after induction of embolic stroke and cerebral tissues were perfused and stained to detect fibrin leakage. K(i), V(p), and k(inv) were the most sensitive early (2 to 3 h) indices of the cerebral tissue that progresses to fibrin leakage. Cerebral blood flow was not significantly different between ischemic tissue with a compromised and an intact BBB. Our data indicate that compromise of the BBB can be sensitively predicted using a select set of MR parameters.
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PMID:Quantitative evaluation of BBB permeability after embolic stroke in rat using MRI. 1571 59

Diffusion MR imaging has improved evaluation of acute ischemic stroke vastly. It is highly sensitive and specific in the detection of infarction at early time points when CT and conventional MR sequences are unreliable. The initial DWI lesion is believed to represent infarction core and usually progresses to infarction unless there is early reperfusion. The initial DWI lesion volume and ADC ratios correlate highly with final infarction volume and with acute and chronic neurologic assessment tests. ADC values may be useful in differentiating tissue destined to infarct from that potentially salvageable with reperfusion therapy. ADC values also may be useful for determining tissue at risk of HT after reperfusion therapy. DTI can quantify differences in the responses of gray versus white matter to ischemia. FA may be important in determining stroke onset time, and tractography provides early detection of wallerian degeneration that may be important in determining prognosis. Finally, DWI can determine which patients who have TIA are at risk for subsequent large vessel infarction and can differentiate stroke from stroke mimics. With improvements in MR software and hardware, diffusion MR undoubtedly will continue to improve the management of patients who have acute stroke.
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PMID:Diffusion-weighted imaging in acute stroke. 1636 May 86

The aim of our study was to investigate the usefulness of high-b-value diffusion-weighted (DW) MR imaging in patients with acute cerebral infarction. DW images at b-values of 1,000, 2,000, and 3,000 s/mm(2) were performed for 32 patients 48 h after the onset of stroke using a 1.5 T clinical imager. The area of restricted diffusion became more distinct and extensive with increasing b-value in 19 of 32 patients, especially in patients with the atherothrombotic-type cerebral infarction. The visualized extent of infarction was almost the same among the area of restricted diffusion on the b=3,000 ADC map, b=3,000 DWI and final infarction in 12 of 15 patients. High-b-value DWI provided better identification of lesion extension in the cerebral ischemia. It is suggested that the size of the final infarction or irreversible cytotoxic edema is more predictable on high-b-value DWIs than on the usual b=1,000 DWI.
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PMID:Usefulness of high-b-value diffusion-weighted imaging in acute cerebral infarction. 1696 37

Owing to its rapid acquisition time and high sensitivity, diffusion-weighted imaging has turned into a routine sequence for brain imaging. This is the case not only for stroke, but also for various diseases such as abscesses or tumors. Being aware of the artifacts is important for optimal interpretation. After a brief review of the normal patterns, the most frequent artifacts, inherent to the echoplanar imaging technique, are described and we provide suggestions to avoid them. Most current traps are caused by T2-weighting of the diffusion images; the key for avoiding erroneous interpretation relies on the ADC map.
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PMID:[Diffusion-weighted imaging of the brain: normal patterns, traps and artifacts]. 1721 68

The purpose of this study is to establish that newborn stroke involving extensive parts of cerebral cortex immediately leads to secondary network injury in pulvinar. Seven term infants with cortical stroke presented with hypersignal in pulvinar on DWI. Stroke types included: complete MCA stroke (n=4); PCA stroke, ICA stroke and multiple artery stroke (1 each). Age range at scanning was between day 2 and 6 after birth (except for 1 infant scanned within 7 days of acute presentation during ECMO). ADC values in secondarily injured pulvinar were significantly higher than in the area with primary (sub)cortical injury (all patients scanned with identical MR image acquisition). In the absence of asphyxia and because pulvinar is outside of the primary area of infarction, we conclude that there are suggestions from imaging for acute secondary injury to pulvinar following primary damage of their cortical targets and/or connecting axons. Acute secondary injury is probably due to excitotoxicity and deafferentiation. The relevance of network injury for prognosis and the impact of early treatment on it have yet to be studied, in stroke but also in other acute perinatal brain disorders.
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PMID:Network injury to pulvinar with neonatal arterial ischemic stroke. 1807 86

Goal of initial imaging study for acute-stage ischemic stroke are to detect focal lesion accurately and to assist the therapeutic decision. With the goal in mind, we investigated feasibilities of MRI for acute-stage ischemic stroke. Firstly, we assessed whether diffusion weighted images (DWI) raised diagnostic accuracy for acute-stage ischemic stroke. We investigated how DWI study changes the diagnosis for the patients with neurological symptom in emergency room. Out of 164 patients who visit the emergency room with neurological symptom, sensitivity, specificity and efficiency for ischemic stroke diagnosis before DWI study were 0.87, 0.85 and 0.89 respectively. DWI raised them to 0.99, 0.98 and 0.99. These result proves feasibility of DWI on diagnosis of acute-stage ischemic stoke. Secondly, we assess whether DWI and perfusion imaging (PI) can provide any information about fate of acute ischemic lesion. We compared the relationships between DWI and PI parameters (ADC, rCBF, MTT, rCBV) and tissue outcome (infracted or survived). In patients with successful recanalization, best predictor was ADC and the cut-off value was 0.90 against contra-lateral hemisphere. In patients without recanalization, rCBF at 0.66 against contra-lateral hemisphere predicted the pathological fate most accurately. This simple guidepost can be help therapeutic decision of acute-stage stroke.
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PMID:[What stroke MRI provides to us]. 1821 Aug 36

Focal imaging abnormalities of the corpus callosum are rare but have been described in various clinical conditions. Because the MRI appearance may mimic acute stroke, clinicians have to be aware of differential diagnoses. We report a patient with a stroke-like episode and transient hypersignal in diffusion with decreased ADC values of the corpus callosum in a setting of sepsis due to a Klebsiella pneumoniae infection. This stroke mimic may be due to an inflammatory process and should be recognized because of therapeutic implications.
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PMID:Transient splenial DWI abnormality of the corpus callosum during a stroke-like episode. 1857 85


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