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Query: UMLS:C0917798 (cerebral ischemia)
 17,036 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The eigenimage filter was used to evaluate the results of a MRI study of cerebral ischemia in a rat model. This linear filter segments a desired feature in an image sequence from other features which may interfere with its observation. The animals were imaged temporally, after occlusion of the middle cerebral artery, to investigate the evolution of the ischemic process. The temporal evolution of ischemia was evaluated by analysis of the "eigenimages," calculated T2 and T1 map images, and images for the angles between signature vectors defined in the eigenimage technique. The eigenimages and angle map images demonstrated an improved visibility of the lesion at all time points, as compared to the original images and T2 and T1 map images. The eigenimages also demonstrated signal intensity changes within the area of ischemia. These changes are speculated to be related to variations in local cerebral blood flow resulting in varying degrees of tissue damage. The eigenimage intensities and the angles between signature vectors demonstrated time-related changes similar to the T2 and T1 values. Since the eigenimage filter and angle calculations are not dependent upon physical models (like T2 and T1), and the errors associated with these models, they may be preferable as methods for tissue characterization.
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PMID:Analysis of the evolution of focal cerebral ischemia in the rat using the eigenimage filter. 151 50

Intravoxel incoherent motion (IVIM*)-MRI has been performed on a clinical system at 0.5 tesla with a b gradient factor of 100 s/mm2, in a feline focal model of cerebral ischaemia. Images were obtained in 26 cats from less than 1 hour and up to 7-12 hours after stroke. The apparent diffusion coefficient (ADC) was decreased at the site of injury when compared to the contralateral normal side, by 30% in the first, 33% in 1-2 h and 27% in 2-4 h; it increased at 7-12 h, when vasogenic oedema occurred. IVIM*-MRI demonstrated early changes, due to cytotoxic oedema, during the acute phase of cerebral ischaemia to which conventional T2-weighted spin-echo imaging was not sensitive.
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PMID:Experimental focal cerebral ischaemia assessed with IVIM*-MRI in the acute phase at 0.5 tesla. 160 12

The gerbil model of unilateral cerebral ischemia has been used to test the temporal and spatial stability of the MRI T2 effects of oxygen-17 water. Following unilateral carotid ligation, symptomatic animals were given a single large intraperitoneal injection of H2(17)O and the distribution and stability of the brain T2 effects were followed with a spin-echo sequence. In contrast to the ischemic areas, the perfused tissue shows a marked and prolonged loss in intensity with little evidence of diffusion of the T2 effect of 17O into the ischemic tissue.
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PMID:The stability of proton T2 effects of oxygen-17 water in experimental cerebral ischemia. 179 91

Two patients with ruptured intracranial dermoids, examined with both CT and MRI are reported. Clinical presentation was transient cerebral ischemia in one patient and acute meningeal signs in the other. CT scan showed typical fat density of the tumor and the subarachnoid space. On MRI both the tumor and the subarachnoid fat, were strongly hyperintense on T1-weighted images.
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PMID:CT and MRI of ruptured intracranial dermoids. 204

We report MRI (magnetic resonance imaging) findings of 31 cases with subarachnoid hemorrhage (SAH) due to ruptured intracranial aneurysm. Among these cases, 25 were studied within 72 hours after onset of SAH. A resistive type MRI scanner operating at a field of 0.2 Tesla was used in obtaining inversion recovery (IR) and saturation recovery (SR) images. IR 1500/43/400 (T1 weighted image, T1W), SR 1000/60 (SR image) and SR 2000/100 (T2 weighted image, T2W) were chosen for analysis. The SR image was usually adopted and coronal and/or sagittal images were added when there was enough time for examination. Slice thickness was 10 mm and slice interval was 15 mm. The scan was not necessarily aimed at the visualization of aneurysm itself. 1) In the acute phase of SAH, subarachnoid spaces near the ruptured aneurysm were appeared as isointensity areas on T1W and as high intensity areas on SR image. In the subacute phase, they were depicted as high intensity areas on both T1W and SR images, and as high intensity areas on T2W. 2) Intraventricular hemorrhage was visualized as a niveau-like high intensity area, especially, within the posterior horns on the SR images. 3) SR and T2W images were suitable for detection of aneurysm itself. In a resistive-type scanner, small aneurysms were not easily visualized due to the lack of high resolution. However, 29% of aneuysms, which were not giant, could be visualized on MRI. 4) Identification of intracerebral hemorrhage and cerebral ischemia from various causes was easy on both T1W and T2W images.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Magnetic resonance imaging of subarachnoid hemorrhage due to ruptured intracranial aneurysm]. 220 43

Nine patients with dissections of the cervical arteries are presented. Dissections cause approximately three per cent of non-haemorrhagic stroke and are usually observed in young and middle-aged patients. Dissections very often give rise to head or neck pain. Carotid artery dissection may lead to lower cranial nerve dysfunction and an incomplete Horner's syndrome in case of subadventitial dissection, and to cerebral ischaemia in case of subintimal spread. Vertebral artery dissection may cause brain stem ischaemia (subintimal dissection) or in rare cases a subarachnoid haemorrhage (subadventitial spread). The history frequently reveals a (trivial) traumatic event. Diagnosis is usually established by angiography or MRI. The prognosis is good and recurrences are rare. Treatment with anticoagulants or acetylsalicylic acid seems recommendable, though scientifically unproven.
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PMID:[Dissection of cervical arteries as a cause of cerebral ischemia or cranial nerve dysfunction]. 221 57

To evaluate the efficacy of tests for selecting patients with hemodynamic compromise, measurement of cerebral blood volume (CBV) with 99mTc-RBC single photon emission computed tomography (SPECT) was performed in thirteen patients with occlusive cerebrovascular disease, and was compared with results obtained by 133Xe SPECT and acetazolamide (Diamox) test. All patients in our study suffered TIA, RIND, or minor complete stroke. Cerebral angiography demonstrated severe stenosis or occlusion in the ipsilateral internal carotid artery or middle cerebral artery, although plain CT scan or MRI revealed no or, if any, only localized infarcted lesions. Regional cerebral blood volume (rCBV) was measured with 99mTc-RBC SPECT and regional cerebral blood flow (rCBF) was measured with 133Xe SPECT before and after intravenous injection of 10 - 12 mg/kg acetazolamide (Diamox). Our results suggest that the ipsilateral rCBV/rCBF (mean transit time) is a more sensitive index of the cerebral perfusion reserve than the use of only rCBV or rCBF of the ipsilateral hemisphere. Also, the ipsilateral rCBV/rCBF is significantly correlated (r = -0.72) with the Diamox reactivity of rCBF, which is considered to represent the cerebral vasodilatory capacity in patients with chronic cerebral ischemia. Postoperative SPECT study revealed remarkable improvement of ipsilateral rCBV/rCBF and Diamox reactivity in four patients who underwent EC/IC bypass surgery to improve the hemodynamic compromise. In conclusion, our results suggest that the measurement of rCBV/rCBF with 133Xe SPECT and 99mTc-RBC SPECT is useful for detecting the hemodynamic compromise in patients with occlusive cerebrovascular disease.
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PMID:[Diagnosis of hemodynamic compromise in patients with chronic cerebral ischemia; measurement of cerebral blood volume (CBV) with 99mTc-RBC SPECT]. 235 76

In summary, then, the major strength of MRI in evaluating cerebral ischemia is in the sensitivity that this methodology provides for detection of the disease process. However, it must be realized that edema is a nonspecific event related to various insults affecting the brain. There is still an uncertain capability of MRI in separating acute hemorrhagic from acute ischemic events. The superior sensitivity of MRI should help in investigations aimed at evaluating various forms of intervention in acute ischemia. Because some of these acute changes are at the biochemical rather than morphologic level, proton MRI alone probably will be insufficient to explore numerous variables. For this reason, the potential offered by MRS in cerebral ischemia research and in clinical settings is important. Vascular imaging is relatively complex. Several techniques show promising results but at the present time have poor resolution in comparison to ultrasound and angiography. For the immediate future, they will remain investigational.
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PMID:Magnetic resonance imaging of cerebral ischemia and infarction. 307 44

The cerebral energy metabolism and brain oedema were investigated in three experimental cerebral ischaemia models using 31P-NMR spectroscopy (MRS) and 1H-NMR imaging (MRI) in the same subject animal. These measurements were performed also in experimental brain oedema models and the findings were compared with each other. 31P-MRS showed an ischaemic pattern in all of the cerebral ischaemia models, that is, ATP and PCr peaks decreased, and the Pi peak increased and shifted to a higher resonant frequency. However, 31P-MRS did not show any remarkable change in the brain oedema models. On the other hand, 1H-MRI clearly demonstrated brain oedema in the brain oedema model. In the cerebral ischaemia models, 1H-MRI findings differed depending upon the type of model, namely the most marked brain oedema was detected in the unilateral middle cerebral arterial occlusion model and no marked change was detected in the temporary four vessel occlusion model. It was thought that this difference depended on the severity of the ischaemic insult. Accordingly, the fundamental pathophysiological problem of cerebral ischaemia was the energy metabolism disturbance with the brain oedema being associated with this disturbance but occurring secondarily. However, in the brain oedema model the main pathological change was the increase in tissue water.
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PMID:Pathophysiological investigation of experimental cerebral ischaemia using in vivo 31P-NMR spectroscopy and 1H-MRI. 321 46

We studied 25 patients with sickle cell anemia and cerebral infarction. We classified lesions as to probable mechanism (large versus small vessel disease) based on the CT/MRI appearance of established infarction. Most patients had CT/MRI patterns of major cerebral vessel occlusion (41%) or border-zone (distal insufficiency) infarcts (31%) best explained by large cerebral vessel vasculopathy. Seven of 25 (28%) had either isolated subcortical (12%) or small cortical branch occlusion (16%) consistent with other mechanisms such as small vessel occlusion or embolism. These results suggest that most clinically recognized cerebral infarctions in sickle cell anemia are caused by large vessel disease, but this mechanism may not account for symptoms of cerebral ischemia in all cases.
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PMID:Cerebral infarction in sickle cell anemia: mechanism based on CT and MRI. 338 16


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