Cerebral magnetic resonance imaging within 6 hours of stroke onset: inter- and intra-observer reproducibility

BACKGROUND: Magnetic resonance imaging (MRI) provides valuable pathophysiological information during the very first hours of cerebral ischemia. However, the reliability of prime-time MRI in the setting of emergency care remains unknown. AIM: To evaluate the reproducibility between and within observers of the assessment of MRI scans in stroke patients. METHOD: We performed a MRI scan within 6 h of stroke onset, with time-of-flight (TOF), T2* gradient echo, FLAIR, diffusion- (DWI) and perfusion- (PWI) weighted images, in 17 consecutive patients. Four observers, blinded to the clinical history, separately performed a visual assessment of all scans, and repeated the assessment 2-8 days later. Two neuroradiologists made volumetric measures of diffusion and perfusion abnormalities using a semi-automatic technique 2 weeks after the 2nd visual assessment. We evaluated: (i) in the whole set of MRI scans, the quality of scans and their ability to identify primary hemorrhages on T2* gradient echo sequences; (ii) in patients with acute cerebral ischemia only, the inter- and intra-observer agreement for the presence of arterial occlusion and cerebral abnormalities on TOF sequences, and (iii) on DWI and PWI sequences, the relationship between visual and automatic assessments for the presence of a mismatch (defined as the difference between the perfusion and diffusion abnormalities) of >20%. Statistics used the kappa (kappa) method. RESULTS: The median delay between clinical onset and MRI was 285 min. Two patients had primary cerebral hemorrhages, 1 a post-ictal deficit, and 14 cerebral ischemia. The quality of the scans was judged as appropriate for all scans in all sequences except for FLAIR. All observers identified the 2 patients with hemorrhages. The inter- and intra-observer reliability was substantial to excellent (kappa values ranging from 0.63 to 1.00) for all sequences. The agreement between visual and automatic assessments for the presence of a mismatch of >20% was excellent in all observers. CONCLUSION: The visual assessment of T2* gradient echo, TOF, diffusion and perfusion sequences at the acute stage of stroke is reproducible between and within observers. The visual assessment is as good as the volumetric assessment to detect a mismatch of >20%.     

Diffusion-weighted magnetic resonance imaging of cerebral ischemia

Functional magnetic resonance imaging is providing new insight into neurologic imaging that was not possible with conventional techniques. Diffusion magnetic resonance imaging is one aspect of functional imaging and it allows detection of acute cerebral ischemia that would not have been identified with standard T2-weighted sequences while also differentiating acute from chronic stroke. These unique characteristics suggest tremendous potential of diffusion imaging to help direct therapy of acute ischemic stroke. An understanding of the principles of diffusion imaging is necessary for optimal application of this technique.     

Stroke: high-field magnetic resonance imaging

Diagnostic modalities for the diagnosis of acute stroke have increased in number and quality. Magnetic resonance imaging has increasingly become a central tool for the management of patients with stroke. New sequences, such as diffusion and perfusion, provide insight into the infarcted core and the hypoperfused brain. The use of higher magnetic fields allows us to gain in signal strength, which can be used to improve imaging speed and/or resolution. Recent additional sequences allow perfusion without contrast and susceptibility-weighted imaging can help identify early bleeding. These new techniques should provide more information about the on going ischemic process.     

Quantitative proton magnetic resonance imaging in focal cerebral ischemia in rat brain

Proton magnetic resonance (MR) imaging has been recommended as a diagnostic tool for the detection of focal cerebral ischemia. We compared microscopic MR images of rat brains after focal cerebral ischemia with evidence of histological damage found on corresponding silver-impregnated or cresyl violet-stained brain sections. Ten male Wistar rats were subjected to permanent unilateral occlusions of the right middle cerebral and common carotid arteries under halothane anesthesia. Twenty-four hours later the area of injury on MR images amounted to 26% of the total slice area, whereas only 9% of the total slice area was necrotic on histological sections from the same animals. The infarcted areas on tissue sections were surrounded by regions of selective neuronal injury in the cerebral cortex and occasionally in the hippocampus. The area of injury on MR images was larger than the combined areas of infarction and selective neuronal injury on histological sections. Areas of increased T2 values on MR images extended medially into noninfarcted striatum and laterally and dorsally into noninfarcted cortex. The lateral and dorsal areas on MR images frequently coincided with cortical areas in which considerable selective neuronal injury was present in the upper cortical layers. We hypothesize that the abnormal areas on MR images above histologically normal brain tissue represent the ischemic penumbra. If true, this is the first demonstration of the ischemic penumbra by MR imaging and may reflect our use of Wistar rats, a new image analysis technique, and ultra-high resolution MR imaging.     

Magnetic resonance perfusion imaging evaluation in perfusion abnormalities of the cerebellum after supratentorial unilateral hyperacute cerebral infarction

Magnetic resonance imaging (MRI) data of 10 patients with hyperacute cerebral infarction (≤6 hours) were retrospectively analyzed.Six patients exhibited perfusion defects on negative enhancement integral maps,four patients exhibited perfusion differences in pseudo-color on mean time to enhance maps,and three patients exhibited perfusion differences in pseudo-color on time to minimum maps.Dynamic susceptibility contrast-enhanced perfusion weighted imaging revealed a significant increase in region negative enhancement integral in the affected hemisphere of patients with cerebral infarction.The results suggest that dynamic susceptibility contrast-enhanced perfusion weighted imaging can clearly detect perfusion abnormalities in the cerebellum after unilateral hyperacute cerebral infarction.     

Metabolic changes in cerebral gliomas within hours of treatment with intra-arterial BCNU demonstrated by phosphorus magnetic resonance spectroscopy

A 40-year-old female with a recurrent mixed astrocytoma/oligodendroglioma was treated with intra-arterial BCNU at six week intervals. Phosphorus magnetic resonance spectroscopy was performed before, and on two occasions after her third treatment. Before treatment, phosphodiesters were 25% less than normal and intracellular pH was 7.14 (normal 6.97 +/- 0.02). Eight hours following treatment phosphocreatine and phosphodiesters were reduced by approximately 40% and pHi increased to 7.24. Thirty-two hours after treatment, phosphocreatine and phosphodiesters had reversed their decline, but pHi had increased further to 7.35. MRI and x-ray CT scans did not show any change during this period. This study demonstrates that chemical changes can be observed in a glioma by magnetic resonance spectroscopy shortly after chemotherapy in a clinical setting and before changes are observable by imaging modalities. This approach evidently offers a possible means of monitoring the acute metabolic response of tumours to chemotherapy or other forms of treatment by a non-invasive repeatable quantitative method.     

T2-weighted magnetic resonance imaging of cerebrovascular reactivity in rat reversible focal cerebral ischemia

Cerebrovascular carbon dioxide (CO₂) reactivity is an important hemodynamic index in cerebrovascular disease. In the present study T2^*-weighted magnetic resonance image (T2^*WI) was evaluated as a non-invasive method to investigate changes in CO₂ reactivity. Fourteen rats were subjected to permanent or, 30 and 90 min of temporary middle cerebral artery occlusion. A series of T2^*WIs and diffusion-weighted magnetic resonance images (DWI) was performed hourly under normo- and hypercapnic conditions. Triphenyltetrazolium chloride (TTC) staining of brain sections was obtained at the end of experiment to evaluate ischemic damage. During ischemia, a 4–6% signal increase upon hypercapnia was observed on T2^*WI in the non-ischemic hemisphere, while no such reactivity was seen in the putamen and cortex ipsilateral to the MCA occlusion. After reperfusion, CO₂ reactivity recovered in the putamen and cortex in the 30 min ischemia group and in the cortex alone of the 90 min ischemia groups. The areas with irreversible CO₂ reactivity dysfunction coincidentally revealed no recovery on DWI and lack of TTC staining. The results indicate that T2^*WI can be used to monitor changes in CO₂ reactivity after various ischemic insults that may indicate tissue viability.     

Application of magnetic resonance imaging for monitoring stem cell transplantation for the treatment of cerebral ischemia

OBJECTIVE:To identify global research trends in the application of MRI for monitoring stem cell transplantation using a bibliometric analysis of Web of Science.DATA RETRIEVAL:We performed a bibliometric analysis of studies relating to the application of MRI for detecting stem cell transplantation for the treatment of cerebral ischemia using papers in Web of Science published from 2002 to 2011.SELECTION CRITERIA:The inclusion criteria were:(a) peer-reviewed articles on the application of MRI for detecting transplanted stem cells published and indexed in Web of Science;(b) year of publication between 2002 and 2011.Exclusion criteria were:(a) articles that required manual searching or telephone access;(b) some corrected papers.MAIN OUTCOME MEASURES:(1) Annual publication output;(2) distribution according to journals;(3) distribution according to institution;(4) distribution according to country;(5) top cited authors over the last 10 years.RESULTS:A total of 1 498 studies related to the application of MRI for monitoring stem cell transplantation appeared in Web of Science from 2002 to 2011,almost half of which were derived from American authors and institutes.The number of studies on the application of MRI for detecting stem cell transplantation has gradually increased over the past 10 years.Most papers on this topic appeared in Magnetic Resonance in Medicine.CONCLUSION:This analysis suggests that few experimental studies have been investigated the use of MRI for tracking SPIO-labeled human umbilical cord blood-derived mesenchymal stem cells during the treatment of cerebral ischemia.     

Pre-treatment of adrenomedullin suppresses cerebral edema caused by transient focal cerebral ischemia in rats detected by magnetic resonance imaging

Recent studies suggest the protective effects of adrenomedullin (AM) on ischemic brain damage. The present study was aimed at investigating the effects of AM and its receptor antagonist, AM_22-52, on ischemia-induced cerebral edema and brain swelling in rats using magnetic resonance imaging. Rats were subjected to 60 min of middle cerebral artery occlusion (MCAO) followed by reperfusion. Intravenous injection of AM (1.0 μg/kg), AM_22-52 (1.0 μg/kg), or saline was made before MCAO. Effects of AM injection just after reperfusion were also investigated. One day after ischemia, increases in T₂-weighted signals in the brain were clearly observed. Total edema volume, as well as brain swelling, was greatly and significantly reduced by pre-treatment of AM (reduced by 53%). Extent of brain swelling was significantly correlated with the volume of cerebral edema. The protective effect of AM against edema was more clearly observed in the cerebral cortex (reduced by 63%) than the striatum (reduced by 31%). Increased T₂ relaxation time in the cortex was recovered partially by pre-treatment of AM. Post-treatment of AM had no effects. Pre-treatment of AM_22-52 tended to exacerbate the edema. In another line of experiment, cocktail administration of AM with melatonin, a pineal product having neuroprotective potential as a free radical scavenger, failed to enhance the protective effects of AM alone. The present study clearly suggests the prophylactic effects of AM against cerebral edema, especially the cortical edema, in a rat stroke model.     

Anticardiolipin antibodies in acute non-hemorrhagic stroke seen within six hours after onset

Introduction – We have undertaken a prospective study to measure anticardiolipin antibodies of IgG isotype within the first few hours of an acute non-hemorrhagic stroke. Material and methods – We have collected blood samples at entry from one hundred patients (53 men and 47 women), mean age 67.4 years, referred within 6 h of a first-ever non-hemorrhagic stroke, and from an equal number of age- and gender-matched control patients. Results – IgG anticardiolipin antibodies were 10 GPL in 26 patients and in 5 controls (p <0.0001, X2 test). After logistic regression analysis, increase of IgG anticardiolipin antibodies remained independently associated with stroke (p = 0.0034), together with hypertension (p = 0.0009) and atrial fibrillation (p = 0.0238). Conclusion – Our data suggest that the occurrence of elevation of IgG anticardiolipin antibodies in stroke patients should antedate stroke onset and might be a risk factor per se .     

磁共振灌注成像评估蛛网膜下腔出血后脑血管痉挛的价值

目的 观察磁共振灌注成像（MR-PWI）对动脉瘤性蛛网膜下腔出血（aSAH）后脑血管痉挛（CVS）脑血流动力学的评估价值。方法 2014年1~12月收治aSAH 80例,根据CVS程度分为无血管痉挛组（23例）,轻度痉挛组（19例）,中度痉挛组（19例）和重度痉挛组（19例）,选取同期收治的颅内未破裂动脉瘤20例作为对照组。均进行DSA和磁共振灌注成像检查,MR-PWI检测的区域包括大脑前动脉（ACA）供血区、大脑中动脉（MCA）供血区以及基底节区（BSGL）,分析MR-PWI相对脑血容量（rCBV）、相对脑血流量（rCBF）、平均通过时间（MTT）以及达峰时间（TTP）等参数与CVS的相关性。结果 重度痉挛ACA供血区、MCA供血区以及BSGL的rCBF、rCBV较对照组明显下降（P<0.05）,而无血管痉挛组、轻度痉挛组、中度痉挛组bsgl的rcbf以及aca供血区的rcbf均明显低于对照组（>P<0.05）;中度痉挛组aca供血区、mca供血区、bsgl的ttp以及mtt均明显高与对照组（>P<0.05）,且随着痉挛程度的加重,变化更加明显（>P<0.05）。cvs程度和rcbv、rcbf呈负相关（>P<0.05）,但是其相关度较低（r><0.4）;cvs程度与ttp、mtt呈正相关（>P<0.05）,为中度相关（0.308><0.744）。>结论 MR-PWI检查能够定量提供脑组织血流灌注的信息,指导CVS的临床诊疗。