Perfusion-weighted Magnetic Resonance Imaging Research Articles

Abstract W P40: Predicting Tissue at Risk for Infarction Within an Optimal Arterial Spin Labeling Cerebral Blood Flow Threshold in Patients with Acute Stroke

Background: and Purpose: The aim of this study was to investigate whether pseudo-continuous arterial spin-labeling (ASL) in combination with an appropriate cerebral blood flow (CBF) threshold can reliably detect tissue at-risk for infarction. Methods: The retrospective study included 50 patients with acute stroke in the middle cerebral artery (MCA) territory who underwent perfusion-weighted magnetic resonance imaging (PW-MRI) within 24 hr of symptom onset and again in the subacute phase. After image co-registration the core and mismatch were segmented on ASL maps. Receiver operating characteristic (ROC) curve analysis was performed to calculate the optimal ASL-CBF threshold. Volumes on PW-MRI were recorded based on their ASL-CBF threshold (≧19-, 20-, 21-, 22-, 23-, 24- and 25 sec). Then the correlation between the penumbral salvage area and infarct growth, defined as the size difference between the lesion on baseline PWI- and the baseline diffusion-weighted images, and the final infarct volume were determined. Results: ROC analysis showed that the optimal threshold was 21.2 mL/100 g/min (area under the curve 0.88). The correlation between infarct growth and the penumbra salvage volume was significantly better for PWI lesions defined by ASL≦21 mL/100 g/min (r=-0.66; p<0.001). In 9 patients without recanalization on MRI obtained in the subacute phase, the ASL≦21 mL/100 g/min threshold more closely predicted the final infarct volume (r=0.82; p=0.006). Conclusion: PWI (ASL≧21 ml/100 g/min) volumes may provide an approximation of the volume of tissue at-risk for infarction in patients with acute stroke in the MCA territory.

Abstract 212: Factors Associated with Symptom Development in Asymptomatic Carotid Artery Stenosis: Multimodal Carotid and Perfusion Imaging Study

Background: The predictors of symptom development in asymptomatic carotid stenosis are still unclear. We sought to identify factors associated with symptom development in asymptomatic carotid stenosis using multimodal imaging technique. Methods: We retrospectively collected patients who had carotid artery revascularization procedures (carotid endarterectomy [CEA] or carotid artery stenting [CAS]) from April 2007 to May 2013. Patients who had event of cerebral ischemic stroke during 6 months before CEA or CAS were categorized as a symptomatic carotid stenosis. Results from carotid Duplex sonography, CT angiography, brain MRI and MRA, perfusion-weighted MRI (PWI), and demographic profiles were compared. Multivariate logistic regression analysis was performed to identify factors associated with symptom carotid stenosis. Results: A total of 684 patients (asymptomatic 58%, symptomatic 42%) with carotid stenosis more than 50% were included. The presence of ischemic heart diseases, peripheral artery occlusive disease and use of statin were higher in the asymptomatic carotid stenosis. On Duplex scan, ulceration, echolucent plaque, and heterogeneous components of plaque were more frequent in symptomatic carotid stenosis. Angiographic data showed the length of plaque was longer in symptomatic carotid stenosis. Presence of deep white matter hyperintensity, FLAIR vessel sign and GRE vessel sign were more frequently observed in symptomatic carotid stenosis. Patients with symptomatic carotid stenosis had increased cerebral blood flow, cerebral blood volume (CBV), and delayed time to peak when compared to the asymptomatic stenosis. Multivariate analysis revealed length of plaque (>20mm), deep white matter hyperintensity and increased CBV were associated with symptomatic carotid stenosis (Odd ratio [OR]=2.339, 95% confidence interval [CI] 1.312-4.169, P=0.004; OR=2.315, 95% CI 1.160-4.619, P=0.017; OR=2.242, 95% CI 1.127-4.463, P=0.021, respectively). Conclusion: Plaque burden, deep white matter hyperintensity, and increased CBV were independent predictors of symptom development in carotid stenosis. Multimodal imaging may be useful to identify high risk patients of ischemic stroke among asymptomatic carotid stenosis.

Abstract T MP52: Probabilistic Atlasing of Acute Ischemic Stroke Topology

Background: Knowing which areas of the brain are most vulnerable to acute ischemic stroke can focus care on more effective, targeted therapies. By displaying lesion incidence, these susceptible regions are clearly illustrated and can be correlated with characteristics common to that population. While previous studies created DWI lesion atlases, we aimed to map the spatio-temporal topology of multi-modal MRI sequences from a large cohort of stroke patients onto a standard atlas coordinate system. Methods: Pre-treatment ADC and perfusion-weighted imaging (PWI) and post-treatment FLAIR MRI sequences for 241 acute ischemic stroke patients which were retrospectively processed. Lesion locations were circumscribed semi-automatically on the ADC and FLAIR images. Perfusion parameters were extracted from the PWI images using Bayesian hemodynamic parameter estimation. To account for anatomical variation, custom software was created to co-register the MRIs onto an atlas. Decomposing by NIHSS score items, the software then created probabilistic maps by overlaying and averaging the subgroup’s lesions and parameters within the atlas. Results: An multi-dimensional set of annotated, co-registered stroke images for ADC, PWI and FLAIR sequences was established. Incidence maps based on NIHSS score items displayed anatomic localization of presenting symptoms in various imaging modes, before and after reperfusion or other therapies (Figure). A software suite was produced that co-registers, atlases, and calculates incidence maps for any set of images. Conclusions: A framework to obtain spatial incidence maps was applied to ADC, PWI and FLAIR MRI of ischemic stroke. This instrument can co-register any annotated imaging parameters and compute lesion maps for any metric of interest. This novel atlasing method may be used to elucidate stroke etiology, predict lesion progression and identify optimal treatments based on individual imaging features at presentation.

Stroke : Highlights of Selected Articles

HomeStrokeVol. 46, No. 2Stroke: Highlights of Selected Articles Free AccessResearch ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessResearch ArticlePDF/EPUBStroke: Highlights of Selected Articles Originally published1 Feb 2015https://doi.org/10.1161/STROKEAHA.114.008576Stroke. 2015;46:321Reliability and Limitations of Automated Arrhythmia Detection in Telemetric Monitoring After StrokeAll patients with acute ischemic stroke should have continuous ECG monitoring during admission to the hospital because of the increased risk of serious cardiac arrhythmia and for the detection of possible atrial fibrillation. Data on the use of continuous cardiac monitoring for patients with stroke are lacking. The current study by Kurka et al aimed to determine the validity of cardiac monitoring in a stroke unit after acute stroke. A total of 151 patients were included in the study, and >4800 hours of monitoring were evaluated. In total, 22 509 alarms were detected. Approximately 73% of all nonlife threatening alarms were correct. In contrast, only 8.6% of the 140 alarms deemed life-threatening arrhythmias were correct. Of these, asystole had the highest false-positive rate, as only 2% of these alarms were true asystole. In summary, continuous cardiac monitoring in acute stroke seems sensitive but not specific. The high false positivity can lead to noise disturbances and alarm fatigue. Further improvement in specificity of continuous cardiac monitoring is needed. See p 560.Bright Vessel Appearance on Arterial Spin Labeling MRI for Localizing Arterial Occlusion in Acute Ischemic StrokeArterial spin labeling (ASL) is a perfusion-weighted MRI sequence. The current study by Yoo et al reviewed the MRIs of 117 patients with acute ischemic stroke. All MRIs were analyzed for the presence or absence of bright vessel signal on ASL, susceptibility vessel sign, fluid-attenuated inversion recovery vascular hyperintensity, and arterial occlusion on MR angiography (MRA). The purpose of the study was to determine whether bright vessel signal on ASL could help localize arterial occlusion on MRI in patients with acute stroke. ASL bright vessel appearance was more common in patients with arterial occlusion seen on MRA than those without occlusion. The bright appearance on ASL was seen both proximal and distal to the site of occlusion. The sensitivity of ASL bright vessel appearance in detecting arterial occlusion was far more sensitive than susceptibility vessel sign when using MRA as a standard reference (94%, 33/35 versus 66%, 23/35; P=0.002). Among the 82 cases of negative MRA, ASL bright vessel appearance detected more peripheral occlusions than susceptibility vessel sign (21%, 17/82 versus 10%, 8/82; P=0.012). Importantly, this study showed that bright vessel signal on ASL may be helpful in identifying arterial occlusions not seen on MRA. Although further confirmatory studies are needed, the use of ASL in acute stroke MRI protocol may be helpful in diagnosing embolic lesions. See p 564.Safety and Effect of Metoclopramide to Prevent Pneumonia in Patients With Stroke Fed via Nasogastric Tubes TrialPneumonia is a major cause of morbidity and mortality after stroke. Dysphagia and aspiration are important causes of pneumonia after stroke. Patients receiving tube feeds via nasogastric tubes are at high risk of pneumonia. Metoclopramide, a dopamine antagonist, is both an antiemetic and gastric prokinetic. The authors hypothesized that the reduction in vomiting and reflux in patients on metoclopramide would lead to a reduction in the risk of aspiration and pneumonia. Metoclopramide to Prevent Pneumonia in Patients With Stroke Fed Via Nasogastric Tubes (MAPS) trial is a randomized, double blind, placebo-controlled trial of prophylactic metoclopramide versus placebo in patients with stroke fed via nasogastric tubes. Sixty patients were enrolled in this study in the 1:1 ratio. Pneumonia was significantly more common in the placebo group compared with the metoclopramide group (rate ratio, 5.24; P<0.001). There were also significantly more episodes of aspiration and days on antibiotics in the placebo group. There was no significant difference in mortality between both treatment groups. Extrapyramidal reactions, such as dystonic reactions and tardive dyskinesia, were not seen in the metoclopramide group. The results of the MAPS study show that the prophylactic use of metoclopramide in patients with stroke with nasogastric tubes is safe and reduces the incidence of pneumonia. Although these results are certainly promising, this study is limited by its size, and thus, larger studies will be needed before best determine the effect of metoclopramide in this stroke population. See p 454. Previous Back to top Next FiguresReferencesRelatedDetails February 2015Vol 46, Issue 2 Advertisement Article InformationMetrics © 2015 American Heart Association, Inc.https://doi.org/10.1161/STROKEAHA.114.008576 Originally publishedFebruary 1, 2015 PDF download Advertisement

Relative CBV ratio on perfusion-weighted MRI indicates the probability of early recanalization after IV t-PA administration for acute ischemic stroke

BackgroundWe hypothesized that the relative cerebral blood volume (rCBV) ratio on perfusion-weighted imaging (PWI) using MRI might serve as a predictor of early recanalization (ER) after intravenous tissue plasminogen activator...

Marchiafava-Bignami disease with asymmetric extracallosal lesions.

Marchiafava-Bignami disease (MBD) is a rare disease in patients with chronic alcoholism and is characterized by symmetric demyelination and necrosis of the corpus callosum. Clinical features include neuropsychiatric disorders, dysarthria, tetraparesis, astasia-abasia, impaired consciousness and symptoms of interhemispheric disconnection. The lesions in MBD are not restricted to the corpus callosum, but also occur in extracallosal regions. However, no case of MBD with extracallosal lesions confined to one side of the brain has been reported. We present a patient with MBD showing asymmetric extracallosal lesions and complete resolution of magnetic resonance imaging (MRI) abnormalities.

Dynamic Susceptibility Contrast Perfusion-Weighted Magnetic Resonance Imaging and Diffusion-Weighted Magnetic Resonance Imaging in Differentiating Recurrent Head and Neck Cancer From Postradiation Changes.

The aim of this study was to assess dynamic susceptibility contrast (DSC) perfusion-weighted magnetic resonance (MR) imaging and diffusion-weighted MR imaging in differentiating recurrent head and neck cancer from postradiation changes. A prospective study was done on 41 patients with head and neck cancer after radiotherapy who underwent diffusion-weighted MR imaging, DSC perfusion-weighted MR imaging, and routine postcontrast MR imaging. The apparent diffusion coefficient (ADC) map and time signal intensity curve of the lesion were created. The ADC value, DSC percentage (DSC%), and contrast enhancement percentage of the lesion were calculated. The final diagnosis was done with biopsy. There was significant difference (P = 0.001) in ADC between recurrent cancer (0.94 ± 0.16 × 10mm/s) and postradiation changes (1.37 ± 0.12 × 10mm/s). There was significant difference (P = 0.001) in DSC% of recurrent cancer (30.9% ± 5.16%) and postradiation changes (12.1% ± 3.06%). Selection of ADC equal to or less than 1.07 × 10mm/s and DSC% greater than 16.6% to predict recurrence have areas under the curve of 0.822 and 0.900 and accuracy of 92.7% and 95.1%, respectively. Combination of ADC and DSC% has are under the curve of 0.992 and accuracy of 97.6%. Combined ADC and DSC% are noninvasive imaging parameters that can play a role in the differentiation of recurrent head and neck cancer from postradiation changes.

Hepatitis C virus-associated neurocognitive and neuropsychiatric disorders: Advances in 2015.

Since its identification in 1989, hepatitis C virus (HCV) has emerged as a worldwide health problem with roughly 185 million chronic infections, representing individuals at high risk of developing cirrhosis and liver cancer. In addition to being a frequent cause of morbidity and mortality due to liver disease, HCV has emerged as an important trigger of lymphoproliferative disorders, owing to its lymphotropism, and of a wide spectrum of extra-hepatic manifestations (HCV-EHMs) affecting different organ systems. The most frequently observed HCV-EHMs include mixed cryoglobulinemia and cryoglobulinemic vasculitis, B-cell non-Hodgkin's lymphoma, nephropathies, thyreopathies, type 2 diabetes mellitus, cardiovascular diseases, and several neurological conditions. In addition, neuropsychiatric disorders and neurocognitive dysfunction are reported in nearly 50% of patients with chronic HCV infection, which are independent of the severity of liver disease or HCV replication rates. Fatigue, sleep disturbance, depression and reduced quality of life are commonly associated with neurocognitive alterations in patients with non-cirrhotic chronic HCV infection, regardless of the stage of liver fibrosis and the infecting genotype. These manifestations, which are the topic of this review, typically occur in the absence of structural brain damage or signal abnormalities on conventional brain magnetic resonance imaging (MRI), although metabolic and microstructural changes can be detected by in vivo proton magnetic resonance spectroscopy, perfusion-weighted and diffusion tensor MRI, and neurophysiological tests of cognitive processing. Several lines of evidence, including comparative and longitudinal neuropsychological assessments in patients achieving spontaneous or treatment-induced viral clearance, support a major pathogenic role for HCV in neuropsychiatric and neurocognitive disorders.

Differentiation of hemangioblastomas from pilocytic astrocytomas using 3-T magnetic resonance perfusion-weighted imaging and MR spectroscopy.

Hemangioblastomas and pilocytic astrocytomas (PAs) present similar imaging features on conventional MR imaging, making differential diagnosis a challenge. The purpose of this study was to evaluate the usefulness of dynamic susceptibility-weighted contrast-enhanced perfusion-weighted imaging (DSC-PWI) and proton MR spectroscopic imaging in the differentiation of hemangioblastomas and PAs. A 3.0-T MR imaging unit was used to perform DSC-PWI and conventional MR imaging on 14 patients with hemangioblastomas and 22 patients with PAs. Four patients with hemangioblastomas and 10 PA patients also underwent proton MR spectroscopy. Parameters of relative peak height (rPH) and relative percentage of signal intensity recovery (rPSR) were acquired by DSC-PWI and variables of N-acetylaspasrtate (NAA)/creatine (Cr), choline (Cho)/Cr, and lactate-lipid (Lac-Lip)/Cr by MR spectroscopy. The sensitivity, specificity, and the area under the receiver operating characteristic curve of all analyzed parameters at respective cutoff values were determined. Higher rPH but lower rPSR values were detected in hemangioblastomas compared to PAs. The NAA/Cr ratio was significantly lower in hemangioblastomas compared with PAs. The threshold values ≥3.2 for rPH provide sensitivity, specificity, positive predictive values, and negative predictive values of 85.7, 95.5, 92.3, and 91.3%, respectively, for differentiating hemangioblastomas from PAs. The optimal threshold values were ≤0.9 for rPSR and ≤1.5 for NAA/Cr ratios in tumor. Significantly higher rPH and lower NAA/Cr were seen in patients with hemangioblastomas when compared with PA patients, suggesting that DSC-PWI and proton MR spectroscopy are helpful in the characterization and differentiation of these two types of tumors.

Impact of Severe Extracranial ICA Stenosis on MRI Perfusion and Diffusion Parameters in Acute Ischemic Stroke.

Purpose: The aim of this study was to investigate the impact of a coexisting internal carotid artery (ICA) stenosis on lesion volumes as well as diffusion and perfusion parameters in acute ischemic stroke resulting from middle cerebral artery (MCA) occlusion.Material and methods: Magnetic resonance imaging data of 32 patients with MCA occlusion with or without additional ICA stenosis imaged within 4.5 h of symptom onset were analyzed. Both groups consisted of 16 patients. Acute diffusion lesions were semi-automatically segmented in apparent diffusion coefficient (ADC) MRI datasets. Perfusion maps of cerebral blood volume (CBV), cerebral blood flow, mean transit time and Tmax were calculated using perfusion-weighted MRI datasets. Tissue-at-risk (TAR) volumes were generated by subtracting the ADC lesion from the hypoperfusion lesion defined by Tmax >6 s. Median ADC and perfusion parameter values were extracted separately for the diffusion lesion and TAR and used for statistical analysis.Results: No significant differences were found between the groups regarding the diffusion lesion and TAR volumes. Statistical analysis of diffusion and perfusion parameters revealed CBV as the only parameter with a significant difference (p = 0.009) contributing a small effect (η2 = 0.11) to the group comparison with higher CBV values for the patient group with a coexisting ICA stenosis, while no significant effects were found for the other diffusion and perfusion parameters analyzed.Conclusion: The results of this study suggest that a coexisting ICA stenosis does not have a strong effect on tissue status or perfusion parameters in acute stroke patients except for a moderate elevation of CBV. This may reflect improved collateral circulation or ischemic preconditioning in patients with a pre-existing proximal stenosis balancing impaired perfusion from the stenosis.

Role of MR-DWI and MR-PWI in the radiotherapy of implanted pulmonary VX-2 carcinoma in rabbits.

To detect the activity of tumor cells and tumor blood flow before and after the radiotherapy of implanted pulmonary VX-2 carcinoma in rabbit models by using magnetic resonance diffusion-weighted imaging (MR-DWI) and magnetic resonance perfusion weighted imaging (MR-PWI), and to evaluate the effectiveness and safety of the radiotherapy based on the changes in the MR-DWI and MR-PWI parameters at different treatment stages. A total of 56 rabbit models with implanted pulmonary VX-2 carcinoma were established, and then equally divided into treatment group and control group. MR-DWI and MR-PWI were separately performed using a Philips Acheiva 1.5T MRI machine (Philips, Netherland). MRI image processing was performed using special perfusion software and the WORKSPACE advanced workstation for MRI. MR-DWI was applied for the observation of tumor signals and the measurement of apparent diffusion coefficient (ADC) values; whereas MR-PWI was used for the measurement of wash in rate (WIR), wash out rate (WOR), and maximum enhancement rate (MER). The radiation treatment was performed using Siemens PRIMUS linear accelerator. In the treatment group, the radiotherapy was performed 21 days later on a once weekly dosage of 1,000 cGy to yield a total dosage of 5,000 cGy. THE ADC PARAMETERS IN THE REGION OF INTEREST ON DWI WERE AS FOLLOWS: on the treatment day for the implanted pulmonary VX-2 carcinoma, the t values at the center and the edge of the lesions were 1.352 and 1.461 in the treatment group and control group (P>0.05). During weeks 0-1 after treatment, the t values at the center and the edge of the lesions were 1.336 and 1.137 (P>0.05). During weeks 1-2, the t values were 1.731 and 1.736 (P<0.05). During weeks 2-3, the t values were 1.742 and 1.749 (P<0.05). During weeks 3-4, the t values were 2.050 and 2.127 (P<0.05). During weeks 4-5, the t values were 2.764 and 2.985 (P<0.05). The ADC values in the treatment group were significantly higher than in the control group. After the radiotherapy (5,000 cGy), the tumors remarkably shrank, along with low signal on DWI, decreased signal on ADC map, and remarkably increased ADC values. As shown on PWI, on the treatment day for the implanted pulmonary VX-2 carcinoma, the t values of the WIR, WOR, and MER at the center of the lesions were 1.05, 1.31, and 1.33 in the treatment group and control group (P>0.05); in addition, the t values of the WIR, WOR, and MER at the edge of the lesions were 1.35, 1.07, and 1.51 (P>0.05). During weeks 0-1 after treatment, the t values of the WIR, WOR, and MER at the center of the lesions were 1.821, 1.856, and 1.931 (P<0.05); in addition, the t values of the WIR, WOR, and MER at the edge of the lesions were 1.799, 2.016, and 2.137 (P<0.05). During weeks 1-1 after treatment, the t values of the WIR, WOR, and MER at the center of the lesions were 2.574, 2.156, and 2.059 (P<0.05) and the t values of the WIR, WOR, and MER at the edge of the lesions were 1.869, 2.058, and 2.057 (P<0.05). During weeks 2-3 after treatment, the t values of the WIR, WOR, and MER at the center of the lesions were 2.461, 2.098, and 2.739 (P<0.05) and the t values of the WIR, WOR, and MER at the edge of the lesions were 2.951, 2.625, and 2.154 (P<0.05). During weeks 3-4 after treatment, the t values of the WIR, WOR, and MER at the center of the lesions were 2.584, 2.107, and 2.869 (P<0.05) and the t values of the WIR, WOR, and MER at the edge of the lesions were 2.057, 2.637, and 2.951 (P<0.05). During weeks 4-5 after treatment, the t values of the WIR, WOR, and MER at the center of the lesions were 2.894, 2.827, and 3.285 (P<0.05) and the t values of the WIR, WOR, and MER at the edge of the lesions were 3.45, 3.246, and 3.614 (P<0.05). After the radiotherapy (500 cGy), the tumors shrank on the T1WI, WIR, WOR, and MER; meanwhile, the PWI parameter gradually decreased and reached its minimum value. MR-DWI and MR-PWI can accurately and directly reflect the inactivation of tumor cells and the tumor hemodynamics in rabbit models with implanted pulmonary VX-2 carcinoma, and thus provide theoretical evidences for judging the clinical effectiveness of radiotherapy for the squamous cell carcinoma of the lung.

Perfusion-weighted magnetic resonance imaging detects recurrent isolated vertigo caused by cerebral hypoperfusion

Aim of the study: The etiology of isolated vertigo has been a substantial diagnostic challenge for both neurologists and otolaryngologists. This study was designed to detect recurrent isolated vertigo due to cerebral hypoperfusion using perfusion-weighted magnetic resonance imaging (PWI). Methods: We recruited isolated vertigo patients whose clinical condition was suspected to be caused by hypodynamics of the brain; these individuals formed the case group. We generated two additional groups: a negative group composed of vertigo patients whose symptoms were caused by problems associated with the ear and a healthy control group. Each subject underwent PWI, and seven regions of interest (ROIs) were chosen. The relative cerebral blood volume (rCBV), relative cerebral blood flow (rCBF), and mean transit time (MTT) were obtained from each ROI. We further calculated the absolute difference of relative parameter values between two mirrored ROIs. Results: The significant difference in the relative MTT from the mirrored cerebellar ROI (|rMTTleft-right|) of the case group was larger than those from the negative and healthy control groups (p = 0.026 and p = 0.038, respectively). Signal differences in |rrCBVleft-right| and |rrCBFleft-right| were not found among the three groups. Conclusions: In summary, disequilibrium in the rMTT of the bilateral cerebellum in the case group implied that hypoperfusion of the posterior circulation could trigger recurrent isolated vertigo and could be shown efficiently using PWI.

Performance of perfusion-weighted Fourier decomposition MRI for detection of chronic pulmonary emboli.

To evaluate the test performance of perfusion-weighted Fourier-decomposition (pw-FD) magnetic resonance imaging (MRI) in comparison to dynamic contrast-enhanced (DCE)-MRI as a reference standard in patients with known or suspected chronic pulmonary embolism (PE). In 64 patients, chronic PE was ruled out or confirmed by DCE-MRI using a time-resolved angiography with stochastic trajectories (TWIST) sequence in one breath-hold. Pw-FD-MRI was performed using a 2D fast low-angle shot (FLASH) sequence in free-breathing. After a nonrigid image registration, FD was applied to generate pw-images. Lungs were scored by two radiologists (2 and 12 years of lung MRI experience) visually for each lobe and segment for hypoperfused areas. For intra- and interobserver variability, the MR images were analyzed 2 months after the first analysis, blinded to the results of the first reader. PE was diagnosed by DCE-MRI in 39 patients. For the pw-FD MRI sensitivity, specificity, accuracy, and positive and negative predictive value for diagnosis of PE were 100%, 95%, 98%, 98%, and 100% on a per-patient basis, 94%, 94%, 94%, 95%, 94% on a per-lobe basis, and 82%, 92%, 88%, 88%, 88% on a segmental basis, respectively. Detection of subsegmental and segmental hypoperfusion using pw-FD MRI showed a moderate agreement with DCE-MRI (kappa of 0.68; 95% confidence interval: 0.64; 0.72). Pw-FD of the lung is a feasible test to diagnose chronic PE on a per-patient level during free-breathing without the use of ionizing radiation or contrast agents.

Systemic inflammation impairs tissue reperfusion through endothelin-dependent mechanisms in cerebral ischemia.

Systemic inflammation contributes to diverse acute and chronic brain pathologies, and extensive evidence implicates inflammation in stroke susceptibility and poor outcome. Here we investigate whether systemic inflammation alters cerebral blood flow during reperfusion after experimental cerebral ischemia. Serial diffusion and perfusion-weighted MRI was performed after reperfusion in Wistar rats given systemic (intraperitoneal) interleukin-1β or vehicle before 60-minute transient middle cerebral artery occlusion. The expression and location of endothelin-1 was assessed by polymerase chain reaction, ELISA, and immunofluorescence. Systemic interleukin-1 caused a severe reduction in cerebral blood flow and increase in infarct volume compared with vehicle. Restriction in cerebral blood flow was observed alongside activation of the cerebral vasculature and upregulation of the vasoconstricting peptide endothelin-1 in the ischemic penumbra. A microthrombotic profile was also observed in the vasculature of rats receiving interleukin-1. Blockade of endothelin-1 receptors reversed this hypoperfusion, reduced tissue damage, and improved functional outcome. These data suggest patients with a raised inflammatory profile may have persistent deficits in perfusion after reopening of an occluded vessel. Future therapeutic strategies to interrupt the mechanism identified could lead to enhanced recovery of penumbra in patients with a heightened inflammatory burden and a better outcome after stroke.

Modern imaging modalities in the assessment of acute stroke.

The aim of this review was to present the modern concepts of diagnostic imaging in acute stroke. Neuroimaging in acute stroke aims at diagnosing the condition as early as possible and assessing the extent of parenchymal perfusion and the intracranial vessels patency. A modern approach would involve a combination of various imaging modalities as multidetector computed tomography and high field magnetic resonance imaging. A non-enhanced computed tomography (CT) is used to detect hemorrhage or to identify early signs of ischemic stroke. CT angiography finds evidence of intravascular thrombi or significant stenoses, and CT perfusion displays brain tissue at risk of irreversible alterations that can be salvaged therapeutically. Magnetic resonance imaging (MRI) is a more sensitive modality than CT in diagnosing acute brain ischemia. MR diffusion-weighted imaging is more sensitive than conventional MR sequences in hyperacute stage. MR angiography as a non-invasive and non-ionizing imaging method is used as an alternative modality to CT angiography. To find brain tissue at risk diffusion- and perfusion-weighted magnetic resonance imaging modalities are used. The authors present briefly the modern neuroimaging modalities used in patients with transient ischemic attack, minor stroke and venous infarction. By combining different imaging techniques in a multimodal approach we can acquire the information necessary for therapeutic planning and differentiate patients who need thrombolysis.

Correlative assessment of tumor microcirculation using contrast‐enhanced perfusion MRI and intravoxel incoherent motion diffusion‐weighted MRI: is there a link between them?

The purpose of this study was to correlate intravoxel incoherent motion (IVIM) imaging with classical perfusion-weighted MRI metrics in human gliomas. Parametric images for slow diffusion coefficient (D), fast diffusion coefficient (D*), and fractional perfusion-related volume (f) in patients with high-grade gliomas were generated. Maps of Fp (plasma flow), vp (vascular plasma volume), PS (permeability surface-area product), ve (extravascular, extracellular volume), E (extraction ratio), ke (influx ratio into the interstitium), and tc (vascular transit time) from dynamic contrast-enhanced (DCE) and dynamic susceptibility contrast-enhanced (DSC) MRI were also generated. A region-of-interest analysis on the contralateral healthy white matter and on the tumor areas was performed and the extracted parameter values were tested for any significant differences among tumor grades or any correlations. Only f could be significantly correlated to DSC-derived vp and tc in healthy brain tissue. Concerning the tumor regions, Fp was significantly positively correlated with D* and inversely correlated with f in DSC measurements. The D*, f, and f × D* values in the WHO grade III gliomas were non-significantly different from those in the grade IV gliomas. There was a trend to significant negative correlations between f and PS as well as between f × D* and ke in DCE experiments. Presumably due to different theoretical background, tracer properties and modeling of the tumor vasculature in the IVIM theory, there is no clearly evident link between D*, f and DSC- and DCE-derived metrics.

Value of perfusion-weighted MR imaging in the assessment of early cerebral alterations in neurologically asymptomatic HIV-1-positive and HCV-positive patients.

Background and PurposeAsymptomatic central nervous system (CNS) involvement occurs in the early stage of the human immunodeficiency virus (HIV) infection. It has been documented that the hepatitis C virus (HCV) can replicate in the CNS. The aim of the study was to evaluate early disturbances in cerebral microcirculation using magnetic resonance (MR) perfusion-weighted imaging (PWI) in asymptomatic HIV-1-positive and HCV-positive patients, as well as to assess the correlation between PWI measurements and the clinical data.Materials and MethodsFifty-six patients: 17 HIV-1-positive non-treated, 18 HIV-1-positive treated with combination antiretroviral therapy (cART), 7 HIV-1/HCV-positive non-treated, 14 HCV-positive before antiviral therapy and 18 control subjects were enrolled in the study. PWI was performed with a 1.5T MR unit using dynamic susceptibility contrast (DSC) method. Cerebral blood volume (CBV) measurements relative to cerebellum (rCBV) were evaluated in the posterior cingulated region (PCG), basal ganglia (BG), temporoparietal (TPC) and frontal cortices (FC), as well as in white matter of frontoparietal areas. Correlations of rCBV values with immunologic data and liver histology activity index (HAI) were analyzed.ResultsSignificantly lower rCBV values were found in the right TPC and left FC as well as in PCG in HIV-1-positive naïve (p = 0.009; p = 0.020; p = 0.012), HIV-1 cART treated (p = 0.007; p = 0.009; p = 0.033), HIV-1/HCV-positive (p = 0.007; p = 0.027; p = 0.045) and HCV-positive patients (p = 0.010; p = 0.005; p = 0.045) compared to controls. HIV-1-positive cART treated and HIV-1/HCV-positive patients demonstrated lower rCBV values in the right FC (p = 0.009; p = 0.032, respectively) and the left TPC (p = 0.036; p = 0.005, respectively), while HCV-positive subjects revealed lower rCBV values in the left TPC region (p = 0.003). We found significantly elevated rCBV values in BG in HCV-positive patients (p = 0.0002; p<0.0001) compared to controls as well as to all HIV-1-positive subjects. There were no significant correlations of rCBV values and CD4 T cell count or HAI score.ConclusionsPWI examination enables the assessment of HIV-related as well as HCV-related early cerebral dysfunction in asymptomatic subjects. HCV-infected patients seem to reveal the most pronounced perfusion changes.

The application of magnetic resonance diffusion tensor and perfusion-weighted imaging in grading of cerebral gliomas

Objective To study the application of magnetic resonance (MR),perfusion-weighted imaging (PWI) and diffusion tensor imaging (DTI) in grading gliomas.Methods 45 patients with intracranial gliomas (22 low-grade and 23 high-grade ghomas) were performed with MR examination,including conventional magnetic resonance imaging (MRI),diffusion tensor imaging (DTI) and perfusionweighted imaging (PWI).Quantitative parameters [average cerebral coefficient(ADC),fractional anisotropy(FA),reginal cerebral blood flowr(CBF),reginal cerebral blood volume (rCBV)] of solid regions of tumors,peritumoral regions and analogous locations in the contralateral WM corresponding to the tumor were measured on corresponding parameter maps generated from DTI or PWI.Then these values were compared between different groups.Receiver operating characteristic (ROC) analyses were performed to determine optimum thresholds for grading and also to calculate the sensitivity and specificity for tumor grading.Results There was a strong correlation between rCBF and rCBV of the solid regions in all 45 cases (R2 =0.9388,P ＜0.01).There was statistical significances between the ADC,FA,rCBF,rCBV values of solid regions,peritumoral region and normal white matter values (P ＜ 0.05).The difference of relative rCBV (rrCBF) and relative ADC (rADC) of solid region between high and low grade gliomas was statistical (P ＜ 0.01).So was that of the rrCBV of peritumoral regions (P ＜ 0.01).The threshold of rrCBF,rrCBV,of solid region were 2.749 and 3.058,respectively,and the diagnostic sensibility and specificity were 87％ and 100％ vs.91.3％ and 95.5％,respectively.All rrCBF,rrCBV,ADC values of solid region showed high diagnostic accuracy.Conclusion The rrCBF,rrCBV,ADC values of solid region of tumors can be used to differentiate high and low grade gliomas.The diagnostic sensitivity and specificity of rrCBF are high,and the area under the ROC curve of rrCBF is the highest,with the value of 0.974. Key words: Glioma; Magnetic resonance imaging; Diffusion tensor imaging; Perfusion-weighted imaging

Imaging of cerebral blood flow in patients with severe traumatic brain injury in the neurointensive care.

Ischemia is a common and deleterious secondary injury following traumatic brain injury (TBI). A great challenge for the treatment of TBI patients in the neurointensive care unit (NICU) is to detect early signs of ischemia in order to prevent further advancement and deterioration of the brain tissue. Today, several imaging techniques are available to monitor cerebral blood flow (CBF) in the injured brain such as positron emission tomography (PET), single-photon emission computed tomography, xenon computed tomography (Xenon-CT), perfusion-weighted magnetic resonance imaging (MRI), and CT perfusion scan. An ideal imaging technique would enable continuous non-invasive measurement of blood flow and metabolism across the whole brain. Unfortunately, no current imaging method meets all these criteria. These techniques offer snapshots of the CBF. MRI may also provide some information about the metabolic state of the brain. PET provides images with high resolution and quantitative measurements of CBF and metabolism; however, it is a complex and costly method limited to few TBI centers. All of these methods except mobile Xenon-CT require transfer of TBI patients to the radiological department. Mobile Xenon-CT emerges as a feasible technique to monitor CBF in the NICU, with lower risk of adverse effects. Promising results have been demonstrated with Xenon-CT in predicting outcome in TBI patients. This review covers available imaging methods used to monitor CBF in patients with severe TBI.

Emerging applications for ferumoxytol as a contrast agent in MRI.

Ferumoxytol is an ultrasmall superparamagnetic iron oxide (USPIO) agent initially approved by the Food and Drug Administration (FDA) as an iron replacement therapy for patients with anemia due to chronic renal failure. Recently, ferumoxytol has been investigated extensively as an intravenous contrast agent in magnetic resonance imaging (MRI). Since it causes regional T1 and T2 * shortening in vivo, conventional pulse sequences can be used following ferumoxytol administration to demonstrate signal enhancement or loss. Ferumoxytol can be administered as a rapid bolus and has a long intravascular half-life on the order of 14-15 hours, making it a potentially useful agent for vascular and perfusion-weighted MRI. In comparison to other USPIOs, ferumoxytol is less limited by allergic and idiosyncratic reactions. Furthermore, since ferumoxytol is an iron-based agent with no potential for causing nephrogenic systemic fibrosis, it may be useful as an alternative to gadolinium-based contrast agents in patients with compromised renal function. Ferumoxytol is ultimately taken up by macrophages/the reticuloendothelial system in the liver, spleen, and lymph nodes, and this uptake mechanism is being explored as a novel imaging technique for vascular lesions, tumors, and lymph nodes. This article reviews the properties of ferumoxytol relevant to MRI as well as many of the uses for the agent currently under investigation.