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Research Interests: Radiology, Magnetic Resonance Imaging, Medicine, Diffusion MRI, Stroke, and 15 moreHumans, Diffusion, Male, Perfusion, Diagnostic Imaging, Clinical Sciences, Aged, Blood Flow, Recombinant Proteins, Cerebrovascular Disorders, Acute Ischemic Stroke, Neurosciences, Plasminogen Activator, Cardiovascular medicine and haematology, and Recombinant tissue plasminogen activator
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Identification of ischaemic stroke subtype currently relies on clinical evaluation supported by various diagnostic studies. The authors sought to determine whether specific diffusion-weighted MRI (DWI) patterns could reliably guide the... more
Identification of ischaemic stroke subtype currently relies on clinical evaluation supported by various diagnostic studies. The authors sought to determine whether specific diffusion-weighted MRI (DWI) patterns could reliably guide the subsequent work-up for patients presenting with acute ischaemic stroke symptoms. 273 consecutive patients with acute ischaemic stroke symptoms were enrolled in this prospective, observational, single-centre NIH-sponsored study. Electrocardiogram, non-contrast head CT, brain MRI, head and neck magnetic resonance angiography (MRA) and transoesophageal echocardiography were performed in this prespecified order. Stroke neurologists determined TOAST (Trial of Org 10172 in Acute Stroke Treatment) classification on admission and on discharge. Initial TOAST stroke subtypes were compared with the final TOAST subtype. If the final subtype differed from the initial assessment, the diagnostic test deemed the principal determinant of change was recorded. These principal determinants of change were compared between a CT-based and an MRI-based classification schema. Among patients with a thromboembolic DWI pattern, transoesophageal echocardiography was the principal determinant of diagnostic change in 8.8% versus 0% for the small vessel group and 1.7% for the other group (p<0.01). Among patients with the combination of a thromboembolic pattern on MRI and a negative cervical MRA, transoesophageal echocardiography led to a change in diagnosis in 12.1%. There was no significant difference between groups using a CT-based scheme. DWI patterns appear to predict stroke aetiologies better than conventional methods. The study data suggest an MRI-based diagnostic algorithm that can potentially obviate the need for echocardiography in one-third of stroke patients and may limit the number of secondary extracranial vascular imaging studies to approximately 10%.
Research Interests: Algorithms, Neurology, Radiology, Magnetic Resonance Imaging, Medicine, and 15 moreElectrocardiography, Stroke, Brain, Prospective studies, Humans, Female, Male, Brain Ischemia, Thromboembolism, Aged, Middle Aged, X ray Computed Tomography, Psychology and Cognitive Sciences, Diffusion magnetic resonance imaging, and Medical and Health Sciences
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The prognosis for high-grade glioma (HGG) remains dismal and the extent of resection correlates with overall survival and progression free disease. Epidermal growth factor receptor (EGFR) is a biomarker heterogeneously expressed in HGG.... more
The prognosis for high-grade glioma (HGG) remains dismal and the extent of resection correlates with overall survival and progression free disease. Epidermal growth factor receptor (EGFR) is a biomarker heterogeneously expressed in HGG. We assessed the feasibility of detecting HGG using near-infrared fluorescent antibody targeting EGFR. Mice bearing orthotopic HGG xenografts with modest EGFR expression were imaged in vivo after systemic panitumumab-IRDye800 injection to assess its tumor-specific uptake macroscopically over 14 days, and microscopically ex vivo. EGFR immunohistochemical staining of 59 tumor specimens from 35 HGG patients was scored by pathologists and expression levels were compared to that of mouse xenografts. Intratumoral distribution of panitumumab-IRDye800 correlated with near-infrared fluorescence and EGFR expression. Fluorescence distinguished tumor cells with 90% specificity and 82.5% sensitivity. Target-to-background ratios peaked at 14 h post panitumumab-IRDy...
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To evaluate the reproducibility of cerebrovascular reactivity (CVR) measurements acquired in children using magnetic resonance imaging (MRI) in combination with a computer-controlled carbon dioxide (CO2 ) stimulus. Ten healthy children... more
To evaluate the reproducibility of cerebrovascular reactivity (CVR) measurements acquired in children using magnetic resonance imaging (MRI) in combination with a computer-controlled carbon dioxide (CO2 ) stimulus. Ten healthy children (age 16.1 ± 1.6 years) underwent CVR imaging on a 3T scanner using a blood-oxygen level-dependent (BOLD) MRI sequence. Targeted hypercapnia was induced during imaging with a CO2 gas challenge delivered using a specialized gas sequencer (RespirAct). A total of four BOLD scans were performed over 2 separate days to test within-day and between-day consistency of the data. CVR values were computed by correlating the relative change in BOLD signal in response to the CO2 stimulus delivered to the each subject. Intraclass correlation coefficients (ICCs) of within-day values show highly reproducible measures in both the gray matter (ICC = 0.857, P < 0.001) and white matter (ICC = 0.895, P < 0.001). Relatively lower between-day reproducibility was observ...
Research Interests: Engineering, Carbon Dioxide, Magnetic Resonance Imaging, Nuclear medicine, Adolescent, and 15 moreMedicine, Brain Mapping, Computers, Brain, Humans, Female, Male, Physical sciences, Motion, White matter, Homeostasis, Reproducibility, Reproducibility of Results, Hypercapnia, and Medical and Health Sciences
Research Interests: Immunology, Multiple sclerosis, Magnetic Resonance Imaging, Biology, Medicine, and 15 moreBrain, Corpus Callosum, Autoimmune Disease, Autoimmune diseases, Animals, Parietal Lobe, Callithrix, Experimental Autoimmune Encephalomyelitis, Reference Values, Clinical Investigation, Encephalomyelitis, epitope, Adoptive Cell Transfer, Medical and Health Sciences, and myelin basic protein
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Research Interests:
Dysprosium diethylenetriamine-pentaacetic acid-bis (methylamide) (DTPA-BMA), a new nonionic contrast medium for magnetic resonance (MR) imaging, produces signal loss on T2-weighted images because of induced magnetic field gradients. The... more
Dysprosium diethylenetriamine-pentaacetic acid-bis (methylamide) (DTPA-BMA), a new nonionic contrast medium for magnetic resonance (MR) imaging, produces signal loss on T2-weighted images because of induced magnetic field gradients. The potential of this agent to delineate myocardial ischemia was investigated in 10 rats with acute (30 minutes) occlusion of the left coronary artery. T2-weighted MR images were acquired before and for 1 hour after intravenous administration of 1 mmol/kg of Dy-DTPA-BMA. Before administration of the contrast medium, signal intensity (SI) in the ischemic region was significantly greater than that in the normal myocardium; however, the borders of the ischemic region were not consistently distinct. The contrast medium caused marked decrease in SI of normal myocardium (18% +/- 3% of the control value), only slight decrease in the jeopardized region (76% +/- 6% of the control value), and no discernible effects on heart rate or blood pressure. Substantial contrast between normal and ischemic myocardium persisted for 1 hour. Moderate signal loss was observed in skeletal muscle. Dy-DTPA-BMA has the potential to demarcate the myocardial area in jeopardy as a region of high signal intensity because it erases signal preferentially in the normal myocardium.
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9 The degree of expansion of the early DWI lesion into the volume of the baseline PWI lesion is variable. In some patients partial recruitment of the DWI lesion volume occurs, while other patients develop a DWI lesion that equals or... more
9 The degree of expansion of the early DWI lesion into the volume of the baseline PWI lesion is variable. In some patients partial recruitment of the DWI lesion volume occurs, while other patients develop a DWI lesion that equals or exceeds the size of the initial PWI volume. We investigated whether a quantitative analysis of the severity of the early perfusion deficit predicted the evolution of the PWI/DWI mismatch. Methods We studied patients with acute ischemic stroke in whom PWI and DWI MRI were performed within 7 hours after symptom onset and after 4–5 days. Maps of CBF, CBV and Mean Transit Time(MTT)were created after deconvolution of the arterial input function with the time-concentration curve. We compared the lesion volume on DWI at f/u with the baseline MTT volume. Patients in whom the lesion volume on DWI at f/u was smaller than the initial PWI deficit (group 1) were compared with patients in whom the DWI lesion at f/u (group 2) was ≥ than the initial PWI volume. Characte...
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OBJECTIVE Patients with brain arteriovenous malformations (AVMs) often require repeat imaging with MRI or MR angiography (MRA), CT angiography (CTA), and digital subtraction angiography (DSA). The ideal imaging modality provides excellent... more
OBJECTIVE Patients with brain arteriovenous malformations (AVMs) often require repeat imaging with MRI or MR angiography (MRA), CT angiography (CTA), and digital subtraction angiography (DSA). The ideal imaging modality provides excellent vascular visualization without incurring added risks, such as radiation exposure. The purpose of this study is to evaluate the performance of ferumoxytol-enhanced MRA using a high-resolution 3D volumetric sequence (fe-SPGR) for visualizing and grading pediatric brain AVMs in comparison with CTA and DSA, which is the current imaging gold standard. METHODS In this retrospective cohort study, 21 patients with AVMs evaluated by fe-SPGR, CTA, and DSA between April 2014 and August 2017 were included. Two experienced raters graded AVMs using Spetzler-Martin criteria on all imaging studies. Lesion conspicuity (LC) and diagnostic confidence (DC) were assessed using a 5-point Likert scale, and interrater agreement was determined. The Kruskal-Wallis test was ...
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While brain connectivity analyses have been demonstrated to identify ill patients for a number of diseases, their ability to predict cognitive impairment after brain injury is not well established. Traditional post brain injury models,... more
While brain connectivity analyses have been demonstrated to identify ill patients for a number of diseases, their ability to predict cognitive impairment after brain injury is not well established. Traditional post brain injury models, such as stroke, are limited for this evaluation because pre-injury brain connectivity patterns are infrequently available. Patients with severe carotid stenosis, in contrast, often undergo non-emergent revascularization surgery, allowing the collection of pre and post-operative imaging, may experience brain insult due to perioperative thrombotic/embolic infarcts or hypoperfusion, and can suffer post-operative cognitive decline. We hypothesized that a distributed function such as memory would be more resilient in patients with brains demonstrating higher degrees of modularity. To test this hypothesis, we analyzed preoperative structural connectivity graphs (using T1 and DWI MRI) for 34 patients that underwent carotid intervention, and evaluated differe...
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This work describes a new method called amplified MRI (aMRI), which uses Eulerian video magnification to amplify the subtle spatial variations in cardiac-gated brain MRI scans and enables better visualization of brain motion. The aMRI... more
This work describes a new method called amplified MRI (aMRI), which uses Eulerian video magnification to amplify the subtle spatial variations in cardiac-gated brain MRI scans and enables better visualization of brain motion. The aMRI method takes retrospective cardiac-gated cine MRI data as input, applies a spatial decomposition, followed by temporal filtering and frequency-selective amplification of the MRI cardiac-gated frames before synthesizing a motion-amplified cine data set. This approach reveals deformations of the brain parenchyma and displacements of arteries due to cardiac pulsatility, especially in the brainstem, cerebellum, and spinal cord. aMRI has the potential for widespread neuro- and non-neuro clinical use because it can amplify and characterize small, often barely perceptible motion and can visualize the biomechanical response of tissues using the heartbeat as an endogenous mechanical driver. Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.
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The objective of this study was to assess the evolution of diffusion-weighted imaging (DWI) and diffusion-tensor imaging (DTI) over the first month of life in asphyxiated newborns treated with hypothermia and to compare it with that of... more
The objective of this study was to assess the evolution of diffusion-weighted imaging (DWI) and diffusion-tensor imaging (DTI) over the first month of life in asphyxiated newborns treated with hypothermia and to compare it with that of healthy newborns. Asphyxiated newborns treated with hypothermia were enrolled prospectively; and the presence and extent of brain injury were scored on each MRI. Apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values were measured in the basal ganglia, in the white matter and in the cortical grey matter. Sixty-one asphyxiated newborns treated with hypothermia had a total of 126 ADC and FA maps. Asphyxiated newborns developing brain injury eventually had significantly decreased ADC values on days 2-3 of life and decreased FA values around day 10 and 1 month of life compared with those not developing brain injury. Despite hypothermia treatment, asphyxiated newborns may develop brain injury that still can be detected with advanced neu...
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MR imaging and spectroscopy were used to investigate whether two calcium channel entry-blockers, nicardipine and RS-87476 (Syntex), would reduce ischaemic brain damage in barbiturate-anaesthetized cats subjected to permanent unilateral... more
MR imaging and spectroscopy were used to investigate whether two calcium channel entry-blockers, nicardipine and RS-87476 (Syntex), would reduce ischaemic brain damage in barbiturate-anaesthetized cats subjected to permanent unilateral occlusion of the middle cerebral artery (MCA). The evolution of cerebral injury was assessed in vivo in a total of 38 cats using a combination of diffusion-weighted and T2-weighted spin-echo proton MR imaging and phosphorus 31 (P-31) and proton (H-1) MR spectroscopy for up to 12 h following arterial occlusion. Immediately thereafter, the volume of histochemically ischaemic brain tissue was determined planimetrically. In untreated control animals, diffusion-weighted MR images obtained with strong gradient strengths (5.5 gauss/cm) displayed increased signal intensity (oedema) in the ischaemic MCA territory less than 45 min after stroke. These changes were closely correlated with the appearance of abnormal P-31 and H-1 metabolite levels evaluated with surface coil MR spectroscopy. Cats injected with i.v. nicardipine (10 micrograms/kg bolus, 8 micrograms/kg/h maintenance) or RS-87476 (2-50 micrograms/kg bolus, 0.7-17.5 micrograms/kg/h maintenance) showed a significant reduction in ischaemic injury in the ipsilateral cerebral cortex, internal capsule and basal ganglia. The results of this study suggest that these calcium entry blockers protect against brain damage induced by acute stroke by stabilizing cellular metabolic processes, reducing lactate formation in ischaemic tissues, and attenuating cytotoxic and vasogenic oedema.
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Parallel imaging facilitates the acquisition of echo-planar images with a reduced TE, enabling the incorporation of an additional image at a later TE. Here we investigated the use of a parallel imaging-enhanced dual-echo EPI sequence to... more
Parallel imaging facilitates the acquisition of echo-planar images with a reduced TE, enabling the incorporation of an additional image at a later TE. Here we investigated the use of a parallel imaging-enhanced dual-echo EPI sequence to improve lesion conspicuity in diffusion-weighted imaging. Parallel imaging-enhanced dual-echo DWI data were acquired in 50 consecutive patients suspected of stroke at 1.5T. The dual-echo acquisition included 2 EPI for 1 diffusion-preparation period (echo 1 [TE = 48 ms] and echo 2 [TE = 105 ms]). Three neuroradiologists independently reviewed the 2 echoes by using the routine DWI of our institution as a reference. Images were graded on lesion conspicuity, diagnostic confidence, and image quality. The apparent diffusion coefficient map from echo 1 was used to validate the presence of acute infarction. Relaxivity maps calculated from the 2 echoes were evaluated for potential complementary information. Echo 1 and 2 DWIs were rated as better than the refe...
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A magnetic resonance imaging method based on the use of radio-frequency (RF) magnetic field gradients to detect molecular motion has been combined with GRASS (gradient-recalled acquisition in a steady state) imaging to detect arterial... more
A magnetic resonance imaging method based on the use of radio-frequency (RF) magnetic field gradients to detect molecular motion has been combined with GRASS (gradient-recalled acquisition in a steady state) imaging to detect arterial blood flow in vivo. The method has been used to selectively attenuate signals from flowing blood in the human finger. Attenuation of signals from arterial blood was greatly reduced when blood flow was decreased with the application of a tourniquet. This result demonstrated the sensitivity of the technique to the rate of blood flow. RF gradient coils can be used to generate very high RF gradients with submicrosecond rise times and minimal eddy currents. Therefore, this method may prove useful for imaging very slow, nonuniform flow through capillary beds and in the extravascular space.
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Recent findings suggest that diffusion-weighted imaging might be an important adjunct to the diagnostic workup of disease processes in the spine, but physiological motion and the challenging magnetic environment make it difficult to... more
Recent findings suggest that diffusion-weighted imaging might be an important adjunct to the diagnostic workup of disease processes in the spine, but physiological motion and the challenging magnetic environment make it difficult to perform reliable quantitative diffusion measurements. Multi-section line scan diffusion imaging of the spine was implemented and evaluated to provide quantitative diffusion measurements of vertebral bodies and intervertebral disks. Line scan diffusion imaging of 12 healthy study participants and three patients with benign vertebral compression fractures was performed to assess the potential of line scan diffusion imaging of the spinal column. In a subgroup of six participants, multiple b-value (5-3005 s/mm(2)) images were obtained to test for multi-exponential signal decay. All images were diagnostic and of high quality. Mean diffusion values were (230 +/- 83) x 10(-6) mm(2)/s in the vertebral bodies, (1645 +/- 213) x 10(-6) mm(2)/s in the nuclei pulposi...
Research Interests: Medicine, Humans, Female, Male, Intervertebral disc, and 15 moreAmerican, Clinical Sciences, Aged, Middle Aged, Image Enhancement, Adult, Microstructures, Reproducibility of Results, Reference Values, Mr Imaging, Neurosciences, Spinal fractures, Mean Diffusivity, lumbar vertebrae, and Diffusion magnetic resonance imaging
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Nuclear magnetic resonance studies of solvent and polymer dynamics in polystyrene solutions
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on behalf of the American Heart Association Stroke Council, Council on Cardiovascular Surgery and Anesthesia, Council on Cardiovascular Radiology and Intervention, Council on Cardiovascular and Stroke Nursing, Council on Epidemiology and Prevention, Council on Peripheral Vascular Disease, and Cou...more