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Find video protocols related to scientific articles indexed in Pubmed.
Prostate MR elastography with transperineal electromagnetic actuation and a fast fractionally encoded steady-state gradient echo sequence.
NMR Biomed
PUBLISHED: 03-14-2014
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Our aim is to develop a clinically viable, fast-acquisition, prostate MR elastography (MRE) system with transperineal excitation. We developed a new actively shielded electromagnetic transducer, designed to enable quick deployment and positioning within the scanner. The shielding of the transducer was optimized using simulations. We also employed a new rapid pulse sequence that encodes the three-dimensional displacement field in the prostate gland using a fractionally encoded steady-state gradient echo sequence, thereby shortening the acquisition time to a clinically acceptable 8-10 min. The methods were tested in two phantoms and seven human subjects (six volunteers and one patient with prostate cancer). The MRE acquisition time for 24 slices, with an isotropic resolution of 2 mm and eight phase offsets, was 8 min, and the total scan, including positioning and set-up, was performed in 15-20 min. The phantom study demonstrated that the transducer does not interfere with the acquisition process and that it generates displacement amplitudes that exceed 100 µm even at frequencies as high as 300 Hz. In the in vivo human study, average wave amplitudes of 30 µm (46 µm at the apex) were routinely achieved within the prostate gland at 70 Hz. No pain or discomfort was reported. Results in a single patient suggest that MRE can identify cancer tumors, although this result is preliminary. The proposed methods allow the integration of prostate MRE with other multiparametric MRI methods. The results of this study clearly motivate the clinical evaluation of transperineal MRE in patients.
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Assessment of portal hypertension and high-risk oesophageal varices with liver and spleen three-dimensional multifrequency MR elastography in liver cirrhosis.
Eur Radiol
PUBLISHED: 02-11-2014
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To assess the value of the liver and spleen viscoelastic parameters at multifrequency MR elastography to determine the degree of portal hypertension and presence of high-risk oesophageal varices in patients with cirrhosis.
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Viscoelastic parameters for quantifying liver fibrosis: three-dimensional multifrequency MR elastography study on thin liver rat slices.
PLoS ONE
PUBLISHED: 01-01-2014
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To assess in a high-resolution model of thin liver rat slices which viscoelastic parameter at three-dimensional multifrequency MR elastography has the best diagnostic performance for quantifying liver fibrosis.
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MR Elastography of the Liver: Defining Thresholds for Detecting Viscoelastic Changes.
Radiology
PUBLISHED: 10-28-2013
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Purpose To define thresholds for detecting significant change in liver viscoelasticity with magnetic resonance (MR) elastography, both for whole-liver measurements and for voxel-wise measurements in relation to spatial resolution. Materials and Methods This prospective study was approved by the institutional review board, and all participants provided written informed consent. Thirty participants (16 volunteers and 14 patients with hepatitis B or C; 18 men; median age, 30.4 years; age range, 18.9-58.6 years) underwent imaging twice while in the same position (intraimage reproducibility), after repositioning (within-day reproducibility), and 1-4 weeks later (between-weeks reproducibility). MR elastography parameters comprised elasticity, viscosity, attenuation parameter ?, and propagation parameter ?. Bland-Altman analysis was used to calculate repeatability indexes for each parameter. Analyses were performed in a region-of-interest and a voxel-by-voxel level. Voxel-wise results were calculated in relation to spatial resolution by applying Gaussian filtering to establish the optimal trade-off point between resolution and reproducibility. Results For elasticity, ?, and ?, within-day and between-weeks results were significantly lower than intraimage results (P ? .018 for all). Within-day and between-weeks results did not differ significantly. Over-time changes of more than 22.2% for elasticity, 26.3% for viscosity, 26.8% for ?, and 10.1% for ? represented thresholds for significant change. The optimal trade-off between spatial resolution and reproducibility was found at a filter size of 8-mm full width at half maximum (FWHM) for elasticity and propagation parameter ? and at 16-mm FWHM for viscosity and attenuation parameter ?. Conclusion Repositioning causes a significant decrease in the reproducibility of MR elastography. The propagation parameter ? is the most reliable parameter, with an over-time threshold for significant change of 10.1% and the ability to reproduce viscoelasticity up to a resolution of 8-mm FWHM. ©RSNA, 2013 Online supplemental material is available for this article.
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In vivo detection of free radicals in mouse septic encephalopathy using molecular MRI and immuno-spin trapping.
Free Radic. Biol. Med.
PUBLISHED: 06-20-2013
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Free radicals are known to play a major role in sepsis. Combined immuno-spin trapping and molecular magnetic resonance imaging (MRI) was used to detect in vivo and in situ levels of free radicals in murine septic encephalopathy after cecal ligation and puncture (CLP). DMPO (5,5-dimethyl pyrroline N-oxide) was injected over 6h after CLP, before administration of an anti-DMPO probe (anti-DMPO antibody bound to albumin-gadolinium-diethylene triamine pentaacetic acid-biotin MRI targeting contrast agent). In vitro assessment of the anti-DMPO probe in oxidatively stressed mouse astrocytes significantly decreased T1 relaxation (p < 0.0001) compared to controls. MRI detected the presence of anti-DMPO adducts via a substantial decrease in %T1 change within the hippocampus, striatum, occipital, and medial cortex brain regions (p < 0.01 for all) in septic animals compared to shams, which was sustained for over 60min (p < 0.05 for all). Fluorescently labeled streptavidin was used to target the anti-DMPO probe biotin, which was elevated in septic brain, liver, and lungs compared to sham. Ex vivo DMPO adducts (qualitative) and oxidative products, including 4-hydroxynonenal and 3-nitrotyrosine (quantitative, p < 0.05 for both), were elevated in septic brains compared to shams. This is the first study that has reported on the detection of in vivo and in situ levels of free radicals in murine septic encephalopathy.
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Rapid acquisition of multifrequency, multislice and multidirectional MR elastography data with a fractionally encoded gradient echo sequence.
NMR Biomed
PUBLISHED: 03-08-2013
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In MR elastography (MRE), periodic tissue motion is phase encoded using motion-encoding gradients synchronized to an externally applied periodic mechanical excitation. Conventional methods result in extended scan time for quality phase images, thus limiting the broad application of MRE in the clinic. For practical scan times, researchers have been relying on one-dimensional or two-dimensional motion-encoding, low-phase sampling and a limited number of slices, and artifact-prone, single-shot, echo planar imaging (EPI) readout. Here, we introduce a rapid multislice pulse sequence capable of three-dimensional motion encoding that is also suitable for simultaneously encoding motion with multiple frequency components. This sequence is based on a gradient-recalled echo (GRE) sequence and exploits the principles of fractional encoding. This GRE MRE pulse sequence was validated as capable of acquiring full three-dimensional motion encoding of isotropic voxels in a large volume within less than a minute. This sequence is suitable for monofrequency and multifrequency MRE experiments. In homogeneous paraffin phantoms, the eXpresso sequence yielded similar storage modulus values as those obtained with conventional methods, although with markedly reduced variances (7.11?±?0.26 kPa for GRE MRE versus 7.16?±?1.33 kPa for the conventional spin-echo EPI sequence). The GRE MRE sequence obtained better phase-to-noise ratios than the equivalent spin-echo EPI sequence (matched for identical acquisition time) in both paraffin phantoms and in vivo data in the liver (59.62?±?11.89 versus 27.86?±?3.81, 61.49?±?14.16 versus 24.78?±?2.48 and 58.23?±?10.39 versus 23.48?±?2.91 in the X, Y and Z components, respectively, in the case of liver experiments). Phase-to-noise ratios were similar between GRE MRE used in monofrequency or multifrequency experiments (75.39?±?14.93 versus 86.13?±?18.25 at 28?Hz, 71.52?±?24.74 versus 86.96?±?30.53 at 56?Hz and 95.60?±?36.96 versus 61.35?±?26.25 at 84Hz, respectively).
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Calibration of a semi-automated segmenting method for quantification of adipose tissue compartments from magnetic resonance images of mice.
Metab. Clin. Exp.
PUBLISHED: 03-01-2013
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To use an automated water-suppressed magnetic resonance imaging (MRI) method to objectively assess adipose tissue (AT) volumes in whole body and specific regional body components (subcutaneous, thoracic and peritoneal) of obese and lean mice.
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Assessment of thermal effects of interstitial laser phototherapy on mammary tumors using proton resonance frequency method.
J Biomed Opt
PUBLISHED: 12-24-2011
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Laser immunotherapy (LIT) uses a synergistic approach to treat cancer systemically through local laser irradiation and immunological stimulation. Currently, LIT utilizes dye-assisted noninvasive laser irradiation to achieve selective photothermal interaction. However, LIT faces difficulties treating deeper tumors or tumors with heavily pigmented overlying skin. To circumvent these barriers, we use interstitial laser irradiation to induce the desired photothermal effects. The purpose of this study is to analyze the thermal effects of interstitial irradiation using proton resonance frequency (PRF). An 805-nm near-infrared laser with an interstitial cylindrical diffuser was used to treat rat mammary tumors. Different power settings (1.0, 1.25, and 1.5 W) were applied with an irradiation duration of 10 min. The temperature distributions of the treated tumors were measured by a 7 T magnetic resonance imager using PRF. We found that temperature distributions in tissue depended on both laser power and time settings, and that variance in tissue composition has a major influence in temperature elevation. The temperature elevations measured during interstitial laser irradiation by PRF and thermocouple were consistent, with some variations due to tissue composition and the positioning of the thermocouples needle probes. Our results indicated that, for a tissue irradiation of 10 min, the elevation of rat tumor temperature ranged from 8 to 11°C for 1 W and 8 to 15°C for 1.5 W. This is the first time a 7 T magnetic resonance imager has been used to monitor interstitial laser irradiation via PRF. Our work provides a basic understanding of the photothermal interaction needed to control the thermal damage inside a tumor using interstitial laser treatment. Our work may lead to an optimal protocol for future cancer treatment using interstitial phototherapy in conjunction with immunotherapy.
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Comparative analysis of protein transport in the N. benthamiana vasculature reveals different destinations.
Plant Signal Behav
PUBLISHED: 11-01-2011
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We investigated the vascular transport of exogenously applied proteins and compared their delivery to various aerial parts of the plant with carboxy fluorescein dye. Alexafluor tagged bovine serum albumin (Alexa-BSA) moves at a low level to upper parts of the plant and unloads to the apoplast. Alexafluor tagged Histone H1 (Alexa-Histone) moves rapidly throughout the plant and is retained in the phloem and phloem parenchyma. Both Alexa-Histone and -BSA were exported from leaf veins class II and III but they unloaded completely into the leaf lamina with barely any residual fluorescence left inside the leaf veins. Fluorescein tagged hepatitis C virus core protein (fluorescein-HCV) moves more rapidly than BSA through the plant and was restricted to the leaf veins. Fluorescein-HCV failed to unload to the leaf lamina. These combined data suggest that there is not a single default pathway for the transfer of exogenous proteins through the plant. Specific protein properties appear to determine their destination and transport properties within the phloem.
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Multiparametric assessment of the anti-glioma properties of OKN007 by magnetic resonance imaging.
J Magn Reson Imaging
PUBLISHED: 04-08-2010
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To demonstrate that OKN007, a disulfonyl derivative of phenyl-tert-butyl nitrone (PBN), has anti-glioma activity in the clinically relevant C6 rat glioma model using multi-parametric magnetic resonance imaging.
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Sepsis-associated encephalopathy: a magnetic resonance imaging and spectroscopy study.
J. Cereb. Blood Flow Metab.
PUBLISHED: 10-21-2009
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Brain dysfunction is frequently observed in sepsis as a consequence of changes in cerebral structure and metabolism, resulting in worse outcome and reduced life-quality of surviving patients. However, the mechanisms of sepsis-associated encephalopathy development and a better characterization of this syndrome in vivo are lacking. Here, we used magnetic resonance imaging (MRI) techniques to assess brain morphology and metabolism in a murine sepsis model (cecal ligation and puncture, CLP). Sham-operated and CLP mice were subjected to a complete MRI session at baseline, 6 and 24 h after surgery. Accumulation of vasogenic edematic fluid at the base of the brain was observed in T(2)-weighted image at 6 and 24 h after CLP. Also, the water apparent diffusion coefficients in both hippocampus and cortex were decreased, suggesting a cytotoxic edema in brains of nonsurvival septic animals. Moreover, the N-acetylaspartate/choline ratio was reduced in brains of septic mice, indicating neuronal damage. In conclusion, noninvasive assessment by MRI allowed the identification of new aspects of brain damage in sepsis, including cytotoxic and vasogenic edema as well as neuronal damage. These findings highlight the potential applications of MRI techniques for the diagnostic and therapeutic studies in sepsis.
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In vivo detection of inducible nitric oxide synthase in rodent gliomas.
Free Radic. Biol. Med.
PUBLISHED: 04-01-2009
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Increased iNOS expression is often found in brain tumors, such as gliomas. The goal of this study was to develop and assess a novel molecular MRI (mMRI) probe for in vivo detection of iNOS in rodent models for gliomas (intracerebral implantation of rat C6 or RG2 cells or ethyl nitrosourea-induced glioma). The probe we used incorporated a Gd-DTPA (gadolinium(III) complex of diethylenetriamine-N,N,N,N,N-pentaacetate) backbone with albumin and biotin moieties and covalent binding of an anti-iNOS antibody (Ab) to albumin (anti-iNOS probe). We used mMRI with the anti-iNOS probe to detect in vivo iNOS levels in gliomas. Nonimmune normal rat IgG coupled to albumin-Gd-DTPA-biotin was used as a control nonspecific contrast agent. By targeting the biotin component of the anti-iNOS probe with streptavidin Cy3, fluorescence imaging confirmed the specificity of the probe for iNOS in glioma tissue. iNOS levels in glioma tumors were also confirmed via Western blots and immunohistochemistry. The presence of plasma membrane-associated iNOS in glioma cells was established by transmission electron microscopy and gold-labeled anti-iNOS Ab. The more aggressive RG2 glioma was not found to have higher levels of iNOS compared to C6. Differences in glioma vascularization and blood-brain barrier permeability between the C6 and the RG2 gliomas are discussed. In vivo assessment of iNOS levels associated with tumor development is quite feasible in heterogeneous tissues with mMRI.
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MR elastography of the head and neck: driver design and initial results.
Magn Reson Imaging
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The purpose was to describe the design and fabrication of a driver suitable for magnetic resonance elastography (MRE) of the head and neck and to assess its performance in evaluating human parotid gland, lymph nodes and thyroid at 3.0 T.
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Fat deposition decreases diffusion parameters at MRI: a study in phantoms and patients with liver steatosis.
Eur Radiol
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Assess the effect of fat deposition on the MRI diffusion coefficients in lipid emulsion-based phantoms and patients with proven isolated liver steatosis.
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Diffusion-weighted MR imaging for the regional characterization of liver tumors.
Radiology
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To determine if diffusion-weighted (DW) magnetic resonance (MR) imaging with measurements of the apparent diffusion coefficient (ADC), pure diffusion coefficient, perfusion-related diffusion coefficient, and perfusion fraction can be used to differentiate between viable tumor and fibrous and necrotic regions within malignant liver tumors.
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MR elastography of liver tumours: value of viscoelastic properties for tumour characterisation.
Eur Radiol
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To assess the value of the viscoelastic parameters in the characterisation of liver tumours at MR elastography.
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Demyelination reduces brain parenchymal stiffness quantified in vivo by magnetic resonance elastography.
Proc. Natl. Acad. Sci. U.S.A.
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The detection of pathological tissue alterations by manual palpation is a simple but essential diagnostic tool, which has been applied by physicians since the beginnings of medicine. Recently, the virtual "palpation" of the brain has become feasible using magnetic resonance elastography, which quantifies biomechanical properties of the brain parenchyma by analyzing the propagation of externally elicited shear waves. However, the precise molecular and cellular patterns underlying changes of viscoelasticity measured by magnetic resonance elastography have not been investigated up to date. We assessed changes of viscoelasticity in a murine model of multiple sclerosis, inducing reversible demyelination by feeding the copper chelator cuprizone, and correlated our results with detailed histological analyses, comprising myelination, extracellular matrix alterations, immune cell infiltration and axonal damage. We show firstly that the magnitude of the complex shear modulus decreases with progressive demyelination and global extracellular matrix degradation, secondly that the loss modulus decreases faster than the dynamic modulus during the destruction of the corpus callosum, and finally that those processes are reversible after remyelination.
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Loss of caveolin-1 impairs retinal function due to disturbance of subretinal microenvironment.
J. Biol. Chem.
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Caveolin-1 (Cav-1), an integral component of caveolar membrane domains, is expressed in several retinal cell types, including photoreceptors, retinal vascular endothelial cells, Müller glia, and retinal pigment epithelium (RPE) cells. Recent evidence links Cav-1 to ocular diseases, including autoimmune uveitis, diabetic retinopathy, and primary open angle glaucoma, but its role in normal vision is largely undetermined. In this report, we show that ablation of Cav-1 results in reduced inner and outer retinal function as measured, in vivo, by electroretinography and manganese-enhanced MRI. Somewhat surprisingly, dark current and light sensitivity were normal in individual rods (recorded with suction electrode methods) from Cav-1 knock-out (KO) mice. Although photoreceptor function was largely normal, in vitro, the apparent K(+) affinity of the RPE-expressed ?1-Na(+)/K(+)-ATPase was decreased in Cav-1 KO mice. Cav-1 KO retinas also displayed unusually tight adhesion with the RPE, which could be resolved by brief treatment with hyperosmotic medium, suggesting alterations in outer retinal fluid homeostasis. Collectively, these findings demonstrate that reduced retinal function resulting from Cav-1 ablation is not photoreceptor-intrinsic but rather involves impaired subretinal and/or RPE ion/fluid homeostasis.
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