bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hypercarbia‐induced changes in cerebral blood volume in the cat: A 1H MRI and intravascular contrast agent study
Authors: Moseley Michael E. , Chew Wil M. , White David L. , Kucharczyk John , Litt Lawrence , Derugin Nikita , Dupon Jean , Brasch Robert C. , Norman David 
Published: March 2007

AbstractCerebral blood volume changes with arterial carbon dioxide were monitored by proton T1‐weighted MR images following administration of the intravascular contrast agent Gd‐DTPA labeled with human serum albumin. Without MR contrast, no significant image intensity changes were observed with PaCO2. Following contrast, regional brain image intensities increased significantly over control (0% inspired CO2) in cortical gray, white, and basal ganglia regions with increasing PaCO2 and returned to control intensities upon return to 0% inspired CO2. Imaging of through‐plane and in‐plane phantoms was performed to assess flow effects. Signal losses of 2 and 6% (relative to no flow) were observed for bulk velocities of 5 mm/s at TE values of 15 ms. An intravascular contrast agent may be useful for MRI monitoring of local cerebral blood volume changes during cerebral perturbations. © 1992 Academic Press, Inc.
Spatially localized in vivo1H magnetic resonance spectroscopy of an intracerebral rat glioma
Authors: Ross Brian D. , Merkle Hellmut , Hendrich Kristy , Staewen R. Scott , Garwood Michael 
Published: March 2007

AbstractSurface coil MRI combined with spatially localized spectroscopy was used to noninvasively detect 1H signals from metabolites within an intracerebral malignant glioma in rats. The MRS pulse sequence was based upon two‐dimensional ISIS, which restricted 1H signals to a column‐shaped volume, combined with one dimensional spectroscopic imaging, which further resolved the signals into 8 or 16 slices along the major axis of the column. All experiments were executed with adiabatic pulses which induced uniform spin excitation despite the inhomogeneous radiofrequency field distribution produced by the surface coil transmitter. Surface coil MRI and MRS experiments were performed on phantom samples, normal rat brains, and rat brains harboring malignant gliomas. Spatially resolved in vivo 1H spectra of intracerebral gliomas revealed significantly decreased concentrations of Nacetyl‐aspartate and creatine and increased lactic acid (or lipids) as compared to the contralateral hemisphere. These results demonstrate that metabolic abnormalities in intracerebral rat gliomas can be spatially resolved in a noninvasive manner using localized in vivo 1H MRS. © 1992 Academic Press, Inc.
Dextran‐magnetite particles: Contrast‐enhanced MRI of blood–brain barrier disruption in a rat model
Authors: Bulte Jeff W. M. , de Jonge Martinus W. A. , Kamman Richard L. , Go K. Gwan , Zuiderveen Fred , Blaauw Bert , Oosterbaan John A. , Hauw T. , de Leij Lou 
Published: March 2007

AbstractDextran‐magnetite particles (DMP) were studied for their use as a MR contrast agent to visualize lesions with a blood‐brain barrier (bbb) disruption. A freezing injury to the rat cerebral cortex was used as a model of bbb disruption. The biodistribution of iv‐injected DMP was studied using atomic absorption spectrophotometry, electron microscopy, and MRI. One hour after injection, focal accumulation of the particles in capillary endothelial cells could be demonstrated in the freezing lesion. Despite the observation that the relaxivity of DMP in vivo appears to be less well pronounced than that in vitro, the MR imaging studies show that DMP can be used to visualize bbb disruption with adequate contrast. © 1992 Academic Press, Inc.
Evaluation of acute brain edema using quantitative magnetic resonance imaging: Effects of pretreatment with dexamethasone
Authors: Olson James E. , Katz‐Stein Abi , Reo Nicholas V. , Jolesz Ferenc A. 
Published: March 2007

AbstractWe developed a quantitative magnetic resonance imaging method to permit a rapid assessment of brain water content during osmotic brain edema produced by intraperitoneal (ip) injection of distilled water. Fifteen minutes after water injection, the normalized mean image intensity (MIn) from a spin‐echo pulse sequence (TE = 80 ms, TR = 1085 ms) was the same as that measured from control animals not injected with water. Sixty minutes after the water injection, the mean ± SEM brain image MIn had increased by 10.8 ± 2.4% compared to 3.4 ± 0.7% in control animals (P < 0.05). Blood plasma osmolality decreased by 6–10% during this time interval. A subsequent ip injection of hypertonic NaCl solution (100 gm/liter) caused the blood plasma osmolality and brain image MIn to return toward their initial values. MIn of cerebral gray matter correlated with tissue water content measured in parallel studies. Animals pretreated with 0.25 mg/(kg day) dexamethasone had cerebral gray matter MIn values during osmotic edema which were lower than those of untreated animals. © 1992 Academic Press, Inc.
Differentiation of human prostate cancer from benign hypertrophy by in vitro1H NMR
Authors: Fowler A. H. , Pappas A. A. , Holder J. C. , Finkbeiner A. E. , Dalrymple G. V. , Mullins M. S. , Sprigg J. R. , Komoroski R. A. 
Published: March 2007

AbstractIn vitro 1H NMR spectra were acquired for perchloric acid extracts of tissue samples ofhuman prostate. Seven patients were diagnosed with prostate cancer, 13 with benign prostatic hypertrophy, and 3 with both conditions. Statistically significant differences between the cancer and benign groups were seen for the metabolite peak arearatios of citrate, creatine, and phosphorylcholine to alanine. and citrate to glutamate. There was no correlation of Gleason grade with any of the ratios measured for the cancer samples. Spectra from different sections of large tumors often yielded substantially different area ratios. confirming the heterogeneous nature of these prostate tumors.
31P NMR studies of resting zone cartilage from growth plate
Authors: Kvam Bjarne J. , Pollesello Piero , Vittur Franco , Paoletti Sergio 
Published: March 2007

Abstract31P NMR of superfused resting cartilage demonstrated the presence of phosphocreatine in chondrocytes. Changes in pH and in the NTP level were followed during carbon source starvation. From 31P spectra of perchloric acid extracts, phosphoethanolamine, phospho‐choline, and the corresponding glycerol diesters were identified as the major phospho‐monoester and phosphodiester components. © 1992 Academic Press, Inc.
MR imaging of anisotropic and restricted diffusion by simultaneous use of spin and stimulated echoes
Authors: Sotak Christopher H. , Li Limin 
Published: March 2007

AbstractA new magnetic resonance imaging technique for evaluating anisotropic and restricted diffusion effects in a single experiment is described. The method is based on a pulse sequence that simultaneously excites a spin echo (SE) and a stimulated echo (STE) and contains two pairs of diffusion‐sensitive gradient pulses. The diffusion attenuation of the SE and STE can be controlled independently by separate adjustment of the parameters associated with each pair of the diffusion‐sensitive gradient pulses. This method can be more time efficient than acquiring separate SE and STE images for the same study. Furthermore, the pulse sequence minimizes the effect of motion and instrumental and physiological variations that occur between separate image acquisitions which can give rise to artifactual results when difference imaging is employed. In addition to applications to anisotropic and restricted diffusion, this technique can be used for: (1) simultaneous acquisition of T2‐weighted and diffusion‐weighted images during cerebral ischemia studies; (2) calculation of diffusion coefficients from a pair of diffusion‐weighted images; (3) separating fast and slow diffusion components in a single imaging experiment; and (4) two‐dimensional velocity‐encoded imaging.
Partial RF echo planar imaging with the FAISE method. I. Experimental and theoretical assessment of artifact
Authors: Melki Philippe S. , Jolesz Ferenc A. , Mulkern Robert V. 
Published: March 2007

AbstractThe fast acquisition interleaved spin‐echo (FAISE) method is a partial RF echo‐planar technique which utilizes a specific phase‐encode reordering algorithm to manipulate image contrast (Melki et al., J. Magn. Reson. imaging 1:319, 1991). The technique can generate “spin‐echo” like images up to 16 times faster than conventional spin‐echo methods. However, the presence of T2 decay throughout the variable k‐space trajectories used to manipulate T2 contrast ensures the presence of image artifacts, especially along the phase‐encode direction. In this work, we experimentally and theoretically examine the type and extent of artifacts associated with the FAISE technique. We demonstrate the existence of well‐defined minima of phase‐encode ghost noise for selected k‐space trajectories, examine the extent of blurring and edge enhancement artifacts, demonstrate the influence of matrix size and number of echoes per train on phase‐encode artifact, and show how proper choice of FAISE sequence parameters can lead to proton density brain images which are practically indistinguishable from conventional spin‐echo proton density images. A comparison of contrast between FAISE and standard spin‐echo methods is presented in a companion article referred to as II.
Single‐Shot GRASE Imaging without Fast Gradients
Authors: Oshio Koichi , Feinberg David A. 
Published: March 2007

AbstractBased on the CPMG sequence, gradient‐ and spin‐echo (GRASE) echo train length is limited by T2 decay rather than the T2* decay and phase error in echo‐planar techniques, permitting a longer image acquisition period. An ultrafast GRASE sequence, utilizing a single excitation, generates a 128 × 56 true T2‐weighted image in 200 ms on an unmodified commercial scanner without fast gradient switching, extreme field homogeneity, or fat signal suppression.
The capillary network: a link between ivim and classical perfusion
Authors: Bihan Denis Le , Turner Robert 
Published: March 2007

AbstractMR measurements based on motion encoding gradients, such as intravoxel incoherent motion imaging, could provide, in principle, information on flowing blood volume and blood velocity. This note shows that, in addition, the knowledge of the capillary network organization may provide a link between these measurements and those obtained by conventional and MR perfusion techniques based on tracer uptake by tissues.
Nuclear magnetic resonance velocity spectra of pulsatile flow in a rigid tube
Authors: Wendt Richard E. , Wong Wai‐Fan 
Published: March 2007

AbstractVelocity spectra can be derived from velocity‐encoded nuclear magnetic resonance (NMR) images. Velocity spectra are histograms showing the amounts of fluid flowing at different velocities in the sensitive volume of the measurement. Velocity spectra may prove to be useful in characterizing the flow of blood in small vessels, for example, in detecting the presence of stenoses and in evaluating their severity. NMR velocity spectra acquired in vivo are sufficiently complicated that a model system was esigned and tested to investigate the velocity spectra of pulsatile flow. This study measured the NMR velocity spectra of pulsatile flow in a rigid tube and compared them to velocity spectra derived from Doppler ultrasound measurements and to velocity spectra inferred from a theoretical model driven by the measured pressure difference function. The experimental results from each technique agree.
Direct Observation of the Magnetization Exchange Dynamics Responsible for Magnetization Transfer Contrast in Human Cartilage in Vitro
Authors: Morris G. A. , Freemont A. J. 
Published: March 2007

AbstractSaturating irradiation far off‐resonance can lead to diminution in the water signal seen in MRI, giving rise to magnetization transfer contrast. This results from transfer of magnetization between “solid” protons with restricted motion, which give rise to a band some tens of kilohertz wide, and the narrow signal from mobile protons. In the work reported here a high‐power pulse spectrometer, which can detect signals from both mobile and immobile protons, was used to investigate the dynamics of magnetization transfer in cartilage in vitro. Magnetization transfer in modified Hoffman‐Forsén inversion transfer experiments was well‐described by a single rate constant model; full analytical solutions are offered for the resultant biexponential magnetization recovery curves. The use of pulsed methods to generate magnetization contrast may in some circumstances offer advantages over the steady‐state saturation methods used hitherto.© 1992 Academic Press,Inc.
A New Frontier of Blood Imaging Using Susceptibility Effect and Tailored RF Pulses
Authors: Ro Y. M. , Cho Z. H. 
Published: March 2007

AbstractIn MRI, image contrast can be controlled by use of the susceptibility effect if an object contains paramagnetic substances. The localized linear gradient dephases spins in the voxel, leading to phase cancellation and thus reduced signal. This signal void phenomenon, can be exploited if the intrinsic linear gradient is either enhanced or compensated by externally applied RF generated phase distributions. In this paper, a new concept which utilizes the susceptibility effect through the use of tailored RF pulses is proposed. As potential applications of the method, two different types of tailored RF pulses are introduced: one for the enhancement of the susceptibility effect and the other for the correction of the susceptibility artifact, respectively. The former, for example, can be applied to angiography utilizing the paramagnetic property of deoxygenated blood, suggesting a new avenue for the angiography which, for the first time, is not based on flow, although the method is currently limited to imaging of venous blood or venography. Both a theoretical study of the method and experimental results are reported.© 1992 Academic Press,Inc.
Selective MR imaging of labeled human peripheral blood mononuclear cells by liposome mediated incorporation of dextran‐magnetite particles
Authors: Bulte Jeff W. M. , Ma Loralie D. , Magin Richard L. , Kamman Richard L. , Hulstaert Caesar E. , Go K. Gwan , The T. Hauw , De Leij Lou 
Published: March 2007

AbstractHuman peripheral blood mononuclear cells (PBMCs) were incubated with large unilamellar vesicles (LUV) containing encapsulated dextran‐magnetite particles (DMP). This resulted in an efficient incorporation of DMP. Electron microscopy revealed the presence of DMP in cells mainly in phagosomes and secondary lysosomes. DMP‐labeled PBMCs showed a strong increase of the transverse relaxation rate (up to 16.6 s−1 for 5 x 107 cells/ml) and, accordingly, a great loss of signal intensity in MR imaging. The fraction of DMP containing PBMCs could be enriched by magnetic cell separation. The major population of the DMP containing cells proved to be monocytes. When PBMCs depleted of monocytes were used for labeling, DMP uptake was observed also in the peripheral blood lymphocytes. The labeling of PBMCs presented here may be used in future studies of selective MR imaging of in vivo cell migration in a variety of immunologically compromised tissue states, e.g., tumors, transplantations, and abscesses.
Functional MRI of human brain activation at high spatial resolution
Authors: Frahm Jens , Merboldt Klaus‐Dietmar , Hänicke Wolfgang 
Published: March 2007

AbstractFunctional activation maps of the human visual cortex were obtained at a spatial resolution almost two orders of magnitude better than achievable by positron emission tomography and within measuring times of a few seconds. Transient alterations in the concentration of paramagnetic deoxyhemoglobin were conveniently detected at 2.0‐T with use of RF‐spoiled FLASH MRI sequences employing gradient echo times of 6 to 60 ms and voxel sizes of 2.5 to 39 μl.
Quantitative velocity images from thick slab 2D phase contrast
Authors: Weber David M. , Wang Yi , Korosec Frank R. , Mistretta Charles A. 
Published: March 2007

AbstractThick slab two‐dimensional phase contrast (2D PC) angiography provides a large amount of anatomical information in a short acquisition time. Quantitative velocity information is, however, destroyed by the necessary projection dephasing gradient. We present a 2D PC acquisition scheme which retains quantitative velocity information in a thick slab acquisition. A thick slab acquisition produces an image which is a projection through an entire vessel. Accurate velocity measurements must take into account the intravoxel phase cancellation caused by a distribution of velocities within the vessel. In addition to the description of the data acquisition scheme, we outline a method for determining the mean velocity within a vessel having a laminar flow distribution. It is shown that without the consideration for intravoxel phase cancellation, the mean velocity measurement from thick slab images overestimates the true mean velocity by 10%.
Specific in vitro labeling of cells with a fluorine‐19 probe encapsulated in antibody ‐ targeted liposomes: A F‐19 NMR spectroscopy study
Authors: Vion‐Dury Jean , Machy Patrick , Confort‐Gouny Sylviane , Leserman Lee , Cozzone Patrick J. 
Published: March 2007

AbstractLiposomes containing dexamethasone phosphate (DMp) were covalently coupled to protein A and then incubated with mu‐rine L929 fibroblast and RDM4 thymoma cells in the presence of monoclonal antibodies specific for the major histocompatibility complex. The detection of the specific F‐19 labeling of cells is rapid (minutes). Such a strategy might be useful to study the kinetics of internalization processes of bound lipo‐somes on cultured living cells.
The visualization of RF probe electric fields
Authors: Chen C‐N. , Hoult D. I. 
Published: March 2007

AbstractAn assembly of resistive paper and liquid crystal sheet, conveniently and cheaply constructed for visual detection of the electric fields associated with an rf probe, is presented. Electrical asymmetries, and “hot‐spots” usually associated with conservative electric fields, are easily visualized by the color patterns displayed. The device is of considerable assistance in probe design and the minimization of dielectric loss.
K‐space description for MR imaging of dynamic objects
Authors: Xiang Qing‐San , Henkelman R. Mark 
Published: March 2007

AbstractThe spatial frequency (k) space concept is extended to describe the imaging of time‐dependent objects. This work builds on the existing k‐space description of MRI and is useful for simplifying the analysis of explanations of motion artifacts, algorithms for the correction of motion, and efficient imaging schemes for dynamic objects. Specific examples of the use of this concept for different imaging techniques are presented.
Diffusion imaging of experimental allergic encephalomyelitis
Authors: Heide A. C. , Richards T. L. , Alvord E. C. , Peterson J. , Rose L. M. 
Published: March 2007

AbstractDiffusion‐weighted magnetic resonance imaging (MRI) was compared with T2‐weighted MRI in longitudinal studies of experimental allergic encephalomyelitis (EAE), an animal model of multiple sclerosis, in five monkeys (Macaca fascicularis). In a region of the brain that had highly directional myelinated fibers (internal capsule) sequential changes were identified on diffusion‐weighted images on and before the day these changes were detected on conventional T2‐weighted images. Changes were also identified on diffusion‐weighted images in brain areas that did not develop T2‐weighted abnormalities. This result suggests that diffusion‐weighted image intensities are sensitive to pathologic conditions of the brain that can not be seen on T2‐weighted images.
High‐resolution variable flip angle 3D MR imaging of trabecular microstructure in vivo
Authors: Jara H. , Wehrli F. W. , Chung H. , Ford J. C. 
Published: March 2007

AbstractTwo conceptually related variable‐flip‐angle 3D spin‐echo pulse sequences were designed for imaging at voxel sizes of 2–5 × 10−3 mm3 corresponding to pixel areas of less than 100 × 100 μm2 and section thicknesses on the order of 300–400 μm on a conventional 1.5 T MR imaging system equipped with 1 G/cm imaging field gradients, providing 12 sections in 10 min imaging time. The pulse sequences make use of the concept of restoring longitudinal magnetization inverted by the 180° phase reversal pulse and are derivatives of pulse sequences previously dubbed “FATE” and “RASEE.” It is shown that even in the small‐voxel regime (< 10−2 mm3 voxel size) and at echo times on the order of 10 ms, gradient echo images are sensitive to intrinsic fields causing artifactual boundary effects, including signal loss from intravoxel phase scrambling and spatial mismapping. At this resolution the variable flipangle spin‐echo pulse sequences are demonstrated to be better suited for imaging magnetically heterogeneous systems such as trabecular bone microstructure in vivo. These pulse sequences are found to be substantially less sensitive to distortions from magnetic dipole fields occurring at the boundaries of two phases of different magnetic permeability.
Double inversion recovery improves water suppression in vivo
Authors: Shen Jie F. , Saunders John K. 
Published: March 2007

AbstractIt is shown that double inversion recovery used for water suppression can be made much less sensitive to pulse imperfections and to the variations in the relaxation times than a single inversion recovery. This insensitivity results in up to 10‐fold improvement in the water suppression in vivo. The excellent water suppression by double inversion recovery is demonstrated experimentally by the in vivo proton spectra obtained from a rat brain.
Resting and end‐diastolic [Ca2+]i measurements in the langendorff‐perfused ferret heart loaded with a 19F NMR indicator
Authors: Harding Deborah P. , Smith Gerry A. , Metcalfe James C. , Morris Peter G. , Kirschenlohr Heide L. 
Published: March 2007

AbstractIntracellular free calcium concentration ([Ca2+]i) was measured in Langendorff‐perfused ferret hearts (30°C, pH 7,4) by loading paced hearts with the 19F NMR calcium indicator, the 5,5′‐difluoro derivative of 1,2‐bis(o‐aminophenoxy) ethane‐N, N,N′,N′‐tetraacetic acid (5FBAPTA), to an initial cytosolic concentration of approximately 120 uM. Increasing the pacing frequency raised the end‐diastolic [Ca2+]i, from 299 ± 44 nM (mean ± SEM) at 0.2 Hz to 522 ± 54 nM at 1.0 Hz and 691 ± 166 nM at 2.0 Hz. Raising [Ca]o from 1.8 to 7.0 mM at a pacing frequency of 1.0 Hz increased end‐diastolic [Ca2+]i to 625 ± 39 nM. In unpaced hearts perfused with diltiazem (100 uM), [Ca2+]i fell rapidly to a steady‐state value of <100 nM after 60 min. Raising [Ca]o from 1.8 to 7.0 mM had no detectable effect on resting [Ca2+]i. The time course of the [Ca2+]i transient was measured in hearts paced at 1.1 Hz and perfused with 1.8 mM [Ca]o. The peak [Ca2+]i was ∼ 2 uM at approximately 150 msec after the pacing pulse, and peak developed LVP occurred at 550 msec compared with 280 msec in control hearts not loaded with 5FBAPTA. Comparisons with data obtained by other techniques, including fluorescent [Ca2+]i indicators, imply that although the end‐diastolic [Ca2+]i values obtained with 5FBAPTA in beating hearts are elevated by the concentrations of intracellular 5FBAPTA required for signal detection, the changes in [Ca2+]i observed in response to experimental interventions are qualitatively consistent with previous data.
Continuous inversion angiography
Authors: Roberts D. A. , Bolinger L. , Detre J. A. , Insko E. K. , Berge P. , Leigh J. S. 
Published: March 2007

AbstractA subtractive time‐of‐flight technique for magnetic resonance anglography is described. In this approach, the arterial supply to an organ is inverted in a steady‐state fashion by applying off‐resonance irradiation in the presence of a linear magnetic field gradient. An angiogram is formed by subtracting an image acquired with arterial inversion from a control image acquired with no arterial inversion. A single coil is used to apply both the inversion and observation pulses. Intracranial angiograms obtained from normal volunteers using a two‐dimensional projective implementation of this technique at 1.5 T illustrate excellent small vessel detail and background suppression.