bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enhancement of nitroxide‐reducing activity in rats after chronic administration of vitamin E, vitamin C, and idebenone examined by an in Vivo electron spin resonance technique
Authors: Matsumoto Seiji , Mori Norio , Tsuchihashi Nobuaki , Ogata Tateaki , Lin Yijing , Yokoyama Hidekatsu , Ishida Shin‐Ichi 
Published: March 2007

AbstractRats were given vitamin E (vit‐E), idebenone (ID), or vitamin (C wit‐C) in their food for 2 or 4 weeks. After feeding, the ability of rats to reduce 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐l‐oxyl (Tempol) in terms of the half‐life of Ternpol was examined as a specific marker. Ternpol was repeatedly injected intravenously, and its half‐life was serially evaluated by an in vivo electron spin resonance (ESR) technique. The radical‐reducing ability in rats was enhanced differently by Vit‐E, ID, and Vit‐C, i.e., slow onset of the ability after Vit‐E and ID (lipid‐soluble antioxidants) and fast onset after Vit‐C (a water‐soluble antioxidant).
A rapid 2D time‐resolved variable‐rate k‐space sampling MR technique for passive catheter tracking during endovascular procedures
Authors: Unal Orhan , Korosec Frank R. , Frayne Richard , Strother Charles M. , Mistretta Charles A. 
Published: March 2007

AbstractA new, fast, 2D MR imaging technique allowing passive catheter visualization adequate for use as a tool for guiding the movement of a catheter during endovascular procedures is described. This imaging technique samples low spatial frequencies more often than high spatial frequencies; it also uses both k‐space view sharing and temporal interpolation. Unlike other techniques for passive visualization that exploit magnetic‐susceptibility–induced artifacts, we have adopted a strategy that takes advantage of the T1‐shortening effect of paramagnetic contrast agents, such as Gd‐DTPA and a projection dephaser. This not only permits visualization of the entire catheter length but also minimizes the risk of intravascular heating. Using this method, a temporal frame rate of up to eight images per second and a tip localization accuracy of ± 1mm (root mean square difference) can be achieved.
Measurement of tumor vascular volume and mean microvascular random flow velocity magnitude by dynamic GD‐DTPA‐Albumin enhanced and diffusion‐weighted MRI
Authors: Wang Zhiheng , Su Min‐Ying , Nalcioglu Orhan 
Published: March 2007

AbstractTumor vascular volume fraction and the magnitude of the mean microvascular random flow velocity were measured in an animal tumor model by combining dynamic Gd‐DTPA‐albumin enhanced MRI and diffusion‐weighted MRI in conjunction with a compartmental modeling analysis. The vascular volume fraction maps were obtained from the dynamic Gd‐DTPA‐albumin enhanced MRI measurement. It was found that the vascular volume fraction for Walker 256 tumor was higher within the outgrowing rim and decreased towards the central region. The average value obtained from five animals was 0.062 ± 0.009 ml/g. By using the vascular volume fraction from the Gd‐DTPA‐albumin enhanced MRI measurement, maps of the magnitude of the mean microvascular random flow velocity were obtained from the diffusion‐weighted MRI measurements with the compartmental modeling analysis. The relative extravascular and intravascular contributions to the diffusion‐weighted MRI signal were determined for three tissue groups with different Gd‐DTPA‐albumin enhancement characteristics, and the flow and molecular diffusion‐induced attenuation factors for the intravascular compartment were also compared. The mean microvascular random flow velocity magnitude maps were obtained with an average value of 0.67 ± 0.06 mm/s.
Diffusional anisotropy of T2 components in bovine optic nerve
Authors: Stanisz Greg J. , Henkelman R. Mark 
Published: March 2007

AbstractA diffusion‐CPMG hybrid experiment was used to analyze the diffusion characteristics of different T2 relaxation components in bovine optic nerve. Data were collected using a pulsed field gradient (PFG) multi spin echo (MSE) CPMG sequence for parallel and perpendicular axon orientation and four diffusion times. The apparent diffusion coefficient (ADC) was evaluated for two observed T2 components as a function of axonal orientation and diffusion time Δ. The short T2 component exhibited minor diffusional anisotropy and larger ADC, whereas the long T2 component showed significant anisotropy effects. This is consistent with the hypothesis that the short T2 component is associated with water within the myelin sheath, which is less restricted than axonal water that is limited by cell membrane permeability.
Functional MRI of the rat somatosensory cortex: Effects of hyperventilation
Authors: Hsu Edward W. , Hedlund Laurence W. , MacFall James R. 
Published: March 2007

AbstractFunctional mapping of the rat somatosensory cortex was performed with T2*‐sensitized MRI using a forepaw electrical stimulation model in α‐chloralose‐anesthetized rats at 7 T under both normocapnia and mild hyperventilation‐induced hypocapnia. A highly localized activation area, consistent with the known somatosensory cortical region, was detected in all seven animals studied during hypocapnia and in five of the same animals during normocapnia. Quantitatively, hypocapnia was found to significantly increase both the size of the fMRl activation area (3.4 ± 0.6 mm2 versus 1.5 ± 0.6 mm2 in normocapnia, mean ± standard error, n = 7, P < 0.03) and the average fMRl signal intensity increase (3.4 ± 0.6% versus 2.7 ± 0.4%, n = 5, P < 0.05). The increased sensitivity of fMRl to functional activation may reflect a widened arterial‐venous oxygenation difference resulting from an increased effective oxygen extraction during hyperventilation. The dependence of the fMRl response on the ventilation state underscores the need to control for physiological parameters in animal fMRl studies.
Feature space analysis of MRI
Authors: Soltanian‐Zadeh Hamid , Windham Joe P. , Peck Donald J. , Mikkelsen Tom 
Published: March 2007

AbstractThis paper presents an MRI feature‐space image‐analysis method and its application to brain tumor studies. The proposed method generates a transformed feature space in which the normal tissues (white matter, gray matter, and CSF) become orthonormal. As such, the method is expected to have site‐to‐site and patient‐to‐patient consistency, and is useful for identification of tissue types, segmentation of tissues, and quantitative measurements on tissues. The steps of the work accomplished are as follows: (1) Four T2‐weighted and two T1‐weighted images (before and after injection of gadolinium) were acquired for 10 tumor patients. (2) Images were analyzed by an image analyst according to the proposed algorithm. (3) Biopsy samples were extracted from each patient and were subsequently analyzed by the pathology laboratory. (4) Image‐analysis results were compared with the biopsy results. Pre‐ and postsurgery feature spaces were also compared. The proposed method made it possible to visualize the MRI feature space and to segment the image. In all cases, the operators were able to find clusters for normal and abnorma tissues. Also, clusters for different zones of the tumor were found. The method successfully segmented the image into normal tissues (white matter, gray matter, and CSF) and different zones of the lesion (tumor, cyst, edema, radiation necrosis, necrotic core, and infiltrated tumor). The results agreed with those obtained from the biopsy samples. Comparison of pre‐ with postsurgery and radiation feature spaces illustrated that the original solid tumor was not present in the second study, but a new tissue component appeared in a different location of the feature space. This tissue could be radiation necrosis generated as a result of radiation.
Sampling errors in projection reconstruction MRI
Authors: Joseph Peter M. 
Published: March 2007

AbstractCertain kinds of artifacts have been reported when projection reconstruction (PR) techniques are used in magnetic resonance imaging (MRI). These will occur if the spacing between samples in k‐space is too large. It has been suggested that PR requires finer k‐space sampling than does two‐dimensional Fourier reconstruction, and that the usual Nyquist criterion is inadequate. This paper examines this problem, with the conclusion that the Nyquist sampling criterion is adequate to avoid aliasing effects, provided that a band‐limited interpolation is used in k‐space. This procedure is motivated by analysis of the PR technique as it is commonly implemented in x‐ray computed tomography. A related problem is shown to be the construction of a filter function in k‐space that gives proper weight to the low spatial frequencies. It is shown that a simple k filter does not satisfy this requirement, and a procedure for deriving a suitable filter is described. The methods are tested in simulated PR profiles of circular disks of two different sizes. It is shown that the combination of the two new methods gives virtually perfect reconstruction for disks up to the size implied by the Nyquist limit.
Partial fourier reconstruction for three‐dimensional gradient echo functional MRI: Comparison of phase correction methods
Authors: Stenger V. Andrew , Noll Douglas C. , Boada Fernando E. 
Published: March 2007

AbstractPartial Fourier (PF) methods take advantage of data symmetry to allow for either faster image acquisition or increased image resolution, Faster acquisition and increased spatial resolution are advantageous for fMRl because of increased temporal resolution and/or reduced partial volume effects, respectively. Standard PF methods, which use a phase reference obtained from a low resolution image, are adequate for the reconstruction of time‐stationary images acquired using either spin echoes or short TE gradient echoes. In fMRI, however, multiple images are acquired using long TE gradient echoes, which introduces possible phase drifts in the fMRl data and high spatial frequencies in the phase reference. This work investigates several techniques developed to reconstruct fMRl data obtained with PF acquisitions. PF methods that account for both high‐frequency spatial variations and time‐dependent drifts in the phase reference are discussed and are quantitatively evaluated using receiver operator characteristic curve analysis.
Optimization of chemical shift selective suppression of fat
Authors: Kuroda Kagayaki , Oshio Koichi , Mulkern Robert V. , Jolesz Ferenc A. 
Published: March 2007

AbstractStrategies to optimize flip angles for chemical shift selective fat suppression are discussed. Mathematical models for fat suppression in spoiled gradient recalled acquisition, spin echo, and RARE, which incorporate steady state conditions and multiple spectral components of fat, are developed. The optimal suppression flip angle is found to be larger than that determined with a single fat component model by more than 10° due to contributions from unflipped components such as olefinic and glycerol protons that lie outside the suppression band.
A motion correction scheme by twin‐echo navigation for diffusion‐weighted magnetic resonance imaging with multiple RF echo acquisition
Authors: Mori Susumu , van Zijl Peter C. M. 
Published: March 2007

AbstractIn this paper, a series of diffusion‐weighted fast spin‐echo (FSE) sequences with a new motion correction scheme are introduced. This correction scheme is based on the navigator echo technique. Unlike conventional spin‐echo imaging, motion correction for FSE is complicated by the phase oscillation between odd‐numbered and even‐numbered echoes and the complex phase relationship between spin echo and stimulated echo components. In our approach, incoherent phase shifting due to motion is monitored by consecutive acquisition of two navigator echoes, which provide information on both inter‐echo and intra‐echo train phase shifts. Applications to both phantom and in vivo studies are presented.
Quantification of intravascular and extravascular contributions to BOLD effects induced by alteration in oxygenation or intravascular contrast agents
Authors: Zhong Jianhui , Kennan Richard P. , Fulbright Robert K. , Gore John C. 
Published: March 2007

AbstractA simple model is presented that allows quantitative separation of the contributions of signals from water in blood and extravascular parenchyma due to changes in blood oxygenation, induced either by brain activation or by alteration of inspired oxygen. The separation is based on the progressive attenuation of the signals in the vasculature of different levels when bipolar field gradient pulses are applied. Diffusion‐weighted spin‐echo echo‐planar imaging sequences were used to measure signal changes under various conditions in both animals and human volunteers. Normoxic‐hyperoxic episodes were induced in rats before and after injection of a superparamagnetic iron oxide contrast agent. Signal changes produced by visual stimulation were measured in human volunteers, and in volunteers subject to alternating normoxic‐hyperoxic episodes, and with administration of Gd‐DTPA. Analysis of the results with our simple model suggests that the apparent diffusion coefficient increases and R2 ( = 1/T2) decreases upon brain activation, with a large component from extravascular water related to the decrease in the blood de‐oxyhemoglobin concentration. Furthermore, this study suggests that apparent diffusion coefficient of the extravascular component alone may provide localization of neuronal activation.
Evidence of muscle BOLD effect revealed by simultaneous interleaved gradient‐echo NMRI and myoglobin NMRS during leg ischemia
Authors: Lebon Vincent , Brillault‐Salvat Cécile , Bloch Gilles , Leroy‐Willig Anne , Carlier Pierre G. 
Published: March 2007

AbstractThe purpose of this work was to investigate the temporal relationship between intensity changes in T2*‐weighted NMR images and tissue oxygen content, measured by myoglobin proton NMR spectroscopy, in the skeletal muscle. During an ischemic stress test, the calf muscles of five healthy volunteers were studied at 3 Tesla. An interleaved NMRI‐NMRS sequence was used, which made it possible to record T2*‐weighted images and myoglobin spectra simultaneously. During ischemia, rapid changes in muscle signal intensity were observed on T2*‐weighted images, which immediately preceded myoglobin desaturation. Bearing in mind the respective P50 of hemoglobin and myoglobin, this observation clearly favored the hypothesis that hemoglobin desaturation was responsible for the changes in T2*. This interpretation was further supported by the temporal coincidence between the experimental NMR data and a model of hemoglobin desaturation solely derived from physiological considerations.
Accurate determination of spin‐density and T1 in the presence of RF‐field inhomogeneities and flip‐angle miscalibration
Authors: Venkatesan Ramesh , Lin Weili , Haacke E. Mark 
Published: March 2007

AbstractA method is presented for the accurate extraction of relative spin‐density (ρo) and spin‐lattice relaxation time (T1) in the presence of RF‐field inhomogeneities and flip‐angle miscalibration. The method requires collecting images at several flip‐angles with a three‐dimensional, spoiled steady‐state, gradient‐echo imaging sequence. Results show that the predominant effect of an overestimated flip‐angle is to shift the T1 estimate to a higher value, whereas reductions in the normalized RF‐field from unity cause ρo and T1 distributions to be skewed toward lower values. Phantom and in vivo results demonstrate that the proposed method overcomes both of these systematic errors. The method was shown to be valid for up to a 50% reduction in RF sensitivity. A self‐consistency argument was used to validate the absence of systematic errors in the extracted ρo and T1 values over a large number of voxels. This made it possible to obtain a very precise estimate of muscle T1 at 1.5 T, yielding a 95% confidence interval of (1077.7 ± 3.5) ms.
One‐shot spatially resolved velocity imaging
Authors: Luk Pat Gerard T. , Pauly John M. , Hu Bob S. , Nishimura Dwight G. 
Published: March 2007

AbstractFor quantitative velocity measurement, we have developed a technique that acquires full velocity spectra without cardiac gating. After a cylindrical excitation restricts imaging to one spatial dimension, data are acquired while an oscillating gradient is played out. After each excitation, an image of velocity versus spatial location is obtained. For a given spatial location, a series of these images can be used to form an image of velocity versus time. Acquisition times are much shorter than for phase‐contrast imaging or Fourier‐encoded velocity imaging, obviating the need for cardiac gating. Although a two‐shot version of this technique has been presented previously, we have developed a one‐shot version that offers higher temporal resolution for a given velocity resolution and superior off‐resonance properties.
Evaluation of respiratory artifact correction techniques in multishot spiral functional mri using receiver operator characteristic analyses
Authors: Noll Douglas C. , Genovese Christopher R. , Vazquez Alberto L. , O'Brien Jennifer L. , Eddy William F. 
Published: March 2007

AbstractNavigator corrections and low‐spatial frequency (LSF) over‐sampling are investigated as methods for reducing respiration‐related effects in multishot functional MRI. Both techniques take advantage of the smoothly varying or nearly constant phase variations linked to the respiration cycle. These techniques were tested in functional MRI studies with spiralk‐space acquisitions. Receiver operator characteristic (ROC) analyses and the temporal variance averaged across the brain were used to evaluate their effectiveness. Both methods were found to increase the area under the ROC curve and to reduce the standard deviation, with the LSF oversampling method being more effective.
Quantitation of circumferential subpixel vessel wall position and wall shear stress by multiple sectored three‐dimensional paraboloid modeling of velocity encoded cine MR
Authors: Oyre Sten , Ringgaard Steffen , Kozerke Sebastian , Paaske William P. , Scheidegger Markus B. , Boesiger Peter , Pedersen Erik M. 
Published: March 2007

AbstractMethods are lacking for accurate, noninvasive circumferential edge detection and wall shear stress calculation. Using stan dard MR phase contrast sequences, parts of the velocity pro files were fitted to a multiple sectored three‐dimensional pa raboloid model enabling exact calculation of vessel wall position and wall shear stress in 24 locations evenly distrib uted around the luminal vessel wall. The model was evaluated by in vitro scans and computer simulations and applied to the common carotid artery of humans. In vitro, the luminal area of a glass tube was assessed with an error of 0.9%. Computer simulations of peak systolic data revealed errors of ±0.9% (vessel area) and ±3.25% (wall shear stress). The in vivo results showed substantial difference between anterior and posterior wall shear stress values due to skewed velocity profiles. A new noninvasive method for highly accurate mea surement of circumferential subpixel vessel wall position and wall shear stress has been developed.
Simultaneous oxygenation and perfbsion imaging study of functional activity in primary visual cortex at different visual stimulation frequency: Quantitative correlation between BOLD and CBF changes
Authors: Zhu Xiao‐Hong , Kim Seong‐Gi , Andersen Peter , Ogawa Seiji , Uğgurbil Kamil , Chen Wei 
Published: March 2007

AbstractA relationship between regional cerebral blood flow (CBF) and blood oxygenation level dependent (BOLD) changes in the primary visual cortex (V1) at varied visual stimulation fre quency has been examined quantitatively using the multislice FAIR technique. A linear correlation in the common activation areas between functional BOLD and CBF maps was observed. This supports the hypothesis that the task‐stimulated BOLD changes in microvasculature are correlated with the CBF changes that presumably reflect the degree of neuronal ac tivity. The linear correlation coefficients for intrasubject com parisons are more significant than those for intersubject com parisons. This suggests that using intrasubject comparisons for quantitative studies of neuronal activity related to different task stimuli and task performances should be more reliable than using intersubject comparisons.
Proton double‐quantum filtered MRI—A new method for imaging ordered tissues
Authors: Tsoref Liat , Shinar Hadassah , Seo Yoshiteru , Eliav Uzi , Navon Gil 
Published: March 2007

AbstractThe imaging of connective tissues such as cartilage and ten dons using standard MRI techniques is hampered by their low signal relative to the surrounding tissues. 1H double‐quantum filtered (DQF) MRI is an imaging method that detects mole cules associated with ordered structures, while the signal from isotropic fluids is filtered out, thus creating a new type of contrast. The technique is demonstrated on an intact rat tail, where the image of the tendons is highlighted. Although the signal‐to‐noise ratio is inferior to that in gradient‐echo MRI, the contrast between the tendons and the surrounding tissues is significantly better in the DQF MRI. It is demonstrated how, by adjusting the parameters of the DQF imaging pulse se quence, one can modify the contrast and enhance the images of specific compartments within an organ. A comparison with 2H DQF imaging of the same tissue is also given.
Synthesis and preliminary evaluation of MP‐2269: A novel, nonaromatic small‐molecule blood‐pool MR contrast agent
Authors: Wallace Rebecca A. , Haar Joe P. , Miller Donald B. , Woulfe Steven R. , Polta John A. , Galen Karen P. , Hynes Michael R. , Adzamli Kofi 
Published: March 2007

AbstractA nonaromatic, small‐molecule, gadolinium(3+)‐chelate code named MP‐2269 was synthesized and evaluated in animals as a potential MR contrast agent for blood pool. The ligand of MP‐2269 was prepared by conjugating a lipophilic, albumin‐binding moiety, 4‐pentylbicyclo[2.2.2]octane‐1‐carboxylic acid, to an amino‐functionalized DTPA derivative by means of a diaspartic acid linker. Proton relaxometry studies in vitro yielded spin‐lattice relaxivities (R1) for MP‐2269 of 6.2, 20.0 and 26.1 mM−1 sec−1 in water, rabbit blood, and human blood, respectively. The enhanced relaxivities in blood indicate sig nificant binding of the agent to blood proteins. At a dose of 45 μmol/kg, MP‐2269 showed a biphasic rabbit blood clearance profile with half‐lives of 4.7 and 142 minutes, respectively, for the fast and slow components. In rats, the agent is cleared predominantly through the hepatobiliary pathway (∼70% in 24 h by this mode). The LD50 value of MP‐2269 is ∼3.0 mmol/kg in mice. Preliminary MR angiograms obtained in the rabbit showed excellent enhancement of blood vessels. Hence, MP‐2269 has potential for future exploitation as a contrast agent for MR angiography.
A comparison between magnetization transfer ratios and myelin water percentages in normals and multiple sclerosis patients
Authors: Vavasour Irene M. , Whittall Kenneth P. , Mackay Alex L. , Li David K. B. , Vorobeychik Galina , Paty Donald W. 
Published: March 2007

AbstractMagnetization transfer and T2 relaxation data were obtained for five white and six gray matter brain structures from 10 normal volunteers and 9 multiple sclerosis patients. Thirty MS lesions were also anatyzed. Magnetization transfer ratios and myelin water percentages were compared. Both techniques showed a significant difference between the average of white and gray matter of the normal volunteers as well as the average of nor mal‐appearing white matter and gray matter of the multiple sclerosis patients. The average magnetization transfer ratio and myelin water percentage for lesions were significantly lower than those of normal‐appearing white matter. Myelin water per centages and magnetization transfer ratios were uncorrelated in white and gray matter but showed a small (R = 0.5, P = 0.005) but significant correlation in multiple sclerosis lesions. In sum mary, the myelin water percentage and the magnetization trans fer ratio provide quantifiable but largely independent measures of multiple sclerosis lesion pathology.