bluuebunny/crossref_metadata_2025_split huggingface dataset:
Design of symmetric‐sweep spectral‐spatial RF pulses for spectral editing
Authors: Cunningham Charles H. , Vigneron Daniel B. , Chen Albert P. , Xu Duan , Hurd Ralph E. , Sailasuta Napapon , Pauly John M. 
Published: June 2004

AbstractSpectral‐spatial RF (SSRF) pulses allow simultaneous selection in both frequency and spatial domains. These pulses are particularly important for clinical and research MR spectroscopy (MRS) applications for suppression of large water and lipid resonances. Also, the high bandwidth of the subpulses (5–10 kHz) greatly reduces the spatial‐shift errors associated with different chemical shifts. However, the use of high‐bandwidth subpulses along with enough spectral bandwidth to measure a typical range of metabolite frequencies (e.g., 300 Hz at 3 T) can require RF amplitudes beyond the limits of the RF amplifier of a typical scanner. In this article, a new method is described for designing nonlinear‐phase 180° SSRF pulses that can be used for spectral editing. The novel feature of the pulses is that the spectral profile develops as a symmetric sweep, from the outside edges of the spectral window towards the middle, so that coupled components are tipped simultaneously and over a short interval. Pulses were designed for lactate editing at 1.5 T and 3 T. The spectral and spatial spin‐echo profiles of the new pulses were measured experimentally. Spectra acquired in phantom experiments showed a well‐resolved, edited lactate doublet, with 91% to 93% editing efficiency. Magn Reson Med 52:147–153, 2004. © 2004 Wiley‐Liss, Inc.
Correction for gradient nonlinearity in continuously moving table MR imaging
Authors: Polzin Jason A. , Kruger David G. , Gurr David H. , Brittain Jean H. , Riederer Stephen J. 
Published: June 2004

AbstractRecently, a number of methods have been demonstrated for large field of view MR imaging using continuous table motion. As with conventional, fixed‐table MRI, the spatial encoding is performed using magnetic field gradients. However, it is demonstrated in this work that as a consequence of every measurement being made at a slightly different displacement between the object and the gradient field, gradient nonlinearities are manifest as blurring in addition to spatial distortion. Moreover, the blurring is spatially dependent. It is also shown that correcting all phase‐encoding steps individually or in groups can reduce these effects. Phantom and in vivo results are shown which demonstrate the effectiveness of the correction. Magn Reson Med 52:181–187, 2004. © 2004 Wiley‐Liss, Inc.
Opiate tolerance by heroin self‐administration: An fMRI study in rat
Authors: Xi Zheng‐Xiong , Wu Gaohong , Stein Elliot A. , Li Shi‐Jiang 
Published: June 2004

AbstractFunctional MRI (fMRI) was employed to determine whether repeated heroin self‐administration (SA) produces tolerance or sensitization in the brain of heroin‐SA rats. Twelve rats were evenly divided into saline and heroin (0.06 mg/kg, 4 hr/day) SA groups. There was a progressive increase in drug‐SA behavior and daily heroin intake during the 8–9 days of heroin‐SA training. Within 24 hr after the last session of daily SA, acute heroin (0.1 mg/kg) administration induced regional blood oxygen level‐dependent (BOLD) signals in both groups of rats. The positive BOLD signals appeared mainly in the cortical regions, including the prefrontal cortex, cingulate, and olfactory cortex, while the negative BOLD signals were predominantly located in subcortical regions such as caudate and putamen, nucleus accumbens, thalamus, and hypothalamus. However, the number of activated voxels or BOLD‐signal intensity was significantly less in heroin‐SA rat in regions of prefrontal cortex, nucleus accumbens, and thalamus, etc., compared to the changes in the saline control rats. Application of γ‐vinyl GABA (100 mg/kg), an irreversible GABA‐transaminase inhibitor, failed to block opiate actions in the heroin‐SA rats. Together, these data suggest that repeated heroin‐SA produces tolerance or desensitization of opiate actions in the rat brain, which may in turn potentiate drug SA behavior and drug intake. Magn Reson Med 52:108–114, 2004. © 2004 Wiley‐Liss, Inc.
Use of spherical harmonic deconvolution methods to compensate for nonlinear gradient effects on MRI images
Authors: Janke Andrew , Zhao Huawei , Cowin Gary J. , Galloway Graham J. , Doddrell David M. 
Published: June 2004

AbstractSpatial encoding in MR techniques is achieved by sampling the signal as a function of time in the presence of a magnetic field gradient. The gradients are assumed to generate a linear magnetic field gradient, and typical image reconstruction relies upon this approximation. However, high‐speed gradients in the current generation of MRI scanners often sacrifice linearity for improvements in speed. Such nonlinearity results in distorted images. The problem is presented in terms of first principles, and a correction method based on a gradient field spherical harmonic expansion is proposed. In our case, the amount of distortion measured within a typical field of view (FOV) required for head imaging is sufficiently large that without the use of some distortion correction technique, the images would be of limited use for stereotaxy or longitudinal studies, where precise volumetric information is required. Magn Reson Med 52:115–122, 2004. © 2004 Wiley‐Liss, Inc.
Signal‐to‐noise ratio behavior of steady‐state free precession
Authors: Reeder Scott B. , Herzka Daniel A. , McVeigh Elliot R. 
Published: June 2004

AbstractSteady‐state free precession (SSFP) is a rapid gradient‐echo imaging technique that has recently gained popularity and is used in a variety of applications, including cardiac and real‐time imaging, because of its high signal and favorable contrast between blood and myocardium. The purpose of this work was to examine the signal‐to‐noise ratio (SNR) behavior of images acquired with SSFP, and the dependence of SNR on imaging parameters such as TR, bandwidth, and image resolution, and the use of multi‐echo sequences. In this work it is shown that the SNR of SSFP sequences is dependent only on pulse sequence efficiency, voxel dimensions, and relaxation parameters (T1 and T2). Notably, SNR is insensitive to bandwidth unless increases in bandwidth significantly decrease efficiency. Finally, we examined the relationship between pulse sequence performance (TR and efficiency) and gradient performance (maximum gradient strength and slew rate) for several imaging scenarios, including multi‐echo sequences, to determine the optimum matching of maximum gradient strength and slew rate for gradient hardware designs. For standard modern gradient hardware (40 mT/m and 150 mT/m/ms), we found that the maximum gradient strength is more than adequate for the imaging resolution that is commonly encountered with rapid scouting (3 mm × 4 mm × 10 mm voxel). It is well matched for typical CINE and real‐time cardiac imaging applications (1.5 mm × 2 mm × 6 mm voxel), and is inadequate for optimal matching with slew rate for high‐resolution applications such as musculoskeletal imaging (0.5 × 0.8 × 3 mm voxel). For the lower‐resolution methods, efficiency could be improved with higher slew rates; this provokes interest in designing methods for limiting dB/dt peripherally while achieving high switching rates in the imaging field of view. The use of multi‐echo SSFP acquisitions leads to substantial improvements in sequence performance (i.e., increased efficiency and shorter TR). Magn Reson Med 52:123–130, 2004. Published 2004 Wiley‐Liss, Inc.
NMR measurement of brain oxidative metabolism in monkeys using 13C‐labeled glucose without a 13C radiofrequency channel
Authors: Boumezbeur Fawzi , Besret Laurent , Valette Julien , Vaufrey Françoise , Henry Pierre‐Gilles , Slavov Velislav , Giacomini Eric , Hantraye Philippe , Bloch Gilles , Lebon Vincent 
Published: June 2004

AbstractWe detected glutamate C4 and C3 labeling in the monkey brain during an infusion of [U‐13C6]glucose, using a simple 1H PRESS sequence without 13C editing or decoupling. Point‐resolved spectroscopy (PRESS) spectra revealed decreases in 12C‐bonded protons, and increases in 13C‐bonded protons of glutamate. To take full advantage of the simultaneous detection of 12C‐ and 13C‐bonded protons, we implemented a quantitation procedure to properly measure both glutamate C4 and C3 enrichments. This procedure relies on LCModel analysis with a basis set to account for simultaneous signal changes of protons bound to 12C and 13C. Signal changes were mainly attributed to 12C‐ and 13C‐bonded protons of glutamate. As a result, we were able to measure the tricarboxylic acid (TCA) cycle flux in a 3.9 cm3 voxel centered in the monkey brain on a whole‐body 3 Tesla system (VTCA = 0.55 ± 0.04 μmol.g−1.min−1, N = 4). This work demonstrates that oxidative metabolism can be quantified in deep structures of the brain on clinical MRI systems, without the need for a 13C radiofrequency (RF) channel. Magn Reson Med 52:33–40, 2004. © 2004 Wiley‐Liss, Inc.
Diffusion measurements free of motion artifacts using intermolecular dipole‐dipole interactions
Authors: Kennedy Scott D. , Zhong Jianhui 
Published: June 2004

AbstractDiffusion encoding, or diffusion weighting, is commonly achieved by applying a pair of balanced pulsed‐field gradients during spin evolution. An alternative way to obtain diffusion measurements is to select dipolar correlation distances using the distant dipolar field (DDF) in systems with abundant spin density, such as water in tissues. Diffusion weighting using this effect is unique in that the refocusing “gradient” is carried within the sample, and thus the macroscopic motion of the sample is not expected to interfere with signal formation. The experiments presented here demonstrate that in moving phantoms, the phase shift of the signal due to linear motion is minimal in diffusion‐weighted (DW) DDF measurements, and that motion artifacts in images of moving phantoms and the abdomen of live mice are small compared to standard pulsed‐field‐gradient methods. The technique may facilitate the use of DWI in typically motion‐prone regions such as the abdomen, lungs, and heart. Magn Reson Med 52:1–6, 2004. © 2004 Wiley‐Liss, Inc.
Ultrasound‐guided MRI: Preliminary results using a motion phantom
Authors: Günther Matthias , Feinberg David A. 
Published: June 2004

AbstractIn principal, both ultrasound (US) imaging and MRI can be performed simultaneously within the magnetic field of the scanner due to their different physical natures (i.e., sound waves vs. electromagnetic radiation). One potential application is to use US information for dynamic spatial organ localization to improve MR imaging, similar to MR navigator echoes. In this work, preliminary results are presented for US‐guided MRI using position and orientation information extracted from US data to update the image slice position of an SSFP sequence in real time. Effective prospective motion compensation is shown for a phantom whose sinusoidal displacement can be fully corrected. Possible applications of simultaneous US‐MRI acquisitions include real‐time US‐guided cardiac MRI or interventional procedures. Magn Reson Med 52:27–32, 2004. © 2004 Wiley‐Liss, Inc.
Development programs for one‐shot systems using multiple‐state design reliability models
Authors: Shevasuthisilp Suntichai , Vardeman Stephen B. 
Published: June 2004

AbstractDesign reliability at the beginning of a product development program is typically low, and development costs can account for a large proportion of total product cost. We consider how to conduct development programs (series of tests and redesigns) for one‐shot systems (which are destroyed at first use or during testing). In rough terms, our aim is to both achieve high final design reliability and spend as little of a fixed budget as possible on development. We employ multiple‐state reliability models. Dynamic programming is used to identify a best test‐and‐redesign strategy and is shown to be presently computationally feasible for at least 5‐state models. Our analysis is flexible enough to allow for the accelerated stress testing needed in the case of ultra‐high reliability requirements, where testing otherwise provides little information on design reliability change. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2004
Central nervous system inflammatory response after cerebral infarction as detected by magnetic resonance imaging
Authors: Saleh Andreas , Wiedermann Dirk , Schroeter Michael , Jonkmanns Cornelia , Jander Sebastian , Hoehn Mathias 
Published: June 2004

AbstractBrain inflammation contributes to the tissue injury caused by ischemic stroke. Macrophages as the most abundant inflammatory cell population in stroke lesions can be visualized using ultrasmall superparamagnetic iron oxide (USPIO) as a cell‐specific contrast agent for magnetic resonance imaging (MRI). The aim of our present study was to delineate the inflammatory response during experimental cerebral infarction by means of USPIO‐enhanced MRI and to correlate the spatial distribution of USPIO‐induced MR signal alterations with cellular infiltration and iron deposition. To this end USPIOs were administered to Wistar rats 5 days after photothrombotic cerebral infarction. MR imaging at 7 T performed 24 h later displayed a rim‐like signal loss around the infarction in the USPIO treated animals. On histological brain sections obtained from the same animals after MRI the distribution of iron and ED1+ phagocytes was in full spatial agreement with the signal loss seen on T2*‐weighted images. Our study validates USPIO‐enhanced MRI as an important tool for the noninvasive visualization of brain inflammation in stroke and other CNS pathologies. Copyright © 2004 John Wiley & Sons, Ltd.
Water diffusion in the different microenvironments of breast cancer
Authors: Paran Yael , Bendel Peter , Margalit Raanan , Degani Hadassa 
Published: June 2004

AbstractThe parameters that characterize the intricate water diffusion in tumors may serve to reveal their distinct pathology. Specifically, the application of diffusion magnetic resonance imaging (MRI) can aid in characterizing breast cancer, as well as monitoring response to therapy. We present here a non‐invasive, quantitative MRI investigation, at high spatial resolution, of water diffusion in hormonal dependent MCF7 breast tumors implanted orthotopically in immunodeficient mice. Distinctive MRI protocols were designed in this study, utilizing a broad range of diffusion times and diffusion gradient strengths. Application of these protocols allowed water diffusion in the tissue extracellular and intracellular compartments to be distinguished, and the effect of restricted diffusion and water exchange on the water diffusion in these compartments to be evaluated. Pixel‐by‐pixel analysis yielded parametric maps of the estimated volume fraction and apparent diffusion coefficient of each compartment. The diffusion of the water in the extracellular microenvironment was approximately two fold slower than that of free water, and in the intracellular compartment was about one order of magnitude slower than that of free water and demonstrated restriction of water diffusion at long diffusion times. Mapping of the water fraction in each compartment was further employed to monitor changes during tumor progression and to assess tumor response to hormonal manipulation with a new antiestrogenic drug, tamoxifen methiodide (TMI). It was found that, in parallel to the growth arrest by this drug, the volume fraction of the slowly diffusing water increased, suggesting a TMI‐induced cell swelling. This study can serve as a basis for extending diffusion breast MRI in the clinical setting. Copyright © 2004 John Wiley & Sons, Ltd.
In vivo elasticity measurements of extremity skeletal muscle with MR elastography
Authors: Uffmann Kai , Maderwald Stefan , Ajaj Waleed , Galban Craig G. , Mateiescu Serban , Quick Harald H. , Ladd Mark E. 
Published: June 2004

AbstractMR elastography (MRE) has been shown to be capable of non‐invasively measuring tissue elasticity even in deep‐lying regions. Although limited studies have already been published examining in vivo muscle elasticity, it is still not clear over what range the in vivo elasticity values vary. The present study intends to produce further information by examining four different skeletal muscles in a group of 12 healthy volunteers in the age range of 27–38 years. The examinations were performed in the biceps brachii, the flexor digitorum profundus, the soleus and the gastrocnemius. The average shear modulus was determined to be 17.9 ( ± 5.5), 8.7 ( ± 2.8), 12.5 ( ± 7.3) and 9.9 ( ± 6.8) kPa for each muscle, respectively. To ascertain the reproducibility of the examination, the stiffness measurements in two volunteers were repeated seven times for the biceps brachii. These examinations yielded a mean shear modulus of 11.3 ± .7 and 13.3 ± 4.7 kPa for the two subjects. For elasticity reconstruction, an automated reconstruction algorithm is introduced which eliminates variation due to subjective manual image analysis. This study yields new information regarding the expected variation in muscle elasticity in a healthy population, and also reveals the expected variability of the MRE technique in skeletal muscle. Copyright © 2004 John Wiley & Sons, Ltd.
1H and13C HR‐MAS spectroscopy of intact biopsy samplesex vivoandin vivo1H MRS study of human high grade gliomas
Authors: Martínez‐Bisbal M. Carmen , Martí‐Bonmatí Luis , Piquer José , Revert Antonio , Ferrer Pilar , Llácer José L. , Piotto Martial , Assemat Olivier , Celda Bernardo 
Published: June 2004

AbstractHigh‐resolution magic angle spinning (HR‐MAS) one‐ and two‐dimensional1H and13C nuclear magnetic resonance (NMR) spectroscopy has been used to study intact glioblastoma (GBM) brain tumour tissue. The results were compared within vitrochemical extract andin vivospectra. The resolution of1H one‐dimensional,1H TOCSY and13C HSQC HR‐MAS spectra is comparable to that obtained on perchloric extracts.13C HSQC HR‐MAS spectra have been particularly useful for the identification of 37 different metabolites in intact biopsy tumours, excluding water and DSS components. To our knowledge, this is the most detailed assignment of biochemical compounds obtained in intact human tissue, in particular in brain tumour tissue. Tissue degradation during the recording of the NMR experiment was avoided by keeping the sample at a temperature of 4°C. Detailed metabolical compositions of 10 GBM (six primary, two secondary and two unclassified) were obtained. A good correlation betweenex vivoandin vivoMRS has been found. Copyright © 2004 John Wiley & Sons, Ltd.
Synthesis of third‐order non‐linear optical polymers based on conjugated poly(heteroarylene methines)
Authors: Yi Wenhui , Feng Wei , Cao Meng , Wu Hongcai 
Published: June 2004

AbstractA series of 10 new poly(heteroarylene methylenes) containing one pyrrole or thiophene ring alternating with a carbon atom in the main chain were synthesized and characterized. The polymers which were synthesized in the air were found to be partially dehydrogenated by the oxygen, that is, the bridge carbon atoms between pyrrole or thiophene rings were partially sp3 atoms and partially sp2 atoms. However the polymers which were synthesized in the flowing nitrogen atmosphere were found to be deoxidized, that is the bridge atoms were sp3 atoms. The deoxidized polymers could be oxidatively dehydrogenated with tetrchlorobenzoquinone. These polymers are useful model systems to investigate the effect of conjugation length on the electronic and optical properties of conjugated polymers. Third‐order optical non‐linearities of the reulting polymers were studied by z‐scan techniques. The results show that the reulting polymers exhibited large third‐order optical non‐linear susceptibilities as large as 10−8 esu. Copyright © 2004 John Wiley & Sons, Ltd.
Electroinduced oxidative copolymerization of N‐vinyl carbazole with methyl ethyl ketone formaldehyde resin
Authors: Ustamehmetoğlu Belkıs , Saraç A. Sezai , Kızılcan Nilgün , Akar Ahmet 
Published: June 2004

AbstractIn this study, a novel procedure to obtain the non‐crosslinked, photoconductive, white form of the linear copolymer of N‐vinyl carbazole (NVCz) and methyl ethyl ketone formaldehyde resin (MEKF‐R) is reported. A possible mechanism of copolymerization is suggested. The yield of the copolymer is increased almost 10 times by the addition of catalytic amounts of ceric ammonium nitrate as an oxidant during the electrochemical polymerization of NVCz in the presence of MEKF‐R in a divided electrochemical cell. Since cerium(III) is readily oxidized to cerium(IV) at the anode, the concentration of cerium(IV) remained constant and the deposition of green poly(NVCz) can be prevented. Copyright © 2004 John Wiley & Sons, Ltd.
Preparation and characterization of a polyimide nanofoam through grafting of labile poly(propylene glycol) oligomer
Authors: Han Sang Hyub , Do Jin‐Sek , Kader M. Abdul , Lee Joong‐Hee , Lee Myong‐Hoon , Nah Changwoon 
Published: June 2004

AbstractPreparation of a polyimide nanofoam (PI‐F) for microelectronic applications was carried out using a polyimide precursor synthesized from poly[(amic acid)‐co‐(amic ester)] and grafted with a labile poly(propylene glycol) (PPG) oligomer. Polyimide precursor was synthesized by partial esterification of poly(amic acid) (PAA) derived from pyromellitic dianhydride (PMDA) and 4,4′‐oxydianiline (ODA). The precursor was then grafted with bromide‐terminated poly(propylene glycol) in the presence of K2CO3 in hexamethylphosphoramide and N‐methylpyrrolidone, imidized at 200°C in nitrogen and the product was subsequently decomposed in air at 300°C to eliminate the labile PPG oligomer to produce PMDA/ODA polyimide nanofoam. Nuclear magnetic resonance spectroscopy (1H‐NMR) and Fourier transform infrared spectroscopy (FT‐IR) techniques were used to characterize the formation of polyimide precursor and extent of grafting of PPG with polyimide. The results of thermogravimetric analysis (TGA) showed three step decomposition of nanofoam with the removal of PPG at 350°C and decomposition of polyimide at around 600°C. The polyimide nanofoams were also characterized by small angle X‐ray scattering (SAXS), field‐emission scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM). The morphology showed nanophase‐separated structures with uniformly distributed and non‐interconnected pores of 20–40 nm in size. Dynamic mechanical analysis (DMA) indicated higher storage modulus for the foamed structure compared to the pure PI with reduction in loss tangent for the former system. Copyright © 2004 John Wiley & Sons, Ltd.