bluuebunny/crossref_metadata_2025_split huggingface dataset:
Specific MR imaging of human lymphocytes by monoclonal antibody‐guided dextran‐magnetite particles
Authors: Bulte Jeff W. M. , Hoekstra Yke , Kamman Richard L. , Magin Richard L. , Webb Andrew G. , Briggs Richard W. , Gwan Go K. , Hulstaert Caesar E. , Miltenyi Stefan , Hauw The T. , De Leij Lou 
Published: March 2007

AbstractHuman lymphocytes were labeled with biotinylated anti‐lymphocyte‐directed monoclonal antibodies, to which streptavidin and subsequently biotinylated dextran‐magnetite particles were coupled. This labeling resulted in a strong and selective negative contrast enhancement of lymphocyte suspensions at 2.0 T, caused predominantly by the specific increase of R2 with a small but significant specific increase of R2. The R1 was found to decrease with increasing field strength. The immunolabeling procedure described here may be used for the selective signal depletion of target cells in MR imaging.
Improved efficiency in 2DFT magnetization‐prepared rapid gradient echo imaging: Application to abdominal imaging
Authors: Bampton Anna E. H. , Riederer Stephen J. 
Published: March 2007

AbstractThe incorporation of the phase offset multiplanar (Pomp) technique into breathheld magnetization‐prepared gradient echo imaging is discussed as a means for improving imaging efficiency without sacrificing resolution. contrast, or SNR improvement. The phase encoding order necessary to preserve the centric approach is described. When combined with interleaving, the Pomp technique enables four 256 × 256 imagesto be acquired in a 12‐s breathhold, doubling the efficiency of the original technique. This scan efficiency is compared with that of other TI‐weighted 2DFT methods.
Localized 13C NMR spectroscopy of myo‐inositol in the human brain in vivo
Authors: Gruetter Rolf , Rothman Douglas L. , Novotny Edward J. , Hulman Robert G. 
Published: March 2007

AbstractNatural abundance 13C NMR spectra obtained from 144‐cm3volumes in the human brain contained well‐resolved resonances of myo‐inositol after 60 min of data accumulation. A mean concentration of 7.2 ± 0.5 pmol/g (±SE, n = 7) was calculated from the comparison with phantoms. 13C NMR spectroscopy thus provides a complementaryrole in the quantitation of metabolites also observed in the crowded 1H spectrum.
NMR studies of erythrocytes immobilized in agarose and alginate gels
Authors: Lundberg Peter , Berners‐Price Susan J. , Roy Sushmita , Kuchel Philip W. 
Published: March 2007

Abstract31P and 13C NMR were used to study the energy metabolism in perfused, human erythrocytes. The erythrocytes were immobilized in agarose threads, Ca‐ or Ba‐alginate beads, and Ba‐alginate‐coated agarose threads. Erythrocytes were easily washed out from the agarose threads, but not from alginate‐containing gels. Various small molecules, such as hypophosphite, dimethyl methylphosphonate, and methylphosphonate, were taken up from the perfusion medium in a normal manner. In addition, the 2,3‐bisphosphoglycerate (2,3‐DPG) chemical shifts were sensitive to the oxygen partial pressure suggesting that O2 molecules were diffusing through the gel and modifying the binding of 2,3‐DPG to hemoglobin. A combination of inosine and pyruvate stimulated the synthesis of 2,3‐DPG. but only if inorganic phosphate was present in the perfusion medium. Inosine only resulted in a dramatic rise in the intracellular sugarphosphate concentrations. Furthermore, [2‐13C]glucose was converted to [2‐13C]lactate by immobilized cells at a rate which was comparable to that in a control suspension. In summary, immobilization in Ba‐alginate‐coated agarose threads was an efficient way of trapping human erythrocytes for whole cell NMR investigations. © 1992 Academic Press, Inc.
Measurement of brain perfusion by volume‐localized NMR spectroscopy using inversion of arterial water spins: Accounting for transit time and cross‐relaxation
Authors: Zhang Weiguo , Williams Donald S. , Detre John A. , Koretsky Alan P. 
Published: March 2007

AbstractThe theoretical model for perfusion measurement by NMR using arterial labeling of endogenous water is extended to include the effects of transit time and cross‐relaxation of tissue water with macromolecules. Water magnetization in rat brain is monitored using the STEAM method to simultaneously determine the transit time, magnetization transfer rate constant, and perfusion. The results show that the transit time in rat brain is quite short, and thus its effect on perfusion measurement is small. It is also demonstrated both theoretically and experimentally that the steady‐state effects of cross‐relaxation with macromolecules on perfusion measurement are accounted for by a proper control experiment. © 1992 Academic Press, Inc.
Effects of the interaction between ferric iron and L‐dopa melanin on T1 and T2 relaxation times determined by magnetic resonance imaging
Authors: Tosk Jeffrey M. , Holshouser Barbara A. , Aloia Roland C. , Hinshaw David B. , Hasso Anton N. , Macmurray James P. , Will A. Douglas , Bozzetti Louis P. 
Published: March 2007

AbstractT1 and T2 relaxation times of agar phantoms containing L‐dopa melanin and Fe3+ were measured under MRI conditions. Fe3+ shortened T1 and T2 relaxation times. Melanin influenced relaxation times only in the presence of Fe3+; thus, contrast in MR images of the basal ganglia may depend upon levels of both paramagnetic iron and neuromelanin.
Design and evaluation of shielded gradient coils
Authors: Carlson J. W. , Derby K. A. , Hawryszko K. C. , Weideman M. 
Published: March 2007

AbstractTechniques are described for the design of shielded gradient coils for superconducting MRI systems. These design methods are suited for constructing the most efficient gradient coil that meets a specified homogeneity requirement. Tradeoffs in coil design of efficiency with coil size and gap size are discussed. Residual eddy currents from coils constructed with a finite number of wires are calculated and give guidelines for the construction of efficient, whole‐body gradient coils.
Volume‐selective proton MRS in vertebral bodies
Authors: Schick Fritz , Bongers Hilmar , Jung Wulf‐Ingo , Skalej Martin , Lutz Otto , Claussen Claus D. 
Published: March 2007

AbstractVolume‐selective 1H magnetic resonance spectra of small volume elements of (13 mm)3 positioned in lumbar vertebral bodies have been investigated in 15 healthy persons of different ages and sexes and in 11 patients with leukemia using double spin‐echo sequences. Signal intensities and positions of the spectral lines have been evaluated. Interindividual spectra of VOI located in the center of vertebral bodies, intraindividual spectra of central VOI in different vertebral bodies, and spectra of different localizations within the same vertebral body have been compared as well as spectra before and partly after cytostatic treatment in leukemia patients. Unexpected phenomena of the signal shapes have been found. The water signal distributions in healthy persons compared to patients after bone marrow transplantation show significant differences. The success of the cytostatic treatment in cases of leukemia is accompanied by an increase in the intensity of the lipid signals and a decrease in the water signals.
Pulsed saturation transfer contrast
Authors: Hu Bob S. , Conolly Steven M. , Wright Graham A. , Nishimura Dwight G. , Macovski Albert 
Published: March 2007

AbstractIn vivo 1H conventional NMR image contrast generation usually relies on the macroscopic T1 and T2 relaxation parameters of the tissues of interest. Recently cross‐relaxation related image contrast has been reported by Wolff and Balaban in animal models. Due primarily to the broad lineshape of the intended saturation spin pool and the use of off‐resonance irradiation, high specific absorption rate and an auxiliary RF amplifier have been necessary to produce these images. The relatively long spin‐lattice relaxation property of this spin pool, however, suggests the use of pulse methods to achieve saturation. In this paper, we show that short‐T2 spin pools can be selectively saturated with short intense RF pulses. Cross‐relaxation time constants can be measured using the technique of saturation recovery. In vivo magnetization‐transfer‐weighted images can be produced using pulses on commercial whole‐body imagers without additional hardware.
Partial RF echo‐planar imaging with the FAISE method. II. Contrast equivalence with spin‐echo sequences
Authors: Melki Philippe S. , Jolesz Ferenc A. , Mulkern Robert V. 
Published: March 2007

AbstractThe fast acquisition interleaved spin‐echo (FAISE) sequence and its dual‐echo version (DEFAISE) are partial RF echo‐planar methods which utilize a specific phase‐encode reordering algorithm to manipulate T2 contrast via an operator‐controlled pseudo‐echo time, pTE. The repetition time, TR, between successive applications of the Carr‐Purcell‐ Meiboom‐Gill (CPMG) echo trains used in FAISE may be reduced to introduce T1 weighting. To quantitatively determine the extent to which FAISE T1 and T2 contrast characteristics agree with spin‐echo methods, signal intensities from FAISE acquisitions were compared with signal intensities from equivalent CPMG acquisitions. In phantoms and in human heads, the contrast Characteristics of FAISE are found to be highly correlated with that obtained with equivalent CPMG sequences. However, conventional SE sequences generally utilize longer echo spacings than employed with FAISE/CPMG. Thus, echo spacing‐dependent mechanisms such as spin‐spin coupling and magnetic susceptibility lead to some differences in contrast between conventional SE and FAISE. Finally, FAISE appears to be more sensitive to magnetization transfer effects than conventional SE sequences since more off‐resonance irradiation is applied to individual slices during multislice acquisitions.
Detection and assignment of the glucose signal in 1h nmr difference spectra of the human brain
Authors: Gruetter Rolf , Rothman Douglas L. , Novotny Edward J. , Shulman Gerald I. , Prichard James W. , Shulman Robert G. 
Published: March 2007

AbstractThe difference between 1H NMR spectra obtained during eu‐ and hyperglycemia exhibited well‐resolved glucose peaks between 3 and 4 ppm as demonstrated by comparison with solution spectra. Estimated increases were consistent with recent 13C NMR quantitations of intracerebral glucose. Difference spectra were measured in 36‐ml volumes from the human brain every 3 min.
Sensitivity ofin vivomrs of the n‐δ proton in proximal histidine of deoxymyoglobin
Authors: Wang Zhiyue , Wang Dah‐Jyuu , Noyszewski Elizabeth A. , Bogdan Andrew R. , Haselgrove John C. , Reddy Ravinder , Zimmerman Robert A. , Leigh John S. 
Published: March 2007

AbstractThe sensitivity ofin vivoMRS of the N‐δ proton of the proximal histidine of deoxymyoglobin in human skeletal muscles is discussed. Longitudinal relaxation time T1of this deoxymyoglobin signal was measured in cuffed human forearms at 1.5 T and found to be 9.9 ms. Deoxymyoglobin spectra can be obtained from a forearm in seconds. The detection sensitivity of deoxymyoglobin in fully ischemic skeletal muscles and that of31P MRS of PCr in normal resting muscles are compared.
The Loss of Small Objects in Variable TE Imaging: Implications for FSE, RARE, and EPI
Authors: Constable R.Todd , Gore John C. 
Published: March 2007

AbstractThe importance to MR image quality of the order of acquisition of different phaseencoded views with sequences that have variable TR and TE has been recently reported. It has been shown that the effective point spread function (PSF) may be manipulated by varying TE or TR, or both, with each phase‐encoding step. This paper explores the behavior of the PSF in a variable TE sequence and its dependence on both imaging and tissue parameters. It is shown that the PSF is different for each tissue type and that its effect on tissue contrast is a function of both the shape and size of the structure. The important problem of signal loss from small objects that arises when the effective PSF is broad and the difficulty in detecting this phenomenon in practical MR images is illustrated. It is shown that the PSF can produce significant blurring and loss of object contrast in fast spin‐echo images but that this blurring may be not be obvious in practice because the noise is unaffected by the PSF. It is also shown that the signal from small lesions with short T2 can easily be lost through this blurring mechanism. The importance of signal loss from small objects and its implication for the clinical use of such sequences as fast spinecho or rapid acquisition relaxation‐enhanced and echo planar imaging is stressed.© 1992 Academic Press,Inc.
Atraumatic quantitation of cerebral perfusion in cats by 19f magnetic resonance imaging
Authors: Branch Craig A. , Ewing James R. , Helpern J. A. , Ordidge R. J. , Butt Shazad , Welch K. M. A. 
Published: March 2007

AbstractWe have noninvasively produced low‐resolution, quantitative nuclear magnetic resonance images of cerebral blood flow in 2‐ml voxels in eight cats. Typical signal‐to‐noise of 4 to 1 was obtained in cerebral voxels in 16.5‐s epochs. Mean flow during normocapnia (paCO2 = 39 ± 4 mm Hg) and hypercapnia (paCO2 = 62 ± 4 mm Hg) was 53 ± 20 ml/100 gmin and 140 ± 36 ml/100 g‐min, respectively. Fast flows in normocapnia were 94 ± 13 and 182 ± 39 ml/100 g‐min in hypercapnia. These results suggest that an atraumatic quantitative imaging assessment of cerebral perfusion may be possible in humans using these techniques.© 1992 Academic Press,Inc.
1 /T1p and Low‐Field 1 / T1 of Tissue Water Protons Arise from Magnetization Transfer to Macromolecular Solid‐State Broadened Lines
Authors: Brown Rodney D. , Koenig Seymour H. 
Published: March 2007

AbstractWe argue that, for solutions of immobilized protein and for tissue, the dependence of 1 / T1 of solvent protons on B0 at low fields and 1 / T1p on B1 for all B0 are both manifestations of the same underlying phenomena: magnetization transfer between mobile water protons and solid‐state broadened protein proton levels. Broadening causes rapid mixing of spin orientation within the transverse plane, at all B0, unless B1 is greater than the protein internal field; this affects 1 / T1p of solvent protons by magnetization transfer. Similarly, decreasing B0 below the internal field mixes all orientations of magnetization, which affects the solvent proton low‐field 1 / T1 and high‐field 1 / T2.© 1992 Academic Press,Inc.
Projection Reconstruction Techniques for Reduction of Motion Effects in MRI
Authors: Glover G. H. , Pauly J. M. 
Published: March 2007

AbstractProjection reconstruction (PR) techniques are shown to have intrinsic advantages over spin‐warp (2DFT) methods with respect to diminished artifacts from respiratory motion. The benefits result from (1) portrayal of artifacts as radial streaks, with the amplitude smallest near the moving elements; (2) streak deployment perpendicular to the direction of motion of moving elements and often residing outside the anatomic boundaries of the subject; (3) inherent signal averaging of low spatial frequencies from oversampling of central k‐space data. In addition, respiratory‐ordered view angle (ROVA) acquisition is found to diminish residual streaking significantly by reducing interview inconsistencies. Comparisons of 2DFT and PR acquisitions are made with and without ROVA. Reconstructions from magnitude‐only projections are found to have increased streaks from motion‐induced phase shifts.© 1992 Academic Press,Inc.
Magnetic Resonance Neurography
Authors: Howe F. A. , Filler A. G. , Bell B. A. , Griffiths J. R. 
Published: March 2007

AbstractWe have made cross‐sectional image “neurograms” in which peripheral nerve has a greater signal intensity than that of other tissue. Neurographic images of the rabbit forelimb were obtained using a spin‐echo magnetic resonance imaging (MRI) technique that combines fat suppression and diffusion weighting. After fat suppression the nerve shows up in relative isolation and is brighter than the surrounding tissue due to its longer T2 relaxation time of ≈︁ 50 ms compared to ≈︁ 27 ms for muscle. The addition of pulsed gradients for diffusion weighting of the MR signal further enhances the intensity of the nerve signal relative to that of surrounding muscle tissue. The greater diffusional anisotropy of nerve tissue (D∥/D∥ = 3.1) compared to that of muscle (D∥/D∥ = 1.9) allows further enhancement of the nerve by a subtraction of two diffusion‐weighted images, one with the gradients oriented parallel and one with the gradients oriented perpendicular to the nerve orientation. We show that by manipulation of the MRI parameters, either echo time or pulsed gradient strength, the nerves can be made to show up as the most intense feature. This verifies the feasibility of generating three‐dimensional “neurographic” images, analogous to angiograms, but which demonstrate the peripheral nerve tracts in apparent isolation.© 1992 Academic Press,Inc.
A three‐dimensional spin‐echo or inversion pulse
Authors: Pauly John M. , Hu Bob S. , Wang Samuel J. , Nishimura Dwight G. , Macovski Albert 
Published: March 2007

AbstractIn theory, multidimensional pulses can be designed to be selective in any number of dimensions. In practice, available gradient power has enforced a limit to two dimensions. We show here that three‐dimensional π pulses are feasible on commercial imaging machines provided that the range of offresonance frequencies are limited.
Determination of saturation factors in 31P NMR spectra of the developing human brain
Authors: Gruetter Rolf , Fusch Christoph , Martin Ernst , Boesch Chris 
Published: March 2007

AbstractIn order to assess the influence of longitudinal relaxation on previously reported variations in 31P NMR signals during brain development, we used an accelerated two‐point technique to determine T1 at 2.35 Tesla in 8 min. Comparison between 10 normal neonates (age range 37–46 weeks postconception) and 10 healthy infants (age range 80–157 weeks postconception) indicated that T1 does not vary substantially during the first year of life, except in the phosphomonoester (PME) region of the spectra. T1 of total PME decreases with age which we could explain by its variable multicomponent nature: The signal from (unresolved) components at the downfield shoulder of PME (attributed mostly to phosphorylethanolamine at 6.72 ppm) with a T1 of at least 6.4 s decreases with age relative to contributions from other phosphomonoester compounds resonating predominantly at the upfield side of the peak (approximately 6.3 ppm), with T1 below 2.9 s. Because the T1 heterogeneity of PME may depend on its relative composition, quantitative 31P NMR spectroscopy may require an assessment of the influence of longitudinal relaxation on the signal amplitudes in each measurement.
The origin of biexponential T2 relaxation in muscle water
Authors: Cole William C. , Leblanc Adrian D. , Jhingran Satish G. 
Published: March 2007

AbstractTwo theories have been proposed to explain the multiexponential transverse relaxation of muscle water protons: “anatomical” and “chemical” compartmentation. In an attempt to obtain evidence to support one or the other of these two theories, interstitial and intracellular macromolecular preparations were studied and compared with rat muscle tissue by proton NMR transverse relaxation (T2) measurements. All macromolecule preparations displayed monoexponential T2 decay. Membrane alteration with DMSO/glycerin did not eliminate the biexponential T2 decay of muscle tissue. Maceration converted biexponential T2 decay of muscle tissue to single exponential decay. It is concluded that the observed two component exponential T2 decay of muscle represents anatomical compartmentation of tissue water, probably intracellular versus extracellular.
Functional mapping of the human visual cortex at 4 and 1.5 tesla using deoxygenation contrast EPI
Authors: Turner R. , Jezzard P. , Wen H. , Kwong K. K. , Le Bihan D. , Zeffiro T. , Balaban R. S. 
Published: March 2007

AbstractThe effects of photic stimulation on the visual cortex of human brain were studied by means of gradient‐echo echo‐planar imaging (EPI). Whole‐body 4 and 1.5 T MRI systems, equipped with a small z axis head gradient coil, were used. Variations of image intensity of up to 28% at 4 T, and up to 7% at 1.5 T, were observed in primary visual cortex, corresponding to an increase of blood oxygenation in regions of increased neural activity. The larger effects at 4 T are due to the increased importance of the susceptibility difference between deoxy‐genated and oxygenated blood at high fields.
Consistent projection reconstruction (CPR) techniques for MRI
Authors: Glover Gary H. , Noll Douglas C. 
Published: March 2007

AbstractMotion of the subject causes inconsistencies In MR scan data which in turn produce streaks in projection reconstruction (PR) scans or ghosts in 2DFT imaging. It is shown that a data manifold consistent with a static object may be extracted from input scan data by applying consistency criteria based on moment or Fourier expansions of the object's projections. The criteria limit the spectrum of azimuthal variation relative to the radial moments or radial spectral components, and their application diminishes k‐space inconsistencies from motion or flow by discarding unallowed expansion terms. This consistent projection reconstruction (CPR) algorithm was applied to the reconstruction of projection data from a moving phantom and from human abdominal sections, and in each case provided reduced motion streaks relative to conventional reconstructions. In addition, CPR was found to be effective when used with 2DFT data by resampling the Cartesian data as radial projections, but to a lesser extent.
Real‐time position monitoring of invasive devices using magnetic resonance
Authors: Dumoulin C. L. , Souza S. P. , Darrow R. D. 
Published: March 2007

AbstractTechniques which can be used to follow the position of invasive devices in real‐time using magnetic resonance (MR) are described. Tracking of an invasive device is made possible by incorporating one or more small RF coils into the device. These coils detect MR signals from only those spins near the coil. Pulse sequences which employ nonselective RF pulses to excite all nuclear spins within the field‐of‐view are used. Readout magnetic field gradient pulses, typically applied along one of the primary axes of the imaging system, are then used to frequency encode the position of the receive coil(s). Data are Fourier transformed and one or more peaks located to determine the position of each receiver coil in the direction of the applied field gradient. Subsequent data collected on orthogonal axes permits the localization of the receiver coil in three dimensions. The process can be repeated rapidly and the position of each coil can be displayed in real‐time.
Measurement of rat brain perfusion by NMR using spin labeling of arterial water: In vivo determination of the degree of spin labeling
Authors: Zhang Weiguo , Williams Donald S. , Koretsky Alan P. 
Published: March 2007

AbstractIn vivo NMR experiments are performed to determine the degree of spin labeling for measurement of tissue perfusion by NMR using spin labeling of arterial water by adiabatic fast passage. Arterial water spins are labeled using flow in the presence of a field gradient and B1 irradiation to fulfill the conditions for adiabatic fast passage spin inversion. It is demonstrated that the NMR‐measured tissue perfusion is not affected by changing the degree of spin labeling as long as the degree of spin labeling is determined and accounted for according to the model used for calculating perfusion. By measuring the degree of spin labeling with different arterial blood flow velocities induced by different arterial pCO2, it is also demonstrated that, when spin labeling is carried out by adiabatic fast passage, the degree of spin labeling is not affected by changes in arterial blood flow velocity over a broad range.