bluuebunny/crossref_metadata_2025_split huggingface dataset:
India ink: A potential clinically applicable EPR oximetry probe
Authors: Swartz Harold M. , Liu Ke Jian , Goda Fuminori , Walczak Tadeusz 
Published: March 2007

AbstractUsing a material that already is in widespread use in humans, India ink, the first EPR measurements in a human have been made, using the India ink in a pre‐existing tattoo. The EPR spectra of India ink are very sensitive to the partial pressure of oxygen (PO2), thereby making it feasible to use this approach to measure pO2 in tissues in patients. This potentially provides a means to measure this parameter directly with a sensitivity, accuracy, and repeatability that have not been available previously, and thereby to be able to individualize and guide treatment of diseases such as cancer and peripheral vascular insufficiency.
13C NMR study of the generation of C2‐ and C3,‐deuterated lactic acid by tumoral pancreatic islet cells exposed to D‐[1‐13C]‐, D‐[2‐13C]‐ and D‐[6‐13C]‐Glucose in 2H2O
Authors: Willem Rudolph , Biesemans Monique , Kayser François , Malaise Willy J. 
Published: March 2007

AbstractTumoral pancreatic islet cells of the RIN5mF line were incubated for 120 min in media prepared in 2H2O and containing D‐[1‐13C]glucose, and D‐[2‐13C]glucose, and D‐[6‐13C]glucose. The generation of C2‐ and C3‐ deuterated lactic acid was assessed by 13C NMR. The interpretation of experimental results suggests that a) the efficiency of deuteration on the C1 of D‐fructose 6‐phosphate does not exceed about 47% and 4% in the phosphoglucoisomerase and phosphomannoisomerase reactions, respectively; b) approximately 38% of the molecules of D‐glyceraldehyde 3‐phosphate generated from D‐glucose escape deuteration in the sequence of reactions catalyzed by triose phosphate isomerase and aldolase; and c) about 41% of the molecules of pyruvate generated by glycolysis are immediately converted to lactate, the remaining 59% of pyruvate molecules undergoing first a single or double back‐and‐forth interconversion with L‐alanine. It is proposed that this methodological approach, based on high resolution 13C NMR spectroscopy, may provide novel information on the regulation of back‐and‐forth interconversion of glycolytic intermediates in intact cells as modulated, for instance, by enzyme‐to‐enzyme tunneling.
Variable‐averaging RARE
Authors: Noll Douglas C. 
Published: March 2007

AbstractThe RARE method and its variants have become popular, rapid‐imaging alternatives to conventional spin‐echo imaging, particularly for long repetition time proton density and T2‐weighted imaging. One variant is to generate both early and late echo images using the same pulse sequence, which has the added benefit of reduced edge artifacts and blurring. Described in this paper is variable‐averaging RARE (VARARE), a method by which independent amounts of averaging can be set for the early and late echo images generated by a single scanning sequence. Through the use of this method, the signal‐to‐noise ratio (SNR) of late echo images can be improved without unnecessarily increasing the number of averages for the early echo image, thus saving scanning time. Comparisons to various alternatives are made with respect to scanning time and image quality. Phantom measurements and in vivo images are given to demonstrate the effectiveness of VA‐RARE as an efficient method for improving SNR of late echo time images in RARE imaging.
Transient cell depolarization after permanent middle cerebral artery occlusion: An observation by diffusion‐weighted MRI and localized 1H‐MRS
Authors: Gyngell Michael L. , Back Tobias , Hoehn‐Berlage Mathias , Kohno Kanehisa , Hossmann Konstantin‐Alexander 
Published: March 2007

AbstractFocal cerebral ischemia causes rapid intensity changes in diffusion‐weighted images (DWI) and elevated lactate as detected by localized proton spectroscopy (1H‐MRS). To investigate whether such changes can also be evoked by peri‐ischemic depolarizations, we combined DWI and 1H‐MRS measurements with DC potential recordings. About 40 min after occlusion of the middle cerebral artery in a rat, a negative DC deflection was observed indicating transient cell depolarization. Coincidentally with the depolarization a transient increase of the DWI signal intensity and a partially reversible increase of lactate occurred in the periphery of the ischemic territory. These results show that peri‐ischemic depolarization, known to contribute to the evolution of cerebral infarction, evokes disturbances that can be detected by DWI and 1H‐MRS.
13C isotopomer analyses in intact tissue using {13C}homonuclear decoupling
Authors: Sherry A. Dean , Zhao Piyu , Wiethoff Andrea , Malloy Craig R. 
Published: March 2007

AbstractEntry of 13C‐enriched acetyl‐CoA into the citric acid cycle results in scrambling of 13C into the various carbon positions of all intermediate pools. The eventual result is that the 13C resonances of all detectable intermediates or molecules exchanging with those intermediates appear as multiplets due to nearest neighbor spin‐spin couplings. We have previously shown that an isotopomer analysis of the glutamate 13C multiplets provides a history of 13C flow through the cycle pools and that relative substrate utilization and relative anaplerotic flux can be quantitated (C.R. Malloy, A.D. Sherry, and F.M.H. Jeffrey, Am. J. Physiol. 259, H987–H995 (1990)). A major limitation of the method for in vivo applications is spectral resolution of multiline resonances required for a complete isotopomer analysis. We now show that (13C)homonuclear decoupling of the glutamate C3 resonance collapses nine‐line C4 and C2 resonances into three‐line multiplets. We demonstrate that these three line 13C multiplets are well resolved in isolated, perfused rat hearts and present steady‐state equations that allow an isotopomer analysis from data obtained in intact tissue. This advancement offers for the first time the possibility of extending 13C isotopomer methods to complex metabolic conditions in vivo.
Determinants of anisotropic water diffusion in nerves
Authors: Beaulieu Christian , Allen Peter S. 
Published: March 2007

AbstractWe report NMR diffusion measurements of water in three central nervous system models, namely the nonmyelinated olfactory, and the myelinated trigeminal and optic nerves of the spotted and long‐nosed garfish. A similar degree of anisotropy of the average diffusion coefficients (DNMR) is observed for all three freshly excised nerve types (DNMR parallel)/DNMR‐(perpendicular) is 3.6 ± 1.2, 3.2 ± 0.9, and 2.6 ± 0.4 for the olfactory, trigeminal, and optic nerves, respectively). The anisotropy of DNHR for the nonmyelinated olfactory nerve argues strongly that myelin is not a necessary determinant of diffusional anisotropy in ordered axonal systems (even though it may contribute when present). Garfish nerves treated with vinblastine, in order to depolymerize microtubules and inhibit fast axonal transport, also exhibit diffusional anisotropy {DNMR(parallel)/DNMR (perpendicular) is 2.6 ± 0.4,2.8 ± 0.8, and 2.2 ± 0.7 for the olfactory, trigeminal, and optic nerves, respectively) thus excluding a significant role for microtubules and fast axonal transport in that observed anisotropy.
MRI characterization of diffusion coefficients in a rat spinal cord injury model
Authors: Ford John C. , Hackney David B. , Alsop David C. , Jara Hernan , Joseph Peter M. , Hand Christopher M. , Black Perry 
Published: March 2007

AbstractApparent diffusion coefficients (ADC) were measured in a rat spinal cord weight‐drop injury model. After sacrifice, the spinal cords were fixed in situ and excised for MR imaging and ADC measurement. Diffusion is anisotropic in normal gray and white matter. There were significant decreases in ADCs measured along the longitudinal axis of the injured cord and increases in ADCs measured transverse to the cord. Injured segments demonstrated reductions in diffusion anisotropy in the white matter. Diffusion was completely isotropic at the epicenter of the weight‐drop injury. Significant decreases in longitudinal ADC and increases in transverse ADC were observed in portions of the cord which appeared normal on conventional spin‐echo and calculated T2 images. Thus ADC measurement may complement routine imaging for evaluation of spinal cord injury.
A one‐dimensional velocity technique for NMR measurement of aortic distensibility
Authors: Hardy Christopher J. , Bolster Bradley D. , McVeigh Elliot R. , Adams William J. , Zerhouni Elias A. 
Published: March 2007

AbstractA technique is presented for rapidly and noninvasively determining aortic distensibility, by NMR measurement of wave velocity in the aorta. A two–dimensional NMR selective‐excitation pulse is used to repeatedly excite a cylinder of magnetization in the aorta, with magnetization read out along the cylinder axis each time. A toggled bipolar flow‐encoding pulse is applied prior to readout, to produce a one‐dimensional phase‐contrast flow image. Cardiac gating and data interleaving are employed to improve the effective time resolution to 2 ms. Wave velocities are determined from the slope of the leading edge of flow measured on the resulting M‐mode velocity image. The technique is sensitive over a range of distensibilities from 10−8 to 10−3 m s2/kg. The average value in the descending thoracic aorta in seven normal subjects was found to be 4.8 × 10−5 m s2/kg, with a significant inverse correlation with age.
Tag contrast in breath‐hold CINE cardiac MRI
Authors: Reeder Scott B. , McVeigh Elliot R. 
Published: March 2007

AbstractContrast between tagged and nontagged myocardium was investigated using rapid gradient echo segmented k‐space CINE MRI. The transient behavior of magnetization was measured in stationary and moving phantoms using gradient recalled acquisition in steady‐state GRASS and spoiled GRASS (SPGR) sequences with TR ≈ 7 ms and TE ≈ 2.5 ms. Bloch equation simulations were used to compute theoretical results. Understanding the transient behavior of magnetization is important because tags only persist in the myocardium during the nonequilibrium transition to steady state. The transition to steady state for both SPGR and GRASS is reproducible after one heartbeat, and including unprocessed data from the first heartbeat leads to image artifacts. In a moving phantom, simulations and experimental results showed that GRASS and SPGR are essentially equivalent. Tag‐tissue contrast in SPGR was very sensitive to imaging tip angle. The optimum tip angle for the scanning parameters used in this study was 11°.
Detection of liver fibrosis with magnetic cross‐relaxation
Authors: Aisen Alex M. , Doi Kei , Swanson Scott D. 
Published: March 2007

AbstractThe utility of MRI using magnetization transfer (MT) enhanced pulse sequences to diagnose hepatic cirrhosis in a rat model was investigated. Hepatic T1 was measured with and without MT off‐resonance RF pulses in 17 treated and six control rats. The livers were evaluated histologically, and the hydroxyproline content quantitatively measured. We did not find a statistically significant linear correlation between the MR relaxation times and the degree of tissue injury. However, the MR measurements performed with MT were superior to those without differentiating the treated and control groups. Specifically, the T1 times were 695 ±76 ms for the treated group, versus 748 ± 61 ms in the controls; P= 0.095. The T1sat times were also lower in the treated group, with statistical significance: 367 ± 51 ms versus 421 ± 38 ms, P = 0.016. Finally, the change in the relaxation rates (the inverse of the relaxation times) with and without saturation were 1.31 ± 0.22 s−1 (treated group) versus 1.05 ± 0.12 s−1 (controls), which differed significantly, P= 0.001.
The effects of linearly increasing flip angles on 3D inflow MR angiography
Authors: Nägele Thomas , Klose Uwe , Grodd Wolfgang , Petersen Dirk , Tintera Jaroslav 
Published: March 2007

AbstractAs recently demonstrated, spin saturation effects in 3D time‐of‐flight (TOF) MR angiography (MRA) can be reduced by using RF pulses with linearly increasing flip angles (ramp pulses) in the main direction of flow. We developed a model for calculating the signal distribution of proton flow within the excitation volume (slab) for different ramp slopes and compared the results with the measured distribution for the lower‐leg arteries. The ramp pulses were generated using the Fourier transformation of the desired excitation profiles. With a bandwidth of 6 kHz and a pulse length of 2.56 ms satisfactory ramps with variable slopes were generated and applied in a standard flow‐compensated 3D FISP sequence. The effects on the signal distribution in the resulting angiograms of the lower limbs revealed a considerable reduction of saturation losses in agreement with the calculations. Calculated optimal ramp slopes are provided for flow velocities ranging from 5 to 50 cm/s and excitation volumes ranging from 5 to 25 cm.
Microscopic susceptibility variation and transverse relaxation: Theory and experiment
Authors: Weisskoff Robert , Zuo Chun S. , Boxerman Jerrold L. , Rosen Bruce R. 
Published: March 2007

AbstractMicroscopic susceptibility variations invariably increase apparent transverse relaxation rates. In this paper, we present comparisons between Monte Carlo simulations and experiments with polystyrene microspheres to demonstrate that this enhanced relaxation can be explained quantitatively for both spin echo and gradient echo imaging experiments. The spheres used (1 to 30 μ), and degree of susceptibility variation (caused by 0‐12 mM Dy‐DTPA) covered a wide range of biologically relevant compartment sizes and contrast agent concentrations. These results show that several regimes of behavior exist, and that contrast dependence is quite different in these regimes. For a given susceptibility, δχ, a small range of particle sizes show peak transverse relaxation. For the range of susceptibilities found in the first pass of a clinical IV contrast agent bolus, this size range is 5 to 10 μ, or roughly capillary sized compartments. In both our simulations and experiments, smaller spheres showed quadratic relaxation versus concentration curves, and larger particles showed sublinear behavior. For particles corresponding to the peak relaxivity, the relaxation‐concentration curves were linear. In addition, we demonstrated that increasing the diffusion coefficient can increase, decrease, or, paradoxically, leave unaffected the apparent relaxation rate. The regime for which the diffusion coefficient is relatively unimportant corresponds to the region of peak relaxivity. By using the Bloch‐Torrey equation to produce scaling rules, the specific Monte Carlo simulations were extended to more general cases. We use these scaling rules to demonstrate why we often find that susceptibility‐induced relaxation rates vary approximately linearly with concentration of injected agent.
Analysis of discrete T2 components of NMR relaxation for aqueous solutions in hollow fiber capillaries
Authors: Bronskill Michael J. , Santyr Giles E. , Walters Blake , Henkelman R. Mark 
Published: March 2007

AbstractAn analysis is presented of proton NMR T2 relaxation times measured for aqueous solutions In simple bundles of hollow fibers. The relaxation times are calculated with a two‐compartment diffusive exchange model using the known relaxation times of the aqueous solutions and the fiber geometry. When the relaxation time outside the fibers is short (∼1 ms), three or more relaxation components are observed from this two compartment system, in agreement with the calculation. The amplitude and relaxation times of the third component are consistent with those of a diffusion‐mediated mode, as suggested theoretically by Brownstein and Tarr (Phys. Rev. A 19, 2446 (1979)). The possible contribution of such modes to the multicomponent relaxation observed in tissues is discussed.
Self‐diffusion in CNS tissue by volume‐selective proton NMR
Authors: Horsfield Mark A. , Barker Gareth J. , McDonald W. Ian 
Published: March 2007

AbstractWe have used a volume‐selective NMR pulse sequence to measure the diffusion coefficient (D) inside a selected cuboid volume. The sequence is a variant of the stimulated echo method for volume‐selective spectroscopy, and allows sequential measurement of D in any of three orthogonal directions and for a range of diffusion times. The echo attenuation from which D is calculated is free from the cross terms that can arise because of interactions between volume selection and diffusion‐sensitizing gradients. Anisotropic and diffusion‐time‐dependent behavior is observed in brain structures known to have axon fibers aligned primarily in one direction.
Reduced phase encoding in spectroscopic imaging
Authors: Maudsley Andrew A. , Matson G. B. , Hugg J. W. , Weiner M. W. 
Published: March 2007

AbstractThe effect of different spatial‐encoding (k‐space) sampling distributions are evaluated for magnetic resonance spectroscopic imaging (MRSI) using Fourier reconstruction. Previously, most MRSI studies have used square or cubic k‐space functions, symmetrically distributed. These studies examine the conventional k‐space distribution with spherical distribution, and 1/2 k‐space acquisition, using computer simulation studies of the MRSI acquisition for three spatial dimensions and experimental results. Results compare the spatial response function, Gibbs ringing effects, and signal contamination for different spatial‐encoding distribution functions. Results indicate that spherical encoding, in comparison with cubic encoding, results in a modest improvement of the re sponse function with approximately equivalent spatial resolution for the same acquisition time. For spin‐echo acquired data, reduced acquisition times can readily be obtained using 1/2 k‐space methods, with a concomitant reduction in signal to noise ratio.
Interleaved echo planar phase contrast angiography
Authors: McKinnon Graeme 
Published: March 2007

AbstractTechnical aspects of a new rapid 2D multiplanar phase contrast angiographic sequence are presented. The sequence uses multiple excitation echo planar imaging concepts. The advantage of using multiple excitations is that the resolution can be increased over that obtainable with single shot echo planar imaging. By combining phase contrast measurements with echo planar imaging, the measurement time is considerably reduced compared with conventional phase contrast magnetic resonance angiography. The present implementation still requires some improvements before being suitable for clinical applications. Future embodiments could, however, permit angiograms of vessels subject to respiratory motion.
An evaluation of the sensitivity of the intravoxel incoherent motion (IVIM) method of blood flow measurement to changes in cerebral blood flow
Authors: Neil Jeffrey J. , Bosch Coleen S. , Ackerman Joseph J. H. 
Published: March 2007

AbstractTo evaluate the sensitivity of the intravoxel incoherent motion (IVIM) technique to changes in cerebral blood flow, we made measurements of IVIM parameters in rat brain under conditions of altered arterial pCO2. The arterial pCO2, was varied over a range which would be expected to change cerebral blood flow from roughly 50 to 500 ml/(100 g·min). The IVIM measurements were made with suppression of extravascular water signal. The parameters f′ (the apparent fraction of spins which have “fast” pseudodiffusion), D (the “fast‐pseudodiffusion” coefficient), and D(the “slow‐pseudodiffusion” coefficient) all showed statistically significant positive linear correlations with arterial pCO2. These results suggest that the IVIM method, when used with suppression of extravascular water signal, is sensitive to changes in blood flow.
MRI signal void due to in‐plane motion is all‐or‐none
Authors: Wedeen Van J. , Weisskoff Robert M. , Poncelet Brigitte P. 
Published: March 2007

AbstractThe process of MRI signal attenuation due to in‐plane intra‐voxel velocity inhomogeneity is described. Given rigid rotation or linear shear, velocity phase‐sensitivity will induce a phase distribution that varies linearly with position, which is exactly equivalent to the effect of a spatial phase encoding gradient pulse. It follows that the effect of such motion on the raw MRI signal is to displace it a fixed distance in k‐space. Attenuation becomes marked when the center of the spinecho reaches an edge of k‐space, which happens when intra‐voxlel phase shifts reach π radianlvoxel. Because spin echoes are typically peaked sharply at center, this attenuation usually is abrupt. Analytic and numerical simulations of linear and nonlinear velocity fields confirm abrupt MRI attenuation where phase dispersion exceeds π radianlvoxel. Examples of this phenomenon include the abrupt loss of blood signal adjacent the vessel wall in laminar flow, abrupt loss of subendocardial signal in early diastole, and sudden disappearance due to rotation of a kidney during a measurement of diffusion.
Optimum flip‐angles for exciting NMR with uncertain T1 values
Authors: Bottomley Paul A. , Ouwerkerk Ronald 
Published: March 2007

AbstractT1 is often ill‐determined. This means that an Ernst angle excitation often cannot be precisely defined for the simple pulse and acquire experiment. Here, published 31P T1 values of metabolites in human muscle, liver, heart, and brain are archived, some new data on heart and brain added, and overall confidence intervals determined. Strategies for setting the flip‐angle based on the confidence intervals are examined, and an optimum flip‐angle derived which minimizes the signal loss relative to what could have been realized if T1 were precisely known. With such optimized pulses, signal loss can be limited to ≤14% for up to a 10‐fold variation in T1, with TR ≤ T1 The effect that an uncertainty in T1 by a factor of two has on the saturation corrected signal is limited to ≤20% in the optimum flip‐angle experiment. Adiabatic B1‐independent rotation phase‐cycled (BIRP) excitation pulses are ideal as optimum flip‐angle pulses as they can be prescribed without calibration.
Observation of a fast response in functional MR
Authors: Ernst Thomas , Hennig Jürgen 
Published: March 2007

AbstractA spectroscopic MR technique was used to investigate the time course of the MR signal following a single visual stimulus. Gated experiments demonstrate there is an early response (500 ms after stimulus) leading to a reduction of the MR signal by −0.25% (P = 0.02), whereas a slower response (>1500 ms after stimulus) results in a signal increase of +0.59% (P = 0.01). The fast negative response may be attributed to increased oxygen consumption, followed by a slower vascular response with overcompensation in blood oxygenatioln. This explanation would be in agreement with the blood oxygenation level dependent (BOLD) contrast mechanism considered the basis of functional MR. However, other physiological events might also be responsible for the signal drop observed.
3‐dimensional functional imaging of human brain using echo‐shifted FLASH MRI
Authors: Duyn Jeff H. , Mattay Venhatha S. , Sexton Roy H. , Sobering Geoffrey S. , Barrios Fernando A. , Liu Guoying , Frank Joseph A. , Weinberger Daniel R. , Moonen Chrit T. W. 
Published: March 2007

AbstractA 3‐dimensional MRI method has been developed for functional mapping of the human brain, based on blood oxygenation level dependent (BOLD) contrast mechanisms. The method uses recently introduced principles of echo‐shifted FLASH to acquire a single 3D data set in 20 s. The technique was tested on a conventional 1.5 Tesla clinical scanner with a standard head coil using visual stimulation with a 8 Hz flashing white light, or a varying checkerboard pattern. Areas of increased signal intensity were identified in the visual cortex, consistent with the known functional organization.