bluuebunny/crossref_metadata_2025_split huggingface dataset:
NMR Measurement of Perfusion Using Arterial Spin Labeling Without Saturation of Macromolecular Spins
Authors: Zhang Weiguo , Silva Afonso C. , Williams Donald S. , Koretsky Alan P. 
Published: March 2007

AbstractWhen measuring perfusion by arterial spin labeling, saturation of tissue macromolecular spins during arterial spin labeling greatly decreases tissue water magnetization, reducing the sensitivity of the technique. In this work, a theory has been developed for perfusion measurement by arterial spin labeling without saturation of macromolecular spins. A two‐coil system was used to achieve arterial spin labeling without saturation of brain tissue macromolecular spins for NMR measurement of rat cerebral perfusion. The effects of crossrelaxation on the measurement of perfusion have been studied in the absence of macromolecular spin saturation, and it is demonstrated that at 4.7 Tesla, perfusion is underestimated by approximately 17% when the effect of cross‐relaxation is neglected in the calculation of perfusion. However, assuming water to be a freely diffusable tracer, the effect of cross‐relaxation is predicted to be flow independent, and it can, thus, be accounted for in the calculation of perfusion. The theory and experiments are presented to estimate tissue perfusion, magnetization transfer rate constants, and spin‐lattice relaxation times of water and macromolecular spins in rat brain.
NOE Enhancements and T1 Relaxation Times of Phosphorylated Metabolites in Human Calf Muscle at 1.5 Tesla
Authors: Brown Truman R. , Stoyanova Radka , Greenberg Tamela , Srinivasan Ravi , Murphy‐Boesch Joseph 
Published: March 2007

AbstractNuclear Overhauser effect (NOE) enhancements and relaxation times of 31P metabolites in human calf were measured in 12 volunteers (4 men and 8 women) at 1.5 T using a dual tuned four‐ring birdcage. The NOE enhancements of inorganic phosphate (P1), phosphocreatine (PCr), γ‐, α‐, and β‐nucleoside triphosphate (NTP) from 19 measurements were 0.51 ± 0.10, 0.64 ± 0.03, 0.53 ± 0.03, 0.56 ± 0.08, and 0.47 ± 0.05, respectively. The relaxation times were independent of proton irradiation and from 23 measurements were 3.49 ± 0.35, 4.97 ± 0.58, 4.07 ± 0.36, 2.90 ± 0.25, and 3.61 ± 0.25 s for P1, PCr, γ‐, α‐, and β‐NTP, respectively. No significant differences between gender and age were observed for either NOE enhancements or relaxation times. Also, among nine volunteers, we observed no significant differences in T1 between the coupled and decoupled cases.
BOLD Based Functional MRI at 4 Tesla Includes a Capillary Bed Contribution: Echo‐Planar Imaging Correlates with Previous Optical Imaging Using Intrinsic Signals
Authors: Menon Ravi S. , Ogawa Seiji , Hu Xiaoping , Strupp John P. , Anderson Peter , Uǧurbil Kǎmil 
Published: March 2007

AbstractWe show that the EPI time course in functional MR imaging at 4 Tesla displays a multiphasic response in response to photic stimulation. Focal areas of gray matter display an initial negative change in signal intensity that reaches a maximum of 1 % about 2 s after the onset of photic stimulation. This component then changes sign, reaching a positive maximum about 5 s after the onset of the stimulus. Other areas, including those where draining veins are visible, show only a positive signal change, reaching a maximum of about 6% after the onset of the visual stimulus. These time constants are in very good agreement with published data obtained with intrinsic optical mapping techniques, where a deoxygenation phase has been shown to occur in functionally specific cortical columns, followed by an increase in blood volume which is more distributed in nature. Thus, we believe there is strong evidence that a sensitivity to capillary oxygenation state is present in high S/N functional MR images obtained with EPI at 4 T.
Respiratory Blur in 3D Coronary MR Imaging
Authors: Wang Yi , Grist Thomas M. , Korosec Frank R. , Christy Paul S. , Alley Marcus T. , Polzin Jason A. , Mistretta Charles A. 
Published: March 2007

Abstract3D MR imaging of coronary arteries has the potential to provide both high resolution and high signal‐to‐noise ratio, but it is very susceptible to respiratory artifacts, especially respiratory blurring. Resolution loss caused by respiratory blurring in 3D coronary imaging is analyzed theoretically and verified experimentally. Under normal respiration, the width for any Gaussian point spread function is increased to a new value that is at least several millimeters (about 3–4 mm). In vivo studies were performed to compare respiratory pseudo‐gated 3D acquisition with breath‐hold 2D acquisition. On average, the overall quality of a pseudo‐gated 3D image is worse than that of the corresponding breath‐hold 2D image (P = 0.005). In most cases, respiratory blur caused coronary arteries in pseudo‐gated 3D data to have lower resolution than in breathhold 2D data.
Susceptibility Artifact Reduction in Fat Suppression
Authors: Mao Jintong , Gao Jia‐Hong , Yan Hong , Ray Ballinger J. 
Published: March 2007

AbstractStrong fat signal in regions where a large susceptibility difference exists, for instance at the interface between air and tissue near the maxillary sinus, may not be eliminated by currently available fat suppression techniques without sacrificing the overall quality of the images. In this article, we show that this fat signal, which appears as a susceptibility artifact, can be significantly reduced by using an optimized presaturation pulse with sharp edges and a broad bandwidth, while causing minimal disturbance of the water signal. Several optimized presaturation pulses can be reproduced by the Fourier coefficients provided in the Appendix.
Coronary Angiography with Magnetization‐Prepared T2 Contrast
Authors: Brittain Jean H. , Hu Bob S. , Wright Graham A. , Meyer Craig H. , Macovski Albert , Nishimura Dwight G. 
Published: March 2007

AbstractA magnetization‐prepared, T2‐weighted sequence (T2 Prep) is used to suppress muscle and venous structures. When combined with lipid suppression, this technique improves the visualization of the coronary arteries. T2 Prep was designed to be robust in the presence of flow as well as B0 and B1 inho‐mogeneities and may be combined with virtually any imaging technique. Here, it is implemented with both a single‐slice spiral acquisition and a multi‐slice spiral method that acquires up to 15 slices in a single breath‐holding interval.
Theoretical Model for Water Diffusion in Tissues
Authors: Szafer Aaron , Zhong Jianhui , Gore John C. 
Published: March 2007

AbstractWater diffusion in a tissue model is studied both analytically and numerically. Tissue is regarded as a periodic array of boxes surrounded by partially permeable membranes (cells), embedded in an extracellular medium, intracellular and extracellular diffusion coefficients may differ. Expressions for the apparent diffusion coefficients (ADC) in isotropic and noniso‐tropic tissues are derived and compared with Monte Carlo simulations. Calculated ADCs disagree with values obtained from the widely used “fast exchange” formula. Effects of differences between intracellular and extracellularT2relaxation times on measured values of ADC andT2are discussed. The general analysis is specifically applied to the changes occurring in ADC following ischemic insults to brain tissue. It is found that although membranes affect ADC significantly, the observed changes in diffusion cannot be due to reduced membrane permeabilities. They may result from the combined effect of changes in cellular volume fraction, extracellular and intracellular diffusion.
31P NMR Study of Acute Toxic Effects of Cadmium Chloride on Rat Liver
Authors: Yoshioka Hiroshi , Itai Yuji , Mitsumori Fumiyuki 
Published: March 2007

AbstractIn this study, acute effects of cadmium ions (Cd2+) on energy metabolism in rat livers were analyzed in vivo after intravenous administration using 31P NMR. Both inorganic phosphate (Pi) and nucleotide triphosphate (NTP) peaks of in vivo Cdtreated livers gradually decreased over a 6‐h period. In the extract, NTP peaks in Cdtreated livers were lower, as in the in vivo experiments, but the Pi peak was significantly higher than the control. The apparent decrease in Pi in in vivo liver treated with Cd could be caused by the reduced visibility of Pi because of its uptake into mitochondria from cytoplasm, accompanied by the uncoupling of oxidative phosphorylation by Cd2+. These results indicated that total Pi in the hepatocytes increases after Cd administration. However, only 10% of Pi was visible in Cd‐treated livers in vivo, whereas 34% of Pi was visible in controls. Significant increases in phosphocholine and glycerophosphocholine were also observed in extracts of Cd‐treated livers.
Application of the Accurate Assessment of Intracellular Magnesium and pH from the 31P Shifts of ATP to Cerebral Hypoxia‐Ischemia in Neonatal Rat
Authors: Williams Gerald D. , Smith Michael B. 
Published: March 2007

AbstractThe authors present a high field in vivo demonstration of our 2‐dimensional calibration methods for determining magnesium ion concentration ([Mg]), under conditions of fluctuating pH, from the three 31P NMR chemical shift differences of ATP. The effect of 3 h of hypoxic‐ischemic insult (HI) on intracellular brain [Mg] was evaluated by using a well established 7‐day‐old rat model of cerebral HI. During the final hour of HI, there was a significant increase (P < 0.001) in free magnesium as well as in the ratio of total [Mg]/[ATP]. The normal, HI, and early (1–2 h) recovery values of free [Mg] were 0.336 ± 0.015, 0.519 ± 0.104, and 0.337 ± 0.071 mM, respectively. These results are consistent with the temporal changes in [ATP]. Our assessment of [Mg] and pH for this high error measurement is general for most in vivo applications and may be routinely implemented.
Tmdotp5− as a 23na shift reagent for the in vivo rat kidney
Authors: Seshan Viswanathan , Germann Martha J. , Preisig Patricia , Malloy Craig R. , Dean Sherry A. , Bansal Navin 
Published: March 2007

AbstractSince transmembrane sodium gradient is essential to many cell functions, there is continuing interest in methods that differentiate intracellular and extracellular Na+. In the kidney, shift reagent (SR) aided 23Na magnetic resonance spectros‐copy (MRS) has been successfully used only in isolated cells, tubules, and the perfused organ. In this report, we demonstrate for the first time that TmDOTP5− can be used to distinguish Na+ compartments in kidneys in vivo. Infusion of 80 mM TmDOTP5− without added Ca2+ produced three resolved 23Na resonances, which we have assigned to intracellular Na+, vascular Na+, and intraluminal Na+. In comparison, infusion of 400 mM DyTTHA3− produced two broad and unresolved resonances. The 31P spectra of the cellular high energy phosphate metabolites indicate that TmDOTP5− is safe for in vivo applications. Washout studies suggest that this SR displays renal clearance similar to that of MR imaging contrast agents. However, the glomerular filtration rate (GFR) in animals infused with TmDOTP5− was reduced by 49% compared with the GFR in control animals, perhaps due to the hypotensive effects of the SR. We conclude that TmDOTP5− is effectively cleared from the blood of live animals but that a different formulation will be required for clinical application.
Interactive selection of optimal section orientations using real‐time MRI
Authors: Hangiandreou Nicholas J. , Debbins Josef P. , Rossman Phillip J. , Riederer Stephen J. 
Published: March 2007

AbstractIn applications where precise image section positioning is vital, the interactive section rotation and offset capabilities of interactive MRI should be valuable. However, due to the independent nature of these two adjustments, the desired structure may often not be visible in the image after a rotation. Valuable time is wasted during relocation. An algorithm is presented that automatically alters the section offset after a rotation to provide continuous viewing of a marked structure, greatly improving section orientation efficiency. The technique is illustrated in the determination of double oblique angulation for through‐plane imaging of the portal vein. This algorithm is expected to prove useful in applications of interactive MRI requiring precise positioning.
Abbreviated moment‐compensated phase encoding
Authors: Cao Guang , Parker Phd Dennis L. , , Sherrill David S. , Du Yiping P. 
Published: March 2007

AbstractTo achieve correct spatial location of blood vessels, first order gradient moment nulling applied to the phase encoding axes can be used. However, gradient moment nulling prolongs echo time (TE), which may degrade the flow image in regions of complex flow. The fact that abbreviated moment compensated phase‐encoding (AMCPE) can be used to apply partial flow compensation to the phase‐encoding axes to prevent spatial misregistration of vessels without requiring the use of long echo times or using arbitrary chosen TE is demonstrated. AMCPE defines two cutoff lines in k‐space. The flow‐induced phase is completely compensated for values between the cutoff lines and partially compensated beyond the cutoff lines. The AMCPE technique has been tested on both a flow phantom and a human volunteer. The AMCPE images from both the in vivo and the in vitro study demonstrate correctly imaged flow. Computer simulations have been performed to analyze the penalty caused by the incomplete flow compensation. The result shows that the ripple artifacts due to the incomplete flow compensation are unobservable when 60%–70% of k‐space is completely flow compensated.
Analytical expressions for the NMR apparent diffusion coefficients in an anisotropic system and a simplified method for determining fiber orientation
Authors: Hsu Edward W. , Mori Susumu 
Published: March 2007

AbstractNMR measurements of anisotropic diffusion were studied using a three‐dimensional random‐walk model. It was found that the apparent diffusion coefficient can be expressed in a canonical form as the product of a diagonal matrix, an orthonormal rotation matrix, and a vector representing the encoding magnetic field gradient. The diffusion coefficient can be interpreted as the sum of the corresponding coefficients measured along the principal diffusion axes, weighted by the squares of the directional cosines of the encoding direction with respect to the principal axes. The analysis revealed that determining the orientation of anisotropy, in a cylindrically symmetric system, requires a minimum of four diffusion measurements. A special pulse sequence which minimized gradient cross‐terms and possible restricted diffusion effects was used to characterize diffusion anisotropy in cut chicken gizzards. Diffusion coefficients parallel to the muscle fibers were found to be approximately two to three times larger than those in the transverse direction. Furthermore, the method was successful in detecting the angular change when the sample was rotated by 30°. Results indicate that the proposed approach to measure fiber orientation is valid and may be used to improve the time efficiency of diffusion anisotropy measurements.
Retrospective estimation and correction of physiological fluctuation in functional MRI
Authors: Hu Xiaoping , Le Tuong Huu , Parrish Todd , Erhard Peter 
Published: March 2007

AbstractImage‐to‐image fluctuation due to physiological motion is a major limitation to the accurate detection of neuronal activity with functional MRI. In this paper, a new and general technique for the estimation and compensation of the physiological effects is presented. By simultaneously monitoring the respiration and heart beat during the acquisition of imaging data, and retrospectively synchronizing the imaging data with physiological activity, physiological effects are estimated and removed. This technique does not rely on the periodicity of the respiration or the heart beat, does not affect the signal changes arising from neuronal activation, and is beneficial to images acquired with any speed. Experimental studies performed with FLASH and EPI sequences have demonstrated that the new technique is effective in reducing physiological fluctuation and improving the sensitivity of functional MRI and is generally applicable.
Pharmacokinetics of the 13C labeled anticancer agent temozolomide detected in vivo by selective cross‐polarization transfer
Authors: Artemov Dmitri , Bhujwalla Zaver M. , Maxwell Ross J. , Griffiths John R. , Judson Ian R. , Leach Martin O. , Glickson Jerry D. 
Published: March 2007

AbstractThe anticancer agent temozolomide labeled with 13C (8‐Carbamoyl‐3‐13C‐methylimidazo‐[5,1‐d]‐1,2,3,5‐tetrazin‐4‐(3H)‐one), was noninvasively detected in subcutaneous RIF‐1 tumors by a selective cross polarization 13C NMR method, at a field strength of 9.4T. Pharmacokinetics of the drug, at a dose of 150 mg/kg, were determined for intravenous and intraperitoneal modes of administration (three animals per mode). The half‐life of the drug in the tumors was approximately 60 min. The uptake and clearance of the drug, however, varied significantly between individual hosts, for both modes of administration. These results demonstrate the feasibility of obtaining pharmacokinetics of anticancer agents for individual tumors without the need for a label that might modify drug activity (e.g., fluorine). The variability of the in vivo measurements, even within the same tumor model, demonstrates the necessity of directly monitoring the tumor to evaluate drug pharmacokinetics.
1H NMR Determination of lactate 13C‐enrichment in skeletal muscle: Using a double quantum filter for the simultaneous editing of 13C‐coupled and 13C‐uncoupled methyl protons resonance
Authors: Bloch Gilles , Jouvensal Laurence , Carlier Pierre G. 
Published: March 2007

Abstract1H NMR simultaneous editing of 13C‐coupled and 13C‐uncoupled methyl protons resonance, using the selection of double quantum coherences by a gradient pulse, was analyzed in vitro and demonstrated in situ on the hindlimb of an exercised rat model postmortem. In vitro calibration showed agreement with theoretical analysis. High‐resolution NMR of muscle extract confirmed the accuracy of the lactate 13C‐enrichment calculated using the in situ NMR data and the calibration factor obtained in vitro.
Regional comparison of tumor vascularity and permeability parameters measured by albumin‐GD‐DTPA and GD‐DTPA
Authors: Su Min‐Ying , Najafi Ahmad A. , Nalcioglu Orhan 
Published: March 2007

AbstractSequential albumin‐Gd‐DTPA and Gd‐DTPA dynamic enhancement studies were performed in an animal tumor model for the comparison of regional vascularity and permeability parameters measured by these two different sizes of contrast agents. The early albumin‐Gd‐DTPA enhancement arises from the vascular compartment, and the averaged signal enhancement derived from the first 3 to first 6 images postinjection can be reliably used to assess vascularity. The signal intensity in the images during the period of 5‐10 min post‐albumin‐Gd‐DTPA injection shows a steady linear variation. The intercept of the linear relationship is another indicator of the vascularity and the slope represents the tumor permeability to albumin‐Gd‐DTPA. The Gd‐DTPA enhancement study was analyzed by a two‐compartmental pharmacokinetic model to calculate the regional vascularity and permeability. The permeability parameters measured from albumin‐Gd‐DTPA and Gd‐DTPA show an excellent correlation. The vascularity parameters measured from albumin‐Gd‐DTPA show good linear correlation with the low vascularity groups measured by Gd‐DTPA, but show saturation for the high vascularity groups. The enhancement mechanisms for both contrast agents are discussed to relate the imaging parameters to the physiological variables.
Compensation of multi‐dimensional selective excitation pulses using measured k‐space trajectories
Authors: Takahashi Atsushi , Peters Terry 
Published: March 2007

AbstractMultidimensional spatially selective excitation pulses rely on the accuracy of gradient waveforms to achieve desired excitation volumes. Unfortunately, the high gradient slew‐rates and magnitudes required by these pulses often lead to distortion of the waveforms produced by imaging systems resulting in poor selection profiles. In this paper, a k‐space calibration procedure, used to determine the actual trajectory produced by the scanner's field gradients, is extended to two spatial dimensions. This measured information is then incorporated in a selective excitation design technique for correcting the RF pulse envelopes to compensate for gradient waveform induced distortion of the excitation volumes.
Optimization of T2‐selective binomial pulses for magnetization transfer
Authors: Pachot‐Clouard Mathilde , Darrasse Luc 
Published: March 2007

AbstractAccurate rules have been established to build binomial pulses up to fifth order, for selectively saturating protons at any given T2 with minimum power deposition. Pulse performance and sensitivity to experimental defects have been evaluated; the third order is generally found to be best suited. It is shown, by combining theory and experiment performed at 0.1 T, that matching the saturation pulse to T2 of the motionally restricted pool is essential to reveal exchange with free water protons. It is emphasized that, to date, lack of magnetization transfer contrast with binomial pulses is due mainly to insufficient RF level available with most MR imaging systems, especially at high magnetic field.
Cine Spiral Imaging
Authors: Liao Jan‐Ray , Sommer F. Graham , Herfkens Robert J. , Pelc Norbert J. 
Published: March 2007

AbstractInterleaved spiral scanning of k‐space is an efficient and fast method for imaging dynamic processes. In this article, a cine version of interleaved spiral imaging is presented. The method is shown to overcome the “lightning‐flash” artifacts of the conventional triggered (gated) method. Compared with the segmented k‐space 2DFT method, it achieves better temporal resolution in a comparable or shorter scan time. Preliminary human studies show that the method is a promising tool for imaging dynamic processes.
Fast anatomical imaging of the heart and assessment of myocardial perfusion with arrhythmia insensitive magnetization preparation
Authors: Tsekos Nikolaos V. , Zhang Yi , Merkle Hellmut , Wilke Norbert , Jerosch‐Herold Michael , Stillman Arthur , Uǧurbil Kǎmil 
Published: March 2007

AbstractA new contrast preparation based on modified driven equilibrium Fourier transfer is introduced and evaluated for generation of T1‐weighted images for assessment of the myocardial perfusion with contrast agent first‐pass kinetics. The new preparation scheme produces T1 contrast with insensitivity to arrhythmias in prospectively triggered sequential imaging thereby eliminating one of the major sources of problems in potential patient studies with previously employed contrast preparations schemes.
High resolution solid‐state 29si nmr spectroscopy of silicone gels used to fill breast prostheses
Authors: Dorne Laurence , Alikacem Nadir , Guidoin Robert , Auger Michèle 
Published: March 2007

AbstractWe have used 29Si solid‐state nuclear magnetic resonance (NMR) spectroscopy to study the chemical structure of the silicone gels in virgin and explanted breast prostheses. Despite evidences of alteration in the morphological appearance of the silicone gel inside the breast prosthesis, our results do not reveal changes in the chemical nature and structure of the silicone gels after implantation. In addition to the main 29Si resonance peak at −22.26 ppm that corresponds to the resonance frequency of the D repeat unit of the polysiloxane chains, the high sensitivity of our NMR technique allows the detection of very low concentrations of silicone compounds. Within our experimental detection limit of 0.2%, no signal between −90 ppm and −150 ppm are observed. This indicates that no silica products are present inside the gel of the prostheses. Furthermore, our 29Si NMR spectra indicate differences in the chemical compositions of the silicone gels from different manufacturers.