bluuebunny/crossref_metadata_2025_split huggingface dataset:
Glucose metabolism in RIF‐1 tumors after reduction in blood flow: An in Vivo13C and 31P NMR study
Authors: Bhujwalla Zaver M. , Shungu Dikoma C. , Chatham John C. , Wehrle Janna P. , Glickson Jerry D. 
Published: March 2007

AbstractLow pH appears to enhance the effectiveness of therapeutic hyperthermia. 13C and 31P NMR spectroscopy have been employed to examine the possibility that elevating glucose in a solid tumor while simultaneously reducing tumor blood flow would induce a more profound acidosis than either treatment alone. When blood flow in RIF‐1 tumors was acutely reduced by administration of hydralazine and additional glucose was delivered locally by intratumoral injection, tumor acidosis (as determined by 31P NMR spectroscopy) during the period of reduced blood flow was not enhanced, relative to administration of hydralarine alone. Tumor NTP/P1 ratios decreased significantly within 20 min of hydralazine administration, whether or not glucose was injected, although NTP/P1 ratios were slightly higher in tumors that received extra glucose. Tumor lactate concentrations were not significantly different in glucose‐supplemented tumors, despite glucose concentratlons that were 4 to 5 times higher. When the added glucose was labeled with 13C, no correlation was detected between the pH in an individual tumor and the intensity of the 3‐[13C]‐lactate resonance in the same tumor.
Quantitation of lipid in biological tissue by chemical shift magnetic resonance imaging
Authors: Wong Wai‐Fan , Northrup S. Robert , Herrick Richard C. , Glornbicki Alan P. , Wood R. Patrick , Morrisett Joel D. 
Published: March 2007

AbstractA method combining several previously used approaches is described for the rapid, accurate quantitation of the fat content of biological tissue based on chemical shift images (CSI) corrected for magnetic field inhomogeneity, and compensated for T1, and T2, effects. The gravimetrically determined lipid content of fatty tissues (pork fat, rabbit and human liver) that had been differentially depleted of lipid by chloroform extraction correlated well (r = 0.99) with the lipid image intensities of the respective tissues. This multi‐point CSI method was used to quantitate lipid in fresh fatty human liver tissue (wet and dry) containing varying amounts of lipid. Plots of integrated lipid intensity versus tissue lipid content gave straight parallel lines for hydrated (r = 0.94) and dehydrated (r = 0.98) tissues, permitting determination of a proportionality constant for measuring absolute amounts of lipid present in a specific biological tissue. These results suggest the feasibility of using the method in vivo for absolute quantitation of lipid in tissues of agricultural (e.g. pork, beef) and medical (e.g. human liver) interest.
A quantitative interpretation of IVIM measurements of vascular perfusion in the rat brain
Authors: Henkelman R. Mark , Neil Jeffrey J. , Xiang Qing‐San 
Published: March 2007

AbstractPulsed gradient spin echo (PGSE) sequences have been used to measure the signal loss of 19F in perfluorinated hydrocarbon blood substitutes moving within the vasculature of the rat brain in the experimental conditions of the study. The signal loss is not characterized by a single apparent pseudodiffusion coefficient. A simple vascular network model based on self‐similarity hss been used to calculate the shape of the signal loss. Excellent agreement with the experiment has been obtained showing that the IVlM measurements are sensitive to flow over a wide range of vessel diameters and flow rates. This model of vascular structure may serve well for other MR measurements that are sensitive to perfusion.
A new method for proton detection of H217O with potential applications for functional MRI
Authors: Ronen Itamar , Navon Gil 
Published: March 2007

AbstractA method is presented for the sensitive detection of minute amounts of H217O. The method is based on the increase of the T2 of the water protons following an irradiation of the 17O resonance frequency, due to the partial or full decoupling of the 1H‐17O spin‐spin interaction. It is demonstrated that when 17O concentrations are low, full decoupling is achieved, and at short echo times the increase in the amplitude of the proton echo signal is proportional to the 17O content of the sample. The potential of the method for indirect 17O imaging is substantiated by a simple one dimensional projection of cylindrical phantoms containing various 17O concentrations. Using interleaved sequences with and without 17O decoupling, errors due to time dependent effects are minimized.
The Effect of Respiration on the Contrast and Sharpness of Liver Lesions in MRI
Authors: Butts Kim , Riederer Stephen J. , Ehman Richard L. 
Published: March 2007

AbstractThis work demonstrates the effects of through‐plane motion due to respiration on contrast and sharpness of liver lesions in MRI. The effects of slice coverage with and without such respiratory motion is also reported. This work is comprised of two parts: a theoretical prediction of liver‐lesion contrast and blur with and without respiration and an experimental validation using gel phantoms of the predicted results. Both theory and experiment show a loss of contrast, increasing with amplitude of the peak‐to‐peak motion. The loss of contrast for a 5‐mm lesion at normal respiration of 15 mm peak‐to‐peak superior‐inferior motion is ≈ 10% with a low order sorted respiratory ordered phase encoding acquisition and ≈ 50% for an unsorted acquisition. Lesion blur is greatest for the low order sorted acquisition while the unsorted and high sort acquisitions maintain edge definition. Breath‐hold imaging is potentially superior to nonbreath‐hold imaging in liver lesion contrast and edge definition, but is more sensitive to inadequate slice coverage.
Diffusion Weighting by the Trace of the Diffusion Tensor within a Single Scan
Authors: Mori Susumu , Van Zijl Peter C. M. 
Published: March 2007

AbstractThe anisotropy of the water diffusion tensor inside brain causes contrast in diffusion images, which depends on the relative orientation of the diffusion gradients and the subject. Because the trace of a tensor is invariant upon rotation, measurement of this trace can reduce the orientation effect. A family of imaging pulse sequences is presented in which the signal intensity is weighted by the trace of the diffusion tensor in a single scan. The methods are demonstrated for chicken gizzard in several orientations with respect to the gradient frame of reference, and for ischemic injury in cat brain after middle cerebral artery occlusion. The sensitivity of the techniques to the presence of background gradients is measured and discussed in detail. As a result, pulse sequences are suggested that provide reliable diffusion constants in both homogeneous and inhomogeneous magnetic fields. The efficiency of the techniques for clinical application is also evaluated.
MR Lymphography with a Lymphotropic T1‐Type MR Contrast Agent: Gd‐DTPA‐PGM
Authors: Harika Liliane , Weissleder Ralph , Poss Kirtland , Zimmer Claus , Papisov Mikhail I. , Brady Thomas J. 
Published: March 2007

AbstractA model system of a paramagnetic lymphotropic MR contrast agent (Gd‐DTPA labeled polyglucose associated macrocomplex, PGM) for T1‐weighted MR imaging of lymph nodes in rats and rabbits was evaluated. Pharmacokinetic (tissue accumulation) and MR imaging data (optimal dose and timing parameters) were obtained in normal rats (n = 88) after subcutaneous (SC) injection of paramagnetic, radiolabeled [111In]Gd‐DTPA‐PGM. A rabbit model of lymph node metastases (n = 8) was ultimately used to demonstrate the potential of MR imaging with Gd‐DTPA‐PGM for nodal tumor detection. Maximum concentrations of Gd‐DTPA‐PGM were found in popliteal and paraaortic lymph nodes within 24 h after SC administration, and highest lymph node SNR values were obtained by MR imaging at this time point. The optimum imaging dose was 6–12 μmol Gd/kg. Tumor‐lymph node contrast increased from 0.0 ± 1.2 precontrast to 19.2 ± 6.5 (spoiled gradient echo sequence, TR 50/TE 7/flip angle 60°) postcontrast and conspicuity of nodal metastases was improved. Gd‐DTPA‐PGM accumulates in lymph nodes after SC administration and significantly enhances lymph node signal intensity of normal animals but not metastatic lymph nodes.
On the Relationship Between Feature‐Recognizing MRI and MRI Encoded by Singular Value Decomposition
Authors: Cao Yue , Levin David N. 
Published: March 2007

AbstractThis paper describes the similarity between two methods of non‐Fourier MRI: feature‐recognizing MRI (FR MRI) and MRI with encoding by singular value decomposition (SVD MRI). Both methods represented images as truncated expansions of non‐Fourier basis functions; these basis images were derived from prior image data by using closely‐related mathematical techniques: the Karhunen‐Loeve decomposition (or principal components analysis) and singular value decomposition, respectively. We demonstrate that FR and SVD MRI are equivalent in the following sense: given the same prior image data, they lead to exactly the same basis functions. FR MRI utilized prior images of the same body part in many “training” subjects, thought to be similar to the “unknown” subject to be imaged. SVD MRI utilized a single prior image of one subject in order to perform dynamic imaging of that subject. We demonstrate that the basis function expansion derived from a single prior image may not be capable of representing new features (features not found in the prior image). Therefore, the SVD basis functions may be inappropriate for dynamic imaging.
In Vivo Selective Measurement of {1−13C}‐Glucose Metabolism in Tumors by Heteronuclear Cross Polarization
Authors: Artemov Dmitri , Bhujwalla Zaver M. , Glickson Jerry D. 
Published: March 2007

AbstractSelective detection of {1−13C}‐glucose and its glycolytic product, {3−13C}‐lactate, was achieved by selective 13C NMR spectroscopy with 1H cross polarization. The total sensitivity of conventional broadband experiments was retained, and peak intensities were at least equivalent to those obtained with the inverse detection technique (i.e., 1H{13C}) for single proton resonances. A key advantage of the method is that it maintains the specific absorption rate (SAR) within FDA limits of 5 W/kg by reducing power deposition during decoupling. In this study we have monitored the kinetics of metabolism of 13C‐labeled glucose to lactate following intravenous infusion of 0.55 ml of 0.18 M labeled glucose. Physiological effects were minimized by a) maintaining total plasma glucose concentrations below 20 mM throughout the course of NMR experiment and b) by avoiding significant heating of the tumor.
Incorporation of A Phosphonium Analogue of Choline Into The Rat Brain as Measured by Magnetic Resonance Spectroscopy
Authors: Jiménez Jilma V. , Richards Todd L. , Heide Aaron C. , Grierson John R. , Shankland Eric G. 
Published: March 2007

AbstractA clear understanding of choline metabolism is important in our goal to modify demyelination and remyelination in multiple sclerosis. To develop a technique capable of measuring metabolic changes in the brain, we have studied the incorporation of a phosphonium analogue of choline (P‐choline) in tissue extracts of rats. After feeding adult rats a choline‐deficient diet supplemented with P‐choline, the analogue was not detectable by in vivo volume‐localized 1H spectroscopy. However, in vitro 31P measurements of brain extracts revealed an 11 % incorporation of P‐choline into phosphatidylcholine. We report that P‐choline incorporates preferentially into the lipid pool over the lipid precursor pool and we provide evidence that the choline peak resolved by in vivo 1H spectroscopy is only composed of small molecular weight choline‐containing compounds.
Susceptibility Insensitive Single Shot MRI Combining BURST and Multiple Spin Echoes
Authors: Gelderen Peter Van , Moonen Chrit T.W. , Duyn Jeff H. 
Published: March 2007

AbstractA single shot MR imaging technique insensitive to magnetic susceptibility effects is introduced. The method allows multislice imaging in areas with poor magnetic field homogeneity, and can be implemented on standard clinical scanners. The design is based on the combination of a BURST excitation with multiple RF refocusing pulses. Images were obtained at 1.5 T on phantoms and human brain with a matrix size of 64 x 54 and a resolution of 4 x 4 mm in 230 ms.
Multi‐Shot EPI for Improvement of Myocardial Tag Contrast: Comparison with Segmented SPGR
Authors: Tang Chao , Mcveigh Elliot R. , Zerhouni Elias A. 
Published: March 2007

AbstractTo assess the potential value of multi‐shot EPI relative to segmented k‐space SPGR for myocardial tagging, we measured tag contrast for both sequences in a phantom and human study and compared it with theoretical predictions. In the human heart, EPI tag contrast was three times that of SPGR at the end of systole. Tag duration was lengthened with EPI to at least 600 ms. In addition, the entire heart was examined in a total of 32 heartbeats with EPI versus 152 heartbeats with SPGR.
Susceptibility Magnetic Resonance Imaging Using Spectral Decomposition
Authors: Ro Yong M. , Cho Zang‐Hee 
Published: March 2007

AbstractSusceptibility differences of materials in magnetic resonance imaging (MRI) usually lead to the intravoxel spin phase variations. Subsequently, the phase variation in the voxel results in a reduction of the signal intensity. This signal intensity reduction is known as the susceptibility effect in MRI and has been studied extensively. In this paper, a new spectral decomposition technique is proposed with which the signal change due to the susceptibility effect can be analyzed. Further, an NMR pulse sequence for the spectral decomposition of the susceptibility was developed and applied to susceptibility imaging of venous blood possessing paramagnetic properties. The computer simulations of the spectral decomposition method and their corresponding experimental results obtained using both a phantom and human volunteers are reported.
GRASE Improves Spatial Resolution in Single Shot Imaging
Authors: Feinberg David A. , Kiefer Berthold , Johnson Glyn 
Published: March 2007

AbstractIn single shot echo train imaging all the data required for a two dimensional image is acquired from a series of echoes generated following a single RF excitation pulse. Spatial resolution is limited because all samples must be acquired before the signal decays. In this paper we show theoretically that more echoes and hence better spatial resolution can be obtained with single shot GRASE imaging than with either echo planar imaging or single shot RARE imaging. This conclusion holds for both conventional imaging hardware and specialized gradient hardware designed for EPI. High quality single shot GRASE images support the theoretical conclusions.
Quantitative Analysis of Dynamic Gd‐DTPA Enhancement in Breast Tumors Using a Permeability Model
Authors: Tofts Paul S. , Berkowitz Bruce , Schnall Mitchell D. 
Published: March 2007

AbstractThe MRI signal enhancement in a breast tumor, measured as a function of time after a bolus injection of Gd‐DTPA, may contain enough information to differentiate malignant from benign tissue. We find a physiological model for measuring capillary permeability and leakage space (P. S. Tofts, A. G. Kermode, measurement of the blood‐brain barrier permeability and leakage space using dynamic MR imaging. 1. Fundamental concepts. Magn. Reson. Med. 17, 357–367 (1991)) fits the data well. The enhancement curve is particularly sensitive to the preinjection T1, of the tumor, the dose, and the time of injection. This model may provide a means of characterizing the pathophysiology of breast tumors from the Gd‐DTPA enhancement curve.
Segmentation and Feature Extraction Techniques, with Applications to MRI Head Studies
Authors: Ashton Edward A. , Berg Michel J. , Parker Kevin J. , Weisberg Jeffrey , Chen Chang Wen , Ketonen Leena 
Published: March 2007

AbstractTo obtain a three‐dimensional reconstruction of the hippocampus from a volumetric MRI head study, it is necessary to separate that structure not only from the surrounding white matter, but also from contiguous areas of gray matter–the amygdala and cerebral cortex. At present it is necessary for a physician to manually segment the hippocampus on each slice of the volume to obtain such a reconstruction. This process is time consuming, and is subject to inter‐ and intra‐operator variation as well as large discontinuities between slices. We propose a novel technique, making use of a combination of gray scale and edge‐detection algorithms and somea prioriknowledge, by which a computer may make an unsupervised identification of a given structure through a series of contiguous images. This technique is applicable even if the structure includes so‐called false contours or missing contours. Applications include three‐dimensional reconstruction of difficult‐to‐segment regions of the brain, and volumetric measurements of structures from series of two‐dimensional images.
Multi‐Slice, Breathhold Imaging of the Lung with Submillisecond Echo Times
Authors: Alsop David C. , Hatabu Hiroto , Bonnet Mathieu , Listerud John , Gefter Warren 
Published: March 2007

AbstractThe signal from the lungs is heavily attenuated by T2 and T2* decay in standard MR images of the thorax. The authors utilized the capabilities of a prototype fast gradient system to develop a multi‐slice gradient echo sequence that can obtain images with an echo time of 0.7 ms. Images acquired in a single breath‐hold are free from respiratory motion artifacts and clearly display signal from lung parenchyma. The use of fast gradients makes short echo times possible without the use of nonstandard RF pulses and spatial encoding techniques and their associated limitations.
Resolving Anatomical Details in Lung Parenchyma: Theory and Experiment for a Structurally and Magnetically Inhomogeneous Lung Imaging Model
Authors: Su Sunyu , Saunders John K. , Smith Ian C. P. 
Published: March 2007

AbstractLung parenchyma is, structurally and magnetically, a very inhomogeneous system. The strong local field gradients due to magnetic susceptibility variation across the air‐tissue interfaces impose a spatially dependent phase on spins that are inhomogeneously distributed. As a result, the slice selection process can cause destructive interference and corresponding partial cancellation of the NMR signals from different parts of the slice. The mechanism of this effect was studied by expanding the internal magnetic field gradient as a Fourier series and determining the Fourier components with a foam model, which consists of air bubbles preferentially at the alveolar diameter. The effect of signal cancellation as a function of slice thickness is characterized by a sinc‐like function with destructive interference of higher orders shown as lobes and the zeroth order as the main peak. Computer simulation of the slice selection process was conducted to illustrate the combined effects of signal cancellation and spatial average, and their dependence on slice thickness. Finally, images of rat lungs are presented to demonstrate the significant improvement in image quality by avoiding the high order destructive interference of NMR signals in the slice selection process.
Vascular transit times in calcarine cortex: Kinetic analysis of R2* changes observed using localized 1H spectroscopy
Authors: Detre John A. , Wang Zhiyue , Stecker Mark M. , Zimmerman Robert A. 
Published: March 2007

AbstractA kinetic analysis of water signal intensity changes measured in human visual cortex by PRESS localized 1H spectroscopy at 500 ms resolution with light‐emitting diode (LED) goggle stimulation was used to determine vascular transit times for transitions between rest and activation. Monoexponential curve fitting was used to determine both R2* values for each free induction decay and the time constants for R2* changes with activation and deactivation. Measured transit time values were in general agreement with the literature, and were significantly shorter for “Off→On” than for “On→Off” transitions, consistent with known alterations in blood flow with activation and deactivation. The differences in transit times between “Off→On” and “On→Off” also varied with stimulus frequency in accordance with known physiology. This type of analysis may provide a useful means of analyzing functional activation data and for quantitatively comparing functional activation results from differing subjects and imaging sessions.
Interleaved asymmetric echo‐planar imaging
Authors: Hennel Franciszek , Nédélec Jean‐François 
Published: March 2007

AbstractA version of interleaved echo‐planar imaging (EPI) is presented in which only one polarity of the readout gradient is used for signal acquisition to avoid ghosting artifacts. Two possible forms of the phase encoding gradient, blipped and constant, are discussed. With the constant phase encoding, interleaving of partial trajectories in the Fourier domain (k‐space) is controlled automatically by the echo train delay. The constant phase encoding gradient introduces a shear distortion of the k‐space grid. A modification of the reconstruction procedure is given which corrects for this effect. The method provides a 128 × 128 image in 1 s on a clinical system with standard gradients.
Magnetization transfer in hemopoietic bone marrow examined by localized proton spectroscopy
Authors: Schick Fritz , Forster JÜRgen , Einsele Hermann , Weiß Burkhard , Lutz Otto , Claussen Claus D. 
Published: March 2007

AbstractThe sensitivity of hemopoietic bone marrow to magnetization transfer is analyzed in 15 healthy volunteers and seven patients with different hematological disorders (inflammation, plasmacytoma, hemopoietic reconstitution after bone marrow transplantation). To obtain sufficient signal‐to‐noise ratio, a 90° −180° −180° double spin echo (PRESS) single voxel spectroscopic method was combined with pulsed magnetization transfer. Several spectra were recorded from each volume element inside the vertebral marrow, alternately with and without prepulses for magnetization transfer. Water signals from marrow with increased content of extracellular water due to inflammation or edema revealed less magnetization transfer effects than marrow with increased intracellular water content due to high cellularity. The preliminary results show magnetization transfer to be a promising tool for the clinically important characterization of the water composition in red bone marrow.
Mr perfusion studies with t1‐weighted echo planar imaging
Authors: Kwong Kenneth K. , Chesler David A. , Weisskoff Robert M. , Donahue Kathleen M. , Davis Timothy L. , Ostergaard Leif , Campbell Terrence A. , Rosen Bruce R. 
Published: March 2007

AbstractThe T1 perfusion model has worked well in brain functional studies where flow changes are measured. Using selective and nonselective inversion pulses, a new method has been developed to study steady‐state brain blood flow. The authors obtained flow‐sensitive images using selective inversion and flow‐insensitive images using nonselective inversion. Subtraction of flow‐insensitive images from flow‐sensitive images gave us flow‐weighted images with good gray‐white flow contrast in cortical gray matter as well as in the thalamus and basal ganglia. Fitting T1S of flow‐insensitive and flow‐sensitive images allowed us to obtain preliminary results of brain blood flow maps. Two specific problems can seriously affect the accuracy of the brain blood flow values and the gray‐white flow contrast of brain blood flow maps. These are the problems of the partial volume effect of CSF and gray matter, and the difference between blood T1 and white matter T1. The authors discuss in detail the character of these problems and present a number of approaches to manage such problems.