bluuebunny/crossref_metadata_2025 huggingface dataset:
A double quantum coherence transfer proton NMR spectroscopy technique for monitoring steady‐state tumor lactic acid levels in Vivo
Authors: Freeman D. M. , Sotak C. H. , Muller H. H. , Young S. W. , Hurd R. E.
Published: March 2007

If proton nuclear magnetic resonance (1H NMR) spectroscopy is to provide a clinically useful modality for monitoring tumor growth and treatment, the technique must be able to unambiguously detect steady‐state metabolite concentrations in human tumors and differentiate these from normal tissue levels. To address this problem, a two‐dimensional double quantum coherence transfer spectroscopy (2DDQCT) method was developed and tested in a series of tumor cell lines implanted in mice. Lactate‐edited proton NMR spectra were determined from a roughly 1‐cm3 region of interest in EMT6, RIF‐1, and fibroma. In two‐dimensional data matrix representations of the 2DDQCT experiments (double quantum frequency on the vertical axis and chemical shift on the horizontal axis) the lactate signal (330 Hz with the transmitter set at the water resonance) was well‐resolved from lipid (480 Hz, 600 Hz). The resolution in the double quantum dimension was also sufficient to conclude that a detectable level of alanine, which would reside at 358 Hz, was not present in the three tumor types. Following the NMR experiment, tumors were chemically assayed for lactate giving 8.17, 9.1, and 6.73 μmol/g wet wt for RIF‐1, EMT6, and fibroma, respectively. This technique is likely to provide a noninvasive method for monitoring the steady‐state lactic acid levels in small tumors before and after therapy, as well as in tissues with impaired oxygen delivery using clinical and research NMR Systems. © 1990 Academic Press, Inc.
MRI signal loss due to microcirculation: Phantom studies
Authors: Duewell S. , Wüthrich R. , Buck A. , von Weymarn C. , von Schulthess G. K.
Published: March 2007

In order to study perfusion effects in MRI under different conditions we developed two different kinds of phantoms. The first phantom exhibits linear capillary flow with several capillaries within one voxel. The second consists of an anion exchange resin with beads forcing the spins to change directions such that they undergo accelerations and decelerations. Both phantoms were imaged with standard spin‐echo sequences and signal intensities were quantified at various echo times. Qualitative and quantitative agreements of the data with the results obtained by computations of signal toss due to spin‐phase phenomena are excellent, thus suggesting that perfusion effects can be fully understood using these phenomena. It is argued that the phantoms used in conjunction with conventional spin‐echo sequences represent a realistic model for studying true capillary networks in conjunction with specialized perfusion sequences. © 1990 Academic Press, Inc.
Sensory stimulation by time‐varying magnetic fields
Authors: Cohen Mark S. , Weisskoff Robert M. , Rzedzian Richard R. , Kantor Howard L.
Published: March 2007

When two human volunteers were imaged with magnetic field gradient dB/dt of 61 T/s RMS, the subjects reported, to our surprise, feeling muscular twitches synchronous with gradient pulses over repeated experiments. No adverse or sustained effects were seen. Experiments in a canine, intended to assess the safety of MR imaging with dB/dt of up to 66 T/s RMS, failed to induce detectable changes in the electrocardiogram or to show any signs of gross response to gradient pulsing. Although these data are preliminary, and largely anecdotal, they suggest a level above which such stimulation may occur. We believe that this is the first report of direct human stimulation in an MRI device and that determination of the stimulation threshold may have impact on the selection of appropriate operating points for magnetic imaging systems. © 1990 Academic Press, Inc.
Spin echo 31P spectroscopic imaging in the human brain
Authors: Maudsley A. A. , Twieg D. B. , Sappey‐Marinier D. , Hubesch B. , Hugg J. W. , Matson G. B. , Weiner M. W.
Published: March 2007

Spectroscopic imaging of phosphorus metabolites in the human brain has been carried out with two data acquisition methods: by observation of the free induction decay (FID) signal and by a short spin echo sequence. The resultant spectral images and spatially resolved spectra are compared. Spin echo observation is found to provide spectra of superior quality, and by suitably selecting the sequence timing, no significant increase in T2 losses, as compared with the FID method, is encountered. 31P images with approximately 3.5 cm spatial resolution are obtained within times of 37 min at 2.0 T field strength. © 1990 Academic Press, Inc.
Phosphate metabolite imaging and concentration measurements in human heart by nuclear magnetic resonance
Authors: Bottomley Paul A. , Hardy Christopher J. , Roemer Peter B.
Published: March 2007

Cardiac‐gated phosphorus (31P) nuclear magnetic resonance (NMR) spectroscopic imaging with surface coils resolves in three dimensions the spatial distribution of high energy phosphate metabolites in the human heart noninvasively. 31P spectra derive from 6‐ to 14‐cm3 volumes of myocardium in the anterior left ventricle, septum, and apex, at depths of up to about 8 cm from the chest, as identified by proton (1H) NMR anatomical images acquired without moving the subject. Spectroscopic images are acquired in 9 to 21 min at 1.5 T. Metabolite concentrations are quantified with reference to a standard located outside the chest, yielding normal in vivo concentrations of phosphocreatine and adenosine triphosphate of about 11.0 ± 2.7 (SD) and 6.9 ± 1.6 μmol/g of wet heart tissue, respectively. High energy phosphate contents did not vary significantly with location in the normal myocardium, but 2,3‐diphosphoglycerate signals from blood varied with Subject and location. © 1990 Academic Press, Inc.
Relaxometry of brain: Why white matter appears bright in MRI
Authors: Koenig S. H. , Brown R. D. , Spiller M. , Lundbom N.
Published: March 2007

The remarkable success of magnetic resonance imaging of adult brain relates to the unusually large ratio of the longitudinal relaxation rates 1 / T1 of white and gray matter, ∼2:1 at physiological temperature and traditional imaging fields. Several investigators have conjectured that myelin is the source of the greater 1 / T1 of white matter without, however, suggesting details of the molecular mechanisms responsible. From measurements of the magnetic field dependence of 1 / T1 (NMRD profiles) of adult and neonatal gray and white matter at 5 and 35°C, we find a thermally activated contribution to the NMRD profile of adult white matter that is not present in the profiles of either adult gray or neonatal gray and white matter. We attribute this contribution to myelin and develop a quantitative model that accounts for the unique relaxation behavior of myelinated white matter. We find that myelin water, 15% of the total, has a relatively short T1 that arises from an unexpectedly large interaction with myelin lipid; when cast in terms of an interaction over the entire myelin bilipid‐water interface, it is sevenfold greater than the analogous protein‐water interfacial interaction. Its magnitude remains to be accounted for, but cholesterol, known to alter the relaxation rates of lipid protons, may play an important role. The contribution of myelin to 1/T1 at physiological temperatures is attributed to thermally activated transmembrane diffusion of water and, hence, more rapid mixing of axonal and the rapidly relaxing myelin water molecules. © 1990 Academic Press, Inc.
Functional cerebral imaging by susceptibility‐contrast NMR
Authors: Belliveau John W. , Rosen Bruce R. , Kantor Howard L. , Rzedzian Richard R. , Kennedy David N. , McKinstry Robert C. , Vevea James M. , Cohen Mark S. , Pykett Ian L. , Brady Thomas J.
Published: March 2007

In vivo measurement of cerebral physiology by dynamic contrast‐enhanced NMR is demonstrated. Time‐resolved images of the cerebral transit of paramagnetic contrast agent were acquired using a new ultrafast NMR imaging technique and a novel mechanism of image contrast based on microscopic changes in tissue magnetic susceptibility. Global hypercapnia in dogs was used to establish the relationship between susceptibility‐induced signal change and brain blood volume, and the response of gray and white matter to this microvascular stimulus was measured. © 1990 Academic Press, Inc.
Is the detection of fucose cancer markers by 2D 1H NMR unequivocal?
Authors: Phillips P. S. , Herring F. G.
Published: March 2007

Fucose is believed to be a marker for cancer that may be detectable by the 2D proton NMR (COSY) of human plasma. However, the COSY technique is time consuming and prone to error. These problems may be alleviated by using the SUPERCOSY pulse sequence; this technique shows that there are many other cross peaks in the region (1.3, 4.2 ppm) which are not readily distinguishable from fucose. © 1990 Academic Press, Inc.
In Vivo13C imaging enhanced by polarization transfer
Authors: Ueshima Yasuhiro , Yamai Satoshi , Ikehira Hiroo , Hashimoto Takahiro , Mori Kazuya , Maki Takeshi , Fukuda Hiroshi , Tateno Yuklo
Published: March 2007

Carbon‐13 NMR imaging has been combined with 1H‐13C polarization transfer to improve image quality. Natural‐abundance carbon images of Fischer rat bodies were obtained within a few minutes. Next 13C‐labeled glucose was administered orally to rats, and spatial distributions of glucose and its derivatives were observed with this technique. © 1990 Academic Press, Inc.
Effects of velocity profile of to‐and‐fro pulsatile flow on magnetic resonance signal intensity
Authors: Fujita N. , Harada K. , Murakami T. , Akai Y. , Kozuka T.
Published: March 2007

The effects of to‐and‐fro pulsatile flow, i.e., an oscillatory fluid motion with no net flow, on signal intensity in gated spin‐echo magnetic resonance imaging are considered both theoretically and experimentally. On the basis of hydrodynamic principles, to‐and‐fro pulsatile flow at large Womersley numbers consists of uniform inner flow and boundary‐layer‐type flow adjacent to a tube wall. Therefore, the velocity profile is “trapezoidal” rather than parabolic at all times during the pulsation period. Contrary to the absence of phase dispersion and loss of signal within the inner flow where no velocity gradient exists, large velocity differences cause phase dispersion and, hence, loss of signal within the boundary layer, whose thickness is inversely proportional to the Womersley number. An understanding of these features of to‐and‐fro pulsatile flow provides the theoretical basis of cerebrospinal fluid flow phenomena in magnetic resonance imaging, since this type of flow exists in cerebrospinal fluid pathways. © 1990 Academic Press, Inc.
A DANTE tagging sequence for the evaluation of translational sample motion
Authors: Mosher Timothy J. , Smith Michael B.
Published: March 2007

A magnetic resonance imaging sequence that is sensitive to translational motion such as that seen with cardiac contraction is presented. The sequence employs DANTE radiofrequency excitation with a continuous magnetic field gradient to generate a grid pattern of lines. There is improved line resolution and reduced eddy‐current formation over Current techniques. © 1990 Academic Press, Inc.
Improved metabolite editing by the 1D soft COSY technique with 270° Gaussian‐shaped pulses
Authors: Stryjewski Detlef , Leibfritz Dieter
Published: March 2007

Recently we proposed Gaussian‐shaped pulses to overcome the dynamic range problem within a 1D Soft COSY pulse sequence for the editing of metabolites in their natural environment. Similar to the development of the application of a COSY technique, the ECZOTIC sequence was introduced for the same purpose. A brief comparison of the abilities of both sequences is given in the first part of this communication, and the second part deals with the improvement of phase behavior within 1D Soft COSY by use of 270° pulses. © 1990 Academic Press, Inc.
Signal‐to‐noise in phase angle reconstruction: Dynamic range extension using phase reference offsets
Authors: Conturo Thomas E. , Smith Gregory D.
Published: March 2007

The dynamic range of phase‐reconstructed magnetic resonance images is compared to that of magnitude‐reconstructed images. From analysis of propagation of errors, the phase angle noise is phase‐independent and given in radians by σ (|I|)/|I|, the noise‐to‐signal ratio of the corresponding magnitude‐reconstructed image. As the phase can range from minus π to π the phase angle dynamic range is 2π times that of the signal magnitude. These results agree with experiment, verifying that the noise in the two receiver channels is uncorrelated. An artifact‐free technique is presented for correcting phase spillover, which further extends the phase angle dynamic range. The reconstruction‐based reference phase is adjusted on a local basis so that the boundary of phase wraparound is reconstructed near the center of the [ − π, π] interval. For a particular flow study, the phase signal‐to‐noise was extended over twofold by spillover correction, to a value 15 times that of the magnitude signal‐to‐noise. © 1990 Academic Press, Inc.
A simple method of generating variable T1 contrast images using temporally reordered phase encoding
Authors: Norris David G. , Böttcher Uwe , Leibfritz Dieter
Published: March 2007

A rapid method of generating T1 images by means of an inversion pulse followed by a fast low‐angle imaging experiment is presented. The T1 contrast is manipulated by a temporal reordering of the phase‐encoding gradient, resulting in an almost completely free choice of T1 contrast, without any extra restriction on the size of the data acquisition matrix. The intrinsic rapidity of the sequence renders it insensitive to motion artifacts and lends itself to multipoint T1 calculations. The method is particularly well suited to high‐field imaging. © 1990 Academic Press, Inc.
The proton NMR of blood plasma and the test for cancer
Authors: Herring F. G. , Phillips P. S. , Pritchard H. , Silver H. , Whittal K. P.
Published: March 2007

The water‐suppressed proton NMR spectra of plasma from healthy controls and cancer patients have been recorded along with the high‐density lipoprotein (HDL) and triglyceride (TG) levels in the plasma. The dependence of the average of methylene and methyl resonance linewidths on the HDL/TG ratio is demonstrated. It is shown that the deranged lipoprotein levels caused by the presence of cancer lead to the serological test for cancer proposed by Fossel. The work provides the formation for a complete understanding of the proposed serological test for cancer. However, the wide variation in lipoprotein composition in the plasma from both healthy adults and cancer patients means that the serological test proposed by Fossel cannot be used as a screen for cancer. © 1990 Academic Press, Inc.
Gadolinium (III) complex equilibria: The implications for Gd(III) MRI contrast agents
Authors: Jackson Graham E. , Wynchank Sinclair , Woudenberg Marianne
Published: March 2007

A computer model of blood plasma which has allowed the effect of Gd(III) contrast agents to be simulated has been developed. Initial binding of Gd(III) is to transferrin. At high concentration the metal ion binds to citrate and salicylate. At a concentrate of 10−3 M, GdCl3 is predicted to effect a redistribution of the in vivo Zn(II), Ca(II), and Fe(II) complexes present in blood plasma. There is little effect on the Cu(II) distribution. At a concentration below lo−5 M EDTA and DTPA have little effect on the free Gd(III) metal ion concentration. Above this concentration though, the metal ion is bound aimost exclusively to the EDTA or DTPA. An attempt is made to relate the toxicity of GdCl3, [Gd(EDTA)]−, and [Gd(DTPA)]2− to the thermodynamic stability of these complexes. The effect of substitution kinetics is also discussed. © 1990 Academic Press, Inc.
Measurement of cerebral blood flow by volume‐selective 19F NMR spectroscopy
Authors: van Zijl Peter C. M. , Ligeti Laszlo , Sinnwell Teresa , Alger Jeffry R. , Chesnick A. Scott , Moonen Chrit T. W. , McLaughlin Alan C.
Published: March 2007

A stimulated echo sequence was used to obtain 19F NMR spectra from within a 4‐ml voxel in a cat brain. The time dependence of the 19F NMR signal from an inert gas (CHF3) was used to calculate the blood flow in the voxel. The position of the voxel was selected using a 1H MR image. © 1990 Academic Press, Inc.
RF cavity resonator and split‐resonator designs
Authors: Mansfield P. , McJury M. , Glover P. , Clemence M.
Published: March 2007

A simple high‐pass cavity resonator has been constructed for NMR imaging use at 500 MHz. A capacitative circuit arrangement is used to drive the device. A novel split‐coil or half‐resonator design is also introduced for lower‐frequency operation with applications in whole‐body medical imaging. © 1991 Academic Press, Inc.
Flow‐independent magnetic resonance projection angiography
Authors: Wright G. A. , Nishimura D. G. , Macovski A.
Published: March 2007

The performance of current, flow‐based sequences for imaging vasculature using MR is severely restricted in regions with inherently slow flow. We address this problem with a flow‐independent imaging method. Specifically, we generate projection images of blood in the limbs while suppressing signal from all other tissues (primarily skeletal muscle, bone marrow, and subcutaneous fat) using a flow‐compensated, water‐selective, short TI inversion recovery sequence with a long echo time. We experimentally evaluate the effectiveness of this sequence and present in vivo results clearly demonstrating the method's potential. © 1991 Academic Press, Inc.
Surface coil spectroscopic imaging: Time and spatial evolution of lactate production following fluid percussion brain injury
Authors: Cohen Y. , Sanada T. , Pitts L. H. , Chang L.‐H. , Nishimura M. C. , Weinstein P. R. , Litt L. , James T. L.
Published: March 2007

Detailed temporal and spatial distributions of lactate production are presented for graded fluid‐percussion brain injury in the rat. A one‐dimensional proton spin‐echo spectroscopic imaging (ID SESI) technique, performed with a surface coil, is presented and evaluated. This technique, which represents a practical compromise, provides spatially localized proton nuclear magnetic resonance (NMR) brain spectra from a series of small voxels (<0.15 cm3) in less than 10 min, thus enabling both spatial and temporal monitoring of lactate production. These high‐resolution lactate maps are correlated with hyperintense regions observed in T2‐weighted images taken 10 h after impact, which, in turn, correlate with histology. The data demonstrate that, following severe trauma there is delayed production and propagation of lactate to regions of the brain that are remote from the trauma site. The extent of lactate production depends on the severity of impact. More significantly, the data show that following severe trauma, local lactate concentrations exceed 15 μmol/ g, the concentration that has been claimed as the threshold for brain injury. Therefore high lactate levels cannot be ruled out a priori as a possible factor in brain injury following severe head trauma. © 1991 Academic Press, Inc.
Multiple‐readout selective inversion recovery angiography
Authors: Wang Samuel J. , Nishimura Dwight G. , Macovski Albert
Published: March 2007

We have developed a variation of selective inversion recovery (SIR) angiography that allows us to obtain a collection of several angiograms within the same acquisition time previously required to obtain a single image. In basic SIR, a single readout is performed after the tagging inversion pulse. In multiple‐readout SIR, a succession of readout pulses is applied following the inversion pulse. By varying the gradients appropriately during the successive readouts, we can obtain a set of multiple projection‐angle angiograms, or, by appropriately spacing the readouts throughout the cardiac cycle, we can obtain a set of time‐resolved angiograms. This technique allows us to obtain additional spatial or temporal information without increasing total scan time. A sequence of increasing flip‐angle read pulses is used to maintain a constant signal level across the images. A trade‐off exists between SNR and the number of images acquired. © 1991 Academic Press, Inc.
Arrays of mutually coupled receiver coils: Theory and application
Authors: Wright Steven M. , Magin Richard L. , Kelton James R.
Published: March 2007

Specialized receiver coils having a small sensitive region can provide an improvement in SNR for MR imaging and spectroscopy, at the expense of limiting the usable field of view. This work presents a technique for designing coil arrays that allows the size and location of the sensitive region to be selected remotely. Only one element of the coil array is directly connected to the receiver, allowing flexibility in system design and implementation. A method is presented for the analysis and design of mutually coupled coil arrays of any number of elements of arbitrary shape. The analysis includes mutual coupling effects between primary coils, to allow multiple primary coils to be used simultaneously. A controller system allows remote selection of the sensitive region and automatically matches the impedance of the array to the preamplifier. Results obtained using a mutually coupled coil array designed for spine imaging are shown. © 1991 Academic Press, Inc.
Effect of oral contraception on water‐suppressed proton NMR spectra of plasma
Authors: Carlier Pierre G. , Vaesen Francis , Gilles Raymond G. , Fradin Elisabeth A. , Rorive Georges L.
Published: March 2007

Lipid linewidths were measured in the plasma proton spectra of young women. The individuals taking a contraceptive pill associating ethinyloestradiol and levonorgestrel or norethisterone were found with an average linewidth 2.5 Hz narrower than controls. As this drug regimen systematically induces an increase in plasma VLDL and a decrease in HDL/LDL ratio, our observation supports the theory that the Fossel test reflects plasma lipids abnormalities in cancer patients. © 1991 Academic Press, Inc.
An evaluation of MRI contrast in the uterus using synthetic imaging
Authors: Lange Robert C. , Duberg Arthur C. , McCarthy Shirley M.
Published: March 2007

Using a 1.5‐T system, we investigated the contrast in MR images of the uterus using a synthetic imaging program that was capable of producing images with TR values of 20 to 10220 ms and TE values of 1 to 511 ms. Synthetic images were calculated from images obtained on six normal women of reproductive age. The synthesized uterine images were essentially indistinguishable from acquired images with the same TR and TE parameters. Cervical and uterine anatomy could be clearly differentiated in synthetic images with a TE = 80 ms when the TR was as low as 100 ms. We conclude that the zonal anatomy of the uterus can be demonstrated using TR values that are much lower than those usually used for demonstrating uterine anatomy. © 1991 Academic Press, Inc.
On the Transverse relaxation rate enhancement induced by diffusion of spins through inhomogeneous fields
Authors: Hardy Peter , Henkelman R. Mark
Published: March 2007

The design of magnetic particles as a magnetic resonance contrast agent will rely on the prediction of their ability to induce transverse relaxation among the surrounding protons. There exists several divergent predictions of the contribution of these agents to 1 / T2. This article points out a problem, commonly overlooked, in the development of expressions for the relaxation enhancement which has led some workers to the derivation of results inappropriate for large magnetic particles. The size of the magnetic inhomogeneity created by the particle precludes the averaging of the interaction over a single proton unless it experiences an average field in the time T between pulses. Computer simulations following the trajectories of diffusing water molecules in inhomogeneous fields are shown to be the correct approach to dealing with large inhomogeneities. © 1991 Academic Press, Inc.
Measurement of the blood‐brain barrier permeability and leakage space using dynamic MR imaging. 1. Fundamental concepts
Authors: Tofts Paul S. , Kermode Allan G.
Published: March 2007

Leakage of Gd‐DTPA through a defective blood‐brain barrier is measured quantitatively using dynamic MRI scanning, in which repeated scans are made after a bolus injection. Image registration artifacts are minimized; a dose of 0.1 mM/kg and an IR sequence enable enhancement to be measured quantitatively. The triexponential enhancement curve is fitted to a theoretical model based on compartmental analysis. The transfer constant, or permeability surface area product per unit volume of tissue (k), and leakage space per unit volume of tissue (y) are measured. Estimates for a quickly enhancing multiple sclerosis lesion are k = 0.050 min−1, v1 = 21%; for a slow one k = 0.013 min−1, v1 = 49%. This implies permeability in the range 4‐17 × 10−6 cm s−1, in broad agreement with other physiological methods. The method is noninvasive and can be used to make serial measurements in patients and in experimental animal models. The time course of pathological aspects of diseases with blood‐brain barrier breakdown, such as multiple sclerosis, tumors, and infections (e.g., HIV) can be studied, along with their response to therapy. The measurements are of physiological variables and are therefore independent of imaging equipment and field. © 1991 Academic Press, Inc.
Applications of nuclear magnetic cross‐relaxation spectroscopy to tissues
Authors: Grad Jonathan , Mendelson Daniel , Hyder Fahmeed , Bryant Robert G.
Published: March 2007

Magnetic cross‐relaxation in aqueous heterogeneous systems is a long established phenomenon that makes the observable decay constants for the system mixtures of more fundamental relaxation times which characterize the relaxation of the coupled components. By exploiting the magnetic relaxation coupling between the water spins and the immobilized spins in a tissue, the water‐proton‐signal intensity may be used to map indirectly a frequency response that is directly related to the 1H NMR spectrum of the immobilized components of the tissue. This method is applied to a number of rat tissues to determine whether there are significant differences among tissues that might be exploited in applications of this experiment to diagnostic magnetic imaging. Significant differences are found among nine rat tissues studied, which suggests that the experimental approach may be used to superimpose fundamentally new information, the dynamic character of the usually unobservable immobilized macromolecular components of the tissue, on a magnetic image. © 1991 Academic Press, Inc.
In vivo Quantitative characterization of trabecular bone by NMR
Authors: Ford John C. , Wehrli Felix W.
Published: March 2007

In trabecular bone the NMR linewidth is found to be governed by the magnetic field inhomogeneity arising from the difference in magnetic permeability between bone and marrow. T21 was measured in vivo in the distal femur by interferometry and localized spectroscopy. Both methods showed T21 to be inversely related to trabecular plate density. © 1991 Academic Press, Inc.
Real‐time flow measurements using echo‐planar imaging
Authors: Guilfoyle D. N. , Gibbs P. , Ordidge R. J. , Manwield P.
Published: March 2007

The ultra‐high‐speed echo‐planar imaging (EPI) method is combined with velocity encoding prior to EPI read‐out, thereby allowing real‐time measurement of flow. Results of EPI flow measurement experiments are presented on phantoms and human volunteers. © 1991 Academic Press. Inc.
Volume rendering and connectivity algorithms for MR angiography
Authors: Cline Harvey E. , Dumoulin Charles L. , Lorensen William E. , Souza Steven P. , Adams William J.
Published: March 2007

Several display algorithms for three‐dimensional angiographic data are evaluated. The mathematical analysis assumes additive Gaussian noise to predict the background distribution function for maximum intensity projection, sum projection, and connectivity display methods. In the maximum intensity projection method the mean noise level increases with the number of voxels in the ray, while in the sum projection the noise distribution width increases with the projection thickness, but the mean level remains constant. Comparisons of maximum intensity projection, sum projection, and connectivity algorithms applied to an MR angiogram of the circle of Willis are made. Measurements of the noise distribution are in agreement with the analysis. Algorithms combining connectivity with maximum intensity and sum projection are also evaluated. In these methods, a projection image is created using only the voxels marked by connectivity, typically with a 6% threshold of the data. Fine vessels are resolved and background noise is reduced in agreement with the analysis. © 1991 Academic Press. Inc.
Sodium MRI with coated magnetite: Measurement of extravascular lung water in rats
Authors: Lancaster Luke , Bogdan Andrew R. , Kundel Harold L. , McAffee Bethanne
Published: March 2007

This study was done to see if signal intensity in sodium images of edematous rat lungs made after iv administration of a negative intravascular contrast agent could serve as a measure of the edema fluid present. First, a method to produce a stable condition of hydrostatic pulmonary edema was developed and verified by CT. Second, dose‐response curves for coated magnetite preparations were constructed by giving edematous rats vaned doses of these preparations and measuring signal intensity changes of various organs by sodium MRI in a 31‐cm‐bore 1.9‐T magnet. Third, rats were given varied levels of pulmonary edema followed by a constant dose of coated magnetite to eliminate the plasma sodium signal. Finally, coated magnetite particles of two sizes were administered to rats, and the differences in effects on signal from various organs were measured. Signal intensity of the lungs after magnetite correlated (r = 0.86) with extravascular lung water measured gravimetrically, suggesting that sodium MRI may be useful for measuring pulmonary edema fluid. Smaller particles appear to remain in the blood longer than larger particles. © 1991 Academic Press, Inc.
Proton chemical‐shift imaging with magnetically and electrically inhomogeneous objects
Authors: Nozokido Tatsuo , Yamamoto Etsuji , Kohno Hideki , Yamamoto Shinji
Published: March 2007

Proton chemical‐shift imaging with the elimination of three kinds of artifacts caused by main magnetic field inhomogeneities, susceptibility distributions of imaging objects, and the electromagnetic properties of radiofrequency (RF) fields is presented in this paper. In addition, the last of these artifacts, which is dependent upon the conductivity distributions of objects, especially in high‐tesla imaging, is also demonstrated experimentally. The method proposed here enables the reconstruction of artifact‐free water/fat separation images by using simple image data manipulations without the complicated phase‐unwrap process, even with main magnetic field inhomogeneities larger than the chemical‐shift difference between water and fat magnetizations. © 1991 Academic Press, Inc.
A technique of double‐resonant operation of 19F and 1H quadrature birdcage coils
Authors: Lu Dongfeng , Joseph Peter M.
Published: March 2007

A technique was developed to change the resonant frequency of a rotating field birdcage coil from 19F resonance (76.14 MHz) to 1H resonance (80.92 MHz). This was done by inserting an additional shield with a smaller radius on the coil which resonates at 19F. It was shown that the inhomogeneity introduced by reducing the shield radius is not significant. A working coil built with this technique produced both 19F and 1H images satisfactorily. © 1991 Academic Press, Inc.
Hybrid MR angiography and Fourier velocity imaging using two echo 3D acquisition
Authors: Hou Ping , Parker Dennis L. , Blatter Duane D. , Robison Ronald O.
Published: March 2007

Fourier velocity imaging can be accomplished without cardiac gating from the second echo of a standard 3D MR angiography sequence. The stepped bipolar velocity encoding gradient is obtained by adding a gradient pulse opposite in area to the spatial phase encoding gradient. In this technique, Fourier images of three spatial coordinates are obtained from the first echo and images of two spatial coordinates and one velocity component are obtained from the second echo. © 1991 Academic Press, Inc.
Functional variations in parenchymal microvascular systems within the brain
Authors: Fenstermacher Joseph , Nakata Hiroyuki , Tajima Atsushi , Lin Shinn‐Zong , Otsuka Tadahiro , Acuff Virgil , Wei Ling , Bereczki Daniel
Published: March 2007

Variations in microvascular system functions were observed among a number of brain areas. The rates of local blood flow varied 18‐fold among areas and were extremely high in neuroendocrine structures. Marked differences in blood flow were also found within some brain structures. The volume of radiolabeled blood in perfused parenchymal micro‐vessels ranged from 5 to 70 μl/g and correlated closely with local cerebral blood flow. The hematocrits within parenchymal microvessels were 45–75% of the arterial hematocrit, which indicates that red cells more rapidly traverse brain microvessels than do plasma proteins. The mean transit times of blood through parenchymal microvessels were extremely short and ranged from 0.3 to 0.6 s. © 1991 Academic Press, Inc.
Diffusion imaging using stimulated echoes
Authors: Merboldt Klaus‐Dietmar , Hänicke Wolfgang , Frahm Jens
Published: March 2007

The application of stimulated echo acquisition mode (STEAM) sequences for NMR imaging of diffusion is especially suited for spins with T1 ≫ T2 as, e.g., encountered in proton NMR studies of biological systems. Molecular self‐diffusion coefficients may be calculated from a set of diffusion‐weighted images acquired with different gradient strengths. A variation of the diffusion time allows the determination of restricted and/or anisotropic diffusion in cellular systems ranging from plants to humans. Problems associated with the presence of unavoidable macroscopic motions in vivo are demonstrated in diffusion studies of human brain. Motion ghosting in diffusion‐weighted images may be overcome by means of a high‐speed STEAM sequence yielding single‐shot images within subsecond acquisition times. © 1991 Academic Press, Inc.
Magnetic resonance diffusion/perfusion phantom experiments
Authors: Lorenz Christine H. , Pickens David R. , Puffer Donald B. , Price Ronald R.
Published: March 2007

Recently, several models for determining microcirculatory parameters using magnetic resonance imaging have been proposed. These include the intravoxel incoherent motion (IVIM) model, the intravoxel coherent motion (IVCM) model, and various tracer models. In order to evaluate these models before extension into physiological systems, phantom studies were used to assess model assumptions, measurement uncertainties, and sensitivity to changes in perfusion. Emphasis is placed on the IVIM model, but the techniques discussed could be extended to evaluation of other models as well. An overview of considerations in pulse sequence development, phantom design, and data interpretation is presented for a variety of phantoms ranging in complexity from stationary volumes of fluid and mechanically pumped phantoms to isolated animal kidneys and finally to an in vivo animal model. © 1991 Academic Press, Inc.
Contrast agents and cerebral hemodynamics
Authors: Rosen Bruce R. , Belliveau John W. , Buchbinder Bradley R. , McKinstry Robert C. , Porkka Leena M. , Kennedy David N. , Neuder Michelle S. , Fisel C. Richard , Aronen Hannu J. , Kwong Kenneth K. , Weisskoff Robert M. , Cohen Mark S. , Brady Thomas J.
Published: March 2007

Contrast‐enhanced magnetic resonance imaging of regional cerebral hemodynamics is discussed. Techniques for measuring cerebral blood volume (CBV) have been validated in animal models and have recently been applied to human studies. Factors affecting CBV measurement in pathologic tissue are addressed. Extension of these techniques to the measurement of cerebral blood flow is presented. © 1991 Academic Press, Inc.
The validation of freely diffusible tracer methods with NMR detection for measurement of blood flow
Authors: Neil Jeffrey J.
Published: March 2007

While the general theory of measuring organ perfusion using exogenously administered freely diffusible tracers was originally formulated over 40 years ago, the application of NMR techniques for tracer detection is a recent development. A brief theoretical review and discussion of the literature validating the use of deuterium and fluorine as NMR‐detectable tracers is provided. © 1991 Academic Press, Inc.
The visibility of the 1H NMR signal of ethanol in the dog brain
Authors: Moxon Leith N. , Rose Stephen E. , Haseler Luke J. , Galloway Graham J. , Brereton Ian M. , Bore Peter , Doddrell David M.
Published: March 2007

In Vivo, high‐resolution, volume‐selected 1H NMR spectroscopy was used to monitor the concentration of ethanol in the dog brain following intravenous injection of ethanol. Equilibration of ethanol in the body water should result in approximately equivalent concentrations of ethanol in the blood and brain. However, the mean equilibrium brain ethanol concentration determined using N‐acetylaspartate as an internal standard was only 23 ± 5% of the blood ethanol concentration. The disparity between blood and brain ethanol concentrations was attributed to underestimation of the ethanol concentration due to overlapping resonances with NAA and to T2 attenuation or possible nondetection of the 1H signal from ethanol bound at the surface of cell membranes and partitioned into the hydrophobic core of membrane lipids. © 1991 Academic Press, Inc.
Gadolinium‐labeled liposomes containing various amphiphilic Gd‐DTPA derivatives: Targeted MRI contrast enhancement agents for the liver
Authors: Kabalka G. W. , Davis M. A. , Moss T. H. , Buonocore E. , Hubner K. , Holmberg E. , Maruyama K. , Huang L.
Published: March 2007

Unique paramagnetic liposomal contrast agents were synthesized and utilized for selective augmentation of T1 MR imaging of the livers of normal Balb/c mice. A series of amphipathic gadolinium complexes, which mimic phospholipids, was incorporated into the lamella of small unilamellar liposomes such that they become an integral part of its surface. The amphipathic complexing agents consisted of DTPA reagents in which two stearyl chains are attached via amide, ester, and thioester linkages. The in vitro stability and the in vivo lifetimes of the new amphipathic agents were dependent on the method used to attach the long‐chain alkyl groups. © 1991 Academic Press, Inc.
31P NMR spectroscopy of 9L cell line in culture: Differential effects of high temperature on anchored cells and spheroids
Authors: Suzuki Nobuyuki , Kwee Ingrid L. , Tamas Laszlo B. , Nakada Tsutomu
Published: March 2007

The differential effects of high temperature on 9L rat gliosarcoma cells cultured in two distinctive forms, namely, anchored monolayer cells and multicellular spheroids, were investigated using 31P nuclear magnetic resonance spectroscopy. The critical temperatures resulting in irreversible changes in cellular energetics were found to be significantly different: 45°C for anchored cells and 43°C for multicellular spheroids, respectively. Phosphonionoester levels in multicellular spheroids were found to be consistently higher than those in anchored monolayer cells regardless of the temperature to which they were exposed. The study demonstrates that tissue derived from a single cell line may exhibit different metabolic properties depending on its growth pattern. © 1991 Academic Press, Inc.
On the use of a slice‐selective 270° self‐refocusing Gaussian pulse for magnetic resonance imaging: Comments on the note by D. M. Doddrell et al.
Authors: Emsley Lyndon , Bodenhausen Geoffrey
Published: March 2007

It is shown that the results obtained by D. M. Doddrell, G. J. Galloway, S. E. Rose, P. J. Moulds, and I. M. Brereton (Magn. Reson. Med. 19, 1991) using self‐refocusing 270° Gaussian pulses for slice selection are consistent with our predictions (Magn. Reson. Med. 10, 273, 1989). © 1991 Academic Press, Inc.
Cerebral glucose is detectable by localized proton NMR spectroscopy in normal rat brain in Vivo
Authors: Gyngell M. L. , Michaelis T. , Hörstermann D. , Bruhn H. , Hänicke W. , Merboldt K. D. , Frahm J.
Published: March 2007

This contribution reports the first direct and noninvasive observation of cerebral glucose in normal anesthetized rats (n = 16) using short‐echo‐time localized proton NMR spectroscopy (2.35 T, STEAM, TR = 6000 ms, TE = 20 ms, 125 μl). In addition to resonances from N‐acetyl aspartate (NAA), glutamate, total creatine, cholines, taurine, and myo‐inositol, all spectra exhibit strongly coupled resonances from glucose (3.43, 3.80 ppm) that are readily identifiable using model solutions. The observed level of cerebral glucose in fasted rats covered a range of 15–4096 of that of NAA giving absolute concentrations of 1.1–2.8 mM when NAA is taken to be 7 mM. The arterial blood glucose concentration was 7.7 ± 0.8 mM in the same group Of animals.
Double‐volume 1H spectroscopy with interleaved acquisitions using tilted gradients
Authors: Ernst Th. , Hennig J.
Published: March 2007

A method is presented by which volume selective in vivo 1H spectra of two different voxels can be acquired in an interlaced mode using PRESS or STEAM spectroscopy. Spatially tilted gradients are employed for voxel definition so as to avoid mutual saturation. Independent volume selective shimming of the voxels is possible. Two spectra of volumes as small as (1.5 cm)3 can be acquired from human brain within 14 min even from very disadvantageous locatins close to air‐bone interfaces. © 1991 Academic Press, Inc.
Correlation of lactate and pH in human skeletal muscle after exercise by 1H NMR
Authors: Pan J. W. , Hamm J. R. , Hetherington H. P. , Rothman D. L. , Shulman R. G.
Published: March 2007

We have made in vivo 1H NMR measurements of the time course of pH and lactate in human skeletal muscle after exercise. Spectra were obtained in a 4.7‐T 30 cm bore Bruker Biospec spectrometer with a 2.5‐cm diameter single surface coil. pH was determined from the shift of the endogenous carnosine H‐C2 peak while lactate concentrations were determined by comparison with endogenous total creatine, taken to be 28.5 mM/ kg wet wt. Fitting the data shows that the exponential decay of lactate (‐0.094 ± 0.014 min ‐1, t 1/2 = 10.6 min) is slower than that of pH (‐0.147 ± 0.015 min‐1, t1/2 = 4.7 min), n = 7 with two different volunteers. These values are significantly different with P < 0.0005. Relaxation times of lactate and creatine were also measured for lactate quantitation: creatine Tl. 1.23 ± 12 s. T2, 136.2 ± 26.4 ms (both in resting human muscle); lactate Tl (in postmortem rabbit muscle), 1.0 ± 11 s and T2, 80 ms (in postexercise human muscle). At the end of intense exercise, the lactate level reached was 25.3 ± 4.0 m M and the average pH drop was 1.0 pH unit. We discuss the implicaions of these measurements in conjunction with existing data on other sources of H+ flux, phosphocreatine resynthesis, H+ transport, and contribution of inorganic phosphate to buffering. © 1991 Academic Press, Inc.
Application of missing pulse steady state free precession to the study of renal microcirculation
Authors: Stromski M. E. , Brady H. R. , Gullans S. R. , Patz S.
Published: March 2007

Missing pulse steady state free precession (MP‐SSFP), an extension of steady state free precession (SSFP), was evaluated for its ability to measure slow fluid flows. In experiments using flow phantoms, the MP‐SSFP signal was sensitive to fluid velocities in the millimeters per second range. Isolated perfused rabbit kidneys were then used to determine if MP‐SSFP could measure perfusion in a biological tissue. The signal intensities in the different anatomical regions of the kidney were observed to be related to the total flow to the organ. Furthermore, increasing the flow sensitivity of the pulse sequence by increasing the gradient strength resulted in decreases in the image signal intensity. The MP‐SSFP signal was more sensitive to flow in the medulla than in the cortex. This can be related to slow flow sensitivity of MP‐SSFP and the known differences in velocity profiles between these two regions. These results suggest that MP‐SSFP may be a powerful tool for the noninvasive measurement of slow fluid flows in different regions of the kidney. © 1991 Academic Press, Inc.
Regional 1H transverse magnetization studies in perfused rabbit kidney
Authors: Mulkern R. V. , Stromski M. E. , Brady H. R. , Gullans S. R. , Sandor T. , Jolesz F. A.
Published: March 2007

A Carr‐Purcell‐Meiboom‐Gill imaging sequence consisting of 128 echoes is used to extract transverse magnetization decay curves (TDCs) at 1.9 T from 1.7 × 1.7 × 5‐mm3 voxels within the cortex, outer medulla, and inner medulla of perfused rabbit kidneys. The spatially localized TDCs within each tissue type are found to be better approximated by biexponential, as opposed to monoexponential, functions. The biexponential parameters characterizing the TDCs demonstrate an improved degree of tissue specificity over that available from monoexponential analyses. The fraction of the quickly relaxing TDC component and the relaxation rate of this component are observed to decrease from cortex to inner medulla. A two‐site exchange analysis is used to convert biexponential TDC parameters into water volume fractions and exchange rates. The exchange rates between the fast and slowly relaxing pools increased from cortex to inner medulla. All exchange rates were less than 1.5 Hz, indicating a relatively slow water exchange process. The imaging methods and subsequent analyses offer the potential to generate unconventional MR images with tissue contrast dependent upon water compartmentation and exchange. © 1991 Academic Press, Inc.
Application of continuous relaxation time distributions to the fitting of data from model systmes and excised tissue
Authors: Menon R. S. , Allen P. S.
Published: March 2007

Biological systems exhibit heterogeneity at many different levels, leading to the expectation of multiple relaxation time components for water protons in tissue samples. Traditional methods which fit the relaxation data to an a priori number of discrete components are open to observer bias in their interpretation of this data, and moreover, are intutively less realistic for heterogeneous systems than methods which produce continuous relaxation time distributions. Previous validations of continuous distribution techniques have been made on simulated data assuming uniform Gaussian noise. In the current work we have investigated the ability of one particular linear inverse theory technique to reproduce known relaxation time distributions from the data on a controllable model system. Furthermore, using the experience gained on the model system, we have applied this same technique to the analysis of in vitro relaxation time measurements on excised brain tissue and found for water protons in white matter, four reproducible components for the transverse relaxation, whereas gray matter gave rise to only two. The lougitudinal relaxation displayed only one component in either white matter or gray matter. © 1991 Academic Press, Inc.