bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental approaches to image localized human31P NMR spectroscopy
Authors: Luyten Peter R. , Groen Jan P. , Vermeulen Jan W. A. H. , Den Hollander Jan A.
Published: March 2007

Experimental procedures for obtaining localized31P NMR spectra of humans by means of the ISIS sequence are discussed in detail. The technique is optimized for use with volume coils and with surface coils in order to measure localized31P NMR spectra ofdifferent tissues and organs. Selective frequency‐modulated (FM) inversion and excitation pulses are applied for optimal inversion or excitation despite B1 inhomogeneity. Pulse imperfection may lead to spurious signal contributions from outside the selected volume; this contamination is reduced by using long pulse intervals, by properly ordering the ISIS acquisitions, and by using FM excitation pulses. Simultaneous measurement of multiple volumes was implemented by including an additional selective inversion pulse, and an extension of the ISIS addition/subtraction scheme. Localized T1 measurements with surface coils are implemented by using a B1‐insensitive inversion pulse in the inversion recovery sequence. The quantitative reproducibility of localized31P NMR spectra was verified. Absolute metabolite concentration can be determined after a suitable calibration of the31P NMR spectrum. Localized shimming is required to obtain localized31P NMR spectra of excellent spectral resolution. This is done by monitoring the1H NMR signal from water by a single‐shot localization technique. The techniques discussed can be applied to obtain spectra of brain, liver, heart, and other organs.31P NMR spectra of intracranial tumors demonstrate its applicability in the examination of patients. © 1989 Academic Press. Inc.
The effect of gadolinium DTPA on tissue water compartments in slow‐ and fast‐twitch rabbit muscles
Authors: Kofi Adzamli I. , Jolesz Ferenc A. , Bleier Alan R. , Mulkern Robert V. , Sandor Tamas
Published: March 2007

Proton T2 relaxation and its biexponential components have been determined in rabbit skeletal muscle in the presence and absence of GdDTPA. The effect of GdDTPA, which distributes only in the extracellular space, was greatest in the longer‐relaxing T2 component (T22). A 27% reduction in T22was measured for slow‐twitch (red) muscle and 17% for fast‐twitch (white) muscle, consistent with the larger extracellular space of the former. Magnetic resonance images demonstrated apparent contrast between red and white rabbit muscles. This contrast was instantaneously enhanced by administration of GdDTPA and returned to near normal levels after approximately 30 min. These functional changes in tissue contrast are consistent with differences in blood perfusion and biological water compartmentation between fast‐ and slow‐twitch skeletal muscles.
Toxicity of dysprosium shift reagents in the isolated perfused rat kidney
Authors: Endre Z. H. , Allis J. L. , Radda G. K.
Published: March 2007

Sodium and water spectra were acquired from the isolated perfused rat kidney by using a double‐tuned probe designed to have high X nucleus sensitivity and low 1H sensitivity. Both DyTTHA and DyPPP were used to distinguish intra‐ and extracellular 23Na resonances before and after the onset of hypoxia. Only DyPPP was useful in separating the two compartments, with a maximal chemical shift difference produced at a concentration of 4.5 mM. Both shift reagents were nephrotoxic at concentrations under 5 mM and produced an immediate decrease in renal‐concentrating capacity and increases in fractional sodium and potassium excretion and increased renal vascular resistance. These disturbances of renal physiological parameters were accompanied by progressive broadening of the renal H2O resonance. 1H NMR may be a subtle means of monitoring nephrotoxicity.
The synthesis of soft pulses with a specified frequency response
Authors: Shinnar Meir , Bolinger Lizann , Leigh John S.
Published: March 2007

We propose a new approach to synthesizing shaped pulses, by first synthesizing a hard pulse sequence and then converting it to a soft pulse. In previous papers, we developed a new approach to synthesizing hard pulse sequences by exactly inverting the Bloch equation, which yields the optimal frequency response. These results can now be applied to shaped pulses. Specifically, one can specify (1) the total duration of the pulse, (2) the frequency range it is desired to perturb, (3) the perturbation desired and, (4) the frequency range it is desired not to perturb. One can then synthesize a shaped pulse which has the desired effect with the least possible error. This enables us to obtain very sharp inversion and π/2 pulses. © 1989 Academic Press, Inc.
In Vivo 31P and 1H NMR studies of rat brain tumor pH and blood flow during acute hyperglycemia: Differential effects between subcutaneous and intracerebral locations
Authors: Ross Brian D. , Mitchell Steven L. , Merkle Hellmut , Garwood Michael
Published: March 2007

Surface coil NMR spectroscopy was used to monitor the hyperglycemia‐induced alterations in pH and blood flow in vivo in C6 gliomas implanted both subcutaneously and intracerebrally in rats. Tumor pH was calculated from the chemical shift difference between PCr and Pi in the 31P NMR spectra. Subcutaneous glioma pH decreased 0.8 units by 1 h after intraperitoneal administration of an aqueous 50% glucose solution (6 g glucose per kg body weight). In contrast, hyperglycemia failed to significantly alter the pH of intracerebral gliomas which were monitored for 90 min following administration of glucose. Tumor blood flow (TBF) was determined both pre‐ and post‐glucose administration using deuterium NMR by monitoring the time course of D2O washout following intratumoral injection of saline D2O. Subcutaneous and intracerebral TBF were found to have an average change of‐78.1 % (range ‐47.4 to ‐93.3%, n = 5) and ‐21.1% (range +6.0 to ‐37.8%, n = 9), respectively. In addition, laser Doppler blood flow measurements of rat skin and subcutaneous glioma revealed a dramatic reduction in blood flow in both tissues following glucose administration. These results indicate that the effects of acute hyperglycemia are site dependent and that hyperglycemia alone is not beneficial for inducing intracellular acidosis in intracerebral tumors. © 1989 Academic Press, Inc.
Effect of inotropic stimulation on cytosolic mg2+ in isolated rat heart: a 31p magnetic resonance study
Authors: Headrick John P , Willis Roger J.
Published: March 2007

Alterations in cytosolic metabolites and [Mg2+], were monitored using 31P magnetic resonance spectroscopy during inotropic stimulation of isolated rat heart [10 n M isoproterenol, 0.6 μM isobutyl‐1‐methylxanthine (IBMX), 5 μM ouabain]. All drugs significantly elevated contractile function (rate‐pressure product) and MVO2 by approximately 100‐150% (P 0.001), decreased cytosolic [creatine phosphate] ([CrP]) and [ATP] (approximately 65 and 80% of control values, respectively) (P 0.001), increased [ Pi ] to more than 180% of pretreatment values, and decreased [ H+] by less than 15% (P 0.05). A significant relative shift in the α‐P and β‐P resonances of ATP (P 0.01) occurred with inotropic stimulation. [Mg2+], calculated on the basis of these shifts was found to be 0.78 ± 0.1 mM in control hearts, and increased to maxima of 1.9 ± 0.2,2.0 ±0.2, and 2.9 ± 0.2 m M during infusion of isoproterenol, IBMX, and ouabain, respectively. Changes in [Mg2+], correlate with cytosolic [ATP] + [CrP] in all hearts (r = 0.89, 0.91, and 0.88 in isoproterenol‐, IBMX‐, and ouabain‐treated hearts, respectively). The significantly higher [Mg2+], with ouabain infusion (P 0.01) at similar workloads and [ATP] + [CrP] supports the proposal that a ouabain‐inhibited Mg2+ pump exists in the plasma membrane. The data support acute changes in [ Mg2+ ]i during alterations in inotropic state that may be important in modulating metabolic and contractile function. © 1989 Academic Press, Inc.
Environmental optimization and shielding for nmr experiments and imaging in the earth's magnetic field
Authors: Favre B. , Bonhe J. P. , Mehier H. , Peyrin J. O.
Published: March 2007

For many years, a number of laboratories have been working on the applications of very low field NMR. In 1985, our laboratory presented the first NMR images using the earth's magnetic field. However, the use of this technique was limited by the weakness of the signal and the disturbing effects of the environment on the signal‐to‐noise ratio and on the homogeneity of the static magnetic field. Therefore experiments had to be performed in places with low environmental disturbances, such as open country or large parks. In 1986, we installed a new station in Lyon, in the town's hostile environment. Good NMR signals can now be obtained (with a signal‐to‐noise ratio better than 200 and a time constant T*2 better than 3 s for 200‐ml water samples and at a temperature of about 40°C). We report here our new technique: A shielded box was built and installed on scaffoldings above the terrace roof of our faculty building. Gradient coils were used to correct the local inhomogeneities of the earth's magnetic field. We show FIDs and MR images of water‐filled tubes made with or without these improvements.
Parameter estimation for in vivo magnetic resonance spectroscopy (mrs) using simulated annealing
Authors: Sekihara K. , Ohyama N.
Published: March 2007

A method for estimating the spectral parameters from a noisy FID is proposed. The method uses a priori information concerning the lower and upper limits between which such parameters' values can exist. Computer simulation results show that, using the proposed method, values of the spectral parameters can be accurately estimated from a noisy FID.
Efficient remote transmission line probe tuning
Authors: Rath Alan R.
Published: March 2007

An approach is described which allows remote tuning of a probe via a length of transmission line, while retaining nearly ideal efficiency relative to the equivalent locally tuned coil. This preservation of efficiency is accomplished through the principle of “partial local matching.” In comparison to common methods of remote tuning which involve half‐wavelength cables, or in which a length of transmission line is itself utilized as a tuning element, the partial matching method results in a substantial increase in the efficiency of power transfer to the coil, and therefore increased B1 field intensity and signal‐to‐noise ratio. Applications in which the use of local variable tuning capacitors is made difficult by either space, accessibility, or environmental considerations should benefit from this method.
Inversion‐recovery echo‐planar imaging (ir‐epi) at 0.5 T
Authors: Stehling M. K. , Ordidge R. J. , Coxon R. , Mansfield P.
Published: March 2007

Echo‐planar imaging is used in combination with a spin preparation phase to produce a T1‐weighted image. The small additional time penalty in this procedure does not detract significantly from the ultrahigh‐speed imaging capability of EPI, allowing a rapid real‐time optimization of tissue parameters in the image display. Results obtained on a head demonstrate this technique. © 1990 Academic Press, Inc.
Measurement of tissue blood flow using intravascular relaxation agents and resonance imaging
Authors: Gore John C. , Majumdar Sharmila
Published: March 2007

Simple concepts of indicator‐dilution techniques are described, and the theoretical basis of measuring regional blood flow via transit time measurements of a blood pool marker is discussed. Using very fast imaging of the effects of an appropriate and efficient relaxation agent, the concentration‐time curve of the agent can be quantified. Preliminary measurements of the transit of superparamagnetic iron oxide through a rat brain at 2.0 T have been obtained. There are problems, however, in relating the NMR signal change to the tissue concentration of an intra vascular relaxation agent when there is not fast exchange of the tissue water with the water in the vasculature, or when the precise efficacy of the agent varies with the geometrical arrangement of the capillaries. Studies of the effects of superparamagnetic iron oxide particles in different media confirm that the in vivo efficacy varies among different tissues, which complicates their use as blood flow markers. © 1990 Academic Press, Inc.
Compatibility of the two‐site exchange model and 1H NMR relaxation rates
Authors: Mulkern R. V. , Bleier A. R. , Sandor T. , Jolesz F. A.
Published: March 2007

We demonstrate a formalism for determining whether 1H longitudinal and transverse magnetic relaxation decay curves are compatible with a model of proton exchange between two sites with inherently different relaxation rates. We apply the method to published data in which both decay curves have been fit to normalized biexponential functions, a prediction of the simplest two‐site exchange model. The analysis is applied to relaxation data of adsorbed water vapor on silica gel (J. R. Zimmerman and J. A. Lasater, J‐ Phys. Chem. 62, 1157 (1958)) and to relaxation data reported in mycelia of Botrytis cinerea Persoon and pupae of the tobacco cutworm (M. Yoshida and K. Nose, Agric. Biol. Chem. 51, 3399 (1987)). Exchange parameters are calculated form these data sets and the compatibility of the two‐site exchange model with the data is discussed for each case. The sensitivity of the calculated exchange parameters to errors in the biexponential fitting parameters is treated in some detail. © 1990 Academic Press, Inc.
Measurement of translational displacement probabilities by NMR: An indicator of compartmentation
Authors: Cory D. G.
Published: March 2007

We introduce and demonstrate an NMR pulsed gradient stimulated echo method of directly obtaining the molecular translational displacement probability (displacement profile) of a liquid. The temporal development of the displacement profile reflects the presence of diffusion, restrictions to diffusion (e.g., walls, membranes), flow, and spatially dependent relaxation sinks. This approach allows the study of compartments which are too small to be observed by conventional NMR imaging methods. The distribution of spatial properties of compartments can be characterized over a spatial field of about 0.1 to 25 μm, completely independent of the absolute spatial location of the individual compartments. © 1990 Academic Press, Inc.
Proton‐enhanced 13C imaging/spectroscopy by polarization transfer
Authors: Swanson Scott D. , Quint Leslie E. , Yeung Hong N.
Published: March 2007

Carbon‐13 magnetic resonance imaging/spectroscopy (CMRI/S) was performed using polarization transfer techniques where sensitivity of the carbon signal was enhanced by transferring the proton spin order to the carbon nuclei. The experimental feasibility of using polarization transfer techniques at 2.0 T was demonstrated with a phantom and an intact chicken egg. The potential clinical applications of CMRI/S with polarization transfer include the assessment of prostate cancer. Preliminary results using human prostate specimens are presented. © 1990 Academic Press, Inc.
T2 of endotoxin lung injury with and without methylprednisolone treatment
Authors: Shioya Sumie , Haida Munetaka , Tsuji Chizuko , Ono Yoshiaki , Miyairi Akira , Fukuzaki Minoru , Ohta Yasuyo , Yamabayashi Hajime
Published: March 2007

NMR relaxation times (T1 and T2) and the water content (WC) of in vitro rat lungs were measured during the course of endotoxin lung injury in rats. Measurements of normal lungs, untreated endotoxin‐injured lungs, and endotoxin‐injured lungs treated with methylprednisolone (MPSL) were compared. The untreated endotoxin lungs showed prolongation of the fast and slow T2 components (T2r and T2s), but no significant changes in T1 or water content. Also, there was no correlation between 1 /WC and relaxation rates or between T1 and T2. MPSL treatment prevented T 2f and T2s prolongation; however, the duration of MPSL effectiveness was limited. Animals which were treated with MPSL more than 7 h prior to measurements showed T2 prolongation. This study indicates that NMR relaxation times, particularly T2, can be useful in evaluating lung injuries and their treatments. © 1990 Academic Press, Inc.
Echo planar imaging of isolated perfused rat hearts at 4.7 T: A comparison of Langendorff and working heart preparations
Authors: Blackband S. J. , Chatham J. C. , O'Delland W. , Day S.
Published: March 2007

The implementation of echo planar imaging at 4.7 T is demonstrated using a home‐built gradient and radiofrequency assembly. The application of such a technique to the study of the isolated perfused rat heart is demonstrated. Langendorff and working heart perfusion preparations are compared and changes in the left ventricular volume shown are to be much larger in the working heart preparation. Such a methodology is expected to provide a useful model for the study of cardiac function and dynamics in the normal and diseased states under controlled perfusion conditions. © 1990 Academic Press, Inc.
Application of interlaced orientation slices in orthogonal planes for system characterization and as a basis for standardized brain sections in multiple‐oblique positions
Authors: Boesch Ch. , Martin E.
Published: March 2007

Interlaced acquisition of orthogonal spin‐echo orientation slices yields saturated intersection lines, which are available for a system characterization (spatial distortions, slice thickness, chemical shift displacement). Additionally, these scout images contain complete information for a transformation of the gradient coordinate system into the oblique coordinate system of the patient, bearing standardized planes for improved image interpretation and quantitative examinations. © 1990 Academic Press, Inc.
Rapid radiofrequency calibration in MRI
Authors: Carlson J. W. , Kramer D. M.
Published: March 2007

A collection of modified procedures for setting rf transmitter levels using a three‐pulse sequence is described. Based on a geometrically weighted ratio of four signals, an estimate of the flip angle is calculated and used for an updating prescription. These techniques are designed to perform rapidly yet eschew systematic errors due to relaxation during the pulse sequence. © 1990 Academic Press, Inc.
Proton spectral editing in the inhomogeneous radiofrequency field of a surface coil using modified stimulated echoes
Authors: Lahrech Hana , Briguet Andre
Published: March 2007

It is shown that the modified stimulated echo sequence, [θ](±x±y)−t1−[θ](+x)−t2/2−[2θ](+x)−t2/2−[θ](+x)−t1−Acq(±x ∓ y), denoted as MSTE[2θ]x according to the exciter phase of the 2θ pulse, is able to perform proton spectral editing without difference spectra. On the other hand, this sequence appears to be suitable for spatial localization. Sensitivity and spatial selectivity of MSTE and conventional stimulated echo sequence (STE) are briefly compared. MSTE is applied to editing lactate in the rat brain using the locally restricted excitation of a surface coil. © 1990 Academic Press, Inc.
Development of a micromanometer‐tip catheter to record high‐fidelity pressures during cine‐gated NMR without significant image distortion
Authors: Dell'italia Louis J. , Carter Bruce , Millar Huntly , Pohost Gerald M.
Published: March 2007

We report a new micromanometer‐tip catheter to record high‐fidelity pressures during cine‐gated gradient echo NMR imaging in an intact animal model. Of the various metals and alloys tested for use in its construction, brass produced the smallest NMR artifact with minimal magnification. With the use of this new catheter design, there was little signal loss and no distortion of endocardial borders during imaging. © 1991 Academic Press, Inc.
Quantitative measurement of tissue perfusion and diffusion in vivo
Authors: Chenevert Thomas L. , Pipe James G. , Williams David M. , Brunberg James A.
Published: March 2007

Magnetic resonance imaging techniques designed for sensitivity to microscopic motions of water diffusion and blood flow in the capillary network are also exceptionally sensitive to bulk motion properties of the tissue, which may lead to contrast artifact and large quantitative errors. The magnitude of bulk motion error that exists in human brain perfusion/diffusion imaging and the inability of cardiac gating to adequately control this motion are demonstrated by direct measurement of phase stability of voxels localized in the brain. Two methods are introduced to reduce bulk motion phase error. The first, a postprocessing phase correction algorithm, reduces coarse phase error but is inadequate by itself for quantitative perfusion/diffusion MRI. The second method employs orthogonal slice selection gradients to define a column of tissue in the object, from which echoes may be combined in a phase‐insensitive manner to measure more reliably the targeted signal attenuation. Applying this acquisition technique and a simplistic model of perfusion and diffusion signal attenuations yields an estimated perfusion fraction of 3.4 ± 1.1% and diffusion coefficient of 1.1 ± 0.2 × 10−5 cm2/s in the white matter of one normal volunteer. Successful separation of perfusion and diffusion effects by this technique is supported in a dynamic study of calf muscle. Periods of normal blood flow, low flow, and reactive hyperemia are clearly distinguished in the quantitative perfusion results, whereas measured diffusion remained nearly constant. © 1991 Academic Press, Inc.
Quantitative 1H magnetization transfer imaging in vivo
Authors: Eng John , Ceckler Toni L. , Balaban Robert S.
Published: March 2007

A major factor contributing to proton (1H) spin‐lattice relaxation in biological tissues is believed to be magnetization transfer between 'H in free bulk water and 1H in restricted motion associated with macromolecules. We have shown recently that saturation transfer is an effective approach for studying this magnetization transfer process. Herein the determination of magnetization transfer rates in biological tissues is further analyzed by considering the time and power dependencies of saturation transfer. Following these analyses, quantitative magnetization transfer rate constant image maps were collected from the kidney in vivo. These rate constant images may prove useful in quantitative tissue characterization and in the determination of tissue‐specific 1H relaxation mechanisms. © 1991 Academic Press, Inc.
31P Spectroscopic localization using pinwheel NMR excitation pulses
Authors: Hardy Christopher J. , Bottomley Paul A.
Published: March 2007

Spectroscopic imaging with a one‐dimensional phase‐encoding gradient and surface‐coil reception relies on the restricted range of sensitivity of the surface coil to provide localization in the dimensions transverse to the coil axis and consequently suffers from relatively poor localization in these dimensions. A two‐dimensional (2D) cylindrically selective excitation pulse with a large spectral bandwidth is presented here to remedy this problem. The gradient waveforms are derived from multiple spirals in k space which form an overall pinwheel pattern, resulting in a pulse which is much shorter than the equivalent single‐spiral trajectory. Nonuniform traversal of the spirals further reduces the pulse width under conditions of gradient slew‐rate limitations, yielding overall gains in bandwidth of up to about 30 compared with the equivalent single‐spiral trajectory traversed at constant angular rate. The accompanying rf waveform is obtained by weighted 2D Fourier transformation of the desired sensitivity profile. A new weighting factor is introduced into the rf waveform to compensate for nonuniform sampling of k space by the pinwheel near the origin. This factor is independent of the weighting used to account for the rate of traversal of the trajectory and is applicable to 2D pulse design in general. Pulse sequences employing pinwheel excitation in conjunction with either phase‐encoding or slice‐selective inversion are used to produce multiple‐voxel and single‐voxel localization in a human heart and a phantom. Pinwheel pulses may be used to advantage on moieties with long spin‐lattice relaxation times and short transverse relaxation times and are therefore ideal for applications in phosphorus (13P) NMR. © 1991 Academic Press, Inc.
Motion‐insensitive volume‐selective pulse sequences for direct and proton‐detected 13C spectroscopy: Detection of glycogen in the human liver in vivo
Authors: Knüttel A. , Kimmich R. , Spohn K.‐H.
Published: March 2007

Two compact pulse sequences are reported for the volume‐selective detection of 13C nuclei. 13C signals are either directly acquired after enhancing the amplitude by polarization transfer from the coupled protons or, preferably, indirectly detected by heteronuclear editing of proton signals of 1H nuclei coupled to 13C. In the latter case, the full sensitivity of proton resonance is achieved, and signals from uncoupled protons or protons coupled to non‐13C nuclei or 13C nuclei of undesired compounds are suppressed. Both sequences are single‐scan procedures and are insensitive to the pulse phases and to motions of the investigated organs. The insensitivity to organ motions is due to the extremely compact character of these sequences avoiding coherence evolution periods as far as possible. This is achieved first by the introduction of double‐resonance sandwich (DORSA) pulses accomplishing the polarization transfer slice selectively in a very short time. The second reason is that the initial evolution interval which is usually part of polarization transfer experiments is avoided by the aid of a doublet line‐selective inversion pulse. Several test experiments in vivo are reported. In particular, it is demonstrated that glycogen can be detected in natural abundance in the human liver in vivo using a 2‐T whole‐body tomograph even without the use of heart or respiration triggers. The total acquisition time was 22 min, and a signal‐to‐noise ratio of 6 was achieved. © 1991 Academic Press, Inc.
Double‐quantum surface‐coil NMR studies of sodium and potassium in the rat brain
Authors: Lyon Robbe C. , Pekar James , Moonen Chrit T. W. , McLaughlin Alan C.
Published: March 2007

Double‐quantum filtered and conventional single‐pulse sodium and potassium NMR spectra were obtained from in situ rat brain at 7.0 T, using a surface coil. In contrast to the ca. 14% decrease observed in single‐pulse sodium NMR spectra upon death, increases as large as ca. 800% were observed in double‐quantum filtered sodium spectra. Conversely, a ca. 26% increase was observed in single‐pulse potassium spectra upon death, while double‐quantum filtered potassium spectra decreased below the noise level, for the shortest preparation time used. The decay rate of double‐quantum sodium coherence in the in situ rat brain after death was dependent upon the double‐quantum preparation time: this behavior results from the nonuniformity of the brain, and may be related to physiological com‐partmentalization. The potential application to sodium NMR imaging of cerebral functionality is briefly discussed. © 1991 Academic Press. Inc.
Lipid bilayer and water proton magnetization transfer: Effect of cholesterol
Authors: Fralix Teresa A. , Ceckler Toni L. , Wolff Steven D. , Simon Sidney A. , Balaban Robert S.
Published: March 2007

Magnetization transfer between macromolecules and water can be a significant factor contributing to tissue water 1H relaxation. Using saturation transfer techniques, the degree of magnetization transfer between the macromolecular matrix and bulk water 1H can be directly measured and magnetization transfer contrast (MTC) can be generated in MR images. A significant degree of MTC has been observed in tissues with high plasma membrane content such as kidney and brain. The purpose of this study was to establish whether lipid bilayers, as models for cell membranes, could exchange magnetization with the water solvent and whether this effect could contribute to MTC observed in intact tissues. Magnetization transfer was measured in aqueous dispersions of egg phosphatidylcholine (EPC) in the presence and absence of cholesterol. It was found that neither EPC bilayers nor cholesterol by themselves significantly exchanged magnetization with bulk water 1H. However, as the concentration of cholesterol was increased, the pseudo‐first‐order magnetization exchange rate increased to a maximum value of ∼1 s−1. The cholesterol‐induced 1H magnetization exchange may be related either to longer correlation times of the lipid or to an increase in the number of water molecules associated with the bilayer. These results indicate that EPC‐cholesterol bilayers exchange 1H magnetization with bulk water. These results are consistent with lipid bilayer contributions to bulk water relaxation and MTC in intact biological tissues. © 1991 Academic Press. Inc.
A simple method for the restoration of signal polarity in multi‐image inversion recovery sequences for measuring T1
Authors: Gowland P. A. , Leach M. O.
Published: March 2007

A simple scheme for the polarity correction of absolute images from inversion recovery multi‐image T1 measurement sequences is described and demonstrated. This method is less sensitive to errors from eddy currents than the conventional full phase correction schemes and does not involve an increase in measurement time as it requires no additional scans. © 1991 Academic Press. Inc.
Three‐point dixon technique for true water/fat decomposition with B0 inhomogeneity correction
Authors: Glover G. H. , Schneider E.
Published: March 2007

An enhancement to Dixon's technique is described which can provide error‐free decomposition of water and fat proton images even in the presence of off‐resonance conditions which result from susceptibility differences, demagnetization, or shim errors. The method uses three measurements with phase shifts of 0, π and − π between the fat and water resonances. The additional information provided by the third measurement is used to calculate an image of the field inhomogeneity in addition to true water and fat images. The signal‐to‐noise ratio (SNR) in the decomposed images is equivalent to that of a 2.7 NEX acquisition (instead of 3 NEX), yielding an SNR imaging efficiency of 95%. In addition, the B0 image which is provided may have diagnostic value in its own right. Examples of head and body scans often portray surprisingly large B0 shifts near interfaces between air or bone and soft tissue. © 1991 Academic Press. Inc.
Restricted and anisotropic displacement of water in healthy cat brain and in stroke studied by NMR diffusion imaging
Authors: Moonen Chrit T. W. , Pekar James , de Vleeschouwer Marloes H. M. , van Gelderen Peter , van Zijl Peter C. M. , Despres Daryl
Published: March 2007

The occlusion of the middle cerebral artery in cat brain was used as an experimental stroke model to investigate the physical basis of the recently reported lowered diffusion constant of water in acute infarcted brain tissue (Moseley et al., Magn. Reson. Med. 14, 330, 1990). The original findings were confirmed in this study of 12 animals investigated with the diffusion‐sensitized stimulated echo sequence. The following additional results were obtained: First, the onset of significant lowering of the diffusion constant in the stroke area varied significantly (up to 2.5 h depending on the animal). Second, the affected area is much more clearly outlined in diffusion‐weighted images than in T2,‐weighted images, even in the period between 3 to 12 h following occlusion. Third, for diffusion times between 50 and 2000 ms, the diffusion constant of water is independent of diffusion time in healthy tissue, as well as in the stroke area. Fourth, the diffusion anisotropy is similar in healthy and in stroke area and remains similar regardless of the diffusion time used. © 1991 Academic Press, Inc.
Multinuclear MR investigation of the metabolic response of the murine RIF‐1 tumor to 5‐fluorouracil chemotherapy
Authors: Sijens Paul E. , Baldwin Nicholas J. , Ng Thian C.
Published: March 2007

The metabolic response of the RIF‐1 tumor to 5‐fluorouracil (a single dose of 260 mg 5FU/kg, ip) was monitored in 10 mice using 19F and 31P MR spectroscopy. 19F MRS revealed a continuous drop in tumor 5FU level and an increase in the fluoronucleotide (Fnuc) signal to a plateau value of 50% of the initial 5FU level, during the first 2 h after chemotherapy. Although the 31P MR spectra of the tumors showed no significant initial changes, the total level of MR visible tumor phosphate decreased and tumor pH increased during the subsequent days. The changes in phosphate metabolism and tumor pH did not correlate with the detected fluorine levels or tumor response. However, the pretreatment Pi level, the plateau Fnuc level, and the 5FU induced decrease in tumor volume showed significant correlation. The indicates that both 19F and 31P MR spectroscopy have potential for predicting reponse to 5FU chemotherapy. © 1991 Academic Press, Inc.
Sequential 2D inflow venography: Initial clinical observations
Authors: Lanzer P. , Gross G. M. , Keller F. S. , Pohost G. M.
Published: March 2007

Sequential 2D inflow NMR (SDI) venography was employed to define venous anatomy and pathology in five healthy subjects and five patients, mean age 48 ± 7 years, with documented deep vein thrombosis. SDI images were graded independently by two observers on a scale of 1,2 nondiagnostic and 3,4 diagnostic categories. All iliac and femoropopliteal SDI venograms were diagnostic. In contrast, only one out of nine calf SDI venograms was diagnostic. SDI is a promising new method to assess the proximal peripheral venous system. Improved imaging strategy is needed to produce flow images of the calf veins. © 1991 Academic Press, Inc.
Quantitation of metabolites by 1H NMR
Authors: Pan J. W. , Hetherington H. P. , Hamm J. R. , Shulman R. G.
Published: March 2007

In this report we describe the three factors that need to be measured when quantitating an edited resonance relative to an internal standard using a surface coil. These factors are necessary by virtue of the water, fat suppressing, and localization schemes used in studying a 1H metabolite. First, use of semi‐selective pulses requires amplitude correction of the edited and reference resonances. Second, use of a single surface coil results in different sensitive volumes for different resonances due to the inhomogeneous B1 and therefore requires separate acquisition of the resonances. Third, editing pulses alter the sensitive volumes and this correction must be made internally by applying the same editing pulse to the reference resonance. A rationalization of this correction is given in terms of rotation operators. We apply these corrections to quantitate edited lactate relative to total creatine in a MnCl2‐doped phantom and find 91% rather than 145% of known concentration. In human skeletal muscle in vivo after exhaustive exercise, we measured the lactate after exercise and found it to be 27.2 mM in two experiments, in reasonable agreement with literature values for the given exercise protocol. © 1991 Academic Press, Inc.
Factors in myocardial “Perfusion” imaging with ultrafast MRI and Gd‐DTPA administration
Authors: Burstein Deborah , Taratuta Eleina , Manning Warren J.
Published: March 2007

Ultrafast magnetic resonance imaging (MRI) and first pass observation of an interstitial contrast agent are currently being used to study myocardial perfusion. Image intensity, however, is a function of several Parameters, inculding the delivery of the contrast agent to the intersitium (coronary flow rate and diffusion into the intersitium) and the relaxation properties of the tissue (contrast agent concentration, proton exchange rates, and relative intra‐and extracellular volume fractions). In this study, image intensity during gadopen tetate dimeglumine (Gd‐DTPA) adminstration with T1 weighted ultrafast MR imaging was assessed in an isolated heart preparation. With increasing Gd‐DTPA concentration the steady‐state myocardial image intensity increased but the time to reach steady state remained unchanged, resulting in an increased slope of image intensity change. A range of physiologic perfusion pressures (and resulting coronary flow rates) had insignificant effects on Gd‐DTPA in wash in or steady‐state image intensity, suggesting that diffusion of Gd‐DTPA into the interstitium is the rate limiting step in image intensity change with this preparation. Following global ischemia and reperfusion, transmural differences in the slope of image intensity change were apparent. However, the altered steady state image intensity (due to postichemic edema) makes interpretation of this finding difficult. The studies described here demonstrte that although Gd‐DTPA administration combined with ultrafast imaging may be a sensitive indicator of perfusion abnormalities factors other than perfusion will affect image intensity. Extensive studies will be required before image intensity with this protocol is fully understood. © 1991 Academic Press, Inc.
Spoiling of transverse magnetization in steady‐state sequences
Authors: Zur Y. , Wood M. L. , Neuringer L. J.
Published: March 2007

A detailed analysis is presented of a method to eliminate transverse magnetization prior to each rf excitation in pulse sequences with TR < T2. It is shown that artifact‐free images with high T1 contrast can be obtained only if a phase shift that is incremented during each TR interval is applied to the transverse magnetization. Computer simulations are used to show that when this phase increment is 117°, the steady‐state transverse magnetization prior to each rf pulse is nulled over a wide range of T1, T2, and rf tip angles, resulting in optimal T1, contrast. Such nulling of steady‐state transverse magnetization cannot be obtained by using large gradient pulses, or gradients of random or linearly incremented amplitude. Images of phantoms and human subjects confirm the theoretical predictions. © 1991 Academic Press, Inc.
From the relaxivity of Gd(DTPA)2− to everything else
Authors: Koenig Seymour H.
Published: March 2007

We resolve the observed magnetic field‐dependent relaxivity of Gd (DTPA)2− into inner and outer sphere contributions by comparison with theory. After noting that the outer sphere part, which contributes comparable to both 1/T1 and 1/T2, is identical to the “susceptibility” effect, we demonstrate the transition from the outer sphere relaxivity of small complexes, e. g. Gd(DTPA)2−, to that of large magnetic particulates, e. g., magnetite, used as T2 agents. This transition is expressed as a shift from a quantum to a classical mechanical description of relaxivity. We next show how to extrapolate the inner sphere contribution of Gd(DTPA)2− to similar small agents with greater structural symmetry, e. g., Gd(NOTA)−, by lengthening the electronic relaxation time and to ternary macromolecular complexes of small agents with protein by lengthening the rotational relaxation time. Finally, we indicate how relatively large lipid vesicles containing either small paramagnetic complexes or magnetized particulates may be considered analogs of Gd(DTPA)2−, with analogous inner and outer sphere contributions. © 1991 Academic Press, Inc.
Gd‐BOPTA/Dimeg: Experimental disease imaging
Authors: Cavagna Friedrich , Daprà Massimo , Maggioni Fabio , De Haën Christoph , Felder Ernst
Published: March 2007

The novel tissue‐specific contrast agent, Gd‐BOPTA/Dirmeg, was tested in MR imaging of experimental focal liver disease and of acute myocardial ischemia in rats. Directly implanted liver tumors and blood‐borne metastases were used as models for focal liver disease and occlusion of the lower anterior descending coronary artery as model for acute ischemia. The studies with implanted tumors, at a dose level of 250 μmol/kg, showed a very high (370%) and persistent (>2h) increase in the tumor‐liver contrast‐to‐noise ratio (CNR), owing to selective enhancement of normal liver parenchyma signal intensity. While all blood‐borne metastases showed a similar late CNR enhancement, some of them experienced early contrast loss due to transient signal intensity enhancement. In myocardial imaging. Gd‐BOPTA/Dimeg produced a signal intensity enhancement in normal myocardium and an injured area‐normal area CNR enhancement which were both much stronger and more presistent than those produced by Gd‐DTPA/Dimeg. © 1991 Academic Press, Inc.
Porphyrins as contrast media
Authors: Nelson James A. , Schmiedl Udo
Published: March 2007

The interest in tissue distribution of variously labeled or otherwise detectable natural and synthetic porphyrins and porphyrin derivatives dates back well over 60 years. Although a considerable interest in fluorescent turnor localization and therapy dominates the history of porphyrin biodistribution studies, many investigators have evaluated the diagnostic and therapeutic characteristics of porphyrins with radioactive, radiopaque, and paramagnetic qualities. In this paper, a review of the use of porphyrins as nuclear medicine, X‐ray, and NMR contrast agents is presented. © 1991 Academic Press, Inc.
Contrast agents for magnetic resonance spectroscopy: A method to obtain increased information in in vivo and in vitro spectroscopy
Authors: Swartz Harold M. , Chen Kai , Hu Huping , Hideg Kalman
Published: March 2007

The concept of contrast, which now is an integral part of many magnetic resonance imaging studies, can be extended successfully to magnetic resonance spectroscopy. It involves the use of paramagnetic molecules whose distribution is restricted in some manner, thereby causing differential effects on the NMR spectra. As an illustrative example, the effects of tipophilic nitroxide stable free radicals on the NMR spectra of serum and lipoproteins are shown. These nitroxides differentially broaden away components of the spectra due to the nuclei of methylene and methyl groups, which enables the usually obscured peaks of lactate to be observed fully. The concept can be applied to differential distribution of the contrast agent on the basis of solubility, charge, and/or compartmentalization. It can be used with any type of NMR spectroscopy and any type of paramagnetic contrast (broadening) agent. © 1991 Academic Press, Inc.
Quantitative Two‐Dimensional time Correlation Relaxometry
Authors: English A. E. , Whittall K. P. , Joy M. L. G. , Henkelman R. M.
Published: March 2007

An experimental and analytical method is presented for obtaining two‐dimensional NMR time correlation spectra of T1 and (T2 and T2) exponential relaxation in heterogeneous samples. The numerical algorithms used in this study do not bias the solution by any a priori assumptions as to the number of required components. The constraints used to overcome the ill‐posed and ill‐conditioned nature of this inverse problem are also described. With this method, the correlations of T1 (or T1) and T2 exponential components in systems of nonexchanging standards and rat muscle tissues are obtained. © 1991 Academic Press, Inc.
Quantification of myocardial blood flow and extracellular volumes using a bolus injection of Gd‐DTPA: Kinetic modeling in canine ischemic disease
Authors: Diesbourg Leo D. , Prato Frank S. , Wisenberg Gerald , Drost Dick J. , Marshall Tara P. , Carroll S. Edwin , O'Neill Blair
Published: March 2007

In order to clarify the relationship between coronary artery disease (including myocardial infarction) and image contrast in gadolinium diethylenetriaminepentaacetic acid (Gd‐DTPA‐enhanced MRI it was decided to model the myocardial tissue distribution and clearance of Gd‐DTPA using the modified Kety equation. Using a canine model, myocardial tissue Gd‐DTPA concentrations ([Gd‐DTPA]m) were measured 1 or 5 min after a bolus injection of Gd‐DTPA or immediately after the end of a constant infusion of Gd‐DTPA in a total of 35 dogs. It was found that within 5 min of a bolus injection [Gd‐DTPA]m is determined primarily by myocardial blood flow (MBF) and after about 10 min primarily by myocardial extracellular volumes (MECV). This study suggests that repeat, rapid (every 2–4 s) measurements of myocardial T1 relaxation rates following the bolus injection of Gd‐DTPA are required to calculate MBF (i.e., myocardial tissue perfusion) and MECV. © 1992 Academic Press, Inc.
Quantitative MRI studies for assessment of multiple sclerosis
Authors: Pannizzo F. , Stallmeyer M. J. B. , Friedman J. , Jennis R. J. , Zabriskie J. , Plank C. , Zimmerman R. , Whalen J. P. , Cahill P. T.
Published: March 2007

Although magnetic resonance imaging (MRI) is a valuable aid in the initial diagnosis of multiple sclerosis (MS), quantitatively MRI has been disappointing in staging and evaluating therapy protocols by means of serial examinations. In this study, image processing algorithms were developed for the global analysis of MR images of the cerebrum. Limited three‐dimensional segmentation was achieved through histogram analysis by these algorithms, which are essentially operator independent. The effects of coil response and tip angles, patient positioning, and interslice gap thicknesses were examined for 10 MS patients with repeated examinations for a total of 72 images. Effects of technique and instrumentation errors were approximately 6%, and agreement between two independent operators for measuring the total MR pixel sum from periventricular effusions and intense MS plaques was better than 97% with a standard deviation of 2.9%. © 1992 Academic Press, Inc.
Error in the calibration of the mgatp chemical‐shift limit: Effects on the determination of free magnesium by 31P NMR spectroscopy
Authors: Mosher Timothy J. , Williams Gerald D. , Doumen Chris , Lanoue Kathryn F. , Smith Michael B.
Published: March 2007

The measurement of free intracellular magnesium (Mg2+) using the 31P chemical shifts of ATP requires the use of appropriate calibration solutions to determine the chemical‐shift limits ΔATPαβ and ΔMgATPαβ. Solutions containing excess Mg2+ contain significant amounts of Mg2ATP and yield positive errors in the value of ΔMgATPαβ. For physiological applications this may overestimate free intracellular Mg2+ by as much as 300%. This error may be minimized if appropriate mole ratios of Mg2+/ATP are used to calibrate ΔMgATPαβ. © 1992 Academic Press, Inc.
Proton overhauser enhancements in human cardiac phosphorus NMR spectroscopy at 1.5 T
Authors: Bottomley Paul A. , Hardy Christopher J.
Published: March 2007

Narrowband irradiation of water protons with a surface coil yields significant nuclear Overhauser enhancement (nOe) of phosphocreatine (PCr) and some adenosine triphosphate (ATP) moieties in localized and unlocalized phosphorus (31P) NMR spectra from chest and heart muscle. In seven normal subjects at 1.5 T the nOe values were 0.6 ± 0.3, 0.6 ± 0.3, 0 ± 0.3, and 0.3 ± 0.2 for myocardial PCr, γ‐ATP, α‐ATP, and β‐ATP, respectively, not significantly different from those in chest muscle. Distortion of the measured PCr/ATP ratios due to differences in the nOe may require accurate correction to realize the full benefit of the effect in studies involving quantitative intergroup comparisons. © 1992 Academic Press, Inc.
Phosphorus‐31 magnetic resonance imaging of hydroxyapatite: A model for bone imaging
Authors: Ackerman Jerome L. , Raleigh Daniel P. , Glimcher Melvin J.
Published: March 2007

One‐dimensional 31P nuclear magnetic resonance images (projections) of syntheticcalcium hydroxyapatite, Ca10(OH)2(PO4)6, have been obtained for samples on the order of 0.5 to 1.0 cm in linear extent at 7.4 T magnetic field strength. Because of the solid state nature of these samples, short 31P spin‐spin relaxation times under 1 ms occur, necessitating echo times of 1 ms and phase‐encoding magnetic field gradient pukesshorter than 500 μs. Optimal projection quality and shortest acquisition times result from pulsedgradient phase‐encoding of the spatial dimension, using a compensating gradient pulse to cancel the distorting effects of gradient waveform transients. The exceedingly long 31P spin‐lattice relaxation times could lead to potentially intolerable image acquisition times; these have been reduced with a flipback pulse technique. In addition to holding great potential as a novel research tool in the study of biomineralization of those organisms containing calcium phosphate solid phases, these methods should be of general utility in the multinuclear imaging of a wide variety of solids of interest in biophysics and materials science.