bluuebunny/crossref_metadata_2025 huggingface dataset:
Three‐dimensional phase contrast angiography
Authors: Dumoulin C. L. , Souza S. P. , Walker M. F. , Wagle W.
Published: March 2007

Bipolar flow‐encoding gradients can be used in a three‐dimensional magnetic resonance imaging procedure to provide a noninvasive measure of in vivo blood flow. The resulting volume angiogram is a three‐dimensional data matrix which can be retrospectively analyzed and displayed in a variety of ways. This angiographic technique provides good suppression of signals arising from stationary tissue, thereby permitting the visualization of small vessels having relatively slow flow. This suppression is obtained by modulating the amplitude of the flow‐encoding gradient pulse to either cancel the stationary tissue signal or displace it relative to the flow signal in the volume image. © 1989 Academic Press, Inc.
Projection flow imaging by bolus tracking using stimulated echoes
Authors: Foo Thomas K. F. , Perman William H. , Poon Colin S. O. , Cusma Jack T. , Sandstrom John C.
Published: March 2007

Previous investigators have employed the concept of bolus tracking using either spin echoes or gradient echoes. In this paper we introduce two methods of bolus tracking using planar‐and volume‐selective stimulated echoes. The planar method employs a selective 90° rf pulse which tags all spins in a particular plane. At a time τ1, later, a nonselective 90° rf pulse is employed, followed after a time r2, by another nonselective rf pulse. Only spins which experience all three rf pulses form a stimulated echo at time τ1 after the third rf pulse. A balanced pair of flow‐compensated dephasing (crusher) gradients further ensures that the stimulated echo is due only to the effect of all three rf pulses while minimizing flow dephasing. The first part of this gradient pair is applied after the initial rf pulse in the first τ1 period to dephase the tagged spins. The second part of this gradient pair is applied after the third rf pulse to rephase the spins. Since the plane of the excited slice is orthogonal to the readout direction, flowing spins are imaged in an angiographic manner as they inove away from the excited slice. A modification to this basic sequence excites only a small volume. In this manner, the suppression of stationary spins is effected by volume‐selective excitation. In both the planar‐and the volume‐selective techniques, the excited spins undergo T1 and T2 relaxation during the τ1 period but only T1 relaxation in the τ2 period. In blood, where T1 is much greater than T2, keeping τ as short as possible minimizes signal loss due to T2 dephasing. These methods demonstrate increased sensitivity compared to similar bolus tracking methods using either spin echoes or gradient echoes. © 1989 Academic Press, Inc.
The effect of aging and storage conditions on excised tissues as monitored by longitudinal relaxation dispersion profiles
Authors: Fischer Helmut W. , Van Haverbeke Yves , Rinck Peter A. , Schmitz‐Feuerhake Inge , Muller Robert N.
Published: March 2007

Knowledge about the dependence of NMR parameters of excised tissues on time and storage conditions is important for correct interpretation of in vivo clinical results based upon in vitro measurements which in many cases are easier to perform. Literature data on this topic are scarce and sometimes contradictory. In this study, we investigated the change of the proton longitudinal relaxation rate (1/T1) of freshly excised rat tissues with storage conditions over a wide range of proton Larmor frequencies (0.01‐50 MHz). Special interest was paid to long‐term storage in the deep frozen state. After deep freezing of tissue samples on dry ice, no significant changes in 1/T1 over the whole frequency range could be observed for brain tissue, whereas for muscle and liver tissue characteristic alterations were detected. We conclude that for normal brain tissue this storage procedure is suitable for the prediction of in vivo 1/T1 results from in vitro studies. © 1989 Academic Press, Inc.
Spectral editing techniques for 31p NMR spectroscopy of blood
Authors: Jayasundar Rama , Norwood Timothy J. , Hall Laurance D. , Bleehen Norman M.
Published: March 2007

Although the measurement of the pH of biological systems using the 31P NMR response of inorganic phosphate is well known, sometimes in blood absolute determination of the intensity and position ofthe Pi resonance is precluded by overlap from the doublet resonance of 2,3‐diphosphoglycerate. Three techniques which overcome this problem by eliminating the doublet are described and their sensitivity to the experimental parameters is assessed. © 1989 Academic Press, Inc.
Three‐dimensional time‐of‐flight magnetic resonance angiography using spin saturation
Authors: Dumoulin C. L. , Cline H. E. , Souza S. P. , Wagle W. A. , Walker M. F.
Published: March 2007

A three‐dimensional Fourier transform magnetic resonance imaging technique is presented. This procedure can be used to selectively detect flowing material such as blood in arteries and veins. Since flow is detected in a manner in which velocity‐induced phase shifts are compensated, signal loss arising from complex flow and turbulence is minimized. The flow image is sensitive to all velocity components of flow. Applications this technique are limited, however, to relatively straight vessels having appreciable flow. Examples of application of this technique to healthy and diseased carotid arteries shown. © 1989 Academic Press, Inc.
Assessment of demyelination, edema, and gliosis by in vivo determination of T1 and T2 in the brain of patients with acute attack of multiple sclerosis
Authors: Larsson H. B. W. , Frederiksen J. , Petersen J. , Nordenbo A. , Zeeberg I. , Henriksen O. , Olesen J.
Published: March 2007

This study intended to investigate the possibility of magnetic resonance (MR) to characterize the acute plaque due to multiple sclerosis (MS). To obtain information, in vivo measurements of relaxation processes were performed in 10 patients with known acute MS plaques, using a whole‐body superconductive MR‐scanner, operating at 1.5 T. The measurements were repeated several times, from onset of the disease and during remission by use of six‐point partial saturation inversion recovery and 32‐echo multiple spin‐echo sequences, giving TI and T2, respectively. We also focused on the issue, whether T1 and T2 relaxation processes in fact were monoexponential. The results of the first T1 and T2 measurements of the acute plaques were not clearly different from T1 and T2 of presumably chronic plaques obtained in a group of chronic MS patients previously (H. B. W. Larsson, J. Frederiksen, L. Kjär, O. Hendriksen, and J. Olesen, Magn. Reson. Med. 7, 43 ( 1988)). In some of the acute plaques a slight initial increase in TI and T2 was seen, when the measurement was repeated in about 10 days. Thereafter T1 decreased slowly in all but one patient as a function of days. In all cases the T1 relaxation process followed a monoexponential course. The T2 relaxation process was a monoexponential function in the acute plaques, when measured within 20 days from onset of disease. After an average of 78 days, however, the T2 relaxation process clearly became biexponential in all but two patients. Later some of the relaxation curves changed back toward monoexponentiality. Thus, the study shows that it is possible to detect significant changes in MR parameters during the evolution of the disease, and these changes are discussed in relation to knowledge of pathoanatomical events in MS.
A dual‐tuned probe and multiband receiver front end for X‐nucleus spectroscopy with proton scout imaging in vivo
Authors: Tropp James , Sugiura Satoshi
Published: March 2007

A dual‐tuned volume coil probe and a novel multituned receiver front end are de‐ scribed, for spectroscopy in vivo of X nuclei with scout imaging of protons. Detailed circuit information is given for the probe, diplexer, receiver protection switch, and preamplifier.
Spin locking for magnetic resonance imaging with application to human breast
Authors: Santyr Giles E. , Henkelman R. Mark , Bronskill Michael J.
Published: March 2007

The dependence of rotating frame spin‐lattice relaxation, T1ρ, on locking field frequency, f1 was measured for phantom materials and human breast tissues. These data were used to predict the relative signal strengths obtainable in a spin‐locking imaging sequence. This imaging sequence was implemented on a 0.15‐T imaging system and measurements of phantom and tissue signal strength for various imaging parameters agreed with predicted signal strengths. Compared to T1 and T2, T1ρ appears to have unique capability to distinguish tumor from normal fat and fibrous breast tissues. The applications of T1ρ, to tissue characterization and imaging at high static field strengths are discussed. © 1989 Academic Press, Inc.
The influence of flow and motion in MRI of diffusion using a modified CE‐FAST sequence
Authors: Merboldt Klaus‐Dietmar , Hänicke Wolfgang , Gyngell Michael L. , Frahm Jens , Bruhn Harald
Published: March 2007

Severe motion and flow artifacts are a problem in MRI of diffusion in vivo due to the application of strong magnetic field gradients. Here it is shown that image artifacts can be removed by using a modified fast‐scan MRI sequence (CE‐FAST) in conjunction with averaging of diffusion‐weighted images. In phantom studies slow (coherent) flow (<1 mm s‐1) in the presence of strong diffusion gradients is shown to cause signal losses in diffusion‐weighted images that depend on the relative orientations of the flow direction and the diffusion gradient. On the other hand, pulsatile motions of macroscopic dimensions (e.g. 1 mm, 1 Hz, in‐plane) lead to smearing and ghosting of signal intensities along the phase‐encoding direction of the images. In both phantoms and rabbit brains in vivo motion artifacts were found to be reducible by averaging 8‐16 images. Unfortunately. the resulting image contrast no longer represents a “true” diffusion contrast but is affected by additional signal losses due to motion averaging. All experiments were performed on a 40‐cm‐borc 2.35‐T Bruker Medspee system. © 1989 Academic Press, Inc.
Design of a 13c {1h} rf probe for monitoring the in vivo metabolism of [1‐13c] glucose in primate brain
Authors: Hammer B. E. , Sacks W. , Bigler R. E. , Hennessy M. J. , Sacks S. , Fleischer A. , Zanzonico P. B
Published: March 2007

The design of an RF probe suitable for obtaining proton‐decoupled 13C spectra from a subhuman primate brain is described. Two orthogonal saddle coils, one tuned to the resonant frequency of 13C and the other to the resonant frequency of 1H, were used to monitor the in vivo metabolism of [1‐13C] glucose in rhesus monkey brain at 2.1 T. Difference spectra showed the appearance of 13C‐enriched glutamate and glutamine 30 to 40 min after a bolus injection of [ 1‐ 13C] glucose.
Quantitation of abdominal aortic wall dynamics in man by gradient echo nmr imaging
Authors: Lanzer P. , McKibbin W. , Bohning D. , Pohost G.
Published: March 2007

To determine the magnitude of the pulsatile (P), translational (T), and composite (C) aortic wall motion and to predict its effect on endothelial edge definition in vascular NMR imaging, 10 healthy volunteers, mean age 42.5 ± 13 years, were studied. In each subject a series of transverse high‐resolution (0.6 × 0.6 mm; TR = 40 ms) gradient echo images spanning the cardiac cycle were generated and the aortic wall motion dynamics were analyzed. The group data expressed as a mean ± SD in millimeters, P = 0.87 ± 0.34 (mm), T = 2.71 ± 1.07, and C = 3.39 51.081, indicate that a significant displacement of the endothelial aortic edge (up to 5.6 pixels in high‐resolution imaging) occurs during the cardiac cycle in normotensive healthy volunteers. The displacement of this magnitude suggests that cardiac cycle synchronized aortic NMR imaging should be used to improve endothelial edge definition. © 1990 Academic Press, Inc.
A simple calf muscle ergometer for use in a standard whole‐body mr scanner
Authors: Quistorff BjøRn , Nielsen Steen , Thomsen Carsten , Jensen Karl Erik , Henriksen Ole
Published: March 2007

A calf muscle ergometer, designed for use in a standard whole‐body MR scanner, is described. The instrument allows isotonic or isometric calf muscle exercise over a continuous range of work loads from 0 to individual maximum work output. Work output may be recorded on a strip chart recorder. A sound encoding provides an effective guidance for the subject tested to accurately reproduce his performance in each contraction cycle at a given work load. The FID recording may be triggered from the ergometer at any point during the contraction cycle. Nonmetal materials are used for the instrument construction in order to eliminate potentially disturbing eddy currents. The force resistance of the ergometer is obtained by a combined hydraulic‐pneumatic system, which is loaded by coupling to an outside source of compressed air equipped with a suitable pressure regulator. When varying the time of data sampling within a repeated 6‐s contraction cycle it was found that the recorded Pi/PCr ratio remained essentially constant at low and moderate work loads. However, at work loads at or above 70% of individual Vmax a pronounced dependence of the time of sampling with the contraction cycle was observed.
Time‐of‐flight MR angiography
Authors: Nishimura Dwight G.
Published: March 2007

Time‐of‐flight effects depend on the displacement of blood with respect to a region of excitation. When combined with static material suppression and projection imaging, time‐of‐flight effects provide a flexible means of flow sensitization for magnetic resonance (MR) angiography. Bolus tracking, flow enhancement by spin replacement, and selective tagging are three classes of methods being pursued for MR angiography. © 1990 Academic Press, Inc.
Displays for MR angiography
Authors: Laub G.
Published: March 2007

There are several MR imaging procedures that result in three‐dimensional data of moving spins. One way to evaluate these data is a sequential observation of 2D slices. A more common and efficient approach is to retrospectively calculate two‐dimensional projection images at different angles representing individual views of the tomographic volume. The display of different views from the same data set will allow a realistic visualization of the blood vessel anatomy. © 1990 Academic Press, Inc.
Magnetic resonance imaging of perfusion
Authors: Le Bihan D.
Published: March 2007

Recent developments have shown that diffusion and blood microcirculation (perfusion) could be imaged and measured noninvasively by MRI. The purpose of this presentation is to overview the different approaches that use B0 field gradients to monitor diffusion / perfusion. The principles of these different methods are discussed together with their limitations and their potential applications. © 1990 Academic Press, Inc.
Peripheral vascular and abdominal applications of MR flow imaging techniques
Authors: Steinberg Fred L. , Yucel E. Kent , Dumoulin Charles L. , Souza Steven P.
Published: March 2007

Many MR flow imaging techniques that have been successfully applied in the carotid arteries and intracranial circulation have been tested in the peripheral and abdominal vasculature. The results have been variable. The lack of success can be attributed to different imaging requirements as well as different patterns of blood flow. These requirements include a large field of view, sensitivity to a wide range of blood flow velocities and complex flow directions, and suppression of overlapping vascular structures and stationary tissue. We have designed strategies using phase contrast MR angiography (MRA) for imaging the arteries and veins of the lower extremity and the abdominal vasculature in normal subjects. This strategy takes advantage of the pulsatile flow pattern present in normal arteries. Overlapping blood flow and stationary tissue were suppressed by a combination of spatial presaturation, optimization of the amplitude and duration of the velocity sensitive gradients, and postprocessing techniques. © 1990 Academic Press, Inc.
Single‐shot localized echo‐planar imaging (STEAM‐EPI) at 4.7 tesla
Authors: Turner Robert , von Kienlin Markus , Moonen Chrit T. W. , van Zijl Peter C. M.
Published: March 2007

The resolution and homogeneity limitations of echo‐planar imaging (EPI) are overcome by zoom imaging of an easily shimmed localized volume. Use of the stimulated echo enables single‐shot localization. In vivo 0.5‐mm resolution EPI images of selected regions of a cat brain at 4.7 T are presented. © 1990 Academic Press, Inc.
Identification of tumor hemorrhage in an animal model using spin echoes and gradient echoes
Authors: Van Bruggen N. , Syha J. , Busza A. L. , King M. D. , Stamp G. W. H. , Williams S. R. , Gadian D. G.
Published: March 2007

We report here how magnetic resonance imaging can be used to gain definitive information about tissue pathology by the combined use of spin‐echo and gradient‐echo sequences. We also show how artifacts arising from respiratory motion can be eliminated by using a simple respiratory gating technique. © 1990 Academic Press, Inc.
In vivo nuclear overhauser effect in 31P‐ {1H} double‐resonance experiments in a 1.5‐T whole‐body MR system
Authors: Bachert‐Baumann P. , Ermark F. , Zabel H.‐J. , Sauter R. , Semmler W. , Lorenz W. J.
Published: March 2007

In 31P‐ {1H} MR experiments of humans in a 1.5‐T whole‐body system, signal intensity enhancements of 1P resonances of up to 68 ± 4% (for phosphocreatine of the calf muscle) have been observed upon irradiation at proton frequency. This observation is explained as a nuclear Overhauser effect due to the dipolar coupling between 1H and 1P spins. © 1990 Academic Press, Inc.
In Vivo NMR spectroscopy of lithium‐7 in humans
Authors: Komoroski R. A. , Newton J. E. O. , Walker E. , Cardwell D. , Jagannathan N. R. , Ramaprasad S. , Sprig J.
Published: March 2007

The pharmacokinetics of lithium uptake was measured by 7Li NMR spectroscopy at 24.83 MHz in vivo in the brain and muscle of a normal subject and a patient suffering from bipolar affective disorder, using a modified General Electric Signa clinical magnetic resonance imaging system. Comparison was made to standard phantoms to estimate Li concentrations. The levels of Li in brain and muscle were similar, were typically less than the level in serum, and generally tracked the level in serum. The Li level at steady state in the brain of a patient suffering from schizoaffective disorder was measured over a 7‐month period. Substantial variation was seen, which showed some correlation with serum level. Serum level peaked about 2 h after a single 300‐mg dose at steady state, and muscle level, immediately thereafter. Brain level peaked considerably later at 4 h. Localized in vivo 7Li NMR spectroscopy was demonstrated by acquisition of a 125‐cm3 DRESS slice from the occipital region in less than 7 min. © 1990 Academic Press, Inc.
Transmural high energy phosphate distribution and response to alterations in workload in the normal canine myocardium as studied with spatially localized 31P NMR spectroscopy
Authors: Robitaille P‐M. , Merkle H. , Lew B. , Path G. , Hendrich K. , Lindstrom P. , From A. H. L. , Garwood M. , Bache R. J. , Uǧurbil K.
Published: March 2007

Spatially localized phosphorus‐31 nuclear magnetic resonance (31P NMR) spectroscopy has been applied to the study of the normal canine myocardium to measure the relative content of high energy phosphates across the left ventricular wall. Transmural NMR data were acquired in five voxels spanning the wall of the left ventricle using the FLAX‐ISIS technique. The validity of the FLAX‐ISIS approach in acquiring localized spectra for transmural studies and in providing quantitative information from the localized spectra was examined rigorously by studies involving phantoms, intact rats, and the canine myocardium in vivo. The results indicated that (1) this technique yields spatially resolved spectra with partial overlap between adjacent voxels and virtually no overlap between every other voxel; (2) in the canine heart, signals from subepicardium, midwall, and sub‐endocardium can be detected separately without cross contamination; and (3) relative metabolite contents within a voxel and among voxels can be quantitated. Transmural 31P NMR spectra were acquired with cardiac gating on 29 separate animals either at early systole or late diastole, and at three different workloads with the heart rate peak systolic pressure product (RPP) increasing from 6000 mmHg/min to 35,000 mmHg/min. The data revealed that in the normal canine myocardium, the creatine phosphate (CP) content and the CP/ATP ratio was significantly lower in the subendocardium than in the subepicardium. ATP levels were transmurally constant. Both the CP content and the CP/ATP ratio measured for each voxel remained unaltered in relation to either the phase of the cardiac cycle or ∼ fourfold increase in workload. Free ADP levels calculated for each voxel showed that ADP was relatively higher in the subendocardium than the subepicardium, and in all transmural layers was higher than its apparent Km for oxidative phosphorylation. In this domain changes in ADP content with workload and MVO2 are not expected and were not observed. © 1990 Academic Press, Inc.
An ESR study of pathologic red blood cell membranes (RBCM)
Authors: Perussi Janice R. , Costa Fernando F. , Baffa Oswaldo , Zago Marco A. , Tintoand Maria H. , Tabak Marcel
Published: March 2007

A comparative study of red blood cell membranes from normal subjects and β‐thalassemia and sickle cell anemia patients was performed by spin labeling at the lipidic and protein phase. The results show that the quantity of bound spin label is the same for sickle, thalassemic, and normal membranes. The data from 5‐doxyl stearic acid suggest an increase in fluidity for the thalassemic membrane. © 1990 Academic Press, Inc.
MR fourier transform arteriography using spectral decomposition
Authors: Cho Z. H. , Jung K. J. , Ro Y. M.
Published: March 2007

Reliable separation of arteries from other stationary tissues is accomplished through spectral decomposition by exploiting the pulsatile nature of the blood flow in the arteries. Fourier transformation of a series of projection images in the temporal direction along the cardiac cycle results in spectral images where the arteries are a part of the harmonic component images while stationary tissues and veins are represented as a dc component image. From the magnitude of the spectral images an arteriogram can be obtained by summation of the harmonic component images excluding the dc component image. This principle is applied to Fourier imaging in a cine mode data acquisition as well as line scan imaging. Since there is no need for the encoding of the flow‐sensitive gradient, this technique is free from eddy current artifacts which have been one of the major obstacles to projection angiography using the flow‐encoding gradient. © 1990 Academic Press, Inc.
Generalized MR interferography
Authors: Hennig J.
Published: March 2007

Generalized MR interferography allows the measurement of parameters which affect the phase of the MR signal. Interference is generated by the simultaneous generation of two echoes in one excitation cycle. Local variations of the signal phase are transformed into displacement of the stripe pattern generated by interference. A number of possible experiments based on this principle are presented. The resulting interferographic images allow the fast determination of parameters such as field inhomogeneity, susceptibility, flow, and motion. © 1990 Academic Press, Inc.
Motion‐insensitive, steady‐state free precession imaging
Authors: Zur Y. , Wood M. L. , Neuringer L. J.
Published: March 2007

Steady‐state free precession (SSFP) pulse sequences employing gradient reversal echoes and short repetition time (TR) between successive rf excitation pulses offer high signal‐to‐noise ratio per unit time. However, SSFP sequences are very sensitive to motion. A new SSFP method is presented which avoids the image artifacts and loss of signal intensity due to motion. The pulse sequence is designed so that the time integral of each of the three gradients is zero over each TR time interval. The signal then consists of numerous echoes which are superimposed. These echoes are isolated by combining the data from N different scans. In each scan a specific phase shift is added during every TR interval. Each of these N isolated echoes produces a motion‐insensitive, artifact‐free image. Because all the echoes are sampled simultaneously, the signal‐to‐noise ratio per unit time in this SSFP method is higher than in existing SSFP techniques which sample only one echo at a time. The new method was implemented and used to produce both two‐ and three‐dimensional images of the head and cervical spin of a human patient. In these images the high signal intensity of cerebrospinal fluid is preserved regardless of its motion. Further work is required to evaluate the imaging parameters (TR, TE, rf tip angle) so as to give optimal tissue contrast for the various echoes. © 1990 Academic Press, Inc.
Visualization of altered myocardial lipids by 1H NMR chemical‐shift imaging following ischemic insult
Authors: Bouchard Alain , Doyle Mark , Wolkowicz Paul E. , Wilson Randall , Evanochko William T. , Pohost Gerald M.
Published: March 2007

Acute myocardial infarction is associated with an accumulation of lipids. Spectroscopic and chemical‐shift imaging strategies which can depict the spatial distribution of these chemical species are evolving. The present study was undertaken to test whether the Dixon method could detect spatially lipids known to accumulate in myocardium after an ischemic insult. Seven dogs underwent a 24‐h coronary artery occlusion (LAD = 4, Cx = 3). Post mortem, hearts were removed and imaged ex vivo. Myocardial samples were also evaluated by high‐resolution 1H NMR spectroscopy. Lipid images revealed regions of increased signal intensity, in the regions corresponding to the myocardial infarction, particularly in the periphery of the infarction. An increase in mobile lipids was observed by 1H NMR spectroscopy of myocardial samples with moderately reduced blood flow and corresponding to regions with increased signal intensity on the lipid image. This study shows that chemical‐shift imaging may be useful for detecting alterations in myocardial lipid levels following an ischemic insult. © 1991 Academic Press, Inc.
Acute Myocardial Infarction: Comparison of T2‐Weighted and T1‐Weighted Gadolinium‐DTPA Enhanced MR Imaging
Authors: Matheijssen Niels A. A. , de Roos Albert , Van Wall Ernst E. Der , Doornbos Joost , Van Ijkman Paul R. M. D , Bruschke Albert V. G. , van voorthuisen Ad E.
Published: March 2007

Magnetic resonance images were obtained from 32 patients with acute myocardial infarction, using a four‐echo technique (echo time (TE) = 30, 60, 90, and 120 ms) pre‐gadolinium(Gd)‐DTPA injection and a TE = 30 ms sequence pre‐ and post‐Gd‐DTPA. Intensity ratios of infarcted and normal myocardium were calculated, as were contrast‐to‐noise and signal‐to‐noise ratios. The four intensity ratios pre‐Gd‐DTPA were 1.20 ±0.15, 1.42 ± 0.22, 1.78 ± 0.38, and 1.99 ± 0.60 for TE = 30, 60, 90, and 120 ms, respectively, and 1.42 ± 0.19 post‐Gd‐DTPA (p = NS for post‐Gd‐DTPA vs TE = 60, p = 0.007 for TE = 90 vs TE = 120, p < 0.0001 for all other comparisons). The four contrast‐to‐noise ratios pre‐Gd‐DTPA were 1.69 ± 0.97, 2.69 ± 1.13, 3.17 ± 1.15, and 2.90 ± 1.09 for TE = 30, 60, 90, and 120 ms, respectively, and 2.71 ± 1.26 post‐Gd‐DTPA (p = NS for post‐Gd‐DTPA vs TE = 60, 90, and 120, p = NS for TE = 120 vs TE = 60 and 90, p< 0.01 for all other comparisons). The four signal‐to‐noise ratios pre‐Gd‐DTPA were 8.67 ± 1.47, 6.52 ± 0.76, 5.20 ± 0.64, 4.17 ± 0.53 for TE = 30, 60, 90, and 120 ms, respectively, and 9.17 ± 1.92 post‐Gd‐DTPA (p = 0.03 for post‐Gd‐DTPA vs TE = 30, p < 0.0001 for all other comparisons). In conclusion, the detectabilities of acute myocardial infarction were similar at TE = 60 ms and at Gd‐DTPA enhanced short‐TE MR imaging. However, image quality proved to be superior using the Gd‐DTPA enhanced short‐TE technique. © 1991 Academic Press, Inc.
Multiple echo SSFP sequences
Authors: Mizumoto Chris T. , Yoshitome Eiji
Published: March 2007

We report a new type of SSFP imaging sequences for acquiring higher‐order echoes. Spins excited during a cycle have, in a sense, a phase memory such that they can be refocused several cycles down the line, and since the spins are pulsed under a steady‐state condition, the resulting echoes have very complicated T1 and T2 dependencies. A steady‐state equation, which describes the T1 and T2 dependencies for the higher‐order echoes, is presented, and the intensity of each echo is calculated and compared with the experimental results. Although the signal intensity of the higher‐order echoes are weaker than the FID or the CE‐FAST echo, these echoes may be used to obtain images with different contrast dependencies previously unobtainable with either of the two signals. © 1991 Academic Press. Inc.
A progressive gradient moment nulling design technique
Authors: Pipe James G. , Chenevert Thomas L.
Published: March 2007

A method is presented for designing motion‐compensated gradients in a progressive manner. The method is easily applicable to many types of waveforms, and can compensate for any order of motion. It can be implemented graphically or numerically. Underlying theory and examples of its application are provided. © 1991 Academic Press, Inc.
MR angiography without subtraction
Authors: Zur Y. , Zou X. , Neuringer L. J.
Published: March 2007

A new NMR method for producing angiograms with strong suppression of the static spin signal and without the need for subtraction is described and demonstrated. A velocity‐selective pulse sequence was implemented whereby the magnetization of all stationary spins is driven to the —z axis and is not detected, while maximizing the signal intensity of the moving spins. A theory of the method is presented and gives good agreement with experimental results obtained on a flow phantom. It is shown theoretically and experimentally that high‐quality velocity‐independent angiograms of the head and neck can be obtained with strong suppression of static spin signal when TR ∼ T1. The method can be extended to produce three‐dimensional angiograms. © 1991 Academic Press, Inc.
19F NMR imaging of cerebral blood flow
Authors: Branch Craig A. , Helpern J. A. , Ewing James R. , Welch K. M. A.
Published: March 2007

Techniques for the quantitative imaging assessment of cerebral blood flow are presented in a cat using 19F NMR imaging of trifluoromethane. The input function of the indicator was acquired noninvasively, while its uptake and clearance were followed in 2‐cc volume voxels from images acquired at 67 sintervals. A single compartment model yielded normal cerebral blood flow estimates. © 1991 Academic Press, Inc.
Multiexponential proton relaxation in model cellular systems
Authors: Menon R. S. , Rusinko M. S. , Allen P. S.
Published: March 2007

Water proton relaxation measurements obtained from model cellular systems composed of red blood cell (RBC) ghosts are presented. The purpose of the investigation was to evaluate hypotheses concerning the possible sources of multiple exponential components in similar relaxation measurements made on tissue. Both laboratory frame transverse and longitudinal relaxation rates, as well as rotating frame relaxation rates, were measured in preparations of RBC ghosts and “extracellular fluid” that were, (a) uniformly mixed or (b) compartmentalized by layering, as the concentration of serum albumin was varied in the “extracellular fluid.” The data show that although transmembrane exchange is too fast to give rise to multiexponential relaxation, multiple components can result from compartmentalization at the level of the cellular organization and do not necessarily require different tissue types. In addition, the data clearly demonstrate the importance of protein adsorption to cellular membranes as a determinant of the concentration of freely mobile solute protein molecules in tissue fluids. © 1991 Academic Press, Inc.
magnetic resonance imaging of lipid deposits in human atheroma via a stimulated‐echo diffusion‐weighted technique
Authors: Altbach Maria I. , Mattingly Mark A. , Brown Michael F. , Gmitro Arthur F.
Published: March 2007

NMR images of subintimal lipid deposits within the vessel walls of atherosclerotic human aortas were obtained at 37 and 27°C at 4.7 T. A combination of a stimulated‐echo and pulsed‐field gradients was used for suppressing the mobile tissue water relative to the less mobile tissue lipids. At 27°C there was also a substantial reduction of the subintimal lipid signal intensity, which is consistent with the characteristic phase transition of cholesteryl esters in human atheroma. These results represent the first direct detection of lipid deposits in nonprotruding atherosclerotic lesions with NMR imaging. © 1991 Academic Press, Inc.
GRASE (Gradient‐and Spin‐Echo) imaging: A novel fast MRI technique
Authors: Oshio Koichi , Feinberg David A.
Published: March 2007

A fast multi‐section MR imaging technique is described. Gradient‐ and spin‐echo (GRASE) imaging utilizes the speed advantages of gradient refocusing while overcoming the image artifacts arising from static field inhomogeneity and chemical shift. Image contrast is determined by the T2 contrast in the Hahn spin echoes. A novel k‐space trajectory temporally modulates signals and demodulates artifacts. © 1991 Academic Press, Inc.
The magnetic field dependence of proton spin relaxation in tissues
Authors: Bryant Robert G. , Mendelson Daniel Ari , Lester Cathy Coolbaugh
Published: March 2007

The magnetic field dependence of water‐proton relaxation is reported for a simple protein solution, a cross‐linked protein solution, and a series of rat tissues, fresh, dried and rehydrated. The shape of the magnetic field dependence associated with water proton relaxation in tissues is accounted for by magnetic dipole‐dipole interactions between the mobile water spins and the immobile spin populations of the nonrotating components of the tissue coupling the behavior of the immobilized spin system to that of the mobile water spin system. The effect of this coupling is to impart the field dependence of the relaxation associated with the immobilized spin population to that of the mobile water spins that are observed in most relaxation and imaging experiments. © 1991 Academic Press, Inc.
High‐resolution 1H NMR imaging of regional ischemia in the isolated perfused rabbit heart at 4.7 T
Authors: Chatham John C. , Ackerman Stacey , Blackband Stephen J.
Published: March 2007

High‐resolution 1H NMR images of the isolated perfused rabbit heart were recorded before and after the induction of regional ischemia while the heart was arrested. On T2‐weighted images the ischemic region appeared darker than the surrounding tissue and a 28% reduction in T2 was measured from the images. Infusion of an NMR contrast agent demonstrated that the hypointense region on the T2‐weighted image was from the ischemic region, which was further confirmed by histological analysis of the heart. It is proposed that the decreased T2 in the ischemic region may be a consequence of changes in water compartmentalization. It is possible that these changes may be used to follow the evolution of tissue injury during ischemia, and therefore provide information regarding the transition between reversible to irreversible injury in the isolated perfused heart. © 1991 Academic Press, Inc.
Transverse relaxivity of particulate MRI contrast media: From theories to experiments
Authors: Muller Robert N. , Gillis Pierre , Moiny Francis , Roch Alain
Published: March 2007

Computer simulations and experimental approach have been used to characterize the properties of particulate MRI contrast agents with special attention paid to the influence of particle size. Up to approximately 50 nm, an increase of the particle diameter leads to a strong enhancement of the transverse magnetization decay rate. For larger grains or aggregates, the decay rate measured without spin‐echo formation reaches a plateau. When observed through a spin‐echo sequence, the transverse magnetization decay rate becomes slower on increasing the particle size or on shortening the echo time. For these large particles, multiexponential decay rates are observed. Definition and measurement of relaxivity in such systems is discussed. © 1991 Academic Press, Inc.
A new lipophilic gadolinium chelate as a tissue‐specific contrast medium for MRI
Authors: Weinmann H.‐J. , Schuhmann‐Giampieri G. , Schmitt‐Willich H. , Vogler H. , Frenzel T. , Gries H.
Published: March 2007

Gd‐Ethoxybenzyl‐DTPA (Gd‐EOB‐DTPA) is a highly water‐soluble paramagnetic contrast agent. Due to its protein binding of about 10% and its lipophilic residue, Gd‐EOB‐DTPA exhibits both renal (30% of the dose) and hepatobiliary (70%) excretion in rats. Despite its lipohilic character, the compound displays a low toxicity (LD50 = 7.5 mmol/kg). T1‐relaxivity of 5.3 liters mmol−1 s−1 in water, 8.7 liters mmol−1 s−1 in plasma, and 16.9 liters mmol−1 s−1 in rat liver together with the hepatocellular uptake explain the liverspecific contrast enhancement of Gd‐EOB‐DTPA. The diagnostic dose is considerably lower than the amount of Magnevist used in abdominal imaging. The preclinical studies suggest its clinical role as being a hepatobiliary contrast agent for MRI. © 1991 Academic Press, Inc.
A new macrocyclic MRI contrast agent: Gd MCTA complex
Authors: Schaefer Michel , Meyer Dominique , Beaute Sylvie , Doucet Didier
Published: March 2007

A new macrocyclic complex Gd‐MCTA has been synthesized which exhibits a higher LD 50 compared to Gd‐DOTA. These two complexes show comparable NMRD profiles. © 1991 Academic Press, Inc.
Clinical experience with contrast enhanced echo‐planar imaging of the brain
Authors: Worthington B. S. , Bullock P. , Stehlings M. , Gowlnad P. , Firth J. L. , Mansfield P.
Published: March 2007

The overall effects of intravenous Gd‐DTPA on tissue signal in intracranial tumors are complex depending on dose, time of administration, pulse sequence, and tissue structure. Ultrahigh speed EPI permits the kinetics of tissue enhancement in intracranial tumors to be studied during the “wash‐in” equilibrium and “wash‐out” phases. Ongoing studies employing dynamic scanning have shown it to be a valuble adjunct to a morphological study of tumors, providing an assessment of vascularity which is important in planning resction; and demonstrating areas with maximal breakdown of the blood‐brain barrier which are most suitable for stereotactic biopsy. There are grounds for anticipating that the alalysis of the temporal profil of enhancement may allow discrimination between different tumor types and provide information on factors which relate to the malignant potential of a single type. © 1991 Academic Press, Inc.
Susceptibility contrast imaging of cerebral blood volume: Human experience
Authors: Rosen B. R. , Belliveau J. W. , Aronen H. J. , Kennedy D. , Buchbinder B. R. , Fischman A. , Gruber M. , Glas J. , Weisskoff R. M. , Cohen M. S. , Hochberg F. H. , Brady T. J.
Published: March 2007

Magnetic resonance (MR) can offer a unique window on the structure/function relationships in the brain, by utilizing the established link between tissue function, metabolism, and hemodynamics. This report focuses on recent applications of MR‐based crebral blood volume (CBV) imaging in humans. Our methodology uses high‐speed “single‐shot” or echo planar imaging techniques, which provide the necessary temporal resolution for maping the rapid cerebral transit of contrast agents. These MR CBV mapping techniques have been used to study normal human brain task activation and in the clinical study of patients with brain tumors. In the latter, positron emission tomography imaging was used for functional metabolic and CBV correlation. Susceptibility contrast CBV imaging should allow us to improve our understanding of the relationship between the detailed physiology and morphology of the microvascular bed and functional attributes of the brain. These techniques can be applied to understanding fundamental questions of cognitive neuroscience and can aid in improving diagnostic sensitivity and specificity in various neuropathologies. © 1991 Academic Press, Inc.
Liposomes as MR contrast agents: Pros and cons
Authors: Unger Evan , Shen De Kang , Wu Guanli , Fritz Thomas
Published: March 2007

Liposomes are generally thought of as being useful for entrapping drugs within their internal aqueous space. When used with MR contrast agents, this has the drawback that water flux across the membrance bilayer is limiting to contrast enhancement. This can be partially overcome by making the liposomes very small, such that surface area is relatively great compared to internal volume, thereby facilitating water exchange. Alternatively the membranes can be designed to be permeable to water but this may render the vesicles unstable in serum. Another approach is to incorporate the contrast agents into the lipid bilayer. By designing novel complexes of manganese with the ligands incorporated onto dual acyl chains, we have achieved R1 and R2 values of over 20/mmol sec−1 or more than five times higher than Gd‐DTPA. Hepatic metastasis detection is significantly improved in rats at doses of only 10 μmol/kg manganese. Membrane‐bound manganese complexes function as highly effective liver imaging agents and merit further study for development as agents to undergo human clinical trials. © 1991 Academic Press, Inc.
Hypercarbia‐induced changes in cerebral blood volume in the cat: A 1H MRI and intravascular contrast agent study
Authors: Moseley Michael E. , Chew Wil M. , White David L. , Kucharczyk John , Litt Lawrence , Derugin Nikita , Dupon Jean , Brasch Robert C. , Norman David
Published: March 2007

Cerebral blood volume changes with arterial carbon dioxide were monitored by proton T1‐weighted MR images following administration of the intravascular contrast agent Gd‐DTPA labeled with human serum albumin. Without MR contrast, no significant image intensity changes were observed with PaCO2. Following contrast, regional brain image intensities increased significantly over control (0% inspired CO2) in cortical gray, white, and basal ganglia regions with increasing PaCO2 and returned to control intensities upon return to 0% inspired CO2. Imaging of through‐plane and in‐plane phantoms was performed to assess flow effects. Signal losses of 2 and 6% (relative to no flow) were observed for bulk velocities of 5 mm/s at TE values of 15 ms. An intravascular contrast agent may be useful for MRI monitoring of local cerebral blood volume changes during cerebral perturbations. © 1992 Academic Press, Inc.
Spatially localized in vivo1H magnetic resonance spectroscopy of an intracerebral rat glioma
Authors: Ross Brian D. , Merkle Hellmut , Hendrich Kristy , Staewen R. Scott , Garwood Michael
Published: March 2007

Surface coil MRI combined with spatially localized spectroscopy was used to noninvasively detect 1H signals from metabolites within an intracerebral malignant glioma in rats. The MRS pulse sequence was based upon two‐dimensional ISIS, which restricted 1H signals to a column‐shaped volume, combined with one dimensional spectroscopic imaging, which further resolved the signals into 8 or 16 slices along the major axis of the column. All experiments were executed with adiabatic pulses which induced uniform spin excitation despite the inhomogeneous radiofrequency field distribution produced by the surface coil transmitter. Surface coil MRI and MRS experiments were performed on phantom samples, normal rat brains, and rat brains harboring malignant gliomas. Spatially resolved in vivo 1H spectra of intracerebral gliomas revealed significantly decreased concentrations of Nacetyl‐aspartate and creatine and increased lactic acid (or lipids) as compared to the contralateral hemisphere. These results demonstrate that metabolic abnormalities in intracerebral rat gliomas can be spatially resolved in a noninvasive manner using localized in vivo 1H MRS. © 1992 Academic Press, Inc.
Dextran‐magnetite particles: Contrast‐enhanced MRI of blood–brain barrier disruption in a rat model
Authors: Bulte Jeff W. M. , de Jonge Martinus W. A. , Kamman Richard L. , Go K. Gwan , Zuiderveen Fred , Blaauw Bert , Oosterbaan John A. , Hauw T. , de Leij Lou
Published: March 2007

Dextran‐magnetite particles (DMP) were studied for their use as a MR contrast agent to visualize lesions with a blood‐brain barrier (bbb) disruption. A freezing injury to the rat cerebral cortex was used as a model of bbb disruption. The biodistribution of iv‐injected DMP was studied using atomic absorption spectrophotometry, electron microscopy, and MRI. One hour after injection, focal accumulation of the particles in capillary endothelial cells could be demonstrated in the freezing lesion. Despite the observation that the relaxivity of DMP in vivo appears to be less well pronounced than that in vitro, the MR imaging studies show that DMP can be used to visualize bbb disruption with adequate contrast. © 1992 Academic Press, Inc.
Evaluation of acute brain edema using quantitative magnetic resonance imaging: Effects of pretreatment with dexamethasone
Authors: Olson James E. , Katz‐Stein Abi , Reo Nicholas V. , Jolesz Ferenc A.
Published: March 2007

We developed a quantitative magnetic resonance imaging method to permit a rapid assessment of brain water content during osmotic brain edema produced by intraperitoneal (ip) injection of distilled water. Fifteen minutes after water injection, the normalized mean image intensity (MIn) from a spin‐echo pulse sequence (TE = 80 ms, TR = 1085 ms) was the same as that measured from control animals not injected with water. Sixty minutes after the water injection, the mean ± SEM brain image MIn had increased by 10.8 ± 2.4% compared to 3.4 ± 0.7% in control animals (P < 0.05). Blood plasma osmolality decreased by 6–10% during this time interval. A subsequent ip injection of hypertonic NaCl solution (100 gm/liter) caused the blood plasma osmolality and brain image MIn to return toward their initial values. MIn of cerebral gray matter correlated with tissue water content measured in parallel studies. Animals pretreated with 0.25 mg/(kg day) dexamethasone had cerebral gray matter MIn values during osmotic edema which were lower than those of untreated animals. © 1992 Academic Press, Inc.
Differentiation of human prostate cancer from benign hypertrophy by in vitro1H NMR
Authors: Fowler A. H. , Pappas A. A. , Holder J. C. , Finkbeiner A. E. , Dalrymple G. V. , Mullins M. S. , Sprigg J. R. , Komoroski R. A.
Published: March 2007

In vitro 1H NMR spectra were acquired for perchloric acid extracts of tissue samples ofhuman prostate. Seven patients were diagnosed with prostate cancer, 13 with benign prostatic hypertrophy, and 3 with both conditions. Statistically significant differences between the cancer and benign groups were seen for the metabolite peak arearatios of citrate, creatine, and phosphorylcholine to alanine. and citrate to glutamate. There was no correlation of Gleason grade with any of the ratios measured for the cancer samples. Spectra from different sections of large tumors often yielded substantially different area ratios. confirming the heterogeneous nature of these prostate tumors.
31P NMR studies of resting zone cartilage from growth plate
Authors: Kvam Bjarne J. , Pollesello Piero , Vittur Franco , Paoletti Sergio
Published: March 2007

31P NMR of superfused resting cartilage demonstrated the presence of phosphocreatine in chondrocytes. Changes in pH and in the NTP level were followed during carbon source starvation. From 31P spectra of perchloric acid extracts, phosphoethanolamine, phospho‐choline, and the corresponding glycerol diesters were identified as the major phospho‐monoester and phosphodiester components. © 1992 Academic Press, Inc.