bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fast limited flip angle mr subtraction angiography
Authors: Tasciyan Talin A. , Lee James N. , Riederer Stephen J. , Decastro Jose B. , Hedlund Laurence W. , Herfkens Robert J. , Spritzer Charles E. 
Published: March 2007

AbstractA fast MR angiography method is introduced that is capable of generating difference images of blood vessels in scan times of 10–20 s. This is an order of magnitude faster than many previous methods. The fundamental concept ofthis approach is to use cardiac gating and acquire several phase encodings at least twice during each cardiac cycle using limited flip angles (LFAs) and repetition times in the 20 to 50 ms range. The encodings acquired during diastole are subtracted from those acquired during systole to generate the difference image. The contrast in the difference image is due both to the influx of unsaturated spins and to the loss of phase coherence of systolic blood moving at high velocity along a magnetic gradient. The systolic peak of the cardiac cycle is determined during reconstruction by shifting the systolic and diastolic “windows” until the difference signal is maximized. Ghost artifacts due to pulsatile flow are eliminated by a phase reordering technique similar in concept to those developed for suppression of breathing artifacts. Arteries in thick slices are successfully imaged and initial in vivo results are presented. © 1988 Academic Press, Inc.
Serial changes in nuclear magnetic resonance relaxation times after myocardial infarction in the rabbit: Relationship to water content, severity of ischemia, and histopathology over a six‐month period
Authors: Johnston Donald L. , Homma Shunichi , Liu Peter , Weilbaecher Donald G. , Rokey Roxann , Brady Thomas J. , Okada Robert D. 
Published: March 2007

AbstractTo determine the serial changes in T1 and T2 relaxation times of myocardial infarction, and their relationship to observed changes in water content, regional myocardial blood flow, and histopathology, rabbits were studied at 14 time intervals ranging from 30 min to 6 months after coronary artery ligation. All values were compared to a control group. Hearts were subdivided into infarct and normal segments for measurement of blood flow, water content, and relaxation times (20‐MHz spectrometer); other hearts were excised intact for histopathologic studies. T1 relaxation time of infarcted myocardium did not change significantly compared to control over the 6‐month study period. T2 relaxation time increased (P < 0.0001) at 3 days and returned to baseline by 2 months. Consonant with the increase in T2 of infarct, nuclear magnetic resonance (NMR) images at 3 days demonstrated an increase in signal intensity of infarct compared to surrounding normal myocardium. At 6 months, marked myocardial thinning was observed without changes in signal intensity. Changes in T2 of infarcted myocardium were not related to changes in water content or seventy of ischemia, but correlated best with infarct healing and scar formation as detected on histopathology. In conclusion, the findings of this study indicate that T2 relaxation time of the infarcted myocardium increases markedly at 3 days and remains elevated for 2 months. These changes correlate best with the onset and progression of infarct healing. These data demonstrate the potential of T2‐weighted NMR imaging for assessing healing patterns following ischemic myocardial injury. © 1988 Academic Press, Inc.
NMR characteristics of “visible” intracellular myocardial potassium in perfused rat hearts
Authors: Burstein Deborah , Litt Harold I. , Fossel Eric T. 
Published: March 2007

AbstractNuclear magnetic resonance (NMR) spectroscopy provides a unique view of ions through its noninvasive character and relaxation time measurements. Several previous studies have demonstrated that only approximately 20% of cardiac intracellular potassium is visible with current NMR techniques. This study investigates the NMR visible intracellular potassium in a perfused rat heart preparation. When shift reagents were used to separate the intra‐ and extracellular signals, an intracellular T1 of 11.8 ± 0.6 ms, and an intracellular T2 with two time constants of 1.3 ± 0.6 ms (33 ± 8%) and 10.1 ± 1.9 ms (67 ± 4%) were measured. Curve stripping techniques used to separate the intra‐ and extracellular components of a bulk relaxation decay yielded an intracellular T1 of 8.4 ± 0.3 ms and an intracellular T2 with two time constants of 1.1 ± 0.6 ms (38 ± 10%) and 8.0 ± 1.6 ms (62 ± 12%). These results demonstrate that there are at least two distinct pools of potassium within the cardiac cell in slow exchange with each other on the NMR time scale. Studies with an enriched 41K perfusate demonstrated that the exchange rate for the visible intra‐ and extracellular potassium is on the order of 15 min. © 1989 Academic Press, Inc.
A fast method for T1 fitting
Authors: Sperber G. O. , Ericsson A. , Hemmingsson A. 
Published: March 2007

AbstractWhen NMR signal amplitudes achieved from spin‐echo sequences with several different repetition times are used to calculate T1, this can be done rapidly by calculating the time coordinate of the center of gravity of the data and determining which T1 should theoretically give this value. In particular, when a large number of similar calculations are made, the time gain may be massive. Simulations suggested that this procedure is only slightly less accurate than least‐squares fitting, and far more rapid. The procedure may also be useful in other types of T1 determination. © 1989 Academic Press, Inc.
Three‐dimensional phase contrast angiography
Authors: Dumoulin C. L. , Souza S. P. , Walker M. F. , Wagle W. 
Published: March 2007

AbstractBipolar 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

AbstractPrevious 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

AbstractKnowledge 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

AbstractAlthough 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

AbstractA 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

AbstractThis 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

AbstractA 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

AbstractThe 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

AbstractSevere 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

AbstractThe 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

AbstractTo 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

AbstractA 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

AbstractTime‐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

AbstractThere 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

AbstractRecent 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

AbstractMany 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

AbstractThe 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

AbstractWe 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

AbstractIn 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.