bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flow suppression in rapid FLASH NMR images
Authors: Frahm Jens , Merboldt Klaus‐Dietmar , Hänicke Wolfgang , Haase Axel 
Published: March 2007

AbstractRapid FLASH (fast low angle shot) NMR images are very sensitive to flow phenomena. In particular, a steady reflow of unsaturated spins from outside the imaging plane results in high image intensities which depend on the flip angle, the repetition time, and the flow velocity. Here we describe a technique that suppresses these signals by saturating remote spins prior to entering the imaging plane, e.g., by intercalating the FLASH sequence with slice‐selective 1–2‐1 pulse packages. Experiments have been carried out on phantoms and human extremities. Flow artifacts in the phase‐encoding direction of the images are strongly reduced. Vascular structures may be easily delineated using difference images obtained with and without flow suppression.
Changes in nuclear magnetic resonance (T2) relaxation of limb tissue with bed rest
Authors: Leblanc Adrian , Evans Harlan , Schonfeld Ernesto , Ford Joseph , Schneider Victor , Jhingran Satish , Johnson Philip 
Published: March 2007

AbstractBed rest is used to simulate the effects of weightlessness on human physiology. A spinecho procedure was used to image the lower leg of 15 normal male volunteers before and after 5 weeks of horizontal bedrest. In addition to noninvasively measuring muscle size changes, accurate T2 images were produced to investigate possible relaxation time changes immediately (2–4 h) and 1–2 days after bed rest. Subcutaneous fat showed no change in T2, bone marrow showed a decrease, and muscle showed no change immediately after bed rest but increased 1–2 days following reambulation. © 1987 Academic Press, Inc.
Detection of myocardial infarction in the mini‐pig using NMR imaging
Authors: Checkley D. , Loveday B. E. , Waterton J. C. , Zhu X. P. , Isherwood I. 
Published: March 2007

AbstractSpin‐echo images of 10 myocardial infarcts in nine mini‐pigs were obtained at 30 h, 3 days, and approximately 10 days postinfarction. Infarcts were not detected at all at 30 h in five out of five cases examined. At 3 days postembolization (six cases) one infarct was certainly detected, whilst at 10 days (nine cases) all infarcts were seen as high‐signal areas in long TE spin‐echo sequences. After 2 weeks no further infarct signal change was detected (three cases), but myocardial thinning became more evident. Using techniques similar to those reported here, early postinfarct changes in the dog have been detected by other authors. Possible reasons for this difference between pig and dog are discussed. © 1987 Academic Press, Inc.
Transverse relaxation of solvent protons induced by magnetized spheres: Application to ferritin, erythrocytes, and magnetite
Authors: Gillis Pierre , Koenig Seymour H. 
Published: March 2007

AbstractSince 1/T2 of protons of tissue water is generally much greater than 1/T1 at typical imaging fields, small single‐ion contrast agents–such as Gd(DTPA), which make comparable incremental contributions and therefore smaller fractional contributions to 1/T2 compared to 1/T1–are not as desirable for contrast‐enhancement as agents that could enhance 1/T2 preferentially. In principle, such specialized agents will only be effective at higher fields because the field dependence (dispersion) of 1/T1 is such that it approaches zero at high fields whereas 1/T2 approaches a constant value. The residual 1/T2 is called the “secular” contribution and arises from fluctuations in time–as sensed by the protons of diffusing solvent or tissue water molecules–of the component of the magnetic field parallel to the static applied field. For solutions or suspensions of sufficiently large paramagnetic or ferromagnetic particles (⋧250 Å diameter), the paramagnetic contributions to the relaxation rates satisfy 1/T2 ≫ 1/T1 at typical imaging fields. We examine the theory of secular relaxation in some detail, particularly as it applies to systems relevant to magnetic resonance imaging, and then analyze the data for solutions, suspensions, or tissue containing ferritin, erythrocytes, agar‐bound magnetite particles, and liver with lowdensity composite polymer‐coated magnetite. In most cases we can explain the relaxation data, often quantitatively, in terms of the theory of relaxation of protons (water molecules) diffusing in the outer sphere environments of magnetized particles. The dipolar field produced by these particles has a strong spatial dependence, and its apparent fluctuations in time as seen by the diffusing protons produce spin transitions that contribute to both 1/T1 and /T2 comparably at low fields, for the larger particles, because of dispersion, the secular term dominates at fields of interest. On the basis of the agreement of theory with data for solutions of small paramagnetic complexes, large magnetite particles, and liver containing low‐density polymer‐coated magnetite agglomerates, it is argued that the theory is sufficiently reliable so that, e.g., for ferritin–for which 1/T2 is unexpectedly large–the source of its large relaxivity must reside in nonideal chemistry of the ferritin core. For blood, it appears that diffusion through intracellular gradients determines 1/T2. © 1987 Academic Press, Inc.
T2‐weighted contrasts in rapid low flip‐angle imaging
Authors: Bendel Peter 
Published: March 2007

AbstractExpressions for the contrast‐to‐noise (C/N) behavior in images obtained from rapid low flip‐angle excitation pulses are derived, taking into account both T1‐ and T2‐dependent contrasts. It is shown, and demonstrated experimentally, that images with T2‐weighted contrasts can be efficiently acquired with such sequences, by a suitable choice of TR, TE and tip angle. © 1987 Academic Press, Inc.
Detection of malignant tumors: Water‐suppressed proton nuclear magnetic resonance spectroscopy of plasma
Authors: Dowd Terry L. , Kaplan Barry A. , Gupta Raj K. , Aisen Philip 
Published: March 2007

AbstractAverage linewidths of methyl and methylene proton resonances of plasma lipoproteins from healthy controls and untreated cancer patients were measured in water‐suppressed proton spectra obtained at 400 MHz. In contrast to a previous report (E. T. Fossel, J. M. Carr, and J. McDonagh, N. Engl. J. Med. 315, 1369 (1986)) no statistically significant difference (P > 0.5) was found between the average linewidths in plasma samples from 20 normal controls (36.0 f 6.4 Hz) and 17 untreated cancer patients (34.6 ± 6.3 Hz). When the effect of lactate was removed by graphical extrapolation, a small but marginally significant (P = 0.08) difference was observed between the average linewidths of the normal controls (35.1 ± 5.8 Hz) and untreated cancer patients (31.8 ± 5.2 Hz). However, there was still a large overlap between the two groups. In addition, substantial day to day variations in the linewidths of samples from the same individuals were observed. We conclude that these measurements cannot be used to detect cancer.
19F magnetic resonance imaging of the reticuloendothelial system
Authors: Ratner Adam V. , Hurd Ralph , Muller Holde H. , Bradley‐Simpson Beverly , Pitts William , Shibata J Dean , Sotak Chris , Young Stuart W. 
Published: March 2007

AbstractIn this study sequential1H and19F magnetic resonance imaging methods were used to map the distribution of fluorinated compoundsin vivo.An intravenously administered emulsion of perfluorooctylbromide (PFOB), an agent known to localize in the reticuloendothelial system, was detected in the liver and spleen of all studied hamsters and mice using19F MRI. Lungs and salivary glands were also affected in some animals. Using a G. E. NMR CSI 2‐T spectroscopy/imaging system, projection19F images were obtained in 4 to 8 min. Subsequent mouse studies using a thick‐slice driven equilibrium pulse sequence produced19F images with an improved signal‐to‐noise ratio in a shorter acquisition time. With PFOB,19F MRI has the capability of detecting macrophages in the reticuloendothelial system and in other sites where macrophages congregate. This is the first report where the reticuloendothelial system was specifically imaged in live animals and where driven equilibrium imaging techniques have been applied to19F MRI. © Academic Press, Inc.
Continuous distributions of NMR relaxation times applied to tumors before and after therapy with X‐rays and cyclophosphamide
Authors: Kroeker Randall M. , Stewart Cindy A. , Bronskill Michael J. , Henkelman R. Mark 
Published: March 2007

AbstractIn vivo measurements of T1 and T2 values in two experimental tumors growing in the legs of mice were made during tumor growth and after treatment of the tumor with either X‐rays or cyclophosphamide. The T1 and T2 values were obtained by fitting the data to continuous distributions of relaxation times. This technique gives broad distributions of relaxation times which are characterized by a number of peaks with characteristic T1 and T2 values. Before treatment, the TI and T2 values increased before a palpable tumor mass could be detected. The response to subcurative doses of either treatment method was a reduction in the T1 and T2 values and a parallel reduction in tumor weight. Although local recurrence was characterized by the same pattern of tumor growth as was observed before treatment, therapy was found to give higher relaxation time values than those measured in untreated tumors. The higher relaxation time values of tumor‐bearing legs were the result of redistribution of the peaks in the distribution and not changes in the relaxation times of the individual peaks. © 1988 Academic Press, Inc.
Time‐resolved magnetic resonance angiography
Authors: Dumoulin C. L. , Souza S. P. , Walker M. F. , Yoshitome E. 
Published: March 2007

AbstractA time‐resolved phase contrast magnetic resonance angiography technique is described. This technique provides a series of angiograms obtained at different phases of the cardiac cycle. Such a series of angiograms can be used to evaluate blood flow dynamics. For example, turbulent flow in the regions of vessel bifurcations is easily demonstrated and followed during systole and diastole. Retrograde flow can also be observed. Dynamic angiography can be particularly useful in distinguishing transient image features, such as signal voids due to turbulent flow, from static features arising from vessel morphology. © 1988 Academic Press, Inc.
Saturation and inversion transfer studies of creatine kinase kinetics in rabbit skeletal muscle in vivo
Authors: Hsieh Paul S. , Balaban Robert S. 
Published: March 2007

AbstractThe steady‐state kinetics of the creatine kinase reaction in rabbit skeletal muscle in vivo was investigated using inversion and saturation magnetization transfer techniques. Both techniques determined the forward rate of this reaction (creatine phosphate ATP) as approximately 0.3 s−1. This corresponds to a flux of 10 μmol creatine phosphate/s/g muscle. The saturation transfer technique underestimated the reverse reaction by approximately 56%. This result is likely due to the participation of ATP in other interactions in skeletal muscle not involving creatine phosphate. © 1988 Academic Press, Inc.
The modification of the RF field distribution of surface coils by weakly conducting saline samples
Authors: Hanstock C. C. , Lunt J. A. , Allen P. S. 
Published: March 2007

AbstractThe modification of the RF field distribution of a surface coil, which is brought about by both loading and skin effect conditions arising from the proximity of weakly conducting saline samples, is demonstrated. A procedure for the calibration of the depth of the spectral acquisition region in depth‐pulse localized in vivo spectroscopy is shown to be acceptable. © 1988 Academic Press, Inc.
Improved sensitivity of proton MR to oxygen‐17 as a contrast agent using fast imaging: Detection in brain
Authors: Hopkins A. L. , Haacke E. M. , Tkach J. , Barr R. G. , Bratton C. B. 
Published: March 2007

AbstractThe potential utility of H217O as a contrast agent has been demonstrated in biological solutions and isolated tissues but its use has been impaired by the need to run heavily T2‐weighted spin‐echo images. By choosing an appropriate steady‐state free precession experiment sensitive to T1/T2, we have improved the available contrast‐to‐noise. per unit time by more than a factor of 5. This allows easy measurement of the proton effects for concentrations as low as 0.4% H217O in less than 1 min. Injection into small animals produces a marked reduction in the overall image intensity. Consecutive imaging at the rate of one every 52 s has been used to follow the rate of change in brain image intensity immediately after injection. © 1988 Academic Press, Inc.
Quantitative magnetic resonance imaging of estradiol‐induced pituitary hyperplasia in rats
Authors: Rudin M. , Briner U. , Doepfner W. 
Published: March 2007

AbstractMagnetic resonance imaging (MRI) has been used for the determination in vivo of rat pituitary size. In midsagittal T2‐weighted sections the pituitary, having a lower T2 value than the surrounding tissue, was visible with pronounced contrast. The size has been estimated by pixel counting. A close correlation (r = 0.96) with the pituitary weights determined postmortem has been obtained, demonstrating the reliability of the in vivo method. Using MRI the effects of Sandostatin, a somatostatin analog, on the pituitary size have been monitored in a rat model of prolactinoma (estradiol‐induced hyperplasia of the pituitary). Treatment with Sandostatin over 4 weeks resulted in a 40% reduction of the hyperplastic pituitaries. These results have been confirmed by determination of pituitary weights postmortem. However, due to a large interindividual variation in size of hyperplastic pituitaries, more animals are required to reach statistical significance when only endpoints of treatment can be measured. In contrast, MRI allows one to monitor individually the drug effects over a long period of time, eliminating interindividual variations. © 1988 Academic Press, Inc.
Problems in the assessment of magnesium depletion in the rat byin vivo31P NMR
Authors: Adam William R. , Craik David J. , Hall Jon G. , Kneen Malea M. , Wellard R. Mark 
Published: March 2007

AbstractPriorin vitrostudies, utilizing31P nuclear magnetic resonance (31P NMR) to measure the chemical shift (σ) of β‐ATP and lengthening of the phosphocreatine spin‐spin (T2) relaxation time, suggested an assessment of their efficacy in measuring magnesium depletionin vivo.Dietary magnesium depletion (M2+↓) produced markedly lower magnesium in plasma (0.44 vs 1.13 mmol/liter) and bone (130 vs 190 μmol/g) but much smaller changes in muscle (41 vs 45μmol/g, P0.01), heart (42.5 vs 44.6 μmol/g), and brain (30 vs 32 μmol/g). NMR experiments in anesthetized rats in a Bruker 7‐T vertical bore magnet showed that in Mg2+↓rats there was a significant change in brain β‐ATP shift (16.15 vs 16.03 ppm,P< 0.05). These chemical shifts gave a calculated free [Mg2+] of 0.71 mM(control) and 0.48mM(Mg2+↓). In muscle the change in β‐ATP shift was not significant (Mg2+↓15.99 ppm, controls 15.96 ppm), corresponding to a calculated free MP of 0.83 and 0.95mM, respectively. PhosphocreatineT2(Carr‐Purcell, spin‐echo pulse sequence) was no different with M2+↓in musclein vivo(surface coil) (Mg2+↓136, control 142 ms) or in isolated perfused hearts (Helmholtz coil) (control 83, Mg2+↓92 ms).31P NMR is severely limited in its ability to detect dietary magnesium depletionin vivo.Measurement of β‐ATP shift in brain may allow studies of the effects of interaction in group studies hut does not allow prediction of an individual magnesium status. © 1988 Academic Press, Inc.
Intravoxel incoherent motion imaging using steady‐state free precession
Authors: Le Bihan Denis 
Published: March 2007

AbstractIVIM MR imaging is a method which generates images of diffusion and perfusion in vivo. Until now, intravoxel incoherent motion (IVIM) images have been obtained using spin‐echo sequences with extragradient pulses, resulting in long acquisition times (typically 2 × 8 min 32 s). A new method is proposed here, using steady‐state free precession (SSFP), which allows IVIM images to be obtained in a couple of minutes. Phantom studies showed that the sensitivity of SSFP to IVIMs is much greater than that of spin echoes. In vivo images are shown. © 1988 Academic Press, Inc.
31P and 1H magnetic resonance spectroscopy of acute alcohol cardiac depression in rats
Authors: Auffermann Wolfgang , Camacho S. Albert , Wu Shao , Litt Lawrence , Parmley William W. , Higgins Charles B. , Wikman‐Coffelt Joan 
Published: March 2007

AbstractCardiac depression in the isolated rat heart perfused with 4% ethanol was correlated with intracellular phosphate energetics and tissue water distributions. Energy metabolites were assessed using 31P magnetic resonance spectroscopy (MRS) and correlated to the mitochondrial redox state using epicardial surface fluorometry. Changes in myocardial water compartmentation were measured by using 1H NMR spectroscopy with an extracellular chemical‐shift reagent (DyTTHA) and correlated to results of 2D echocardiography (2DE). During alcohol perfusion there was a significant decrease in developed pressure and in coronary flow. No change was seen in ATP, PCr, pHi, Pi, or NADH. After withdrawal of alcohol from the perfusate cardiac function reverted to control values without a depletion of energy levels. During alcohol perfusion 'H MRS showed a marked redistribution of water from the intra‐ to the extracellular space, corresponding to a 35% left ventricular wall thinning confirmed by 2DE. The results indicate that acute alcohol cardiac depression is related to a dehydration of myocardial cells, but is not associated with intracellular acidosis or energy depletion. 0 1988 Academic Press, Inc. © 1988 Academic Press, Inc.
Suppression of radiofrequency interference in cardiac gated MRI: A simple design
Authors: Shetty Anil N. 
Published: March 2007

AbstractA simple design is proposed to suppress the noise pickup in the ECG leads from RF and gradient pulses during NMR imaging. The ECG signal is passed through a low‐pass filter and a common‐mode‐rejection amplifier to reduce erroneous signal generated by the electrical ground loops. The output is gated through a CMOS switch to blank the preamplifier from the NMR during data acquisition. © 1988 Academic Press, Inc.
Rapid31P spectroscopy on a 4‐T whole‐body system
Authors: Hardy C. J. , Bottomley P. A. , Roemer P. B. , Redington R. W. 
Published: March 2007

AbstractInitial31P spectroscopy results from a 4‐T whole‐body system are reported. Localized spectra from the human head, liver, and calf were obtained using DRESS, slice‐inter‐leaved DRESS, and volume 3DFT spectroscopic imaging techniques. Substantial reductions in data acquisition times to 10 s–4 min were achieved relative to previous similar experiments at 1.5 T. Some gain in spectral resolution (as measured in ppm) was also realized in the head. © 1988 Academic Press, Inc.
In vivo1H NMR spectroscopy of an intracerebral glioma in the rat
Authors: Remy C. , Von Kienlin M. , Francois A. , Benabid A. L. , Decorps M. 
Published: March 2007

AbstractHigh‐resolution 1H surface coil NMR spectroscopy (MRS) was used to evaluate in vivo the cerebral metabolism changes in rat brain induced by a glial tumor growing in situ. Tumor cells (C6 glioma cells) were stereotaxically placed in the right hemisphere superficially. 1H MRS was performed using 5‐mm surface coils implanted over the right hemisphere and the water was suppressed using a binomial sequence. As the intracerebral tumor size increased, there was a marked decrease in the N‐acetyl aspartate level and an increase in the 1.3 ppm peak. Edition of this peak showed that lactate increased but lipids increased much more than lactate. Moreover the ratio between the choline‐phosphocholine and creatine‐phosphocreatine peaks changed. This study demonstrates that high‐resolution surface coil 1H MRS can be used to monitor changes in metabolism associated with growth of an experimentally induced rat brain tumor in situ. © 1989 Academic Press, Inc.
Magnetization transfer contrast (MTC) and tissue water proton relaxation in vivo
Authors: Wolff Steven D. , Balaban Robert S. 
Published: March 2007

AbstractIn this study the exchange between 1H magnetization in “free” water (1Hf) and that in a pool with restricted motion (1Hr) was observed in tissues in vivo using NMR saturation transfer methods. Exchange between these two pools was demonstrated by a decrease in the steady‐state magnetization and relaxation times of 1Hf with radiofrequency irradiation of 1Hr. The pseudo‐first‐order rate constant for the movement of magnetization from 1Hfto 1Hr was ∼ Is−1 in kidney and ∼3s−1 in skeletal muscle in vivo. Proton NMR imaging demonstrated that this exchange was tissue specific and generated a novel form of NMR image contrast. The extent of exchange between 1Hf and 1Hr as well as the topological correlation ofthe exchange with relaxation weighted images suggests that this pathway is a major determinant of the observed relaxation properties of water 1H in vivo. © 1989 Academic Press. Inc.
A comparison of double‐tuned surface coils
Authors: Fitzsimmons J. R. , Brooker H. R. , Beck B. 
Published: March 2007

AbstractThe combined acquisition of proton images and localized spectra is considered essential to the practical application of NMR techniques to human and animal research. Double‐tuned surface coils which have been introduced to the literature are intended to address the problem: however, a careful evaluation of available designs is lacking. The “trap” method, the loop gap resonator design, and the transformer‐coupled double‐tuned design are evaluated here using bench tests of signal intensity and Q as well as signal‐to‐ noise measurements on a 2‐T imager/spectrometer. Comparisons are made relative to optimized single‐tuned circuits of the same size for both protons at 85 MHz and phosphorus at 34 MHz. The results suggest that the “trap” design and the transformer coupled design are very efficient (98%) in the low‐frequency mode (34 MHz) while the loop gap resonator is relatively inefficient (82%). In the high‐frequency mode (85 MHz) the loop gap resonator is 75% efficient while the “trap” design and the transformer coupled coil are closer to 50% efficient. © 1989 Academic press. Inc. © 1989 Academic Press, Inc.
Assessment of the NMR visibility of intraerythrocytic sodium by flame photometric and ion‐competitive studies
Authors: Nissen Henrik , Jacobsen Jens Peter , Hørder Mogens 
Published: March 2007

Abstract23Na nuclear magnetic resonance (NMR) studies of intraerythrocytic sodium concentrations were performed at 37°C and the accuracy of the method was evaluated through concomitant emission flame photometric analysis. NMR visibility of intraerythrocytic sodium was estimated to be 75 ± 3%. Verification of the presence of an NMR invisible intraerythrocytic sodium pool and assessment of the mechanisms explaining this invisibility was achieved by measurement of 23Na NMR signal intensities and T1 relaxation times of erythrocyte hemolysate during ion‐competitive sodium release from association sites. Signal intensities after addition of small quantities of K+ and Mg2+ to the hemolysates were significantly larger than that expected from dilution of the sample, implying that the additions have resulted in the release of formerly invisible sodium. Furthermore, the intensities following the addition of K+ were significantly larger than those after the addition of Li+ and choline+. This signifies a specificity of the association sites at which sodium has decreased visibility. Increased T1 values following the additions confirmed the release of bound sodium. © 1989 Academic Press, Inc.