bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intensity artifacts in MRI caused by gradient switching in an animal‐size NMR magnet
Authors: Hughes D. G. , Robertson S. , Allen P. S. 
Published: March 2007

AbstractThe switching of magnetic field gradients in MRI gives rise to eddy currents in the structural components of superconducting magnet systems. The associated magnetic fieldscause intensity artifacts which are particularly severe in some animal‐size systems. We treat theoretically three mechanisms which cause intensity artifacts in one‐dimensional projection images obtained by a spin‐echo technique. The first is an off‐resonance effect, caused by applying the refocusing pulse before the read compensation gradient pulse has decayed sufficiently. The other two mechanisms are caused by a spatial dependence of the phase accumulated by the spins at the time of formation of the echo. as a result of the eddy current fields. First, interference causes aloss of transverse magnetization because of a variation in the phase of spins which lieon the same isochromat during the read gradient pulse. Second, a variation of the phaseof the spins in a direction orthogonalto the isochromats causes spins throughout the sample to refocus at different times. These two mechanisms are fundamentally different, since interference can occur even if the main magnetic field is homogeneous, whereas improper refocusing does not. It is shown that there is no loss of intensity by the interference mechanism if phase encoding is used to form two‐dimensional images. This maywell be a major reason why images obtained by 2DFT have been found to be generally superior to thoseobtained by projection reconstruction. Experimentally, the distributionof intensity in one‐dimensional projection images of a square slice phantom is compared with theoretical intensities, estimated using eddy current fields reported in the preceding paper.
Decrease of glucose in the human visual cortex during photic stimulation
Authors: Merboldt Klaus‐Dietmar , Bruhn Harald , Hanicke Wolfgang , Michaelis Thomas , Frahm Jens 
Published: March 2007

AbstractLocalized proton NMR spectroscopy was used to study cerebral metabolism in the visual cortex of healthy adults during rest and photic stimulation. Basal lactate levels showed considerable interindividual differences ranging from below detectability (mM) to about 1 mM without consistent alterations during photic stimulation. Local brain glucose levels were significantly reduced (≈ 50%) during the entire period of photic stimulation and recovered to resting levels (≈0.8 mM)within 10 minafter the end of stimulation. This decrease reflects the establishment of a new equilibrium due to enhanced delivery (blood flow) and enhanced consumption. The absence of lactate accumulation supportsthe hypothesis of a rapid efflux of lactate from brain tissue under activated conditions.
Application of self‐refocusing band selective RF pulses for spectroscopic localization
Authors: Marshman Margaret F. , Brereton Ian M. , Rose Stephen E. , O'Connor Anthony J. , Doddrell David M. 
Published: March 2007

AbstractA new self‐refocusing slice selection 90° pulse is presented and its incorporation in the Space localization sequence described. Experimental comparisons are made with the self‐refocusing pulse reported by Geen (H. Geen, S. Wimperis and R. Freeman, J. Magn. Reson. 85, 620 (1990)). The main source of localization error in the Space sequence is traced to the hard π/2 pulse and the development of a shaped‐pulse version of the sequence is described. This required the calculation of a slice‐selective pulse capable of rotating coherent transverse magnetization to the z‐axis. The RF power requirements for these experiments are also discussed. © 1992 Academic Press, Inc.
Chemical shift imaging with phase‐encoding RF pulses
Authors: Hennig J. 
Published: March 2007

AbstractAn inherent problem of conventional chemical shift imaging is signal contamination into adjacent voxels. This is especially severe in proton spectroscopy of the central nervous system, where the lipid signal from the skull is several orders of magnitude higher than the metabolite resonances from the brain. The reason for the contamination lies in the fact that the distribution of spins does not coincide with the discrete sampling matrix of the discrete Fourier transformation if a continuous phase‐encoding scheme using magnetic field gradients is being used. This problem can be overcome if phase encoding is performed by appropriately phase‐modulated RF pulses. It is demonstrated that contamination free spectra can be acquired from voxels immediately adjacent to the skull. Using small voxels of 1 × 1 × 2‐ml regional variations of N‐acetyl aspartate in the cerebellum of patients with oligopontine cerebellar atrophy could be observed. © 1992 Academic Press, Inc.
In vivo7Li NMR imaging and localized spectroscopy of rat brain
Authors: Ramaprasad S. , Newton J. E. O. , Cardwell D. , Fowler A. H. , Komoroski R. A. 
Published: March 2007

AbstractLithium‐7 in vivo NMR spectroscopy and imaging techniques have been developed at 4.7 T for rat head. The pharmacokinetics of lithium (Li) uptake in rat head has been measured using STEAM localized spectroscopy for the whole brain, which showed relatively rapid uptake of Li and a steady level of Li from about 5 to 20 h. Localized spectroscopy on brain sections revealed no differences in Li concentration among the front, middle, and rear of the brain. The spin‐lattice relaxation time showed a single exponential decay for the head. The spin‐spin relaxation time for head showed a biexponential behavior. Using a 1H‐7Li double coil assembly,7Li images were generated for rat head, as was the corresponding 1H image for anatomic localization. The 7Li image (7‐mm slice thickness, 4‐mm in‐plane resolution) recorded after the last dose in a multiple ip dose protocol shows the Li distribution in the head and neck. Based on 7Li images, the Li level in muscle was about twice that in the brain. Variations of 7Li intensity level across the brain were typically small. © 1992 Academic Press, Inc.
Experimental analysis of T1 imaging with a single‐scan, multiple‐point, inversion‐recovery technique
Authors: Zhang Y. T. , Yeung H. N. , Carson P. L. , Ellis J. H. 
Published: March 2007

AbstractLook and Locker's single‐scan, multiple‐point, T1 determination technique modified for imaging applications was evaluated experimentally for its accuracy and reliability with respect to the pulse sequence parameters. in particular. to the interpulse delay, TD, and the tip angle, α. T1 imaging experiments were performed with a 0.5‐T imaging system on a phantom which consisted of an array of vials containing 2% agarose gels doped with various amount of Mn2+ using different combinations of the parameter set {TD. α}. T1, results obtained with this technique were compared with those measured by a conventional inversion‐recovery procedure using the same spectrometer. Strategic choice of pulse sequence parameters to minimize experimental errors and the criteria for these choices will be discussed. © 1992 Academic Press, Inc.
Magnetization transfer time‐of‐flight magnetic resonance angiography
Authors: Pike G. Bruce , Hu Bob S. , Glover Gary H. , Enzmann Dieter R. 
Published: March 2007

AbstractTime‐of‐flight (TOF) angiography based on inflow enhancement is limited by the steady‐state signal differences between blood and the surrounding stationary tissues. We present a new TOF sequence in which magnetization transfer contrast is used to supplement wash. in effects. Angiograms demonstrating the superior performance of this technique are presented. © 1992 Academic Press, Inc.
An aqueous gastrointestinal contrast agent for use in echo‐planar MR imaging
Authors: Hahn Peter F. , Saini Sanjay , Cohen Mark S. , Goldberg Mark , Reimer Peter , Mueller Peter R. 
Published: March 2007

AbstractFour volunteers were imaged with echo‐planar imaging before and after ingesting a dilute barium preparation. The contrast material improved bowel visibility by increasing lumen signal intensity, without increasing noise. Long T2 gastrointestinal contrast material can be used in T2‐weighted imaging when motion artifacts are suppressed by ultrashort acquisitions. © 1992 Academic Press, Inc.
Time course EPI of human brain function during task activation
Authors: Bandettini Peter A. , Wong Eric C. , Hinks R. Scott , Tikofsky Ronald S. , Hyde James S. 
Published: March 2007

AbstractUsing gradient‐echo echo‐planar MRI, a local signal increase of 4.3 ± 0.3% is observed in the human brain during task activation, suggesting a local decrease in blood deoxyhemoglobin concentration and an increase in blood oxygenation. Images highlighting areas of signal enhancement temporally correlated to the task are created. © 1992 Academic Press, Inc.
31P magnetization transfer studies in the monkey brain
Authors: Mora Bassem N. , Narasimhan P. T. , Ross Brian D. 
Published: March 2007

AbstractThe forward and reverse rates through the creatine‐kinase (CK) catalyzed reaction, phosphocreatine + ADP + H+ \documentclass{article}\pagestyle{empty}\begin{document}$\'\mathop \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} \limits_{kr}^{kr} \{$\end}document} creatine + ATP in the in vivo monkey brain were measured using the techniques of saturation transfer (ST) and inversion transfer (IT) 31P nuclear magnetic resonance (NMR) spectroscopy. Independent checks on the ST apparent longitudinal relaxation (τ) data could be obtained from the parameters determined from the IT analyses. At near‐equilibrium it is assumed that the forward‐to‐reverse flux ratio lies close to 1.0. In the monkey brain the value for the forward‐to‐reverse flux ratio obtained is 1.37 ± 0.26 calculated from ST with average τ values from IT initial slopes, a value which is not significantly different from unity. The present NMR data point to the CK reaction in the living monkey brain being maintained at or near equilibrium.
A fast gradient‐recalled MRI technique with increased sensitivity to dynamic susceptibility effects
Authors: Moonen Chrit T. W. , Liu Guoying , Gelderen Peter Van , Sobering Geoffrey 
Published: March 2007

AbstractA fast imaging method that is based on gradient‐recalled echoes of spins whose excitation and echo formation are separated by more than one TR period is presented. This method does not incorporate chemical‐shift refocusing and thus results in drastically increased sensitivity to dynamic susceptibility erects, while maintaining a short total imaging time. The efficiency of the new technique is demonstrated in dynamic contrast‐enhanced experiments (bolus tracking) in the cat brain using a duration of 600 ms for each image. Blood volume maps are derived with expected contrast between white and gray matter.
The impact of the ISIS experiment order on spatial contamination
Authors: Burger C. , Buchli R. , Mckinnon G. , Meier D. , Boesiger P. 
Published: March 2007

AbstractWhen performing volume‐localized spectroscopy measurements, the amount of spatial contamination is an important quality criterion. With the ISIS localization technique contamination cannot only arise from the transition regions around the volume of interest, but also from remote regions of the sample. The latter contamination component is a consequence of inhomogeneous excitation pulses, if short repetition times TR are used. Its severity depends both on the order of the eight phase cycling experiments needed for an ISIS measurement, and on the ratio TR/T1. Here it is theoretically discussed from which regions of the sample contamination can arise for a specific phase cycling order. For the worst orders the contaminating regions are almost three times as large as for the optimal orders. The ratio for the effectively measured contamination, however, can be moderated in real experiments, because cancellation effects occur due to the phase distribution of the contaminating signals. 31P phantom experiments clearly demonstrate that contamination is present even if adiabatic excitation pulses are applied and that spatial contamination can be reduced to about a third by an optimal choice of the phase cycling order.
Dynamic studies of gadolinium uptake in brain tumors using inversion‐recovery echo‐planar imaging
Authors: Gowland P. , Mansfield P. , Bullock P. , Stehling M. , Worthington B. , Firth J. 
Published: March 2007

AbstractEcho‐planar imaging has been used to observe the dynamics of Gd‐DTPA uptake in brain tumors. It has been possible to examine both vascular uptake and diffusion across the blood‐brain barrier in a single experiment, by using the IR‐MBEST echo‐planar sequence which combines a high temporal resolution (approximately 3 s) with strong T1 weighting. To model the uptake it is necessary to know the arterial concentration of Gd‐DTPA; in this study the signal in the sagittal sinus was measured to avoid the need to take repeated blood samples. The time constant for transfer across the blood‐brain barrier was measured to be between 20 and 1050 s for different tumors. The results of the modeling correlated with the results of other assessments of tumor vascularity.
Recursive RF excitation
Authors: Christy P. S. , Grimm R. C. , Greenleaf J. F. , Ehman R. L. 
Published: March 2007

AbstractWe have investigated the properties of a recursive process in which the output signal from a given RF excitation pulse may be used as the input (excitation) pulse of a subsequent iteration. This recursive excitation technique increases contrast and improves feature segmentation for the purpose of motion tracking.
Breast coil design for low‐field mri
Authors: Komu Markku , Kormano Martti 
Published: March 2007

AbstractFour double‐breast coils were designed for the low‐field resistive magnet MR imaging of female breasts at 0.02, 0.04, and 0.1 T. The signal‐to‐noise ratio is optimized by shaping the coils, by constructing two different size coils at 0.02 T, and by using special wire for the turns of the solenoidal coils. The approximate linear dependence of the SNR on the Larmor frequency is estimated.
T1values of phosphomonoester and phosphocreatine of brain show no significant change during development
Authors: Hida Kazutoshi , Kwee Ingrid L. , Nakada Tsutomu 
Published: March 2007

AbstractChanges in apparent 31P spin‐lattice relaxation times (T1) associated with brain development were investigated in rat pups. While analysis of variance showed strong age dependency in [PME]/[ATP] and [PCr]/[ATP], the T1 values of PME, PCr, and ATP did not show any age dependency. The studies indicate that in contrast to the data which indicated aging‐related changes in the T1 values of PME, the observed changes in PME during neonatal development are likely to be quantitative in nature.
T1 snapshot flash measurement of rat brain glioma: kinetics of the tumor‐enhancing contrast agent manganese (iii) tetraphenylporphine sulfonate
Authors: Hoehn‐Berlage Mathias , Norris David , Bockhorst Kurt , Ernestus Ralf‐Ingo , Kloiber Otmar , Bonnekoh Petra , Leibfritz Dieter , Hossmann Konstantin‐Alexander 
Published: March 2007

AbstractThe ultrafast inversion recovery snapshot FLASH technique was used to determine the kinetics of the contrast agent manganese (III) tetraphenylporphine sulfonate (MnTPPS) in experimental brain tumors in rats. In the first part of the investigation this technique was validated with the conventional inversion recovery spin‐echo method by comparing in vivo T1 data of a normal rat brain. Agreement between T1 values obtained from both techniques was complete, as tested for a large number of pixels in identical coronal slices. In the second part the fast IR snapshot FLASH method was applied to study the effect of the NMR contrast agent MnTPPS on the T1 relaxation time of experimental gliomas in rat brains. T1 of normal brain tissue (1024–1035 ms), tumor (1217 ms), and edema (1199 ms) was determined with the inversion recovery version of the snapshot FLASH imaging technique. After intraperitoneal injection of MnTPPS (0.25 mmol/kg body wt) T1 decreased exponentially to 56% of control in tumor and to 62% in muscle. In normal and edematous brain tissue no significant changes in T1 were observed up to 5 h after injection of the contrast agent. Once the T1 contrast between tumor and peritumoral brain tissue had reached a saturation, the enhancement persisted for several hours to days. Therefore application of this contrast agent resulted in a sharp demarcation between glioma and peritumoral edema.
Spin‐echo m‐mode nmr imaging
Authors: Matsuda Tetsuya , Shimizu Koji , Sakurai Tsunetaro , Yamasaki Kazunari , Nagano Yutaka , Okada Ikutaro , Miki Shinji , Kawai Chuichi 
Published: March 2007

AbstractA nuclear magnetic resonance (NMR) imaging and display method for the observation of the continuous motion of objects is presented. By modifying a line scan technique, the spin‐density distribution along a line is displayed in succession. Although spatial information is limited to only one dimension, the motion of the object is recorded at intervals of 55 ms by using a commercially available NMR imaging system. In a phantom study, this method yielded accurate velocity measurements along a single axis. When the method was applied to the human chest, an image analogous to that of M‐mode echocardiography was obtained. This method, which can be called spin‐echo M‐mode NMR imaging, approaches the functional analysis of cardiac wall motion in regions where echocardiography is not possible. The effects of respiratory motion on the left ventricular wall were recorded in addition to its intrinsic contractile motion in an image obtained along a line parallel to the cranio‐caudal axis of the body. The advantages of this method to assess cardiac wall motion in a patient with an arrhythmia were also demonstrated.
31p nme spectroscopic study of the effects of γ‐irradiation on rif‐1 tumor cells perfused in vitro
Authors: Ng Cheng E. , Mcgovern Kathy A. , Wehrle Janna P. , Glickson Jerry D. 
Published: March 2007

AbstractIn order to examine the mechanisms underlying radiation‐induced changes in phosphorus metabolite levels observed in RIF‐1 tumors in vivo, RIF‐1 cells in culture were perfused for up to 70 h following γ‐irradiation with 0‐25 Gy and monitored continuously by, 31P NMR spectroscopy at 8.5 T. Cells immobilized in the sample volume by incorporation into calcium alginate beads were bioenergetically stable, but did not replicate at the cell density used. Following an initial increase in PCr and NTP, which occurred in both control and irradiated cells, a dramatic decline in high‐energy phosphates was detected beginning 24‐30 h after irradiation with 15 or 25 Gy. In contrast, unirradiated cells or cells treated with 10 Gy remained metabolically stable for up to 72 h. The metabolic changes induced by irradiation of the cultured cells, which reflected cell death and lysis, were distinctly different from those observed in RIF‐1 tumors in vivo during the same postirradiation time interval‐an increase in high–energy relative to low‐energy phosphates. This suggests that the spectral changes in vivo do not result from direct modification of cellular energy metabolism by radiation injury.
A noninvasive assessment of myocardial oxygen tension: 19f nmr spectroscopy of sequestered perfluorocarbon emulsion
Authors: Mason Ralph P. , Jeffrey F. Mark H. , Malloy Craig R. , Babcock Evelyn E. , Antich Peter P. 
Published: March 2007

AbstractFluorine NMR spectroscopy of sequestered perfluorocarbon emulsion has been used to measure myocardial oxygen tension. This novel application provides a rapid noninvasive assessment of changes in oxygen tension in response to ischemia and reperfusion. Rats were predosed with Oxypherol‐ET (emulsion of perfluorotributylamine). Following vascular clearance of the emulsion the heart was excised and perfused using the Langendorff retrogradetechnique. 19F spin‐lattice relaxation time measurements provided an accurate estimate of myocardial pO2. Using a two‐point determination with a time resolution of 1 s, the loss of oxygen was found to be complete within 40 s of the onset of global ischemia. The fall in oxygen tension correlated closely with an observed loss of ventricular pressure. Magnetic resonance imaging showed that perfluorocarbon was distributed throughout the heart; thus, this reporter molecule provides a global measurement of oxygen tension.
Mr imaging of cerebral perfusion by phase‐angle reconstruction of bolus paramagnetic‐induced frequency shifts
Authors: Conturo Thomas E. , Barker Peter B. , Mathews Vincent P. , Monsein Lee H. , Bryan R. Nick 
Published: March 2007

AbstractPhase‐angle images are acquired dynamically during bouls paramagnetic contrast injection and demonstrate a phase‐enhancement effect in perfused cerebral tissues. Signal‐to‐noise is comparable to that of susceptibility‐based signal loss (ΔR) images. Assuming that phase shift is proportional to the tissue paramagnetic agent concentration, as supported by experimental data, the integrated area of the phase time response curves estimated the relative gray to white matter blood volume as 1.8:1 and was sensitive to acute ischemia. The relation between tissue phase shift and concentration is considered.
Simultaneous MR Acquisition of Arterial and Brain Signal‐Time Curves
Authors: Perman William H. , Gado Mokhtar H. , Larson Kenneth B. , Perlmutter Joel S. 
Published: March 2007

AbstractRegional cerebral blood flow (rCBF) provides important information about local neuronal functional and cerebrovascular status. Determination of rCBF requires sequential measurements of tracer concentration in arterial blood and brain tissue unless the tracer is trapped in the brain in proportion to rCBF. Since gadopentate dimeglumine is not trapped within brain tissue, we have developed the simultaneous dual FLASH pulse sequence (SDFLASH) which sequentially measures the MR signal change in both the internal carotid artery and brain parenchyma simultaneously during the passage of a bolus of paramagnetic contrast material.© 1992 Academic Press,Inc.
Quantitative MRI of the Prostate and Uterus in Monkeys
Authors: Waterton John C. , Larcombe‐Mcdouall Jacqueline B. , Miller Diane 
Published: March 2007

AbstractQuantitative MRI has been carried out in the prostate, seminal vesicles, uterus, and ovaries in the pig‐tailed monkey, Macaca nemestrina. T2‐weighted, fat‐suppressed, multislice experiments were performed at 2.35 T. Eight males, 14 ovariectomized females, and 20 intact females were studied. In the prostate, the caudal and cranial lobe were readily distinguished since the latter had a longer T2 value. For all tissues and organs, interanimal variations were large (up to 12‐fold variation in volume), but reproducibility was excellent in the prostate and in the ovariectomized monkey uterus with coefficients of variation (CV) of 3 and 5%, respectively. In the intact monkey uterus, cycle‐cycle reproducibility was good with CVs of 6–10% in the myometrium and 14–18% in the endometrium. In the follicular phase, endometrial growth (+3.8% day‐1, P < 0.001) was accompanied by myometrial shrinkage (‐1.6% day‐1, P < 0.001), while in the luteal phase, growth was seen in both tissues (+4.3% day‐1, P < 0.001 and +1.4% day−1, P < 0.001, respectively). The great value of these MRI techniques in obtaining data in pharmacological efficacy studies of endocrine drugs, and in limiting the number of animals used, is discussed.© 1992 Academic Press,Inc.
Fast Spiral Coronary Artery Imaging
Authors: Meyer Craig H. , Hu Bob S. , Nishimura Dwight G. , Macovski Albert 
Published: March 2007

AbstractA flow‐independent method for imaging the coronary arteries within a breath‐hold on a standard whole‐body MR imager was developed. The technique is based on interleaved spiral k‐space scanning and forms a cardiac‐gated image in 20 heartbeats. The spiral readouts have good flow properties and generate minimal flow artifacts. The oblique slices are positioned so that the arteries are in the plane and so that the chamber blood does not obscure the arteries. Fat suppression by a spectral‐spatial pulse improves the visualization of the arteries.© 1992 Academic Press,Inc.