bluuebunny/crossref_metadata_2025_split huggingface dataset:
Perfusion imaging
Authors: Detre John A. , Leigh John S. , Williams Donald S. , Koretsky Alan P. 
Published: March 2007

AbstractMeasurement of tissue perfusion is important for the functional assessment of organs in vivo. Here we report the use of 1H NMR imaging to generate perfusion maps in the rat brain at 4.7 T. Blood water flowing to the brain is saturated in the neck region with a sliceselective saturation imaging sequence, creating an endogenous tracer in the form of proximally saturated spins. Because proton T1 times are relatively long, particularly at high field strengths, saturated spins exchange with bulk water in the brain and a steady state is created where the regional concentration of saturated spins is determined by the regional blood flow and regional T1. Distal saturation applied equidistantly outside the brain serves as a control for effects of the saturation pulses. Average cerebral blood flow in normocapnic rat brain under halothane anesthesia was determined to be 105 ± 16 cc. 100 g−1. min−1 (mean ± SEM, n = 3), in good agreement with values reported in the literature, and was sensitive to increases in arterial pCO2. This technique allows regional perfusion maps to be measured noninvasively, with the resolution of 1H MRI, and should be readily applicable to human studies. © 1992 Academic Press, Inc.
Multispectral analysis of uterine corpus tumors in magnetic resonance imaging
Authors: Taxt Torfinn , Lundervold Arvid , Fuglaas Bjørn , Lien Hans , Abeler Vera 
Published: March 2007

AbstractThe goal of this prospective study was to evaluate multispectral analysis techniques for automatic recognition of uterine cancer in magnetic resonance (MR) imaging. The first part of this study was an open training phase in which the statistical parameters of the various normal and pathological tissue types were estimated. This was followed by a test phase that was done as a blind experiment. Results from an extensive pathological examination of the surgically removed organs served as the reference for the diagnosis and various geometric measurements of the lesions. A radiological examination of the MR images was also performed. All malignant test tumors were correctly or close to correctly classified. However, parts of normal endometrium and other mucosal linings were also classified as adenocarcinomas. In addition, parts of some of the malignant tumors were classified as normal endometrium. The geometrical extension of the tumor and its relationship to the surroundings were slightly better predicted than those obtained by the radiologist. The results indicate that it is possible to differentiate and determine the local extension of some types of uterine malignancies based on the information present in MR images. © 1992 Academic Press, Inc.
On the precision of diffusion/perfusion imaging by gradient sensitization
Authors: Pekar James , Moonen Chrit T. W. , van Zijl Peter C. M. 
Published: March 2007

AbstractComputer simulation is used to assess the precision and accuracy of diffusion and perfusion parameters derived from a set of gradient‐sensitized images. Under ideal experimental conditions, a moderate signal‐to‐noise level (ca. 40) suffices to estimate diffusion coefficients to within 20% relative precision. However, estimation of a typical cerebral perfusion fraction of 5% to within 20% relative precision requires signal‐to‐noise levels of ca. 400. Simulations also show that systematic errors in perfusion fraction estimation, as well as understimation of the uncertainties in perfusion parameters (by X‐squared analysis), will be found at moderate signal‐to‐noise levels. © 1992 Academic Press, Inc.
Diffusion imaging of the human brain in vivo using high‐speed STEAM MRI
Authors: Merboldt Klaus‐Dietmar , Hänicke Wolfgang , Bruhn Harald , Gyngell Michael L. , Frahm Jens 
Published: March 2007

AbstractThis paper describes a new method for diffusion imaging of the human brain in vivo that is based on a combination of diffusion‐encoding gradients with high‐speed STEAM MR imaging. The single‐shot sequence 90°‐TE/2‐90°‐TM‐(α‐TE/2‐STE)n generates n = 32–64 differently phase‐encoded stimulated echoes STE yielding image acquisition times of 576 ms for a 48 ×128 data matrix. Diffusion encoding is performed during the first TE/2‐interval as well as during each readout period. Phantom studies reveal a quantitative agreement of calculated diffusion coefficients with literature values. EKG triggering completely eliminates motion artifacts from diffusion‐weighted single‐shot STEAM images of human brain in vivo. While signal attenuation of the cerebrospinal fluid (CSF) is predominantly due to flow, that observed for gray and white matter results from diffusion. Evaluated diffusion coefficients yield (1.0 ± 0.1) × 10−5 cm2 s−1 for gray matter, (0.5 ± 0.1) × 10−5 cm2 s−1 for white matter with the diffusion encoding parallel to the main orientation of the myelin sheath of the neurofibrils, and (0.3 ± 0.1) × 10−5 cm2 s−1 for white matter and a perpendicular orientation. All studies were performed at 2.0 T using a conventional 10 mT m−1 gradient system. © 1992 Academic Press, Inc.
Effects of RF amplifier distortion on selective excitation and their correction by prewarping
Authors: Chan Frandics , Pauly John , Macovski Albert 
Published: March 2007

AbstractIn a magnetic resonance imaging system, an RF power amplifier is employed to boost an RF pulse to sufficient strength to excite the nuclear spins in a subject. The nonideal behavior of this amplifier distorts a selective‐excitation pulse, and this distortion in turn degrades the slice profile. We have found two types of nonideal behavior particularly troublesome: nonlinearity and incidental phase modulation. One of their effects is the introduction of an unwanted “skirt” in the out‐of‐slice region of a slice profile. We present an effective method of correction in which a selective‐excitation pulse is prewarped to compensate for the distortion. © 1992 Academic Press, Inc.
Correction of chemical‐shift artifacts in 19F imaging of PFOB: A robust signed magnitude method
Authors: Lee H. K. , Nalcioglu O. , Buxton R. B. 
Published: March 2007

AbstractThis paper describes a method for correcting the chemical‐shift artifacts in 19F NMR imaging of perfluoroctylbromide emulsion (PFOB) by utilizing the two spectral peaks of PFOB which have a long T2 value in conjunction with the Dixon method. Corrected images are obtained from the magnitude of the measured images using the sign determined from the phase images. The method was tested in the presence of several phase deformation factors, such as static magnetic field inhomogeneity and inaccurate time shift of the π refocusing pulse, which affect the phase errors of each pixel in the reconstructed image. The advantage of the signed magnitude method is demonstrated experimentally by comparing it with the currently used complex and magnitude summation/subtraction methods. © 1992 Academic Press, Inc.
Measurement of the T2 relaxation time of ethanol and cerebral metabolites, in vivo
Authors: Rose Stephen E. , Crozier Stuart , Brereton Ian M. , Moxon Leith N. , Galloway Graham J. , Bore Peter , Doddrell David M. 
Published: March 2007

AbstractThe SPACE volume selection technique was combined with a spin‐echo sequence to measure the transverse relaxation time of the resonances of ethanol and cerebral metabolites in the dog brain, in vivo. The method was extended to measure brain metabolite T2, values in the rat using 1H NMR microspectroscopy. The T2 decays for the resonances of the metabolites N‐acetylaspartate, creatine/phosphocreatine, and choline/phosphorylcholine were found to be biexponential with long T2 components of 490, 260, and 350 ms for the dog and 490, 220, and 355 ms for the rat brain, respectively. The existence of a second T2 component may originate from J‐coupled nonresolved metabolite resonances. The relaxation decay for the ethanol triplet could be fitted to a single exponential giving a T2 relaxation time of 335 ms. However, given the large errors in the measurement of ethanol peak intensities at short echo times because of overlapping lipid signal and the effects of J‐modulation, a biexponential decay with a long T2 component of 335 ms cannot be ruled out. Ambiguities regarding the reported partial detection of the 1H NMR signal of ethanol in the brain are discussed. © 1992 Academic Press, Inc.
The effect of postinfarction intramyocardial hemorrhage on transverse relaxation time
Authors: Lotan Chaim S. , Miller Sandra K. , Cranney Gregory B. , Pohost Gerald M. , Elgavish Gabriel A. 
Published: March 2007

Abstract1H NMR imaging has been used to define zones of myocardial infarction (MI), which appear as areas of relatively increased signal intensity (SI). However, zones of decreased SI have been observed within or around the areas of infarction in NMR images acquired at high magnetic fields. To determine the cause of these areas of reduced SI, ex vivo spin‐echo 1H NMR imaging at 1.5 T was performed in eight dogs following 72 h of coronary artery occlusion. In all dogs, a zone of increased SI (122 ± 7% compared to control myocardium; P < 0.01) was observed in the territory of the occluded coronary artery. In seven of the dogs, additional zones were also seen, within or around the central zone of increased SI, which displayed SI that was reduced in comparison with the local enhanced intensity, but was similar to the intensity of normal myocardium (97± 7% compared to control; P = NS). Gross inspection and histological assessment of sliced myocardium disclosed hemorrhage in these regions characterized by locally decreased NMR SI. Image‐derived calculation of T2 in the various infarct regions revealed a significant shortening of T2, in the hemorrhagic infarct zones characterized by decreased SI, in comparison with the nonhe‐morrhagic infarct zones characterized by increased SI (59 ± 7 ms vs 73 ± 10 ms, P < 0.05). No difference was found, however, between the observed T2 of hemorrhagic infarct and of control tissue (57 ± 4 ms). Using a biexponential analysis of T2 from the hemorrhagic infarct zones, the intrinsic T2 of water protons affected by hemorrhage was determined to be 43 ± 9 ms, significantly reduced in comparison with the values obtained with the standard monoexponential fit. The reduction in T2 in the hemorrhagic zone is consistent with the paramagnetic effects of deoxyhemoglobin associated with intramyocardial hemorrhage. Thus the apparent T2, measured in hemorrhagic infarct tissue, represents the result of an averaging effect of infarct and hemorrhage on T2 relaxation times. These observations improve our understanding of the changes in NMR SI within the infarcted regions, and may provide a noninvasive method for the detection and quantitative assessment of intramyocardial hemorrhage. © 1992 Academic Press, Inc.
Theory of paramagnetic contrast agents in liposome systems
Authors: Barsky D. , Pütz B. , Schulten K. , Magin R. L. 
Published: March 2007

AbstractWe develop a theoretical description of nuclear spin relaxation mediated by MRI contrast agents and transport processes in liposome systems. Such systems compartmentalize the physical space such that paramagnetic contrast agents, which enhance relaxation, are trapped in some subvolume. Due to diffusive transport across compartmental barriers, i.e., across liposome membranes, nuclear spins in the whole volume exhibit fast relaxation. The description developed is based on the diffusion–Bloch equations for the nuclear magnetization with appropriate boundary and continuity conditions. From this set of equations a new inhomogeneous differential equation for the local relaxation times is derived. For simple geometries of compartmentalized spaces the equation can be solved analytically. A simple formula for average relaxation times in liposome systems is presented. The resulting relaxation times agree well with observations. © 1992 Academic Press, Inc.
Measurement of relative regional tumor blood flow in mice by deuterium NMR imaging
Authors: Evelhoch Jeffrey L. , McDouall Jacqueline B. Larcombe , Mattiello James , Simpson Nicholas E. 
Published: March 2007

AbstractA noninvasive method to measure relative regional tumor blood flow (rTBF) throughout murine tumors which uses deuterium NMR imaging to observe regional uptake of HOD after bolus iv injection of D2O is introduced. HOD uptake images are formed by subtraction of a background (preinjection) image from 94‐s gradient‐refocused deuterium NMR images acquired starting 30 s and 10 min after D2O injection. The pixel intensity in the HOD uptake image acquired starting 30 s after injection is directly related to rTBF with a limit of detection estimated at 7 ml/(100 g‐min). The image acquired 10 min after D2O injection extends the estimated limit of detection for rTBF to 3 ml/(100 g‐min). Heterogeneity in rTBF and regional effects of photodynamic therapy within RIF‐1 tumors are readily perceived. This method may provide a valuable tool to further our understanding of the relationship between blood flow and therapeutic response in tumors. © 1992 Academic Press, Inc.
Investigation of the magnetic properties of iron oxide nanoparticles used as contrast agent for MRI
Authors: Pouliquen D. , Perroud H. , Calza F. , Jallet P. , Le Jeune J. J. 
Published: March 2007

AbstractSuperparamagnetic iron oxide particles, a new class of contrast agents for MRI, are extremely good enhancers of proton relaxation. However, the development of such particle systems has resulted in a wide range of preparations whose physico‐chemical properties differ greatly. We have conducted a set of physical experiments: X ray diffraction analysis, relaxivity measurements, susceptibility determinations, and thermomagnetic cycling on different preparations of superparamagnetic particles. Our results demonstrate a good correlation between susceptibilities measured in liquid samples at room temperature and the R2/RI ratio. Susceptibility measurements between liquid nitrogen temperature and room temperature show three different types of behavior dependent on the size of iron oxide crystals. Comparison of heating and cooling curves from strong field thermomagnetic cycles provides information about the maghemite/magnetite crystal content. The information on magnetic properties reported in this study may help to characterize and to select these materials for use as MRI contrast agents. © 1992 Academic Press, Inc.
Radial scanning technique for volume selective 31P spectroscopy
Authors: Rim C. Y. , Ra J. B. , Cho Z. H. 
Published: March 2007

AbstractAn interlaced radial scanning method that is ideally suited for 31P spectroscopy with short T2 components and a wide spectral range is presented. The proposed method, which uses an additional radial gradient and radial scans in the k‐space, minimizes T2 decay during the selection time and also optimizes the volume selectivity in a given gradient field strength. Simulation and experimental results with a short selection time of 2 ms demonstrate that the proposed method is suitable for volume selective 31P spectroscopy. © 1992 Academic Press, Inc.
In vivo T1 values from guinea pig brain depend on body temperature
Authors: Youl B. D. , Hawkins C. P. , Morris J. K. , Duboulay E. P. G. H. , Tofts P. S. 
Published: March 2007

AbstractT1 and T2 values were calculated from guinea pig brain in vivo at 0.5 T. T1 values showed significant dependence on body temperature, but the effect varied significantly from animal to animal and from one tissue type to another. Mean dependencies were 8.2 ms/°C for corpus callosum, 14.7 ms/°C for gray matter, and 21.5 ms/°C for hemispheric white matter (1.7, 2.6, and 4.5%/°C, respectively), all with respect to core temperature. These findings suggest that body temperature monitoring and control may be needed when sensitive measurements of T1 are being made. There was evidence for regulation of brain temperature within the hyperthermic range of body temperature. © 1992 Academic Press, Inc.
Liver tissue characterization by in vitro NMR: Tissue handling and biological variation
Authors: Moser Ewald , Holzmueller Peter , Gomiscek Gregor 
Published: March 2007

AbstractThe extraction of reliable and useful relaxation time data for tissue characterization by NMR requires strict protocols, optimized for each type of biological tissue, which include parameters like storage duration and temperature as well as measurement parameters. Spin‐lattice relaxation times in liver tissue vary not only with NMR frequency but also with their “time‐after‐excision characteristics,” while spin‐spin relaxation times are almost independent of most parameters which influence T1 at 20 MHz in normal liver tissue (e.g., species, sex, circadian rythm, starvation). T2, however, being more sensitive to water content and pH changes, is well suited for detecting nonspecific tissue alterations (e.g., due to ischemia, chemical toxins). Following the suggestions outlined herein, investigation of at least 120 min of time‐after‐excision (storage) effects allows the significant distinguishing of various physiological differences in normal liver tissue as well as improvement of early detection of liver pathologies. © 1992 Academic Press, Inc.
Experimental design and fabrication of birdcage resonators for magnetic resonance imaging
Authors: Vullo Thomas , Zipagan Raymond T. , Pascone Romeo , Whalen Joseph P. , Cahill Patrick T. 
Published: March 2007

AbstractAlthough the birdcage resonator has been theoretically described for single‐ and multinuclear operation, this study provides the basic experimental guidelines needed for the fabrication and testing of such coils for various geometries and resonant frequencies from 10 to 95 MHz. The correlation of coil dimensions and resonant frequencies with individual inductance elements, L1, and L2, is also shown. Experimentally derived algorithms are presented for the determination of the capacitance needed for low‐pass resonators based on measurements of the coil's “global” inductance. Ten low‐pass birdcage coils with eight legs were evaluated and their four resonant frequencies were within 4% of theoretical predictions. © 1992 Academic Press, Inc.
A data adaptive reprojection technique for MR angiography
Authors: Korosec F. R. , Weber D. M. , Mistretta C. A. , Turski P. A. , Bernsteins M. A. 
Published: March 2007

AbstractInability to detect vessel overlap and vascular loops can compromise the interpretation of magnetic resonance angiograms. A data‐adaptive ray tracing (DART) technique was developed to produce the appropriate variations in signal intensity at points of vessel overlap in order to simulate the standard angiographic representation of vessels. In this technique a threshold is utilized to identify vessels in the image slices composing a 3D angiographic data set. A mask, which defines regions slightly larger than the vessel boundaries, is obtained by blurring the vessel information surviving the initial threshold. This mask is converted to binary form prior to multiplication by the original angiographic data set. Following application of an additional threshold to the masked data, line integrals through the regions defined by the mask are performed to obtain an angiographic signal proportional to the integrated vessel signal as in conventional angiography. This integrated reprojection is then uniquely combined with a maximum intensity pixel (MIP) reprojection to produce the final DART image. The application of the DART technique to 2D time‐of‐flight and 3D phase‐contrast angiograms successfully enabled the identification of overlapping vessels and vascular loops. DART was also found to produce less vessel narrowing than the MIP technique. © 1992 Academic Press, Inc.
Creatine kinase activity in rat skeletal muscle with intermittent tetanic stimulation
Authors: Le Rumeur E. , Le Moyec L. , De Certaines J. D. 
Published: March 2007

AbstractATP synthesis from PCr through creatine kinase reaction was measured in vivo in rat leg muscle using 31P NMR magnetization transfer and progressive saturation. Both techniques determined a spin‐lattice relaxation time for PCr of 3 s at rest and an identical forward rate constant of 0.22‐0.26 s−1. In stimulated muscles, magnetization transfer showed that flux was not changed with a steady‐state PCr of 54% of initial level. During stimulation inducing a PCr decrease to 38% of initial value, flux was significantly lowered by 30%. These findings could result from an accumulation of ions and water increases or from compartmentation of ATP and PCr in different pools either in the muscle cell or in the different muscle fibers. In addition, these results could reinforce the hypothesis against a crucial role for creatine kinase shuttle in the ATP supply in skeletal muscle. © 1992 Academic Press, Inc.
MRI susceptometry: Image‐based measurement of absolute susceptibility of MR contrast agents and human blood
Authors: Weisskoff Robert M. , Kiihne Suzanne 
Published: March 2007

AbstractWe present a novel NMR imaging technique that allows absolute determination of the magnetic susceptibility constant, χ, of a solution. By comparing the phase difference of MR images produced with an instant (echo planar) “offset” spin‐echo sequence, we obtain a direct measure of the magnetic field perturbations caused by the solution. We demonstrate this method with Gd(DTPA), Dy(DTPA), human red blood cells, and superparamagnetic iron oxide particles. © 1992 Academic Press, Inc.
Scan time reduction in snapshot flash MRI
Authors: Jakob P. M. , Haase A. 
Published: March 2007

AbstractWe describe the speeding up of snapshot FLASH MRI by placing a slice selection experiment before the whole imaging sequence. In conventional snapshot FLASH slice selection is made in every projection, thus consuming a great deal of experimental time. This problem can be overcome by applying only one slice‐selective procedure before starting the imaging. The idea is to make a selective saturation of the outer volume and to interrogate the unaffected slice by a train of rapid, hard, low‐angle pulses. By this new method the measuring times of snapshot FLASH can be further reduced. © 1992 Academic Press, Inc.
Concurrent quantification of tissue metabolism and blood flow via 2h/31P NMR in Vivo. 11. validation of the deuterium nmr washout method for measuring organ perfusion
Authors: Neil Jeffrey J. , Song Sheng‐kwei , Ackerman Joseph J. H. 
Published: March 2007

AbstractThe deuterium washout technique of measuring tissue blood flow is based upon NMR detection of HOD (administered as D2O saline, but typically detected as HOD because of rapid proton‐deuteron exchange) as a freely diffusible tracer. Though this method is coming into more general use, it has not yet been rigorously validated in vivo against an accepted, independent measure of tissue blood flow. To this end, simultaneous radiolabeled micro‐sphere and HOD washout blood flow measurements were made in rat gastrocnemius muscle. D2O saline was administered either intramuscularly or intraarferially (near the aortic bifurcation), and the sciatic nerve was electrically stimulated to increase the muscle blood flow rate. Over a range of flows of 2 to 80 ml/(100 g. min), comparison of micro‐sphere and HOD washout measurements showed good agreement, with r = 0.92 (n = 16) for intramuscular administration and r = 0.91 (n = 12) for intraarterial administration. These data strongly suggest thatthe HOD washout technique provides accurate blood flow measurements in skeletal muscle.