bluuebunny/crossref_metadata_2025_split huggingface dataset:
Resolution of phospholipid molecular species by 31P NMR
Authors: Pearce J. M. , Komoroski R. A. 
Published: March 2007

AbstractPhosphorus‐31 NMR chemical shifts of phospholipids (PLs) solubilized in bile salts were studied with respect to variations in the structure of the acyl substituents. The presence of double bonds in the acyl chains of phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and phosphatidic acid (PA) induced small but consistent upfield shifts relative to the corresponding disaturated acyl PL signals. The magnitudes of the unsaturation‐related upfield shifts were approximately twice as large in sodium cholate as in sodium deoxycholate. Chemical shift separations of PC, PE, and PG dipalmitoyl‐dioleoyl species pairs increased slightly at lower temperatures. Resolution of the PC species pair was maximized and nearly independent of cholate‐to‐PL ratio at values greater than about 100 in 2% cholate. Only the PA species resolution varied significantly over the pH range 6.5 to 9.5, in the vicinity of its pK2. Shift differences for a homologous series of disaturated acyl PCs showed a logarithmic dependence on chain length. Spectra for a variety of PC standards were used to interpret the composite PC signals from egg yolk extract, soybean extract and whole human amniotic fluid. The 31P NMR analyses were consistent with published chromatographic studies. Interpretation of composite PL signals in the cholate system is simplified for mixtures having restricted acyl chain length and degree of unsaturation.
Echo‐planar spin‐echo and inversion pulses
Authors: Pauly John , Spielman Dan , Macovski Albert 
Published: March 2007

AbstractThe echo‐planar k‐space trajectory can be used as the basis for any two‐dimensional selective pulse. The main application is spectral‐spatial pulses, which must be based on the echoplanar trajectory. In this paper we show how echo‐planar spinecho (EPSE) pulses may be designed.
Analysis of systematic and random error in MR volumetric flow measurements
Authors: Wolf Ronald L. , Ehman Richard L. , Riederer Stephen J. , Rossman Phillip J. 
Published: March 2007

AbstractThe spatial aspects of error in 2D MR cine phase‐velocity mapping are considered in order to define acquisition strategies which will minimize error in measuring volumetric flow. Error was separated into two categories: systematic and random. Potential sources of systematic error examined were intravoxel phase dispersion (IVPD), partial volume effects, misalignment of flow axis and flow‐encoding gradients, and improper choice of vessel voxels for flux calculations. Random error was addressed using analysis of propagation of variance. Analytical expressions for sources of error were derived; and computer models were used to test the analytical models. Flow phantom studies examining error in MR volumetric flow measurements were performed and compared with error predicted by the analytical models. Expected error in several clinical situations of interest was then derived to find appropriate acquisition strategies. Spatial resolution, signal to noise ratio, velocity sensitivity and the ratio of the modulus of moving isochromats to that of static isochromats were found to be the most important parameters in controlling error and were found to cause competing effects with respect to systematic and random error.
Three‐Dimensional NMR microscopy of rat spleen and liver
Authors: Zhou Xiaohong , Magin Richard L. , Alameda Jay C. , Reynolds Harry A. , Lauterbur Paul C. 
Published: March 2007

AbstractThree‐dimensional microscopic NMR images of spleen and liver specimens from rats injected wlth dextran magnetite particles and from controls were obtained at 4.7 T, using a specially designed probe in conjunction with a 3D filtered back projection reconstruction algorithm. All of the images were reconstructed as 643 arrays with (25 μm)3 isotropic voxels. With the aid of the MR contrast agent, the red pulp and marginal zone of the spleen and the portal triad of the liver could be distinguished from the surrounding tissue in T2‐weighted images. For mature rat spleen, natural contrast in T2‐weighted images was found to distinguish the same features. Histolog‐ical examinations of the tissues with and without contrast agent were also performed using an optical microscope. Microscoplc NMR images, despite their lower resolution, clearly revealed many features seen in the optical images.
A pitfall associated with determination of transverse relaxation times of the 31P NMR signals of ATP using the Hahn spin‐echo
Authors: Jung Wulf‐Ingo , Straubinger Klaus , Bunse Michael , Widmaier Stefan , Schick Fritz , Küper Klaus , Dietze Günther , Lutz Otto 
Published: March 2007

AbstractT2 measurements of 31P NMR signals of ATP using the Hahn 90°–180° spin‐echo sequence imply difficulties whenever the 180° pulse angle is not completely perfect. The reason for this finding is the crucial influence of the J ‐couplings of the ATP signals which result in intensity modulations and consequently in false T2 values even when the echo times are chosen to TE = n/J. Examinations on the calf muscles of healthy volunteers were performed to demonstrate this effect and its influence on in vivo T2 determinations. The T2 relaxation times evaluated with the Hahn spin‐echo in combination with a Helmholtz coil are far shorter than the true T2 values.
Improved myocardial tagging contrast
Authors: Fischer S. E. , McKinnon G. C. , Maier S. E. , Boesiger P. 
Published: March 2007

AbstractMyocardial tagging is a new noninvasive MRI method that allows the study of myocardial motion with high accuracy. However, with conventional tagging techniques tagging contrast is impaired at later heart phases due to longitudinal relaxation. An improved method, called Complementary SPAtial Modulation of Magnetization (CSPAMM), which separates the component of the magnetization with the tagging information from the relaxed component by subtraction of two measurements with first a positive and then a negative tagging grid, is presented. This technique improves the grid contrast and greatly facilitates the automatic evaluation of the myocardial motion. Thus the motion assessment of the entire heart cycle becomes possible. The improvements are documented by numerical simulations and by experiments on phantoms and on human volunteers.
Fast MRI by creating multiple spin echoes in a CPMG sequence
Authors: Oshio Koichi , Jolesz Ferenc A. 
Published: March 2007

AbstractA fast multislice imaging technique has been developed. RASTER (Rapid Acquisition with Stimulated Echo Refocusing) is based on RARE (Rapid Acquisition with Relaxation Enhancement), and creates multiple spin echoes/each 180° pulse utilizing stimulated echoes, and phase encode each differently. The sequence can be much faster than RARE while keeping the same spin echo image contrast. The main limitation of the technique is reduced signal‐to‐noise ratio.
MRI evaluation of myocardial perfusion without a contrast agent using magnetization transfer
Authors: Prasad P. V. , Burstein D. , Edelman R. R. 
Published: March 2007

AbstractWe propose a new magnetic resonance imaging (MRI) technique that is sensitive to myocardial tissue perfusion that obviates the use of an extrinsic contrast agent. Significant advantages of such a technique are that it avoids accumulation of contrast agent when repeated studies are performed on the same subject and that it is completely noninvasive. The method makes use of a combination of magnetization transfer (MT) and T1sut (measured spin‐lattice reiaxation time in the presence of MT) weighting. in this Communication, we present observations from experiments with an isolated rat heart model that demonstrate increase of MT‐weighted signal Intensity and T1sut with flow. Also included are data showing that these effects can be made synergistic for enhancing the sensitivity to perfusion. We have observed about a 3% change in MT‐weighted intensity end up to 10% change in MTT1sut‐weighted intensity for a change of 1 ml/min in global flow rate.
Feature‐recognizing MRI
Authors: Cao Yue , Levin David N. 
Published: March 2007

AbstractWe describe a new theory of MR imaging that utilizes prior information in the form of a set of “training” images thought to be similar to the “unknown” objects to be scanned. First, the training images are processed to find an orthonormal series representation of these images that is more convergent than the usual Fourier series. The coefficients in this new series can be calculated from a subset of the phase‐encoded signals needed to construct the Fourier image representation. The characteristics of the training images also determine exactly which phase‐encoded signals should be measured in order to minimize error in the image reconstruction. The optimal phase‐encodings are usually scattered nonuniformly in k‐space. Good results were obtained when this theory was applied to imaging data from simulated objects and to experimental data from phantom scans. This theory provides the basis for developing efficient scanning and image reconstruction techniques that are “tailored” to each body part or to particular disease states.
Accurate measurement of T1in vivo in less than 3 seconds using echo‐planar imaging
Authors: Gowland P. , Mansfield P. 
Published: March 2007

AbstractThis paper describes a rapid and accurate method for meassuring T1 in vivo using an echo‐planar imaging version of the Look‐Locher sequence. T1 values from 76 to 1330 ms have been measured in 3 s with a mean accuracy of 4.6%.
Motion suppression improves quantification of rat liver volume in vivo by magnetic resonance imaging
Authors: Cockman M. D. , Hayes D. A. , Kuzmak B. R. 
Published: March 2007

AbstractIn response to the presence of certain compounds, rat liver weight can increase. Under the assumption that the liver density does not change, the liver volume will increase as well. To develop the capability to monitor this process noninvasively over time, we used liver volumes determined from MR images to estimate the in vivo liver volumes and weights of normal rats. We acquired multislice, spin‐echo images from 18 rats using several protocols for suppression of motion artifacts. We found that volumes determined from data obtained using a combination of gradient moment mulling and respiratory gating, or a combination of signal averaging and “retarded” (after the π pulse) phase‐encoding, produced the most accurate estimates of in vivo liver volume and weight.
Localized real‐time velocity spectra determination
Authors: Hu Bob S. , Pauly John M. , Nishimura Dwight G. 
Published: March 2007

AbstractThe accurate measurement of flow velocity has long been a subject of NMR research. In the field of medical imaging, a variety of techniques primarily based on the principle of Fourier encoding have been described. Due to time constraints, necessary trade‐offs exist between spatial versus velocity spectral resolution. In general, either the average velocity of individual pixels is displayed or velocity spectral determinations are made at the cost of spatial localization. The recent development of multidimensional excitation pulses makes spatial localization possible during the excitation phase of the pulse sequences. This approach, coupled with time varying gradient readout, can be used to obtain single‐shot localized velocity spectra. Using these concepts, we have obtained in vivo real‐time measurements of localized velocity spectra on our clinical imager.
Generalized K‐space analysis and correction of motion effects in MR imaging
Authors: Louis Lauzon M. , Rutt Brian K. 
Published: March 2007

AbstractA new approach to understanding and reducing motion artifacts in magnetic resonance imaging (MRI) is introduced. This paper presents a novel technique for correcting generalized motion artifacts arising from translation, rotation, dilation, and compression, or any combination thereof. We also describe a new pulse sequence and a specialized postprocessing technique required to suppress these motion artifacts. The correction algorithm corrects for generalized motion. The theoreticial basis of the correction scheme is founded upon the (k,t)‐space formalism and the concept of pulse sequence contrast mapping functions. The proposed (k,t) formalism is based on the Fourier projection slice theorem and allows us to determine how motion artifacts arise. The correction technique currently suffers from some spatial resolution and signal‐to‐noise ratio limitations, and works better for small object than large objects. These problems will be investigated in subsequent studies.
31P NMR spectra of intact red blood cells: Quantitation of UDPGlucose and UDPGalactose
Authors: Wehrli Suzanne L. , Palmieri Michael J. , Reynolds Robert A. , Segal Stanton 
Published: March 2007

AbstractThe combined levels of uridine diphosphogalactose (UDPGal) and uridine diphosphoglucose (UDPGlu) were measured directly by 31P NMR spectroscopy in intact fully oxygenated erythrocytes. Quantitative analysis was obtained using a sealed capillary of methylene diphosphonate (MDP) calibrated with standard solutions of UDPGlu and UDPGal of known concentration prepared in KRB/BSA. The combined peaks of UDPGlu and UDPGal were integrated after subtraction of the underlying broad component originating from membrane phospholipids. The average concentration of 27.16 ± 5.18 nmole/ml or 8.08 ± 1.36 μmole/100 g hemoglobin obtained for these metabolites correlated well with their total determined by HPLC of trichloracetic acid (TCA) extracts of the same samples.
31P relaxation rates to evaluate physiological events in the heart
Authors: Osbakken Mary D. , Wroblewski Krzysztof , Zhang Danning , Ivanics Tamas , Wehrli Suzanne 
Published: March 2007

AbstractThe present study was performed to determine whether 31P NMR relaxation times (T1) of adenosine triphosphate (ATP) might be used to monitor the resultant altered myocardial physiology produced by ischemia and possibly to explain mechanisms of altered physiology. To this end, pre‐and post‐ischemic T1s were determined in hearts perfused in the Lan‐gendorff mode, using 31P NMR inversion recovery methods. In hearts without any pretreatment (CON), post‐ischemic ATP Ti values were significantly decreased compared with pre‐isch‐emic values (P <0.05): Pre‐isch: γ = 0.58 ± 0.08; α = 62 ± 0.06; β = 0.38 ± 0.08; Post‐isch: γ = 0.33 plusmn; 0.05; α = 0.43 ± 0. 03; β = 0. 23 plusmn; 0.05. In groups pretreated with creatine (CR), cyclocreatine (CY), or superoxide dismutase plus catalase (SOD‐CAT) before ischemia, the post‐ischemic ATP T1 values were simlilar and were not significantly changed from pre‐ischemic values. These combined data suggest that T1s of ATP might be used to monitor altered myocardial physiology and could provide insight into mechanisms of alteration.
Assessment of human colorectal biopsies by 1H MRS: Correlation with histopathology
Authors: Lean Cynthia L. , Newland R. C. , Ende D. A. , Bokey E. L. , Smith Ian C. P. , Mountford Carolyn E. 
Published: March 2007

AbstractSamples (3 mm3 of histopathologically normal (n = 15) and carclnomatous tissue (n = 15) were obtained from colectomy specimens and examined by 1H MRS. A combination of one‐and two‐dimensional spectra, obtained with appropriate acquisition and processing parameters, provide multiple diagnostic parameters allowing the distinction between normal and carcinomatous tissue. The diagnostic parameters include rosonances from choline, choline‐based, and other metabolites, cell surface fucosylation, and altered lipid profiles. Tissues histopathologically classified as normal, while remaining distinct from the malignant spectral profile, were found to fit into two categories, one of which had some of the spectral characteristics of malignancy. These results indicate that 1H MRS identifies abnormal colorectal mucosa, which is not morphologically manifest.Such abnormalities have been reported previously to exist in premalignant colorectal tissue by monoclonal antibody studies. Collectively, these results suggest that a clinical study of colorectal biopsies by 1H MRS could provide support for the use of MRS as an adjunct to current pathological procedures.
Oxygen tension in a murine tumor: A combined EPR and MRI study
Authors: Bačić G. , Liu K. J. , O'Hara J. A. , Harris R. D. , Szybinski K. , Goda F. , Swartz H. M. 
Published: March 2007

AbstractThe effects of fusinite, a new agent for the measurement of the concentration of oxygen in vivo by EPR, on MRI images have been studied. There was little effect on spin‐echo T1‐weighted images, but the fusinite resulted in large effects on T2‐weighted images. Especially large effects could be observed when using spoiled gradient echo sequences (SPGR). The observed measurements of oxygen by EPR corresponded to the relative vascularity at the site of the fusinite both histologically and by MRI studies of vascularity using Gd‐DTPA as a contrast agent. We conclude that by using the effects of fusinite on magnetic susceptibility, it can be located accurately and noninvasively with MRI and thereby the value of the use of fusinite to measure concentration of oxygen in vivo is enhanced.
Relaxometry, animal biodistribution, and magnetic resonance imaging studies of some new gadolinium (III) macrocyclic phosphinate and phosphonate monoester complexes
Authors: Geraldes C. F. G. C. , Sherry A. D. , Lázár I. , Miseta A. , Bogner P. , Berenyi E. , Sumegi B. , Kiefer G. E. , McMillan K. , Maton F. , Muller R. N. 
Published: March 2007

AbstractThe Gd3+ complexes of three new phosphorus containing tetraaza macrocycles (1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetrakis (methylene ethylphosphonic acid), H4DOTEP; 1,4,7,10‐tetraazacyclododecane‐l,4,7,10‐tetrakis (methylene phosphonic acid monoethylester), H4DOTPME; and the corresponding n‐butyl ester, H4DOTPMB) were prepared and examined for possible use as MRI contrast agents. Although thermodynamically and kinetically less stable than Gd(DOTA)− in saline and HSA solution, the stability of these new macrocyclic complexes appears to be sufficiently high for in vivo applications. NMRD relaxivity profiles of the three complexes indicate that the number of inner sphere water molecules for these chelates is ≤1 and that the more hydrophobic chelate, Gd(DOT‐PMB), binds to human serum albumin (HSA). Biodistribution studies of the radioactive 153Sm or 159Gd chelates in rats, gamma imaging of the 153Sm chelates in rats, and proton MRI studies of the nonradioactive Gd3+ chelates in rabbits all indicate that the DOTPMB complexes accumulate preferentially in the liver, spleen, and small intestines while the more hydrophilic DOTEP and DOTPME complexes appear to display renal clearances similar to other low molecular weight contrast agents.
Measurement of regional blood oxygenation and cerebral hemodynamics
Authors: Hoppel Bernice E. , Weisskoff Robert M. , Thulborn Keith R. , Moore John B. , Kwong Kenneth K. , Rosen Bruce R. 
Published: March 2007

AbstractAn echo planar linewidth mapping technique, Shufflebutt, has allowed temporal measurements of changes in linewidth caused by static inhomogeneities (ΔLWSI) and transverse relaxation rate (ΔR2) in models of hypoxia and hypercapnia. We demonstrate these changes are due to intravascular susceptibility differences(ΔX) between the blood and tissue. Contrast agent injections at a /ΔX equivalent to that of deoxygenatetd blood showed a twofold difference between the contrast agent and physiological anoxia values. Hypercapnia decreased both ΔLWSI and ΔR2 consistent with an increase in blood oxygenation. We attribute these findings to constant oxygen extraction during an increase in blood flow, resulting in less deoxygenated venous blood and thus reduced ΔX. For in vivoperturbations we found that ΔR/ΔR2′ ≈ 0.33, a ratio much different from that measured in whole blood phantoms (ΔR/ΔR2′ ≈ 2). This demonstrates that signal changes in these studies are produced predominantly by dephasing of extravascular protons due to field inhomogeneities produced by intravascular deoxygenated hemoglobin (deoxyHb).
A rapid interleaved method for measuring signal intensity curves in both blood and tissue during contrast agent administration
Authors: Taylor N. J. , Rowland I. J. , Tanner S. F. , Leach M. O. 
Published: March 2007

AbstractA method has been developed that uses dynamic MR imaging to measure simultaneously the changes in signal intensity due to paramagnetic contrast agent in blood and tissue, using interleaved single‐angle projection and imaging sequences. The basic projection/image sequence has a projection time resolution of 50 ms and can measure rapid changes in the blood signal intensity. Variants with a tissue suppression slab have time resolutions of 57 or 75 ms. Orientation of the projection and image planes can be defined independently. This technique will facilitate functional measurements using MR contrast agents, allowing the blood input function to be determined with excellent time resolution.
Intravascular susceptibility contrast mechanisms in tissues
Authors: Kennan Richard P. , Zhong Jianhui , Gore John C. 
Published: March 2007

AbstractThe factors affecting the rate of loss of transverse magnetization in gradient echo and spin‐echo pulse sequences have been quantified using computer modeling for media containing arrays of susceptibility variations. The results are particularly relevant for describing the signal losses that occur in tissues containing capillaries of altered intrinsic susceptibility from the administration of exogenous contrast agents or arising from changes in blood oxygenation. The precise magnitudes and relationship of gradient echo and spin‐echo decay rates depend on geometrical factors such as the sizes and spacings of the inhomogeneities, the rate of water diffusion, field strength, and echo times. The conventional separation of contributions to transverse decay rates arising from so‐called static field effects and diffusion is shown to be inappropriate for many situations of practical interest because diffusion introduces a motional averaging of the static field even in gradient echo sequences. The result of diffusion in some regimes is to reduce the decay rate from field inhomogeneities in gradient echo sequences, so that T2* is longer in media such as tissue where water diffuses reasonably rapidly, than would be the case for stationary nuclei. The effects of different types of contrast agent and the implications for functional imaging based on the effects of deoxyhemoglobin in brain tissue are considered.