bluuebunny/crossref_metadata_2025 huggingface dataset:
Persistent ascites and low serum sodium identify patients with cirrhosis and low MELD scores who are at high risk for early death
Authors: Heuman Douglas M. , Abou-Assi Souheil G. , Habib Adil , Williams Leslie M. , Stravitz Todd R. , Sanyal Arun J. , Fisher Robert A. , Mihas Anastasios A.
Published: March 2007

Despite the adoption of “sickest first” liver transplantation, pretransplant death remains common, and many early deaths occur despite initially low Model for End-stage Liver Disease (MELD) scores. From 1997-2003, we studied 507 cirrhotic United States veterans referred for consideration of liver transplantation to identify additional predictors of early mortality. Most of the patients were male (98%) with cirrhosis caused by hepatitis C and/or alcohol (88%). Data for 296 patients referred prior to February 27, 2002 (training group), were analyzed; findings were validated in 211 patients referred subsequently (validation group). In the training group, 61 patients (21%) died within 180 days without transplantation; their median initial MELD score was 21. MELD score, persistent ascites, and low serum sodium (< 135 meq/L) were independent predictors of early mortality. In patients with a MELD score of less than 21, only low serum sodium and persistent ascites were independent predictors of mortality; for MELD scores above 21, only MELD was independently predictive. Prognostic significance of persistent ascites and low serum sodium for low MELD score patients was confirmed in the validation group. Risk varied continuously with worsening hyponatremia. Modifying MELD, by including points for persistent ascites and low serum sodium, improved prediction of early pretransplant mortality in low MELD score patients. In conclusion, persistent ascites and low serum sodium identify patients with cirrhosis with high mortality risk despite low MELD scores. Ascites, hyponatremia, and other findings indicative of hemodynamic decompensation merit further prospective study as prognostic indicators in patients awaiting liver transplantation, and should be considered in setting minimal listing criteria. Supplementary material for this article can be found on the Hepatology website (http://interscience.wiley.com/jpages/0270-9139/suppmat/index.html). (Hepatology 2004;40:802-810).
Serum bilirubin levels in the U.S. Population: Gender effect and inverse correlation with colorectal cancer
Authors: Zucker Stephen D. , Horn Paul S. , Sherman Kenneth E.
Published: March 2007

Bilirubin, the primary end product of heme catabolism, is a key marker of liver and hematological disorders, and important cytoprotective properties have been ascribed to this bile pigment. The Third National Health and Nutrition Examination Survey, a comprehensive assessment of health and nutrition in the United States, was analyzed to determine the demographics and correlates of serum bilirubin levels in the general population. Men and women aged 17 and older were included in the weighted analysis, representing a total of 176,748,462 subjects. The mean serum total bilirubin in the adult population is 0.62 ± 0.003 mg/dL (SEM), with a 97.5% cut-off of 1.4 mg/dL. Serum bilirubin levels are significantly higher in men (0.72 ± 0.004) than in women (0.52 ± 0.003 mg/dL) and are lower in non-Hispanic blacks (0.55 ± 0.005 mg/dL) compared with non-Hispanic whites (0.63 ± 0.004 mg/dL) and Mexican Americans (0.61 ± 0.005 mg/dL). Bilirubin concentrations are unrelated to body weight but are reduced in active smokers. Individuals with a history of nondermatological malignancy exhibit significantly lower serum bilirubin concentrations compared with those who do not have a history of nondermatological cancer. In particular, each 1-mg/dL increase in serum bilirubin is associated with a markedly decreased prevalence of colorectal cancer (OR = 0.257; 95% CI 0.254-0.260). In conclusion, serum bilirubin levels vary significantly with gender, race, and smoking status. The observed inverse correlation between serum bilirubin concentrations and a history of nondermatological malignancy, particularly colorectal cancer, warrants further investigation of a potentially important chemopreventive function of bilirubin. (Hepatology 2004;40:827-835).
STAT-3 and the liver: A new station on our way to understand diabetes?
Authors: Kortylewski Marcin T. , Barthel Andreas
Published: March 2007

The transcription factor, signal transducer and activator of transcription-3 (STAT-3) contributes to various physiological processes. Here we show that mice with liver-specific deficiency in STAT-3, achieved using the Cre-loxP system, show insulin resistance associated with increased hepatic expression of gluconeogenic genes. Restoration of hepatic STAT-3 expression in these mice, using adenovirus-mediated gene transfer, corrected the metabolic abnormalities and the alterations in hepatic expression of gluconeogenic genes. Overexpression of STAT-3 in cultured hepatocytes inhibited gluconeogenic gene expression independently of peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1 alpha), an upstream regulator of gluconeogenic genes. Liver-specific expression of a constitutively active form of STAT-3, achieved by infection with an adenovirus vector, markedly reduced blood glucose, plasma insulin concentrations and hepatic gluconeogenic gene expression in diabetic mice. Hepatic STAT-3 signaling is thus essential for normal glucose homeostasis and may provide new therapeutic targets for diabetes mellitus.
Magnetization exchange in capillaries by microcirculation affects diffusion‐controlled spin‐relaxation: A model which describes the effect of perfusion on relaxation enhancement by intravascular contrast agents
Authors: Bauer Wolfgang R. , Hiller Karl‐Heinz , Roder Fridtjof , Rommel Eberhard , Ertl Georg , Haase Axel
Published: March 2007

The effect of perfusion on relaxation time in tissue has only been considered for first‐pass kinetics of NMR‐signal after application of contrast agents. The importance of perfusion on relaxation has not yet been studied for steady state conditions, i.e., when the intravascular relaxation rate is constant in time. The aim of this study is to develop a model in which T, relaxation is derived as a function of perfusion and intracap‐illary volume fraction (regional blood volume). Tissue is considered to be two‐compartment system, which consists of intracapillary and extravascular space. Intracapillary relaxation differs from relaxation in the arterial system due to diffusion‐exchange of magnetization from extravascular to intracapillary space. Perfusion tends to attenuate this difference and thus counteracts the effect on intracapillary relaxation. Relaxation in the extravascular space becomes a function of perfusion because extravascular and intracapillary magnetization are linked by diffusion. This dependence is presented in analytical form and a generic equation is derived. A T1 experiment is considered in which all spins of tissue and blood are inverted at the beginning. Calculations are performed for the fast exchange model of tissue. Perfusion increases relaxation enhancement of intravascular contrast agents. This effect is considerable in highly perfused tissue like myocardium. The dependence of relaxation on perfusion implies an overestimation of the regional blood volume when the calculation of the latter is based on tissue models that neglect perfusion. The model presented here is applied to predict the effect of perfusion on T1 imaging with FLASH‐pulse sequences because this technique has been proven to be a powerful method to obtain T1 maps within a short time interval. For the fast exchange model, two algorithms are suggested that determine perfusion and regional blood volume from T1 imaging in the presence and absence of intravascular contrast agents.
Echo‐volumar imaging (EVI) at 0.5 T: First whole‐body volunteer studies
Authors: Harvey Paul R. , Mansfield Peter
Published: March 2007

Improvements in the echo‐volumar imaging (EVI) technique and its application in whole‐body studies are described. Using an in‐house built 0.5 T echo‐planar imaging system, complete modulus three‐dimensional image data are acquired in 102 ms with real‐time display. Hardware limitations have restricted the maximum array size achievable to 64 × 32 × 8 voxels. Representative voxel dimensions are X = 6.0 mm; y = 4.0 mm, and z = 10.0 mm. Results on human volunteers are presented, showing cardiac, liver, and bladder images. Also shown are the first EVI gastric filling and emptying results.
Magnetic resonance chondro‐crassometry (MR CCM): A method for accurate determination of articular cartilace thickness?
Authors: Eckstein Felix , Sittek Harald , Gavazzeni Antonia , Schulte Erik , Milz Stefan , Kiefer Berthold , Reiser Maximilian , Putz Reinhard
Published: March 2007

A method for the assessment of articular cartilage thickness based on MRI is presented and tts accuracy and reproducibil‐tty tested. Six specimens of human patellae were imaged, using a fat‐supressed FLASH 3D sequence, and sectioned with a high‐precision band saw. The reglonal dlstribution of articular cartilage thickness was determined from the MR images and from the anatomical sections (intervals of 0.5 mm). Wtth image analysis 50–90% of the image points were found to lie within exactly the same thickness interval in corresponding patterns, and tess than 17% deviated more than 0.5 mm. More than 85% of ali pixels were reproducible wtth MRI after new positioning of the Joint No influence of the read‐out direction and no important differences between areas of thin and thick cartilage could be detected. The authors conclude that MR chondro‐crassometry can provide accurate and reproducible Information on cartilage thickness.
Reduction of physiological fluctuations in fMRI using digital filters
Authors: Biswal Bharat , Deyoe Edgar A. , Hyde James S.
Published: March 2007

Data obtained from functional magnetic resonance imaging are often limtted by a low signal‐to‐noise ratio. The time‐course data obtained from activated regions contain both system noise and physiological noise, primarily linked to the heart and respiratory rates, that are superimposed on task induced signals. Time averaging of a practical number of data sets is not very effective in improving the signal‐to‐noise ratio because netther system nor physiological noise is truly random. In this paper, a method is presented for fittering un‐wanted physiological fluctuations, including aliased signals that are formed as a result of long repetition time (TR) values. A pulse oximeter was used to obtain cardiac and respiratory Information during the scanning period. Fintte impulse response band‐reject digital fitters were designed to remove the physiological fluctuations. For comparison, cross‐correlation analyses were performed at the same tevel of statistical significance on both fittered and unfiltered data. We demonstrate that this method can improve the detection of weak signals without increasing the probability of false positives.
Artifacts and signal loss due to flow in the presence of Bo inhomogeneity
Authors: Drangova Maria , Pelc Norbert J.
Published: March 2007

An in vitro study was performed to investigate the effects of Bo inhomogeneity on magnetic resonance images of flow. Controlled inhomogeneity gradients (G1) were applied and the magnitude of the artifacts produced was quantified for different echo delay times (TE). Both steady and pulsatile flows were examined. In the presence of an inhomogeneity gradient, signal loss is apparent if the flow is pulsatile and/or if the slice thickness is large. The signal loss increases with increasing TE and G1. With pulsatile flow, ghosting artifacts are also generated. These increase in intensity with increasing TE and G1. In vivo, field inhomogeneity due to susceptibility variations is large enough to produce these effects. Representative time‐of‐flight images obtained of a normal volunteer with two different TEs demonstrate the effect in vivo. Flow‐related signal loss and artifacts, therefore, increase with increasing TE independent of the moments of the applied gradients.
A multipurpose MRI phantom based on a reverse micelle solution
Authors: Roe Jo E. , Prentice Wayne E. , Hornak Joseph P.
Published: March 2007

Many chemical solutions for use in magnetic resonance imaging phantoms have been reported in the literature. Each of these solutions has its application‐specific advantages and disadvantages. We propose a single reverse micelle phantom solution, which, although not a universal phantom solution, may find applications in testing of the radio frequency transmit and receive fields of an imaging coil, the homogeneity of the static magnetic field, and the suppression in a fat or water saturation imaging sequence. The solution is thermodynamically stable and biologically inert, it possesses a smaller standing wave artifact than water, and its overall spin lattice relaxation times may be adjusted.
Multiplet structure of 13C NMR signal from glutamate and direct detection of tricarboxylic acid (TCA) cycle intermediates
Authors: Lewandowski E. Douglas , Doumen Chris , White Lawrence T. , Lanoue Kathryn F. , Damico Lisa A. , Yu Xin
Published: March 2007

For the first time, 13C NMR signals are shown from 13C‐en‐riched, low‐level tricarboxylic acid (TCA) cycle intermediates from extracts of normal cardiac tissue. As the low tissue content of the key intermediates α‐ketoglutarate (α‐KG) and succinate (SUC) in normal, well perfused tissues has until now precluded direct NMR detection from intact tissues and tissue extracts, 13C NMR signal from glutamate has generally been used to infer the isotopomer patterns of intermediates that are in chemical exchange with glutamate. However, the required assumptions regarding intracellular compartmentation for such indirect analysis have not been previously tested, as glutamate is largely cytosolic while the TCA cycle enzymes are located in the mitochondria. Chromatographic isolation of α‐KG and SUC from heart tissue extracts allowed isotopomer analysis to be performed for comparison with that of glutamate. At steady state, a direct relationship between glutamate and α‐ketoglutarate isotopomers was found, but succinate isotopomers matched those of glutamate only in hearts that displayed negligible contributions from the oxidation of unla‐beled endogenous carbon sources.
In vivo phosphorus spectroscopy of human skin
Authors: Bohning Daryl E. , Wright Alexander C. , Spicer Kenneth M.
Published: March 2007

Skin 31P MRS measurements might detect metabolic damage from irradiation, chemotherapy, or ischemia. Although rat and cadaver data have demonstrated this potential (C. D. Cuono, et al., Wast Reconstr. Surg. 81,1–11 (1988), H. W. Klein, et al., Ann. Plast Surg. 20, 547–551 (1988)), few studies of in vivo phosphorus human skin spectra have been published (A. Zemtsov, et al., J. Dermatol. Surg. Oncol. 15, 1207–1211 (1989), A Zemtsov, et al., J. Am. Acad. Dermatol. 30, 959–965 (1994)), and those likely reflect underlying muscle as much as skin. To separate 31P skin and muscle spectra, we have developed a unique two‐layer “flotation” phantom for mapping coil sensitivity and an associated semiempirical two‐power RF depth‐resolved technique. Phantom and method have been applied in a study of 17 normal volunteers to obtain human in vivo 31P skin spectra uncompromised by muscle contamination and to quantitate ratios of major phosphometabolites. Skin results consistently showed low ratios of phosphocreatine (PCr) to adenosine triphosphate (ATP), high levels of phosphomonoester (PME), Pi, and phosphodiester (PDE) relative to PCr, and demonstrated a shift in pH toward greater alkalinity, compared to that with simultaneous muscle results.
Simultaneous extraction of cellular lipids and water‐soluble metabolites: Evaluation by NMR spectroscopy
Authors: Tyagi Rakesh Kumar , Azrad Anat , Degani Hadassa , Salomon Yoram
Published: March 2007

A method for simultaneous extraction of lipids and water‐soluble metabolites from a single cell sample was developed and optimized for NMR spectroscopy. Intermediary metabolites in cultured M2R mouse melanoma cells and changes therein in response to challenge with melanotropin were studied by 31P and 13C NMR. Cells were extracted with methanol, chloroform, and water (1:1:1, v/v/v). The contents of the chloroform and methanol‐water phases were separated and quantitatively recovered. The contents of the upper and lower phases compared well with the homologous fractions obtained by perchloric acid and Folch's lipid extraction methods. The pH of the extracts remained within the physiologic range, eliminating potential deleterious effect on cellular metabolites. The water phase contained minimal amounts of salts, making these extracts amenable to subsequent analytical procedures. Obtaining lipid‐ and water‐soluble metabolites from the same sample enables characterization of metabolic pathways that bridge the two cellular components in a quantitative manner.
Lanthanide‐based susceptibility contrast agents: Assessment of the magnetic properties
Authors: Fossheim Sigrid , Johansson Christer , Fahlvik Anne K. , Grace David , Klaveness Jo
Published: March 2007

The T2* contrast efficacy of paramagnetic contrast agents is dependent on their magnetic properties. Vibrating sample magnetometry (VSM) and the Live Chan NMR method have been used to evaluate the influence of ligand structure on the bulk magnetic susceptibility (BMS) of low‐molecular weight (LMW) lanthanide chelates. VSM was also used for the BMS assessment of LMW lanthanide chelates covalentiy attached to cross‐linked starch particles. The ligand structure had no influence on the BMS of the gadolinium (Gd) and dysprosium (Dy) chelates. The mean BMS value of the Dychelates was 1.8 fold higher than that of the Gd‐chelates. The holmium (Ho) OTPA‐BMA chelate had a similar BMS to that of Dy‐DTPA‐BMA while the lowest BMS was found for europium (Eu(lll)) DTPA‐BMA. The covatent attachment of Gd‐DTPA and Dy‐DTPA to a cross‐linked starch particle had no impact on their intrinsic magnetic properties. The BMS data were in good accordance with those obtained for non‐particulate bound LMW Dy‐ and Gd‐chelates. The magnetic susceptibility of the Gd‐OTPA labeled particles was described by the Curie law, indicative of no magnetic interactions between Gd‐DTPA molecules. The magnetic susceptibility of the Dy‐DTPA labeled particles followed the Curie‐Weiss law with a Curie‐Weiss temperature of about ‐2 K, indicating magnetic interactions. The magnetic susceptibility of Dy‐DTPA will, however, not be affected by such magnetic interactions at physiological temperatures.
Multiexponential T2 relaxation in degenerating peripheral nerve
Authors: Does Mark D. , Snyder Richard E.
Published: March 2007

The multiexponential T2 relaxation spectrum of peripheral nerve undergoing Wallerian degeneration has been measured both in vivo and in vitro. Degeneration of the sciatic nerve of the amphibian Xenopus laevis was induced by crush injury, and T2 relaxation spectra of the nerve were measured at several times up to 35 days following injury. Histologic evidence verified that the nerve underwent Wallerian degeneration. Relaxation spectra were observed to undergo measurable changes as degeneration progressed, the most evident being a reduction from three well‐resolved T2 components to one and a decline in the fraction of the spectra associated with the shortest T2 component The former appears to reflect the collapse and loss of myelinated fibers, while the latter a combination of interstitial edema and myelin loss.
Imaging of the active B1 field in vivo
Authors: Stollberger Rudolf , Wach Paul
Published: March 2007

The authors describe a method for accurate In vivo muttislice imaging of the active component of the B1 field which is based on a previously proposed method, which uses the signal intensity ratio of two images measured with different excitation angles, and a repetition time TR≥ 5 T1 The new method essentially reduces repetition and scan time by means of an additional compensating pulse. The suppression of T1 effects by this pulse are verified with simulations and measurements. Further investigations concerned the influence of slice selective excitation and magnetization transfer in multislice imaging to the B1 field determination. The stability and accuracy of the presented method is shown by several phantom and in vivo measurements. With the described method the active B1 field can be determined in vivo in 23 cross‐sections in less than 6 min.
An algorithm for eddy currents symmetrization and compensation
Authors: Zur Yuval , Stokar Saul
Published: March 2007

Eddy currents, which are induced in the magnet cryostat by pulsed magnetic field gradients in MRI, generate undesired eddy fields within the imaging volume. In this work, an automated and computerized algorithm to compensate these eddy currents is presented. The compensation is done in two steps: (i) Eddy fields are symmetrized electronically with an R‐C filter, (ii) The symmetric eddy fields are compensated by another R‐C filter. The compensation algorithm is iterative; therefore, errors that remain from one iteration are eliminated in the next iteration. Hence, the compensation process is very robust and accurate. It is shown that all the even harmonics of the eddy fields are eliminated by the symmetrization process, but the odd field harmonics remain. The amplitude of these odd harmonics can be significantly reduced if the gradient coils are designed so that the field they generate is spatially similar to the eddy fields.
Single‐shot, B1‐insensitive slice selection with a gradient‐modulated adiabatic pulse, BISS‐8
Authors: de Graaf Robin A. , Nicolay Klaas , Garwood Michael
Published: March 2007

An adiabatic pulse has been developed to accomplish uniform slice‐selective excitation with a spatially inhomogeneous B1. This new pulse can generate a uniform, arbitrary flip angle that is determined by four adjustable phase shifts in the pulse. Self‐refocused slice selection is achieved by modulating a Bo gradient in concert with the pulse frequency (or phase) modulation. B1‐compensated, self‐refocused slice selection is demonstrated in computer simulations and phantom experiments using a surface transmitter/receiver coil. This adiabatic pulse can provide optimal performance in multislice MRI and localized spectroscopy when transmitting with an inhomogeneous B1.
Abnormal cerebral metabolism in polydrug abusers during early withdrawal: A 31P MR spectroscopy study
Authors: Christensen James D. , Kaufman Marc J. , Levin Jonathan M. , Mendelson Jack H. , Holman B. Leonard , Cohen Bruce M. , Renshaw Perry F.
Published: March 2007

Phosphorus magnetic resonance spectroscopy (31P MRS) at 1.5 T was performed on nine polysubstance abusing men. All nine patients met DSM‐III‐R criteria for concurrent cocaine and heroin dependence, were neurologically normal, were negative for the human immunodeficiency virus, and had normal clinical brain MRI scans. Patients were scanned 2‐7 days after admission to a drug treatment unit. Eleven age‐matched control subjects also were studied. The ISIS localized phosphorus spectra were obtained from a 5‐cm thick axial brain slice and a 100‐cc white matter volume. In the brain slice, the phosphorus metabolite signal expressed as a percentage of total phosphorus signal was 15% higher for phosphomonoesters, 10% lower for nucleotide triphosphates (β‐NTP), and 7% lower for total nucleotide phosphates in polydrug abusers compared with those in controls. Phosphodiesters, inorganic phosphate, phosphocreatine, total phosphorus, pH, and free magnesium concentration were unchanged. None of these parameters correlated with the methadone dose or the number of days abstinence. Single photon emission computed tomographic imaging of a subgroup of the patients revealed abnormal cerebral perfusion in 80% of the patients scanned. These data suggest that cerebral high energy phosphate and phospholipid metabolite changes result from long term drug abuse and/or withdrawal and that these changes can be detected and studied by 31P MRS.
Removal of lipid artifacts in 1H spectroscopic imaging by data extrapolation
Authors: Haupt Christine I. , Schuff Norbert , Weiner Michael W. , Maudsley Andrew A.
Published: March 2007

Proton MR spectroscopic imaging (MRSI) of human cerebral cortex is complicated by the presence of an intense signal from subcutaneous lipids, which, if not suppressed before Fourier reconstruction, causes ringing and signal contamination throughout the metabolite images as a result of limited k‐space sampling. In this article, an improved reconstruction of the lipid region is obtained using the Papoulis‐Gerchberg algorithm. This procedure makes use of the narrow‐band‐limited nature of the subcutaneous lipid signal to extrapolate to higher k‐space values without alteration of the metabolite signal region. Using computer simulations and in vivo experimental studies, the implementation and performance of this algorithm were examined. This method was found to permit MRSI brain spectra to be obtained without applying any lipid suppression during data acquisition, at echo times of 50 ms and longer. When applied together with optimized acquisition methods, this provides an effective procedure for imaging metabolite distributions in cerebral cortical surface regions.
Improved MR images of arterial specimens by submersion in trichlorotrifluoroethane
Authors: Chu Kenneth C. , Martin Alastair J. , Rutt Brian K.
Published: March 2007

MR Images of ex vivo arterial specimens immersed in 1,1,2‐trichloro‐1,2,2‐trifluoroethane (R‐113) have improved signal‐to‐noise ratio and contrast‐to‐noise ratio. R‐113 has no hydrogen atoms, so it yields no proton signal; hence, the contrast between the specimen and its background is maximized. SNR is maximized because (i) R‐113 is nonconductive so that coil loading and inductive noise are minimized, and (ii) the volume susceptibility of R‐113 closely matches that of water and tissue so that T2* effects are minimized. Short‐term submersion of porcine aortas in R‐113 was found to have no significant effect on the artery's hydration level, relaxation time, tensile strength, and structure or quantity of elastin, collagen, or smooth muscle cells.
NMR studies on human, pathologically changed synovial fluids: Role of hypochlorous acid
Authors: Schiller Jürgen , Arnhold Jürgen , Sonntag Kerstin , Arnold Klaus
Published: March 2007

Recently, it has been reported that hypochlorous acid (HOCl), a special product of neutrophil myeloperoxidase, degrades N‐acetyl groups of N‐acetylglucosamine, chondroitin sulfate, hyaluronic acid, and minced articular cartilage via a transient product to acetate. This work concerns 1H NMR investigations of synovia! fluids of patients with rheumatoid arthritis (RA). Synovial fluids of patients with severe forms of this disease are characterized by enhanced 1H NMR signals for N‐acetyl groups (˜2.0 ppm) and acetate (1.90 ppm) and the appearance of a broad but less intense signal at 2.35 ppm. It is likely that this signal corresponds to the transient, chlorinated product of degradation of N‐acetyl groups by hypochlorous acid. Moreover, 1H NMR signal intensities of N‐acetyl groups and acetate strongly correlate with the myeloperoxidase activities in synovial fluids from patients with rheumatoid arthritis. These results have been confirmed by treatment of native sheep synovial fluid with sodium hypochlorite, resulting in the formation of the same resonances as observed in pathologically changed synovial fluids from humans. Thus, it is concluded that HOCI plays an important role for the cartilage degradation during rheumatoid arthritis.
Multislice interleaved excitation cycles (MUSIC): An efficient gradient‐echo technique for functional MRI
Authors: Loenneker Thomas , Hennel Franciszek , Hennig Jürgen
Published: March 2007

A method providing improved slice efficiency for gradient‐echo imaging requiring long echo times, such as in functional neuromagnetic resonance imaging, is presented. To enhance the volume coverage while maintaining the short imaging time of a conventional single‐slice gradient‐echo technique, an interleaved muttislice excitation is performed during the echo time. This technique allows detection of susceptibility changes, e.g., the acquisition of stimulated human cortical activation maps, on clinical MR instruments at multiple planes within total imaging times of a few seconds. The efficiency of the technique is demonstrated in the detection of temporary changes in T2* in functional MRI experiments of the human visual cortex at magnetic field strengths of 2 Tesla and 3 Tesla. Fourteen 128 × 128 slices can be acquired in 13 s to cover a large volume‐of‐interest in the same time that would be required for single‐slice acquisition using the conventional technique.
Improvement of measurement precision in absorption spectra by apodization
Authors: Wang Zhiyue
Published: March 2007

In in vivo MR spectroscopy studies, it is desirable to determine metabolite peak parameters with good precision and to estimate the uncertainties. How to achieve optimal precision for an apodized MR spectrum by using a weighted least squares estimator is discussed and demonstrated. Analytic methods for calculating the uncertainties of all parameters obtained from least squares estimators are described. The time domain apodization before Fourier transformation can substantially decrease the minimum variance bound in parameters obtained from the frequency domain absorption spectrum. A weighted least squares estimation is needed to reach the Cramer‐Rao lower bound. When an unweighted least squares estimation is performed, the time domain apodization also leads to improvement in precision.
Decay characteristics of bone marrow in the presence of a trabecular bone network: In vitro and in vivo studies showing a departure from monoexponential behavior
Authors: Newitt David C. , Majumdar Sharmila , Jergas Michael D. , Genant Harry K.
Published: March 2007

In this study, we examine MRI T2′ decay characteristics for bone marrow in trabecular bone networks, using an asymmetric spin‐echo sequence to isolate the inhomogeneous decay due to susceptibility variations between bone and marrow or water. In in vitro measurements on trabecular bone specimens from human vertebral bodies, tibia, and radii, we find significant deviations from a monoexponential signal decay. The initial decay is seen to have a Gaussian decay character, switching to a primarily exponential decay at later decay times. A similar trend is observed in in vivo measurements in the distal radius. Unlike an exponential decay, which may be characterized by a single decay rate, this is indicative of a significant variation in the decay rate with time. The deviations from exponential decay are seen to be orientation dependent, being most significant when the primary trabecular orientation is perpendicular to the static magnetic field.
Observation of resolved glucose signals in 1H NMR spectra of the human brain at 4 Tesla
Authors: Gruetter Rolf , Garwood Michael , Uǧurbil Kǎmil , Seaquist Elizabeth R.
Published: March 2007

Measurement of the resonances of glucose between 3.2 and 3.9 ppm in 1H NMR spectra from the human brain is difficult due to spectral overlap with peaks from more concentrated metabolites. The H1 resonance of α‐D‐glucose at 5.23 ppm is resolved from other metabolite peaks, but potentially overlaps with the intense water signal at 4.72 ppm. This paper demonstrates that the increased resolution at 4 Tesla permits to suppress the water signal sufficiently to reliably detect glucose directly at 5.23 ppm by 1H MRS and the estimated peak intensity is consistent with previous 13C NMR quantification.
Quantitative 1H spectroscopic imaging of human brain at 4.1 T using image segmentation
Authors: Hetherington Hoby P. , Pan Jullie W. , Mason Graeme F. , Adams Dorothy , Vaughn Michael J. , Twieg Donald B. , Pohost Gerald M.
Published: March 2007

Metabolic differences in the content of N‐acetylaspartate (NAA), creatine (CR), and choline (CH) in cerebral gray and white matter can complicate the interpretation of 1H spectroscopic images. To account for these variations, the gray‐and white‐matter content of each voxel must be known. To provide these data, a T1‐based image segmentation scheme was implemented at 4.1 T. The tissue composition of each voxel was determined using the point‐spread function of the spectroscopic imaging acquisition and the segmented anatomical image. Pure gray‐ and white‐matter values for CR/NAA and CH/NAA, and the content of CR, CH, and NAA, were determined using a linear‐regression analysis of 984 voxels acquired from 10 subjects using white‐matter CR as an internal standard. This information was used to establish means and confidence intervals for CR/NAA and CH/NAA from a voxel of arbitrary tissue composition. Using a single‐tailed t test, the extent and locations of the metabolic abnormalities (P < 0.05) in a patient with multiple sclerosis were identified.
Dynamic changes in water ADC, energy metabolism, extracellular space volume, and tortuosity in neonatal rat brain during global ischemia
Authors: van der Toorn Annette , Syková Eva , Dijkhuizen Rick M. , Vořišek Ivan , Vargová Lydia , Škobisová Evan , van Lookeren Campagne Menno , Reese Torsten , Nicolay Klaas
Published: March 2007

To obtain a better understanding of the mechanisms underlying early changes in the brain water apparent diffusion coefficient (ADC) observed in cerebral ischemia, dynamic changes in the ADC of water and in the energy status were measured at postnatal day 8 or 9 in neonatal rat brains after cardiac arrest using 1H MRS/MRI and 31P MRS, respectively. The time courses of the MR parameters were compared with changes in the extracellular space (ECS) volume fraction (α) and tortuosity (λ), determined from concentration‐time profiles of tetramethylammonium applied by iontophoresis. The data show a decrease of the ADC of tissue water after induction of global ischemia of which the time course strongly correlates with the time course of the decrease in the ECS volume fraction and the increase in ECS tortuosity. This indicates that cell swelling is an important cause for the ADC decrease of water.
A 31P NMR study of preconditioned isolated perfused rat heart exposed to intermittent ischemia
Authors: Sharoni Ram , Olivson Abira , Chandra Mukul , Merin Gideon , Uretzky Gideon , Borman Joseph B. , Chisin Roland , Schwalb Herzl , Berman Elisha
Published: March 2007

Exposure to a short ischemic period (ischemic preconditioning, IP) will protect the heart from damage following a subsequent longer ischemic episode. The aim of the study was to test whether IP is cardioprotective in the setting of repeated ischemia‐reperfusion cycles. Thus, Langendorff‐perfused hearts, exposed to IP, were subjected to three consecutive ischemia‐reperfusion (10/15 min) cycles. Myocardial energetics, manifested by 31P NMR spectroscopy, was correlated with hemodynamics. ATP recovery was significantly higher for the IP group compared with control (P < 0.02) during reperfusions. However, there was no significant difference in ATP recovery during the three ischemic intervals. The supernormal recovery of phosphocreatine recorded during reperfusion was lower for the IP group (∼120%) compared with control (∼135%, P < 0.065). Better recovery of the left ventriculardeveloped pressure was noted during reperfusions for the IP group and became significant only during the last reperfusion (86% versus 68%, P < 0.025). In conclusion, the above results support prolonged IP cardioprotection.
Estimation of brain iron in vivo by means of the interecho time dependence of image contrast
Authors: Ye Frank Q. , Martin W. R. Wayne , Allen Peter S.
Published: March 2007

An imaging protocol for a quantitative estimation of disease‐induced variations in brain iron is proposed and then validated, first, on a phantom and second, on a group of 11 healthy volunteers. The relative estimate of brain iron is achieved from a rate difference image that measures the enhancement, δR2app, of the transverse relaxation rate of water protons brought about by the heterogeneous accumulation of iron in the glial cells. At 1.5 T, the phantom study demonstrates, over the range 0‐6 A/m, a linear dependence of δR2app on the magnetization difference between micro‐spheres and a paramagnetic gel, with a sensitivity of ∼2 s−1 A−1 m. In the group of healthy volunteers (mean age 33 ± 7 years) devoid of disease‐related or appreciable age‐related accumulations of iron, the precision of δR2app was still sufficient to distinguish the globus pallidus and the putamen from all of the other iron‐containing brain structures in a manner that was significant at the 99% confidence level.
Artifact reduction in EPI with phase‐encoded reference scan
Authors: Hu Xiaoping , Le Tuong Huu
Published: March 2007

Echo‐planar imaging is becoming widely used for various applications. However, because of inherent limitations, images obtained with EPI are often degraded by artifacts arising from the inconsistency between the odd and even echoes in the acquired data. Several correction techniques, including those based on reference measurement, have been previously reported. In this paper, a correction method based on phase‐encoded reference measurement is described. This technique is demonstrated with experimental data obtained at 4 Tesla and compared with techniques that use nonphase‐encoded reference scan. Results from experimental studies indicate that the present approach reduces the ghost intensity by a factor of 2‐3.
Some new observations on pulse sequence dependent diffusion related edge enhancement in MR microscopy
Authors: Cho Zang‐Hee , Hong In‐Ki , Ro Yong‐Man
Published: March 2007

Self‐diffusion of nuclear spins has been suggested to cause edge enhancement in images especially on a microscopic scale. According to previously published work, theory suggests that edge enhancement is caused by motional narrowing due to the boundaries and spin self‐diffusion during the data acquisition period. More careful examination reveals that edge enhancement due to motional narrowing develops only under a few specific conditions. This lack of generality of motional narrowing theory, as well as experimental observations, indicate that edge enhancement due to effects other than motional narrowing alone can exist. It is found that edge enhancement depends greatly on the data acquisition mode; therefore, the images obtained are different depending on the pulse sequence employed. For example, excessive attenuation of DC components due to diffusion can result in edge enhancement in the spin echo signal. However, in the case of FID‐like signals, DC components are preserved while positive high frequency parts are attenuated, thereby degrading resolution. The new phenomenon observed has been termed selective spectral suppression since the observed edge enhancement results from the selective attenuation of certain frequency components in the nuclear signals due to diffusion‐dependent signal attenuation for a given pulse sequence.
Measurement of spin‐lattice relaxation times and kinetic rate constants in rat muscle using progressive partial saturation and steady‐state saturation transfer
Authors: Horská Alena , Spencer Richard G. S.
Published: March 2007

31P spin‐lattice relaxation times (T1) of metabolites in rat calf muscle at 1.9 Tesla and the forward rate through the creatine kinase (CK) reaction have been measured using a new method based on modeling progressive saturation explicitly incorporating the effect of chemical exchange. In a separate series of experiments, we compared our method with inversion recovery both in vitro and in vivo, finding agreement between the techniques. We found that the T1 values of phosphocreatine (PCr) (6.6 ± 0.3 s), γ‐ATP (2.6 ± 0.6 s), α‐ATP (2.4 ± 0.4 s) and β‐ATP (2.2 ± 0.2 s) are unchanged by stimulation of sufficient intensity to induce a 32% drop in PCr level. The errors in T1 values which arise when chemical exchange is neglected are calculated. These are found to be on the order of 20% for PCr and 30–50% for γ‐ATP under typical conditions. Use of longer repetition times results in larger errors in measured values of T1. This source of error can be effectively eliminated by use of sufficiently short repetition times. We found that the rate constant of the forward CK reaction was increased 60% by stimulation, from 0.20 ± 0.03 s−1 to 0.32 ± 0.03 s−1, but that the phosphorus flux did not change.
T2 maximum likelihood estimation from multiple spin‐echo magnitude images
Authors: Bonny Jean‐Marie , Zanca Michel , Boire Jean‐Yves , Veyre Annie
Published: March 2007

An optimal maximum likelihood (ML) method is described for an unbiased estimation of monoexponential T2 from magnitude spin‐echo images. The algorithm is based on a Gaussian assumption of noise distribution. The validity of this assumption was checked by a statistical x2 test on spin‐echo and fast low‐angle shot surface coil images. Monte‐Carlo simulations of magnitude data showed that the ML estimate standard deviation is lower than that produced by a weighted leastsquares fitting on signal logarithm. Correction schemes are proposed to reduce bias deriving from magnitude reconstruction. The variance of the ML estimate converged rapidly toward the theoretical algebraic expression of the Cramér‐Rao lower bound.
Committees from the Leadership Perspective
Authors: Peabody Robert L.
Published: March 2007

Party leaders and committee leaders in the United States Congress, while sometimes adversaries, are more often collaborators in the legislative process. Much congressional research has centered upon committee structure and operations; another extensive focus of study has been party leadership. Unfortunately, we have only a rudimentary knowledge about the range of possible relationships between party leaders and committee leaders. This paper explores several alternative, if not supplementary, mechanisms for strengthening the party leadership and committee structure in the House of Representatives. First, it outlines some developments taking place in the House Democratic Caucus during the opening months of the 93rd Congress—1973 to 1974. Second, the paper speculates on the implications of creating two new supracommittees—a Committee on the Budget and a Committee on the Agenda—adding the party leadership and bringing about a wholesale consolidation of the remaining House committees. Neither House nor Senate committee structure and jurisdiction can be analyzed in a vacuum: what affects committee powers will obviously have an effect on party leadership. It does not follow, however, that relationships between party leaders and committee leaders are a zero sum game in which the gains of one are necessarily the losses of the other. On the contrary, it may be possible to strengthen party leadership, to enhance the organization and the effectiveness of the committees and, ultimately, to increase the overall powers of the Congress.
Housing Problems of Black Mayor Cities
Authors: Bryce Herrington J. , Cousar Gloria J. , Mccoy William
Published: March 2007

A common concern of black mayors is the housing condition in their cities. While housing is a common problem of all mayors, a disproportionately high percentage of black mayors see this factor as most critical in reversing their declining cities. This paper reviews specific policies undertaken by cities with black mayors. The success of these policies is dependent upon other policies taken by surrounding jurisdictions and by state and federal governments.
The Council on Learning Project on Undergraduate Education: Education and the World View
Authors: Black Robert , Bonham George W.
Published: March 2007

The Council on Learning's Education and the World View (E and WV) project was conceived in the face of changed world circumstances that do not appear to be properly reflected in the American undergraduate curriculum. The E and WV project is surveying feasible and effective programs in international and global studies across the country, assessing what college freshmen and seniors know about the world, and, in its catalytic role in higher education, helping point the academic community and concerned leaders toward what is feasible and necessary for under graduate learning about the world. Because of the highly pluralistic nature of undergraduate education in the United States, its success in reaching its goals stresses the use of the intelligent and innovative eye of college and university faculty and the concern of administrators in the mainstream of the educational endeavor. By use of exemplary programs, a data base about college student global knowledge, and a series of publications on the findings, the E and WV project will provide the academic community with the tools that can be used in individual situations on particular campuses to remedy the present state of affairs and prepare a young citizenry that can survive in tomorrow's world, the Global Century.
The Attitude-Action Connection and the Issue of Gun Control
Authors: Schuman Howard , Presser Stanley
Published: March 2007

This article examines the claim that opponents of gun permit laws feel much more intensely about the matter than do proponents and that this helps explain the political success of the opponents, despite their smaller number. Surprisingly, results from a national sample survey provide no support for the claim at the purely subjective level. In fact, when respondents were asked how strongly they felt about the issue of gun permits, supporters of a permit law responded with slightly more intensity. However, when asked whether they had ever acted on the issue—written letters, contributed money, or both—opponents were markedly more likely to respond in the affirmative. The apparent inconsistency between these findings seems to be due to the fact that strength of feeling and taking action are highly related for permit op ponents, but not for proponents. Thus among respondents who believe the issue to be most important, opponents are quite likely to act on their beliefs, whereas this is not so for proponents —a difference that may well reflect the superiority in organizational effectiveness of the forces opposed to gun control. The concept of single issue politics is therefore more complex than is often realized and requires investigation of both the individual and the organizational levels, as well as of the connection between them.
The Lash of Inflation on a Developing Economy: Puerto Rico, A Case Study
Authors: Aponte Juan B.
Published: March 2007

This article discusses the social effects of inflation in a developing economy, based primarily on the Puerto Rican experience. The first part covers some pertinent general notions concerning inflation and economic development. The relationships among Puerto Rico's unique socio-political conditions, the economic achievements attained, and the social changes experienced throughout the years of relative economic stability from World War II to 1973 are then presented. As a sequel in the discussion, it shall examine the 1974 inflationary period and the recession that followed, from which the Island is not still fully recovered, as well as the inflationary trend that has prevailed since 1978, and the difficulties that the economy is now experiencing. The article delves into factors that have accounted for the reversal in the Island's development trend and emphasizes its increasing dependence on external capital, United States' markets, and federal transfers payments. Finally, the social effects that have been observed and/or are anticipated as a result of the level of inflation that has prevailed in the economy in the last four years and the measures that are being proposed as a part of President Reagan's economic plan to curb inflation are pondered.