bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantitative determination of Gd‐DTPA concentration in T1‐weighted MR renography studies
Authors: Bokacheva Louisa , Rusinek Henry , Chen Qun , Oesingmann Niels , Prince Chekema , Kaur Manmeen , Kramer Elissa , Lee Vivian S. 
Published: May 2007

AbstractA method for calculating contrast agent concentration from MR signal intensity (SI) was developed and validated for T1‐weighted MR renography (MRR) studies. This method is based on reference measurements of SI and relaxation time T1 in a Gd‐DTPA‐doped water phantom. The same form of SI vs. T1 dependence was observed in human tissues. Contrast concentrations calculated by the proposed method showed no bias between 0 and 1 mM, and agreed better with the reference values derived from direct T1 measurements than the concentrations calculated using the relative signal method. Phantom‐based conversion was used to determine the contrast concentrations in kidney tissues of nine patients who underwent dynamic Gd‐DTPA‐enhanced 3D MRR at 1.5T and 99mTc‐DTPA radionuclide renography (RR). The concentrations of both contrast agents were found to be close in magnitude and showed similar uptake and washout behavior. As shown by Monte Carlo simulations, errors in concentration due to SI noise were below 10% for SNR = 20, while a 10% error in precontrast T1 values resulted in a 12–17% error for concentrations between 0.1 and 1 mM. The proposed method is expected to be particularly useful for assessing regions with highly concentrated contrast. Magn Reson Med 57:1012–1018, 2007. © 2007 Wiley‐Liss, Inc.
Effects of formalin fixation and collagen cross‐linking on T2 and magnetization transfer in bovine nasal cartilage
Authors: Fishbein Kenneth W. , Gluzband Yehezkiel A. , Kaku Masaru , Ambia‐Sobhan Hasina , Shapses Sue A. , Yamauchi Mitsuo , Spencer Richard G. 
Published: May 2007

AbstractEndogenous collagen cross‐links influence cartilage biomechanical properties and resistance to degradation. Formalin fixation modifies collagen residues and forms new cross‐links in a dose‐dependent manner. We tested the hypothesis that magnetization transfer (MT) effects and T2 depend on collagen cross‐linking in cartilage. These parameters were measured in bovine nasal cartilage (BNC) prior to fixation, after 9 weeks of immersion in formalin solutions ranging in concentration from 0% to 10%, and after NaBH3CN reduction and washing. T2 decreased by 59.4% ± 1.1% upon fixation in 10% formalin, and was 32.2% ± 5.2% shorter than initial values after washing. The apparent MT rate increased 25.9% ± 3.7% and 52.8% ± 7.1% over baseline under these conditions. Biochemical assays showed no significant differences in water, proteoglycan, natural cross‐link, or collagen content between the 0% and 10% formalin‐treated samples, while amino acid analysis demonstrated losses in (hydroxy)lysine and tyrosine, and new peaks consistent with methylene cross‐links in fixed samples only. We conclude that formalin fixation of cartilage results in significant decreases in T2 and increases in MT parameters that persist after removal of unreacted formaldehyde. The collagen cross‐links thus created are associated with large changes in MT and T2, indicating that interpretation of T2 and MT values in terms of cartilage macromolecular content must be made with caution. Magn Reson Med 57:1000–1011, 2007. Published 2007 Wiley‐Liss, Inc.
Detection of 17O‐tagged phosphate by 31P MRS: A method with potential for in vivo studies of phosphorus metabolism
Authors: Thelwall Peter E. 
Published: May 2007

AbstractWe present a method for MR detection of 17O‐labeled phosphate groups. The method employs the T2 relaxivity effect of 17O on 31P nuclei to distinguish between 17O‐labeled and unlabeled phosphate groups, and uses spin‐echo (SE) acquisitions with RF decoupling at the 17O frequency to generate 31P spectra that show only 17O‐labeled phosphate groups. The method provides an alternative to spin‐labeling experiments, which are limited to the study of rapidly exchanging phosphate groups by the T1 relaxation rates of phosphorus nuclei. We demonstrate separation of MR signals from labeled and unlabeled phosphate‐containing compounds, and characterization of the T2 effect of 17O on phosphate nuclei in 17O‐labeled phosphate groups. Previous 17O and 18O phosphate‐labeled studies used mass spectrometry or high‐resolution MR spectroscopy (MRS) to detect the presence of an isotopic label, which requires ex vivo sample preparation. In our method the detection of 17O‐labeled phosphate is manifested as a large change in 31P T2, and thus allows in vivo detection using simple MR methods. Thus this method may have potential for in vivo studies of bioenergetics and the metabolism of phosphate‐containing compounds. Magn Reson Med 57:1168–1172, 2007. © 2007 Wiley‐Liss, Inc.
Fast method for 1D non‐cartesian parallel imaging using GRAPPA
Authors: Heidemann Robin M. , Griswold Mark A. , Seiberlich Nicole , Nittka Mathias , Kannengiesser Stephan A.R. , Kiefer Berthold , Jakob Peter M. 
Published: May 2007

AbstractMRI with non‐Cartesian sampling schemes can offer inherent advantages. Radial acquisitions are known to be very robust, even in the case of vast undersampling. This is also true for 1D non‐Cartesian MRI, in which the center ofk‐space is oversampled or at least sampled at the Nyquist rate. There are two main reasons for the more relaxed foldover artifact behavior: First, due to the oversampling of the center, high‐energy foldover artifacts originating from the center ofk‐space are avoided. Second, due to the non‐equidistant sampling ofk‐space, the corresponding field of view (FOV) is no longer well defined. As a result, foldover artifacts are blurred over a broad range and appear less severe. The more relaxed foldover artifact behavior and the densely sampled centralk‐space make trajectories of this type an ideal complement to autocalibrated parallel MRI (pMRI) techniques, such as generalized autocalibrating partially parallel acquisitions (GRAPPA). Although pMRI can benefit from non‐Cartesian trajectories, this combination has not yet entered routine clinical use. One of the main reasons for this is the need for long reconstruction times due to the complex calculations necessary for non‐Cartesian pMRI. In this work it is shown that one can significantly reduce the complexity of the calculations by exploiting a few specific properties ofk‐space‐based pMRI. Magn Reson Med 57:1037–1046, 2007. © 2007 Wiley‐Liss, Inc.
Whole‐heart coronary vein imaging: A comparison between non‐contrast‐agent‐ and contrast‐agent‐enhanced visualization of the coronary venous system
Authors: Rasche Volker , Binner Ludwig , Cavagna Friedrich , Hombach Vinzenz , Kunze Markus , Spiess Jochen , Stuber Matthias , Merkle Nico 
Published: May 2007

AbstractThe feasibility of three‐dimensional (3D) whole‐heart imaging of the coronary venous (CV) system was investigated. The hypothesis that coronary magnetic resonance venography (CMRV) can be improved by using an intravascular contrast agent (CA) was tested. A simplified model of the contrast in T2‐prepared steady‐state free precession (SSFP) imaging was applied to calculate optimal T2‐preparation durations for the various deoxygenation levels expected in venous blood. Non‐contrast‐agent (nCA)‐ and CA‐enhanced images were compared for the delineation of the coronary sinus (CS) and its main tributaries. A quantitative analysis of the resulting contrast‐to‐noise ratio (CNR) and signal‐to‐noise ratio (SNR) in both approaches was performed. Precontrast visualization of the CV system was limited by the poor CNR between large portions of the venous blood and the surrounding tissue. Postcontrast, a significant increase in CNR between the venous blood and the myocardium (Myo) resulted in a clear delineation of the target vessels. The CNR improvement was 347% (P < 0.05) for the CS, 260% (P < 0.01) for the mid cardiac vein (MCV), and 430% (P < 0.05) for the great cardiac vein (GCV). The improvement in SNR was on average 155%, but was not statistically significant for the CS and the MCV. The signal of the Myo could be significantly reduced to about 25% (P < 0.001). Magn Reson Med 57:1019–1026, 2007. © 2007 Wiley‐Liss, Inc.
Fast decomposition of water and lipid using a GRASE technique with the IDEAL algorithm
Authors: Li Zhiqiang , Gmitro Arthur F. , Bilgin Ali , Altbach Maria I. 
Published: May 2007

AbstractThree‐point Dixon techniques achieve good lipid‐water separation by estimating the phase due to field inhomogeneities. Recently it was demonstrated that the combination of an iterative algorithm (iterative decomposition of water and fat with echo asymmetry and least‐squares estimation (IDEAL)) with a fast spin‐echo (FSE) three‐point Dixon method yielded robust lipid‐water decomposition. As an alternative to FSE, the gradient‐ and spin‐echo (GRASE) technique has been developed for efficient data collection. In this work we present a method for lipid‐water separation by combining IDEAL with the GRASE technique. An approach to correct for errors in the lipid‐water decomposition caused by phase distortions due to the switching of the readout gradient polarities inherent to GRASE is presented. The IDEAL‐GRASE technique is demonstrated in phantoms and in vivo for various applications, including pelvic, musculoskeletal, and (breath‐hold) cardiac imaging. Magn Reson Med 57:1047–1057, 2007. © 2007 Wiley‐Liss, Inc.
Single‐scan acquisition of registered hyperpolarized 3He ventilation and ADC images using a hybrid 2D gradient‐echo sequence
Authors: Wild Jim M. , Woodhouse Neil , Teh Kevin 
Published: May 2007

AbstractThe pulse sequences for hyperpolarized 3He lung MRI that have made the most clinical impact to date are 1) those that supply regional apparent diffusion coefficient (ADC) measurements, which provide insight into early emphysematous destruction of the alveoli in the lungs, and 2) high‐resolution ventilation images that provide regional indicators of airway obstruction in obstructive airway disease, such as asthma, cystic fibrosis, and chronic obstructive pulmonary disease (COPD). In this work a hybrid 2D ADC‐ventilation sequence was used with low flip angles to acquire both sets of data in the same breath‐hold. The performance of the sequence was investigated in vivo in a healthy subject and a subject with mild emphysema, and compared with conventional 2D gradient‐echo (GRE) 3He ventilation and ADC imaging sequences. Acquisition of the ADC and ventilation images in one breath‐hold provides ventilation images with equal or better SNR (∼20) and the same spatial resolution (3.75 mm × 3.3 mm in plane) with simultaneous accurate, high‐resolution ADC images. The hybrid sequence offers a means of conserving gas by using two‐thirds of the 3He gas needed for separate ADC and ventilation exams, and saves the subject from having to perform an extra breath‐hold. The data are inherently spatially and temporally registered, allowing quantitative cross‐correlation between high‐spatial‐resolution ADC and ventilation data. Magn Reson Med 57:1185–1189, 2007. © 2007 Wiley‐Liss, Inc.
Array compression for MRI with large coil arrays
Authors: Buehrer Martin , Pruessmann Klaas P. , Boesiger Peter , Kozerke Sebastian 
Published: May 2007

AbstractArrays with large numbers of independent coil elements are becoming increasingly available as they provide increased signal‐to‐noise ratios (SNRs) and improved parallel imaging performance. Processing of data from a large set of independent receive channels is, however, associated with an increased memory and computational load in reconstruction. This work addresses this problem by introducing coil array compression. The method allows one to reduce the number of datasets from independent channels by combining all or partial sets in the time domain prior to image reconstruction. It is demonstrated that array compression can be very effective depending on the size of the region of interest (ROI). Based on 2D in vivo data obtained with a 32‐element phased‐array coil in the heart, it is shown that the number of channels can be compressed to as few as four with only 0.3% SNR loss in an ROI encompassing the heart. With twofold parallel imaging, only a 2% loss in SNR occurred using the same compression factor. Magn Reson Med 57:1131–1139, 2007. © 2007 Wiley‐Liss, Inc.
Prepolarized fast spin‐echo pulse sequence for low‐field MRI
Authors: Kegler C. , Seton H.C. , Hutchison J.M.S. 
Published: May 2007

AbstractClinical MRI systems use magnetic fields of at least 0.5T to take advantage of the increase in signal‐to‐noise ratio (SNR) with B0. Low‐field MRI apparatus is less expensive and offers the potential benefit of improved T1 contrast between tissues. The poor inherent SNR at low field can be offset by incorporating prepolarizing field pulses with the MRI pulse sequence. The prepolarizing field does not need to be as homogeneous as the detection field, so it can be generated by a relatively inexpensive electromagnet. Prepolarizing hardware for a 0.01T MRI system was developed together with a prepolarized MRI pulse sequence that incorporates fast imaging techniques to reduce acquisition times by a factor of 5 relative to standard methods. Comparison images of test objects show that most of the enhanced SNR is retained with the fast method. Low‐field images of a human wrist acquired using the fast prepolarized method are also shown. Magn Reson Med 57:1180–1184, 2007. © 2007 Wiley‐Liss, Inc.
Performance of an automated segmentation algorithm for 3D MR renography
Authors: Rusinek Henry , Boykov Yuri , Kaur Manmeen , Wong Samson , Bokacheva Louisa , Sajous Jan B. , Huang Ambrose J. , Heller Samantha , Lee Vivian S. 
Published: May 2007

AbstractThe accuracy and precision of an automated graph‐cuts (GC) segmentation technique for dynamic contrast‐enhanced (DCE) 3D MR renography (MRR) was analyzed using 18 simulated and 22 clinical datasets. For clinical data, the error was 7.2 ± 6.1 cm3 for the cortex and 6.5 ± 4.6 cm3 for the medulla. The precision of segmentation was 7.1 ± 4.2 cm3 for the cortex and 7.2 ± 2.4 cm3 for the medulla. Compartmental modeling of kidney function in 22 kidneys yielded a renal plasma flow (RPF) error of 7.5% ± 4.5% and single‐kidney GFR error of 13.5% ± 8.8%. The precision was 9.7% ± 6.4% for RPF and 14.8% ± 11.9% for GFR. It took 21 min to segment one kidney using GC, compared to 2.5 hr for manual segmentation. The accuracy and precision in RPF and GFR appear acceptable for clinical use. With expedited image processing, DCE 3D MRR has the potential to expand our knowledge of renal function in individual kidneys and to help diagnose renal insufficiency in a safe and noninvasive manner. Magn Reson Med 57:1159–1167, 2007. © 2007 Wiley‐Liss, Inc.
Joint image reconstruction and sensitivity estimation in SENSE (JSENSE)
Authors: Ying Leslie , Sheng Jinhua 
Published: May 2007

AbstractParallel magnetic resonance imaging (pMRI) using multichannel receiver coils has emerged as an effective tool to reduce imaging time in various applications. However, the issue of accurate estimation of coil sensitivities has not been fully addressed, which limits the level of speed enhancement achievable with the technology. The self‐calibrating (SC) technique for sensitivity extraction has been well accepted, especially for dynamic imaging, and complements the common calibration technique that uses a separate scan. However, the existing method to extract the sensitivity information from the SC data is not accurate enough when the number of data is small, and thus erroneous sensitivities affect the reconstruction quality when they are directly applied to the reconstruction equation. This paper considers this problem of error propagation in the sequential procedure of sensitivity estimation followed by image reconstruction in existing methods, such as sensitivity encoding (SENSE) and simultaneous acquisition of spatial harmonics (SMASH), and reformulates the image reconstruction problem as a joint estimation of the coil sensitivities and the desired image, which is solved by an iterative optimization algorithm. The proposed method was tested on various data sets. The results from a set of in vivo data are shown to demonstrate the effectiveness of the proposed method, especially when a rather large net acceleration factor is used. Magn Reson Med 57:1196–1202, 2007. © 2007 Wiley‐Liss, Inc.
How close is close enough? Evaluating propensity score matching using data from a class size reduction experiment
Authors: Wilde Elizabeth Ty , Hollister Robinson 
Published: May 2007

AbstractIn recent years, propensity score matching (PSM) has gained attention as a potential method for estimating the impact of public policy programs in the absence of experimental evaluations. In this study, we evaluate the usefulness of PSM for estimating the impact of a program change in an educational context (Tennessee's Student Teacher Achievement Ratio Project [Project STAR]). Because Tennessee's Project STAR experiment involved an effective random assignment procedure, the experimental results from this policy intervention can be used as a benchmark, to which we compare the impact estimates produced using propensity score matching methods. We use several different methods to assess these nonexperimental estimates of the impact of the program. We try to determine “how close is close enough,” putting greatest emphasis on the question: Would the nonexperimental estimate have led to the wrong decision when compared to the experimental estimate of the program? We find that propensity score methods perform poorly with respect to measuring the impact of a reduction in class size on achievement test scores. We conclude that further research is needed before policymakers rely on PSM as an evaluation tool. © 2007 by the Association for Public Policy Analysis and Management
Welfare and child support program knowledge gaps reduce program effectiveness
Authors: Meyer Daniel R. , Cancian Maria , Nam Kisun 
Published: May 2007

AbstractThere is little research on knowledge of the policy rules that could affect individuals, either in general or in evaluations of new programs. The lack of research is surprising, given that knowledge gaps could limit the effectiveness of reforms or lead to incorrect inferences regarding the effects of a policy change. In this article, we use survey data to examine the level and sources of welfare participants' policy knowledge in the context of a substantial change in child support and welfare policy in Wisconsin. We find very low levels of knowledge of child support policy rules. Multivariate analyses suggest that people tend to learn policy rules by experience; we find less consistent support for knowledge being primarily imparted through interactions with caseworkers. A difference‐in‐difference analysis suggests that if participants had been more knowledgeable, program impacts would have been larger. Implications of this research for policy implementation and policy evaluations are discussed. © 2007 by the Association for Public Policy Analysis and Management
Nonpoor children in head start: Explanations and implications
Authors: Besharov Douglas J. , Morrow Jeffrey S. 
Published: May 2007

AbstractAccording to the Head Start Act (1998), children are income‐eligible for the program if their “families' incomes are below the poverty line.” There are a number of statutory exceptions to this general rule and, according to the Head Start Bureau, the result is that about 6 percent of the children in the program are not poor. But the major national surveys of Head Start families report that 30 percent or more of Head Start children are not “poor.” This paper confirms and explains the high proportion of nonpoor children in Head Start: at enrollment, at least 28 percent are not poor; at midyear, at least 32 percent are not poor; and by the end of the program year, at least 34 percent and perhaps more than 50 percent are not poor. Although the presence of some of these nonpoor children seems to be an appropriate or at least understandable aspect of running a national program with Head Start's current organizational structure, the presence of others seems much less warranted and raises substantial questions of horizontal equity. Moreover, taken together, the large number of nonpoor children suggests that the program is not well targeted to fulfill its mission of providing compensatory services to developmentally disadvantaged children—and reveals the essential ambiguity of Head Start's role in the wider world of early care and education. The income and program dynamics that have led to so many nonpoor children being in Head Start are also at work in many other programs, and, thus, our findings demonstrate the need to understand better how income eligibility is determined across various means‐tested programs.
A “politically robust” experimental design for public policy evaluation, with application to the Mexican Universal Health Insurance program
Authors: King Gary , Gakidou Emmanuela , Ravishankar Nirmala , Moore Ryan T. , Lakin Jason , Vargas Manett , Téllez‐Rojo Martha María , Hernández Ávila Juan Eugenio , Ávila Mauricio Hernández , Llamas Héctor Hernández 
Published: May 2007

AbstractWe develop an approach to conducting large‐scale randomized public policy experiments intended to be more robust to the political interventions that have ruined some or all parts of many similar previous efforts. Our proposed design is insulated from selection bias in some circumstances even if we lose observations; our inferences can still be unbiased even if politics disrupts any two of the three steps in our analytical procedures; and other empirical checks are available to validate the overall design. We illustrate with a design and empirical validation of an evaluation of the Mexican Seguro Popular de Salud (Universal Health Insurance) program we are conducting. Seguro Popular, which is intended to grow to provide medical care, drugs, preventative services, and financial health protection to the 50 million Mexicans without health insurance, is one of the largest health reforms of any country in the last two decades. The evaluation is also large scale, constituting one of the largest policy experiments to date and what may be the largest randomized health policy experiment ever. © 2007 by the Association for Public Policy Analysis and Management
Synthesis of conducting polypyrrole by radiolysis polymerization method
Authors: Karim M. R. , Lee C. J. , Lee M. S. 
Published: May 2007

AbstractConducting polypyrrole (PPy) has been synthesized by the in situ gamma radiation‐induced chemical oxidative polymerization method. This method takes advantages of the specialties of radiation‐induction, and a highly uniform polymer morphology was obtained. The resultant nanosize polypyrrole particles were characterized by Elemental Analysis, Fourier transform infrared (FT‐IR), scanning electron microscope (SEM), transmission electron microscopy (TEM) and X‐ray Diffraction (XRD). Measurements of polymer particle sizes were obtained at <500 nm. A standard four‐point probe revealed that the chemical synthesis of PPy has a good electrical property. Also thermal stability, checked by Thermal Gravimetric Analysis in air, was ensured by this novel synthesis. Copyright © 2007 John Wiley & Sons, Ltd.