bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiband dual patch antennas with polarization compensation for WLAN applications
Authors: He Wei , Jin Ronghong , Geng Junping , Lampe Mattias
Published: May 2007

In this article, an antenna system with orthogonal spiral‐patches design capable of multiband operation at about 2.38–2.5 GHz and 4.20–6.00 GHz is presented. Simulated and measured results for main parameters such as return loss, impedance bandwidth, radiation pattern, and gains are presented and discussed herein. By combining two patches and exploiting the simple antenna diversity scheme supported by today's WLAN chip sets with related algorithms as maximal ratio combining (MRC), nonideal circular polarizing and nonsymmetrical radiation patterns can be compensated and a semispherical radio coverage can be approximated, which make this design a suitable candidate for IEEE 802.11a/b/g/n WLAN applications. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1907–1911, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22584
Stepped coupled‐line balun design for enhanced bandwidth operation
Authors: Chen Guan‐Yu , Sun Jwo‐Shiun
Published: May 2007

This letter presents a practical design method for the stepped impedance coupled‐line balun using an effective and simple way to increase the balanced output bandwidth of the coupled lines in the conventional planar Marchand balun. A new structure of collateral multi‐section with quarter wavelength coupled‐line balun is developed to increase at least 40% more balanced bandwidth and to achieve a better return loss than the traditional planar Marchand coupled‐line balun. The structure of the designed planar microstrip circuit is fairly simple, practical and easy to fabricate. The measured results of the design show fine agreements with the simulated data. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1877–1879, 2007; Published online in Wiley Inter‐Science (www.interscience.wiley.com). DOI 10.1002/mop.22585
Wideband microstrip bandpass filter based on intercoupled split‐ring resonator
Authors: Wu Jack , Qiu S. N. , Qiu C. X. , Shih I.
Published: May 2007

A new design of wideband microwave bandpass filter based on intercoupled split‐ring resonator is proposed. The split‐ring resonator structure is well‐know for its unique resonance feature that exhibit a negative permeability. By implementing the split‐ring resonator directly on a microstrip transmission line, a bandpass filter with a large fractional bandwidth has been achieved. The novel periodic intercoupled split‐ring resonator bandpass filter is compatible with microwave planar technology and the passband region is controllable. The filter design has been validated and demonstrated in both simulations and experimental measurements. A bandpass filter with a fractional bandwidth of 50% at a center frequency of 14 GHz was achieved with a maximum insertion loss of 0.75 dB in the passband region. Meanwhile, the fractional bandwidth has been demonstrated to be controllable and this was reduced to 37% by sacrificing the periodicity of the intercoupled split‐ring resonator structure. Therefore, the flexible characteristics and the simple implementation method may render the proposed filter to be very useful in many frequency‐selective and oscillation‐suppression applications. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1809–1813, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22588
Defected‐ground coupled microstrip lines bandpass filter with suppressed spurious resonances
Authors: Salah‐Eddin Muhammad A. , Safwat Amr M. E.
Published: May 2007

Defected‐ground coupled microstrip lines (DCL) bandpass filter is proposed. The length of the proposed filter is quarter the length of conventional coupled‐line filter and it has a wide stopband and suppressed spurious resonances up to 4f0, where f0 is the filter central frequency. Five hundred and fifty megahertz single‐section and two‐section DCL filters were designed and fabricated. Simulations and measurements show that the rejection levels of the spurious resonances at 2f0, 3f0 as well as 4f0 are better than −11 and −14 dB for single‐section DCL and double‐section DCL, respectively. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2038–2039, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22590
Investigation on quality factor of substrate‐integrated waveguide resonance cavity
Authors: Che Wenquan , Wang Dapeng , Xu Lei , Li Cuixia
Published: May 2007

An investigation has been made on the quality factor of substrate‐integrated waveguide (SIW) resonance cavity. The ohmic losses at the sidewalls, front/end walls, and top/bottom planes of the SIW resonance cavity are derived, respectively, resulting in the quality factor formula of the SIW resonance cavity for the first time. The sidewalls and the front/end walls of the SIW resonance cavity are formed by cylinder posts, the discrete integral on the surfaces of the cylinder posts must be considered. The calculated quality factor from this formula at several frequency bands have been obtained, agreeing well with the numerical simulations. The maximum deviations at S‐, X‐ and K‐bands are 1.52%, 1.84%, and 2.98%, respectively, all less than 3%, demonstrating the validity of the proposed quality factor formula for the SIW resonance cavity. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2007–2010, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22592
A dual‐band antenna design for GPS and UMTS applications
Authors: Sim Chow‐Yen‐Desmond , Row Jeen‐Sheen , Chen Shing‐Hau
Published: May 2007

The design of an integrated dual‐band antenna for global positioning system (GPS) and universal mobile telecommunications system (UMTS) is presented. A circularly polarized square‐ring corner truncated microstrip antenna is designed for GPS application, and a monopolar shorted square patch antenna embedded within the center of the square‐ring is designed for UMTS application. Both proposed antenna elements demonstrated desirable isolation, radiation pattern; polarization, and bandwidth requirement. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1935–1939, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22597
A planar bandpass filter using butterfly radial stub
Authors: Joshi Ravi Kumar , Harish A. R.
Published: May 2007

A bandpass filter using a single‐slotted butterfly radial stub connected in shunt with a short‐circuited section of a microstrip transmission line is proposed. A two pole filter based on the proposed structure has been designed, analyzed, and fabricated. A good agreement between the measured and the simulated results is observed. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1872–1875, 2007; Published online in Wiley Inter‐Science (www.interscience.wiley.com). DOI 10.1002/mop.22600
Comparative approach of printed reflectarray with/without electromagnetic bandgap ground plate
Authors: Liu Zhen‐Guo , Zhang Wen‐Xun , Wu Zhi‐Hang , Ge Zhi‐Chen
Published: May 2007

In this article, the printed reflectarray with/without electromagnetic bandgap (EBG) ground plate are compared. The result shows that incorporating EBG structure into reflectarray cannot always improve the gain as said in reference except in some special situation. The theoretical discussion is given as well as the specific design samples to verify the results. At the same time, the third‐dimension‐directional radiation mechanism for 2D EBG structure within bandgap is also discussed. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1968–1971, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22610
Compact microstrip bandpass filter using composite right/left‐handed transmission lines
Authors: Li Jiusheng , Yunyun Zhuang
Published: May 2007

A compact microstrip bandpass filter utilizing composite right/left‐handed (CRLH) transmission lines (TLs) is designed, fabricated, and measured. The simulated and measured results show that the proposed filter has low insertion loss in passband, compact dimensions, easy fabrication, and low cost. The novel measured performances of the bandpass filter based on CRLH TL are almost identical with the simulated results. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1929–1931, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22613
Push‐push voltage controlled dielectric resonator oscillator using a LTCC technology
Authors: Yom In‐Bok , Shin Dong‐Hwan , Oh Seung‐Hyeub , Ryu Keun‐Kwan
Published: May 2007

A push–push voltage‐controlled dielectric resonator oscillator (VCDRO) with a modified frequency tuning structure is investigated. The push–push VCDRO designed at 16 GHz is manufactured using a low temperature cofired ceramic (LTCC) technology to reduce the circuit size. The frequency tuning structure is embedded in a layer of A6 substrate by an advantage of LTCC process. Experimental results show that the fundamental frequency suppression is above 30 dBc, and a phase noise of push–push VCDRO presents a good performance of −103 dBc/Hz at 100 kHz offset frequency from carrier. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1824–1827, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22619
Q‐band to V‐band 1D and 2D elliptical lens antenna arrays
Authors: Yang Lu , Domier Calvin W. , Luhmann N.C.
Published: May 2007

An investigation of the receiving properties of both 1D 13‐element and 2D 8 × 4‐element dual dipole antenna arrays on an elliptical MACOR lens from Q‐ to V‐band is reported. Theoretical and measurement results agree well. The intended application is for millimeter wave plasma radar reflectometric imaging, although the results have broader applicability (Munsat et al., Rev Sci Instrum 74 (2003) 1426–1432). © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1798–1801, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22620
Optical mm‐wave generation based on phase modulation along with optical filtering
Authors: Ma Jianxin , Yu Jianjun , Jia Zhensheng , Yu Chongxiu , Chang Gee Kung
Published: May 2007

We have investigated the generation and transmission of optical millimeter (mm)‐wave signal based on optical phase modulator (PM) and fiber Bragg grating (FBG) filter. With an optimized modulation depth of PM and a higher carrier suppression ratio via a notch filter, the generated optical mm‐wave can be transmitted over a long‐distance without fading. We have also theoretically analyzed the impact of time shift on the eye closure of optical and electrical signal due to the fiber dispersion, which is well in accord with the experimental results. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1787–1793, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22622
A novel via‐free composite right‐ and left‐handed transmission line using defected ground structure
Authors: Park Jae‐Hyun , Ryu Young‐Ho , Lee Jae‐Gon , Lee Jeong‐Hae
Published: May 2007

In this letter, a novel via‐free composite right‐ and left‐handed transmission line (CRLH TL) is proposed using defected ground structure (DGS). The required shunt inductance and series capacitance for left‐handed transmission line are provided by the mender‐line of DGS and inter‐digital gap in signal line, respectively. The dispersion relations are analyzed using the derived equivalent circuit and Bloch‐Floquet theory. The measured results of dispersion curves of CRLH TLs have good agreements with those of simulation and theory. A proposed via‐free CRLH TL has broad LH bandwidth of 88.7% below 1 GHz. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1989–1993, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22624
New general formulation of the Cauchy method for the accurate model extraction of higher order microwave systems
Authors: Traina Daniele , Macchiarella Giuseppe , Sarkar Tapan K.
Published: May 2007

It is well known that a Vandermonde matrix generates an ill‐conditioned system matrix when applied with finite numerical precision. This deficiency affects the Cauchy method by restricting its application to only lower order systems. This paper presents an innovative and accurate general formulation of the Cauchy method to rectify this limitation and make the Cauchy method suitable for the model extraction of a higher order microwave systems. It has been successfully verified using examples of microwave base‐station filters and duplexers. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1957–1961, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22627
Compact L‐shaped notched printed antennas with dual slits for multiband and wideband applications
Authors: Kiran K. U. , Yadahalli R. M. , Vani R. M. , Farida Sara F. , Hunagund P. V.
Published: May 2007

In this paper, compact L‐shaped notched printed antennas with dual slits for multiband and wideband applications are presented. Here, an L‐shaped notch is cut on one side of the nonradiating edge of the rectangular patch with dual narrow slits cut on the other side. This patch is kept 2 mm away from the ground plane. The size of the ground plane is taken to be 38 × 10.8 mm2. Here, the study consists of the study of the proposed antenna with two types of ground planes, one with rectangular ground plane and the other with modified ground plane. Using rectangular ground plane, wideband and multiband operation is achieved with overall bandwidth of 6.84 GHz (110%). Again, by using modified ground plane, the overall bandwidth of the antenna is further increased to 7.86 GHz (114.5%). Moreover, the overall size of the proposed antennas is quite compact i.e., 38 × 38 mm2. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2022–2026, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22638
Broadband planar DTV antenna in the portable media player held by the user's hands
Authors: Li Wei‐Yu , Wong Kin‐Lu , Row Jeen‐Sheen
Published: May 2007

Effects of the user's hands on the broadband planar DTV antenna in the portable media player (PMP) are studied. The antenna has a wide operating bandwidth covering the 470–806 MHz band for DTV signal reception and a one‐layer equivalent simulation hand model including the user's forearm with a relative permittivity of 33.5 and a conductivity of 0.47 S/m is used for the simulation study. Three different conditions of the user's hands (right hand only, left hand only, and both hands) holding the PMP are studied, and their effects on the return loss, radiation efficiency, and radiation patterns of the studied DTV antenna are analyzed. In addition, effects of the user's hands holding the PMP at different positions relative to the studied DTV antenna are analyzed. Results have shown that, for the worst case, the radiation efficiency of the studied DTV antenna is still larger than 60% over the operating band, making the antenna very promising for practical applications. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1841–1844, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22639
Assessment of solvent effects: do weak alignment media affect the structure of the solute?
Authors: Shahkhatuni Astghik A. , Shahkhatuni Aleksan G. , Panosyan Henry A. , Sahakyan Aleksandr B. , Byeon In‐Ja L. , Gronenborn Angela M.
Published: May 2007

Alignment media used for measuring residual dipolar couplings, such as solutions of filamentous phages, phospholipid mixtures, polyacrylamide gels and various lyotropic liquid crystalline systems were investigated with respect to solvent effects on molecular structure. Structural parameters of the small rigid model compound13C‐acetonitrile were calculated from dipolar couplings and variations from expectation values were used for assessment of solvent effects. Only minor solvent effects were observed for most of the media employed and the measured structural data are in good agreement with microwave data and theoretical predictions. Copyright © 2007 John Wiley & Sons, Ltd.
Guttiferic acid, a novel rearrangement product from minor chromenoxanthone pigments of Garcinia morella Desr.
Authors: Rajagopal Rao D. , Gurudutt K. N. , Mamatha S. , Mohan Rao L. J.
Published: May 2007

Morellic and isomorellic acids (2 and 3), present in the seed coat as well as resinous exudate of Garcinia morella Desr., are geometric isomers and structurally related to morellin (1), the major chromenoxanthone pigment. Both form crystalline complexes with pyridine and afford guttiferic acid (7), a novel skeletal rearrangement product, when heated with mild alkali. Structure of the latter has been deduced mainly by a comparative study of 1H and 13C NMR spectra of methyl morellate (5), methyl‐O‐methyl morellate (6), guttiferic acid (7) and dimethyl guttiferate (8). Copyright © 2007 John Wiley & Sons, Ltd.
Janocchio—a Java applet for viewing 3D structures and calculating NMR couplings and NOEs
Authors: Evans David A. , Bodkin Michael J. , Baker S. Richard , Sharman Gary J.
Published: May 2007

We present a Java applet, based on the open source Jmol program, which allows the calculation of coupling constants and NOEs from a three‐dimensional structure. The program has all the viewing features of Jmol, but adds the capability to calculate both H–H and H–C 3‐bond couplings constants. In the case of HH couplings, the Altona equation is used to perform this. The program also calculates NOEs using the full relaxation matrix approach. All these calculations are driven from a simple point and click interface. The program can calculate values for multi‐structure files, and can produce input files for the conformational fitting program NAMFIS. Copyright © 2007 John Wiley & Sons, Ltd.
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

A 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

Endogenous 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

We 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

MRI 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

The 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

Three‐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

The 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

Arrays 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

Clinical 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

The 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

Parallel 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

In 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

There 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

According 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

We 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

Conducting 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.
Speech‐language and hearing complaints of children and adolescents with brain tumors
Authors: Gonçalves Maria Inês R. , Radzinsky Tatiana Couto , da Silva Nasjla Saba , Chiari Brasília Maria , Consonni Daniella
Published: May 2007

Central nervous system (CNS) tumors generally leave sequelae that may compromise speech, language, swallowing, hearing, and voice functions. This report describes the incidence of speech‐language and hearing complaints and disorders in children and adolescents with CNS tumor under treatment at one of the most important Brazilian reference center for pediatric cancer. One‐hundred ninety patients were examined for speech‐pathology screening and analysis: forty‐two percent presented with complaints and symptoms. From the remaining patients, 68% presented clinical symptoms and 32% were actually free from any speech‐language and hearing‐related symptoms. The high incidence of complaints and symptoms indicate that these patients might benefit from specific rehabilitation interventions. Pediatr Blood Cancer 2008;50:706–708. © 2007 Wiley‐Liss, Inc.
pH stability of individual folates during critical sample preparation steps in prevision of the analysis of plant folates
Authors: De Brouwer Veerle , Zhang Guo‐Fang , Storozhenko Sergei , Van Der Straeten Dominique , Lambert Willy E.
Published: May 2007

The stability and eventual interconversion of nine mono‐glutamate folates (5‐methyl‐tetrahydrofolate, tetrahydrofolate, 5‐formyltetrahydrofolate, 5,10‐methenyltetrahydrofolate, 5,10‐methylenetetrahydrofolate, dihydrofolate, 10‐formylfolic acid, 10‐formyltetrahydrofolate and folic acid) during the typical sample preparation steps (heat treatment for 10 min at 100°C and incubation for 2 h at 37°C) at different pH values have been investigated by LC‐MS/MS. An LC‐MS/MS method with isotopically labelled [13C5]5‐methyltetrahydrofolate and [13C5] folic acid as internal standards has been developed with enhanced sensitivity using a Chromolith RP‐18 column. 5‐Methyltetrahydrofolate, folic acid and 10‐formylfolic acid are relatively stable at different pHs (from 2 to 10) with and without heat treatment. Tetrahydrofolate shows instability at low pH. 5‐Formyltetrahydrofolate and 5,10‐methenyltetrahydrofolate can interconvert by changes in pH. Tetrahydrofolate and 5,10‐methylenetetrahydrofolate can interconvert with formaldehyde or by changes in pH. Incubation at 37°C for 2 h is much less aggressive for most folates as compared with heat treatment at 100°C. At 37°C most folates are stable at pH values between 4 and 8 except tetrahydrofolate and dihydrofolate, which are degraded at low pH. 10‐Formyltetrahydrofolate and 5,10‐methylenetetrahydrofolate cannot be quantified in the present method because these compounds are converted to 5,10‐methenyltetrahydrofolate and tetrahydrofolate, respectively, in the acidic mobile phase. This study provides useful information for the analysis of folates in the future as well as for the interpretation of quantitative results from earlier work. Copyright © 2007 John Wiley & Sons, Ltd.
Prenatal evaluation of facial clefts by three‐dimensional extended imaging
Authors: Wang L M. , Leung K Y. , Tang Mary
Published: May 2007

Objectives

To determine the prenatal diagnostic accuracy of two‐dimensional ultrasound (2DUS) alone versus 2DUS in conjunction with three‐dimensional ultrasonography (3DUS) including orthogonal display (OGD) and three‐dimensional extended Imaging for cleft lip and primary palate.

Materials and Method

Fetuses being suspected of having a facial cleft by previous ultrasound examination or family history were examined sequentially with 2DUS and then 3DUS.

Results

Of a total of 30 infants, 22 had cleft lip and nine also had cleft palate at birth. The use of 2DUS with or without 3DUS correctly identified all cases of cleft lips prenatally. However, the use of 2DUS in conjunction with 3DUS correctly identified more cleft primary palate than 2DUS alone (88.9% vs 22.2%, P < 0.01). Cleft primary palate was well demonstrated in both the multi‐slice view (MSV)™ and OGD modes. In one case, a cleft palate was shown in the MSV™ mode but not in the Oblique view™ (OBV)™ mode. All the unaffected fetuses were reported as no cleft palate with the use of MSV™ mode.

Conclusions

Combined approach of 2DUS and 3DUS with both OGD and MSV™ modes significantly improved the prenatal detection rate for a cleft palate compared with 2DUS alone (88.9% vs 22.2%) without decreasing the specificity. Copyright © 2007 John Wiley & Sons, Ltd.
Molecular and cytogenetic investigation of Y chromosome deletions over three generations facilitated by intracytoplasmic sperm injection
Authors: Minor Agata , Wong Edgar Chan , Harmer Karynn , Ma Sai
Published: May 2007

Background

The azoospermic factor (AZF) region is critical for normal spermatogenesis since microdeletions and partial deletions have been associated with infertility. We investigate the diagnostic ability of karyotyping in detecting clinically relevant Y chromosome deletions. The clinical significance of heterochromatin deletions, microdeletions and partial AZFc deletions is also evaluated.

Methods

A patient with a Yq deletion, affected by severe oligoasthenoteratozoospermia, underwent intracytoplasmic sperm injection (ICSI) which resulted in the birth of a healthy baby boy. The patient, his father and his son underwent Y chromosome microdeletion and partial AZFc deletion screening. We also studied the aneuploidy rate in the sperm of the patient by fluorescent in situ hybridization.

Results

AZF microdeletions were absent in the family. However, microdeletion analysis confirmed that the Yq deletion was limited to the heterochromatin. We found a partial AZFc gr/gr deletion in all three family members. We observed an increased rate of sex chromosome aneuploidy in the infertile patient.

Conclusions

Cytogenetic analysis was misleading in identifying the Yq breakpoint. Infertility observed in the patient was associated with the gr/gr partial deletion. However, because of the incomplete penetrance of gr/gr deletions, the consequence of the vertical transmission of the deletion through ICSI remains unknown. Copyright © 2007 John Wiley & Sons, Ltd.
An experimental study on improving the atomic oxygen resistance of epoxy resin/silica nanocomposites
Authors: Wang Xin , Zhao Xiaohu , Wang Mingzhu , Shen Zhigang
Published: May 2007

To improve the atomic oxygen (AO) resistance of the spacecraft resin matrix material, inorganic silica nanoparticles were filled into the epoxy resin. Samples of the epoxy/silica nanocomposites were prepared and AO exposure experiments were conducted in a ground‐based AO effects simulation facility. The samples exhibited significantly less mass loss and erosion yield than the corresponding pristine epoxy resin. Analysis of the surface morphology, composition and chemical structures showed that some organic structures still resides on the nanocomposites surface after the AO exposure experiment. The silica nanoparticles and the organic structures could serve as a barrier to resist further erosion. POLYM. ENG. SCI., 47:1156–1162, 2007. © 2007 Society of Plastics Engineers