bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrophilic interaction liquid chromatography method for the determination of ascorbic acid
Authors: Nováková Lucie , Solichová Dagmar , Pavlovičová Soňa , Solich Petr
Published: April 2008

Hydrophilic interaction liquid chromatography (HILIC) method using internal standard for the determination and stability study of ascorbic acid was developed. HILIC method was very fast and simple using the following analytical conditions: ZIC HILIC (150×2.1 mm, 3.5 μm) chromatographic column and mobile phase composed of ACN and 50 mM ammonium acetate buffer pH 6.8 (78:22 v/v). Diode array detection was performed and chromatograms were processed at 268 nm, the maximum wavelength of absorbance of ascorbic acid. An extensive stability study of ascorbic acid as a function of various factors including temperature, stabilizing agents, oxygen presence and its concentration in solution was performed in order to gain information about the quantitative influence of individual stability factors. Low temperature and stabilizing agents (o‐phosphoric acid and oxalic acid) were found to be key factors enabling substantial enhancement of the stability of ascorbic acid.
Synthesis of a polyrotaxane‐based macroporous polymer as stationary phase for capillary electrochromatography via host–guest complexation of N,N ′‐ethylenedianilinediacrylamide with statistically methylated β‐cyclodextrin
Authors: Wahl Annika , Al‐Rimawi Fuad , Schnell Ingo , Kornysova Olga , Maruska Audrius , Pyell Ute
Published: April 2008

A synthetic route to acrylamide‐based monolithic stationary phases for CEC with rotaxane‐type immobilized derivatized β‐CD was explored. N,N′‐Ethylenedianilinediacrylamide was synthesized as the water‐insoluble crosslinker forming water‐soluble inclusion complexes with statistically methylated β‐CD. Mixed‐mode stationary phases were synthesized by free radical copolymerization of the bisacrylamide‐CD host–guest complex with water‐soluble monomers and an additional water‐soluble crosslinker in aqueous solution. Complex formation in solution and inclusion of the pseudorotaxane into the polymeric network (formation of a polyrotaxane architecture) were studied by means of 1H‐NMR chemical shift analysis, CD modified micellar EKC (CD‐MEKC), 2D‐NOESY spectroscopy, and solid state 13C‐NMR spectroscopy. The presence of a mixed‐mode selectivity of the stationary phase based on hydrophobic and hydrophilic interaction was confirmed by CEC with neutral polar and nonpolar solutes.
HILIC for separation of co‐eluted flavonoids under RP‐HPLC mode
Authors: Zhang Hui , Guo Zhimou , Zhang Feifang , Xu Qing , Liang Xinmiao
Published: April 2008

Hydrophilic interaction chromatography (HILIC) was employed to separate the co‐eluted flavonoids from licorice extract under RP‐HPLC mode. HILIC separations were carried out with the Atalantis HILIC Silica column and the CD‐based column. The co‐eluted flavonoids were well retained and separated on the two HILIC columns under HILIC mode. Similar results were obtained in the separation of another isoflavones sample, from kudzu extract under HILIC mode.
Chain Expulsion out of Dense Polymer Brushes
Authors: Merlitz Holger , He Gui‐Li , Sommer Jens‐Uwe , Wu Chen‐Xu
Published: April 2008

Langevin dynamics simulations are used to study the expulsion of single chains out of dense polymer brushes in a good solvent. The dynamic scaling model is able to correctly predict certain features of the expulsion process, but it fails to describe details of the time‐resolved dynamics of monomers. The center of mass velocity of the moving chain is not strictly constant but accelerating during the expulsion process. The driving force of the expulsion process, the (negative) vertical gradient of the brush density profile, undergoes a qualitative change when the brush profile is transformed from a parabolic to a box‐like profile at high densities.

magnified image
Automatic passive tracking of an endorectal prostate biopsy device using phase‐only cross‐correlation
Authors: de Oliveira André , Rauschenberg Jaane , Beyersdorff Dirk , Semmler Wolfhard , Bock Michael
Published: April 2008

MR‐guided transrectal prostate biopsy is currently a time‐consuming procedure because the imaging slice is often manually realigned with the biopsy needle during lesion targeting. In this work a pulse sequence is presented that automatically follows a passive marker attached to a dedicated MR biopsy device holder, thus providing an alternative to existing active tracking methods. In two orthogonal tracking FLASH images of the marker the position of the needle axis is automatically identified using a phase‐only cross‐correlation (POCC) algorithm. The position information is then used to realign a trueFISP imaging slice in real time. In phantom experiments the sensitivity of this technique to initial misalignments of the marker and to the signal‐to‐noise ratio was evaluated. In several puncture experiments the precision of the needle placement was analyzed. The POCC algorithm allowed for a precise identification of the marker in the images even under severe initial misalignments of up to 45°. At a frame rate 1 image/s a precision of the needle placement of 1.5 ± 1.1 mm could be achieved. Magn Reson Med 59:1043–1050, 2008. © 2008 Wiley‐Liss, Inc.
Toward improved grading of malignancy in oligodendrogliomas using metabolomics
Authors: Erb G. , Elbayed K. , Piotto M. , Raya J. , Neuville A. , Mohr M. , Maitrot D. , Kehrli P. , Namer I.J.
Published: April 2008

In spite of having been the object of considerable attention, the histopathological grading of oligodendrogliomas is still controversial. The determination of reliable biomarkers capable of improving the malignancy grading remains an essential step in working toward better therapeutic management of patients. Therefore the metabolome of 34 human brain biopsies, histopathologically classified as low‐grade (LGO, N = 10) and high‐grade (HGO, N = 24) oligodendrogliomas, was studied using high‐resolution magic angle spinning nuclear magnetic resonance spectroscopy (HRMAS NMR) and multivariate statistical analysis. The classification model obtained afforded a clear distinction between LGOs and HGOs and provided some useful insights into the different metabolic pathways that underlie malignancy grading. The analysis of the most discriminant metabolites in the model revealed the presence of tumoral hypoxia in HGOs. The statistical model was then used to study biopsy samples that were classified as intermediate oligodendrogliomas (N = 6) and glioblastomas (GBMs) (N = 30) by histopathology. The results revealed a gradient of tumoral hypoxia increasing in the following direction: LGOs, intermediate oligodendrogliomas, HGOs, and GBMs. Moreover upon analysis of the clinical evolution of the patients, the metabolic classification seems to provide a closer correlation with the actual patient evolution than the histopathological analysis. Magn Reson Med 59:959–965, 2008. © 2008 Wiley‐Liss, Inc.
In vitro labeling of glioma cells with gadofluorine M enhances T1 visibility without affecting glioma cell growth or motility
Authors: Nolte Ingo S. , Gungor Sevil , Erber Ralf , Plaxina Elena , Scharf Johann , Misselwitz Bernd , Gerigk Lars , Przybilla Heike , Groden Christoph , Brockmann Marc A.
Published: April 2008

Gadofluorine is a novel macrocyclic, amphiphilic gadolinium‐based contrast agent. We found that malignant glioma cells could be labeled in vitro using Gadofluorine without the need for transfection agents or any other additional means. Labeling with Gadofluorine enhanced the visualization of glioma cells in T1‐weighted sequences, even if the cells had been cultured in medium without Gadofluorine over several days. The intracellular uptake of Gadofluorine was measured and the loss of relevant amounts of Gadofluorine into the cell culture medium was ruled out by MRI. Confocal laser fluorescence microscopy revealed Cy‐5‐labeled Gadofluorine in the perinuclear cytoplasmic region, but neither within the nucleus nor bound to the cell membrane. Adverse effects of cellular Gadofluorine uptake were ruled out by proliferation and migration assays. Finally, in vivo analyses provided good visibility of labeled glioma cells in T1‐weighted sequences after intracerebral injection in mice for more than 2 weeks. We thus conclude that Gadofluorine can easily be used to label glioma cells in vitro without affecting glioma cell biology. Gadofluorine provides an interesting alternative for cellular labeling if iron oxide particles are incorporated insufficiently by target cells or if the vicinity of susceptibility artifacts prohibits the use of signal‐decreasing contrast agents. Magn Reson Med 59:1014–1020, 2008. © 2008 Wiley‐Liss, Inc.
Resting‐state functional connectivity of the rat brain
Authors: Pawela Christopher P. , Biswal Bharat B. , Cho Younghoon R. , Kao Dennis S. , Li Rupeng , Jones Seth R. , Schulte Marie L. , Matloub Hani S. , Hudetz Anthony G. , Hyde James S.
Published: April 2008

Regional‐specific average time courses of spontaneous fluctuations in blood oxygen level dependent (BOLD) MRI contrast at 9.4T in lightly anesthetized resting rat brain are formed, and correlation coefficients between time course pairs are interpreted as measures of connectivity. A hierarchy of regional pairwise correlation coefficients (RPCCs) is observed, with the highest values found in the thalamus and cortex, both intra‐ and interhemisphere, and lower values between the cortex and thalamus. Independent sensory networks are distinguished by two methods: data driven, where task activation defines regions of interest (ROI), and hypothesis driven, where regions are defined by the rat histological atlas. Success in these studies is attributed in part to the use of medetomidine hydrochloride (Domitor) for anesthesia. Consistent results in two different rat‐brain systems, the sensorimotor and visual, strongly support the hypothesis that resting‐state BOLD fluctuations are conserved across mammalian species and can be used to map brain systems. Magn Reson Med 59:1021–1029, 2008. © 2008 Wiley‐Liss, Inc.
Interleaved narrow‐band PRESS sequence with adiabatic spatial‐spectral refocusing pulses for 1H MRSI at 7T
Authors: Balchandani Priti , Pauly John , Spielman Daniel
Published: April 2008

Proton magnetic resonance spectroscopic imaging (1H MRSI) is a useful technique for measuring metabolite levels in vivo, with Choline (Cho), Creatine (Cre), and N‐Acetyl‐Aspartate (NAA) being the most prominent MRS‐detectable brain biochemicals. 1H MRSI at very high fields, such as 7T, offers the advantages of higher SNR and improved spectral resolution. However, major technical challenges associated with high‐field systems, such as increased B1 and B0 inhomogeneity as well as chemical shift localization (CSL) error, degrade the performance of conventional 1H MRSI sequences. To address these problems, we have developed a Position Resolved Spectroscopy (PRESS) sequence with adiabatic spatial‐spectral (SPSP) refocusing pulses, to acquire multiple narrow spectral bands in an interleaved fashion. The adiabatic SPSP pulses provide magnetization profiles that are largely invariant over the 40% B1 variation measured across the brain at 7T. Additionally, there is negligible CSL error since the transmit frequency is separately adjusted for each spectral band. in vivo 1H MRSI data were obtained from the brain of a normal volunteer using a standard PRESS sequence and the interleaved narrow‐band PRESS sequence with adiabatic refocusing pulses. In comparison with conventional PRESS, this new approach generated high‐quality spectra from an appreciably larger region of interest and achieved higher overall SNR. Magn Reson Med 59:973–979, 2008. © 2008 Wiley‐Liss, Inc.
Accelerated proton echo planar spectroscopic imaging (PEPSI) using GRAPPA with a 32‐channel phased‐array coil
Authors: Tsai Shang‐Yueh , Otazo Ricardo , Posse Stefan , Lin Yi‐Ru , Chung Hsiao‐Wen , Wald Lawrence L. , Wiggins Graham C. , Lin Fa‐Hsuan
Published: April 2008

Parallel imaging has been demonstrated to reduce the encoding time of MR spectroscopic imaging (MRSI). Here we investigate up to 5‐fold acceleration of 2D proton echo planar spectroscopic imaging (PEPSI) at 3T using generalized autocalibrating partial parallel acquisition (GRAPPA) with a 32‐channel coil array, 1.5 cm3 voxel size, TR/TE of 15/2000 ms, and 2.1 Hz spectral resolution. Compared to an 8‐channel array, the smaller RF coil elements in this 32‐channel array provided a 3.1‐fold and 2.8‐fold increase in signal‐to‐noise ratio (SNR) in the peripheral region and the central region, respectively, and more spatial modulated information. Comparison of sensitivity‐encoding (SENSE) and GRAPPA reconstruction using an 8‐channel array showed that both methods yielded similar quantitative metabolite measures (P > 0.1). Concentration values of N‐acetyl‐aspartate (NAA), total creatine (tCr), choline (Cho), myo‐inositol (mI), and the sum of glutamate and glutamine (Glx) for both methods were consistent with previous studies. Using the 32‐channel array coil the mean Cramer–Rao lower bounds (CRLB) were less than 8% for NAA, tCr, and Cho and less than 15% for mI and Glx at 2‐fold acceleration. At 4‐fold acceleration the mean CRLB for NAA, tCr, and Cho was less than 11%. In conclusion, the use of a 32‐channel coil array and GRAPPA reconstruction can significantly reduce the measurement time for mapping brain metabolites. Magn Reson Med 59:989–998, 2008. © 2008 Wiley‐Liss, Inc.
Off‐resonance‐dependent slice profile effects in balanced steady‐state free precession imaging
Authors: Staehle F. , Leupold J. , Hennig J. , Markl M.
Published: April 2008

The purpose of this study was the simulation and measurement of balanced steady‐state free precession (bSSFP) slice profiles for a detailed analysis of the influence of off‐resonance effects on slice profile shape and bSSFP signal intensity. Due to the frequency response function of the bSSFP sequence, measurements that are not on‐resonance result in broadened effective slice profiles with different off‐resonance‐dependent shapes and signal intensities. In this study, bSSFP slice profile effects and their dependence on off‐resonance were investigated based on bSSFP signal simulations of phantom data as well as blood and tissue. For a better assessment of the similarity of measured and simulated slice profiles the field map was integrated in the slice profile simulations. The results demonstrate that simulations can accurately predict bSSFP slice profiles. Both measurements and simulations indicate that there is a substantial increase in signal intensity close to the banding artifacts, i.e., at spatial locations with off‐resonance frequencies corresponding to a dephasing/TR = ± π resulting in signal void (bands). For routine bSSFP imaging, off‐resonance‐dependent slice broadening may thus result in a substantial difference between nominal and true slice thickness and lead to spatially varying slice thickness and signal intensities across the imaging slice. Magn Reson Med 59:1197–1202, 2008. © 2008 Wiley‐Liss, Inc.
Wireless self‐gated multiple‐mouse cardiac cine MRI
Authors: Esparza‐Coss Emilio , Ramirez Marc S. , Bankson James A.
Published: April 2008

Despite the excellent image‐contrast capability of MRI and the ability to synchronize MRI with the murine cardiac cycle, this technique is underused for assessing mouse models of cardiovascular disease because of its perceived cost and complexity. This perception stems, in part, from complications associated with the placement and adjustment of electrocardiographic leads that may interact with gradient pulses and the relatively long acquisition times required with traditional gating schemes. To improve the efficiency and reduce the cost and complexity of using cardiac MRI in mice, we combined wireless self‐gating techniques (with which we derived cardiac synchronization signals from acquired data) with an imaging technique that acquires multislice cardiac cine images from four mice simultaneously. As a result, the wireless self‐gated acquisitions minimized animal preparation time and improved image quality. The simultaneous acquisition of cardiac cine data from multiple animals greatly increased throughput and reduced costs associated with instrument access. Magn Reson Med 59:1203–1206, 2008. © 2008 Wiley‐Liss, Inc.
Evaluation of temporal and spatial characteristics of 2D HYPR processing using simulations
Authors: Wu Yan , Wieben Oliver , Mistretta Charles A. , Korosec Frank R.
Published: April 2008

Highly constrained back‐projection (HYPR) is a data acquisition and reconstruction method that provides very rapid frame update rates and very high spatial resolution for a time series of images while maintaining a good signal‐to‐noise ratio and high image quality. In this study we used simulations to evaluate the temporal and spatial characteristics of images produced using the HYPR algorithm. The simulations demonstrate that spatial accuracy is well maintained in the images and the temporal changes in signal intensity are represented with high fidelity. The waveforms representing signal intensity as a function of time obtained from regions‐of‐interest placed in simulated objects track the true curves very well, with variations from the truth occurring only when objects with very different temporal behavior are very close to each other. However, even when objects with different temporal characteristics are touching, their influences on each other are small. Magn Reson Med 59:1090–1098, 2008. © 2008 Wiley‐Liss, Inc.
Regional metabolite T2 in the healthy rhesus macaque brain at 7T
Authors: Liu Songtao , Gonen Oded , Fleysher Lazar , Fleysher Roman , Soher Brian J. , Pilkenton Sarah , Lentz Margaret R. , Ratai Eva‐Maria , González R. Gilberto
Published: April 2008

Although the rhesus macaque brain is an excellent model system for the study of neurological diseases and their responses to treatment, its small size requires much higher spatial resolution, motivating use of ultra‐high‐field (B0) imagers. Their weaker radio‐frequency fields, however, dictate longer pulses; hence longer TE localization sequences. Due to the shorter transverse relaxation time (T2) at higher B0s, these longer TEs subject metabolites to T2‐weighting, that decrease their quantification accuracy. To address this we measured the T2s of N‐acetylaspartate (NAA), choline (Cho), and creatine (Cr) in several gray matter (GM) and white matter (WM) regions of four healthy rhesus macaques at 7T using three‐dimensional (3D) proton MR spectroscopic imaging at (0.4 cm)3 = 64 μl spatial resolution. The results show that macaque T2s are in good agreement with those reported in humans at 7T: 169 ± 2.3 ms for NAA (mean ± SEM), 114 ± 1.9 ms for Cr, and 128 ± 2.4 ms for Cho, with no significant differences between GM and WM. The T2 histograms from 320 voxels in each animal for NAA, Cr, and Cho were similar in position and shape, indicating that they are potentially characteristic of “healthy” in this species. Magn Reson Med 59:1165–1169, 2008. © 2008 Wiley‐Liss, Inc.
System identification theory in pharmacokinetic modeling of dynamic contrast‐enhanced MRI: Influence of contrast injection
Authors: Aerts H.J.W.L. , van Riel N.A.W. , Backes W.H.
Published: April 2008

Optimization of experimental settings of dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI), like the contrast administration protocol, is of great importance for reliable quantification of the microcirculatory properties, such as the volume transfer‐constant Ktrans. Using system identification theory and computer simulations, the confounding effects of volume, rate and multiplicity of a contrast injection on the reliability of Ktrans estimation was assessed. A new tracer‐distribution model (TDM), based on in vivo data from rectal cancer patients, served to describe the relationship between the contrast agent injection and the blood time‐course. A pharmacokinetic model (PKM) was used to describe the relation between the blood and tumor tissue time‐courses. By means of TDM and PKM in series, the tissue‐transfer function of the PKM was analyzed. As both the TDM and PKM represented low‐frequency‐pass filters, the energy‐density at low frequencies of the blood and tissue time‐courses was larger than at high frequencies. The simulations, based on measurements in humans, predict that the Ktrans is most reliable with a high injection volume administered in a single injection, where high rates only modestly improve Ktrans. Magn Reson Med 59:1111–1119, 2008. © 2008 Wiley‐Liss, Inc.
Generalized k‐space decomposition with chemical shift correction for non‐cartesian water‐fat imaging
Authors: Brodsky Ethan K. , Holmes James H. , Yu Huanzhou , Reeder Scott B.
Published: April 2008

Chemical‐shift artifacts associated with non‐Cartesian imaging are more complex to model and less clinically acceptable than the bulk fat shift that occurs with conventional spin‐warp Cartesian imaging. A novel k‐space based iterative decomposition of water and fat with echo asymmetry and least‐squares estimation (IDEAL) approach is introduced that decomposes multiple species while simultaneously correcting distortion of off‐resonant species. The new signal model accounts for the additional phase accumulated by off‐resonant spins at each point in the k‐space acquisition trajectory. This phase can then be corrected by adjusting the decomposition matrix for each k‐space point during the final IDEAL processing step with little increase in reconstruction time. The technique is demonstrated with water‐fat decomposition using projection reconstruction (PR)/radial, spiral, and Cartesian spin‐warp imaging of phantoms and human subjects, in each case achieving substantial correction of chemical‐shift artifacts. Simulations of the point‐spread‐function (PSF) for off‐resonant spins are examined to show the nature of the chemical‐shift distortion for each acquisition. Also introduced is an approach to improve the signal model for species which have multiple resonant peaks. Many chemical species, including fat, have multiple resonant peaks, although such species are often approximated as a single peak. The improved multipeak decomposition is demonstrated with water‐fat imaging, showing a substantial improvement in water‐fat separation. Magn Reson Med 59:1151–1164, 2008. © 2008 Wiley‐Liss, Inc.
Simultaneous acquisition of MR angiography and venography (MRAV)
Authors: Du Yiping P. , Jin Zhaoyang
Published: April 2008

A dual‐echo pulse sequence for simultaneous acquisition of MR angiography and venography (MRAV) is developed. Data acquisition of the second echo for susceptibility‐weighted imaging–based MR venography is added to the conventional three‐dimensional (3D) time‐of‐flight (TOF) MRA pulse sequence. Using this dual‐echo acquisition approach, the venography data can be acquired without increasing the repetition time, and, therefore, the scan duration of routine TOF MRA scans is maintained. The feasibility of simultaneous acquisition of MRAV is presented in brain scans at different spatial resolutions. The effect of spatial resolution on vein‐to‐background contrast is also demonstrated. Venous contrast is improved in high‐resolution (0.52 × 0.52 × 1.6 mm3) images compared to that in standard‐resolution (0.78 × 0.78 × 1.6 mm3) images. This MRAV technique enables the acquisition of MR venography without the need of an extra scan or injection of contrast agent in routine clinical brain exams at 3T. Magn Reson Med 59:954–958, 2008. © 2008 Wiley‐Liss, Inc.
Evidence for enhanced functional activity of cervical cord in relapsing multiple sclerosis
Authors: Agosta F. , Valsasina P. , Rocca M.A. , Caputo D. , Sala S. , Judica E. , Stroman P.W. , Filippi M.
Published: April 2008

Functional MRI (fMRI) was used to assess proprioceptive‐associated cervical cord activity in 24 relapsing multiple sclerosis (MS) patients and 10 controls. Cord and brain conventional and diffusion tensor (DT) MRI were also acquired. fMRI was performed using a block design during a proprioceptive stimulation consisting of a passive flexion‐extension of the right upper limb. Cord lesion number, cross‐sectional area, mean diffusivity (MD) and fractional anisotropy (FA), whole brain and left corticospinal tract lesion volume (LV), gray matter (GM) MD, and normal‐appearing white matter (NAWM) MD and FA were calculated. MS patients had higher average cord fMRI signal changes than controls (3.4% vs. 2.7%, P = 0.03). Compared to controls, MS patients also had a higher average signal change in the anterior section of the right cord at C5 (P = 0.005) and left cord at C5–C6 (P = 0.03), whereas no difference was found in the other cord sections. Cord average signal change correlated significantly with cord FA and brain left corticospinal tract LV, GM‐MD, and NAWM‐FA. This study shows an abnormal pattern of activations in the cervical cord of MS patients following proprioceptive stimulation. Cord fMRI changes might have a role in limiting the clinical consequences of MS associated with irreversible tissue damage. Magn Reson Med 59:1035–1042, 2008. © 2008 Wiley‐Liss, Inc.
Semiautomatic off‐resonance correction in spiral imaging
Authors: Chen Weitian , Meyer Craig H.
Published: April 2008

Spiral scanning is a promising MRI method, but one limitation is that off‐resonance effects can cause image blurring. Most current off‐resonance correction methods for spiral imaging require an accurate field map, which is difficult to obtain in many applications. Automatic methods can perform off‐resonance correction without acquiring a field map. However, these methods are computationally inefficient and relatively prone to estimation error. This study describes a new semiautomatic off‐resonance correction method that combines an automatic method with a low resolution field map acquisition for off‐resonance correction in spiral scanning. Experiments demonstrate that this method is more robust than conventional automatic off‐resonance correction and can provide more accurate off‐resonance correction than conventional field map based methods. The proposed method is also computationally efficient and has been implemented for online reconstruction. Magn Reson Med 59:1212–1219, 2008. © 2008 Wiley‐Liss, Inc.
Optimization framework for calibration of constitutive models enhanced by neural networks
Authors: Obrzud Rafał F. , Vulliet Laurent , Truty Andrzej
Published: April 2008

A two‐level procedure designed for the estimation of constitutive model parameters is presented in this paper. The neural network (NN) approach at the first level is applied to achieve the first approximation of parameters. This technique is used to avoid potential pitfalls related to the conventional gradient‐based optimization techniques, considered here as a corrector that improves predicted parameters. The feed‐forward NN (FFNN) and the modified Gauss–Newton algorithms are briefly presented. The proposed framework is verified for the elasto‐plastic modified Cam Clay model that can be calibrated based on standard triaxial laboratory tests, i.e. the isotropic consolidation test and the drained compression test. Two different formulations of the input data to the NN, enhanced by a dimensional reduction of experimental data using principal component analysis, are presented. The determination of model characteristics is demonstrated, first on numerical pseudo‐experiments and then on the experimental data. The efficiency of the proposed approach by means of accuracy and computational effort is also discussed. Copyright © 2008 John Wiley & Sons, Ltd.
Retrospective analysis of 65 Chinese children with acute promyelocytic leukemia: A single center experience
Authors: Zhang Li , Zhao Hui , Zhu Xiaofan , Chen Yumei , Zou Yao , Chen Xiaojuan
Published: April 2008

Background

There are very limited data reported about childhood acute promyelocytic leukemia (APL), especially with arsenic trioxide (As2O3) treatment. We review the clinical course and treatment outcome of 65 children APL.

Procedure

Between January 1999 and December 2005, 65 children (<18 years) with newly diagnosed APL were treated.

Results

Three groups of patients were identified according to the different induction regimens. Forty patients were given ATRA alone (group 1, G1), 8 patients were given As2O3 alone (group 2, G2), 15 patients (group 3, G3) were treated with combination of ATRA and As2O3. Two patients received cytosine arabinoside and died at days 2 and 4, respectively. The CR rate of G1 was 95% (38/40). The overall CR rate of G2+G3 was 91.3% (21/23). Toxicity of ATRA and As2O3 were minimal and recoverable during induction. Five children had a hematologic relapse and two developed molecular relapse. Five of them were successfully treated with ATRA alone or combined with As2O3. The 5‐year estimate of EFS, DFS and OS between G1 and G2+G3 has no difference.

Conclusion

As2O3 is an effective and well tolerable therapy for children with APL and it may be used in those who have dose limiting side effects of ATRA, but also for those with newly diagnosed or relapsed APL. Pediatr Blood Cancer 2008;51:210–215. © 2008 Wiley‐Liss, Inc.
Comparison of gallium and PET scans at diagnosis and follow‐up of pediatric patients with Hodgkin lymphoma
Authors: Hines‐Thomas Melissa , Kaste Sue C. , Hudson Melissa M. , Howard Scott C. , Liu Wei A. , Wu Jianrong , Kun Larry E. , Shulkin Barry L. , Krasin Matthew J. , Metzger Monika L.
Published: April 2008

Background

Positron emission tomography (PET) and gallium scans facilitate diagnosis and staging, evaluation of response to therapy, and monitoring for relapse in Hodgkin lymphoma (HL), but have not been compared in pediatric HL.

Procedure

We performed concurrent PET and gallium scans on 44 pediatric HL patients at diagnosis, early response, off chemotherapy, and off‐therapy evaluations. PET and gallium scans were compared to each other and to computed tomography (CT) alone to determine whether either modality led to a change in stage or modified the results of the early response evaluation, which was used to determine the radiation dose.

Results

PET upstaged four patients at diagnosis (2 from stage I to II, one II to III, and one III to IV), but did not lead to a change in therapy in any of them. It changed response category in two patients at early response evaluation, leading to a change in radiation dose for 1 patient (25.5 Gy instead of 15 Gy to the spleen). Gallium did not change the stage of treatment for any patient. The negative predictive values for eventual lymphoma relapse of PET and gallium scans at off therapy were 89% and 83%, respectively; the positive predictive value of PET at off therapy is 29%.

Conclusion

PET appears to be superior to gallium in pediatric HL; future studies will determine the optimal timing of PET to assess early response and the utility of quantitative interpretation of the avidity of specific nodal sites. Pediatr Blood Cancer 2008;51:198–203. © 2008 Wiley‐Liss, Inc.
Methadone analgesia for children with advanced cancer
Authors: Davies Dawn , DeVlaming Deborah , Haines Christina
Published: April 2008

Background

Methadone is frequently used in the treatment of adults with advanced cancer. A criticism of relevant research is the use of single or fixed doses, which does not reflect use in clinical practice. Literature about use of methadone in the treatment of pediatric patients is limited to case reports. The objective of this study is to describe methadone use as primary opioid analgesic for advanced pediatric cancer over a 6.5‐year period.

Procedure

All 17 patients who received methadone as their primary opioid analgesic through the Northern Alberta Children's Cancer Program from January 2000 to June 2007 were included. Children who received combination opioid therapy were excluded.

Results

Rotation to methadone was usually by a complete switch from primary opioid. Conversion ratios of morphine equivalent daily dose (MEDD)/methadone daily dose (TMDD) ranged widely from 1:2 in one patient with sudden pain crisis just prior to death, to 60:1 in a patient who had been treated with opioids for months. Methadone was used for a total of 925 patient‐days. There were no significant adverse events in any patient, and all but one patient remained on methadone until the time of their death. Clinically, the effectiveness of analgesia clearly improved at time of conversion in 16 patients.

Conclusion

With close monitoring, methadone therapy can be done safely in pediatric oncology patient populations in both inpatient and outpatient settings. Our experience suggests improvement in analgesia with the use of methadone, with 16 patients remaining on methadone until they died. Pediatr Blood Cancer 2008;51:393–397. © 2008 Wiley‐Liss, Inc.
Seasonal variation and environmental predictors of exhaled nitric oxide in children with asthma
Authors: Spanier Adam J. , Hornung Richard W. , Kahn Robert S. , Lierl Michelle B. , Lanphear Bruce P.
Published: April 2008

The fraction of exhaled nitric oxide (FeNO), a measure of airway inflammation, shows promise as a noninvasive tool to guide asthma management, but there is a paucity of longitudinal data about seasonal variation and environmental predictors of FeNO in children. The objective of this project was to evaluate how environmental factors affect FeNO concentrations over a 12‐month study period among children with doctor diagnosed asthma. We conducted a prospective cohort study of 225 tobacco‐smoke exposed children age 6–12 years with doctor‐diagnosed asthma including measures of FeNO, medication use, settled indoor allergens (dust mite, cat, dog, and cockroach), and tobacco smoke exposure. Baseline geometric mean FeNO was 12.4 ppb (range 1.9–60.9 ppb). In multivariable analyses, higher baseline FeNO levels, atopy, and fall season were associated with increased FeNO levels, measured 6 and 12 months after study initiation, whereas inhaled steroid use, summer season, and increasing nicotine exposure were associated with lower FeNO levels. In secondary analyses of allergen sensitization, only sensitization to dust mite and cat were associated with increased FeNO levels. Our data demonstrate that FeNO levels over a year long period reflected baseline FeNO levels, allergen sensitization, season, and inhaled steroid use in children with asthma. These results indicate that FeNO levels are responsive to common environmental triggers as well as therapy for asthma in children. Clinicians and researchers may need to consider an individual's baseline FeNO levels to manage children with asthma. Pediatr Pulmonol. 2008; 43:576–583. © 2008 Wiley‐Liss, Inc.
High temperature Ohmic contacts to p‐type GaN for use in light emitting applications
Authors: Voss L. F. , Stafford L. , Hlad M. , Gila B. P. , Abernathy C. R. , Pearton S. J. , Ren F. , Kravchenko I.
Published: April 2008

Achieving low resistance contacts to p‐type Gallium Nitride is a critical requirement for the fabrication of reliable AlGaN/InGaN laser diodes and nitride‐based light‐emitting diodes (LEDs). Three separate groups of materials are examined. The first is a family of borides, including W2B, W2B5, CrB2, TiB2, and ZrB2; the second is a group of nitrides, TaN, TiN, and ZrN; and the third is the refractory metal Ir. Using these materials both directly on the surface of p‐GaN as well as a diffusion barrier for Ni/Au‐based Ohmic contacts, specific contact resistances as low as ∼1x10–4 Ω.cm2 have been achieved. In addition, the boride and iridium based contacts display superior aging characteristics with minimal degradation of the contact resistance and of the turn on voltage of light emitting diodes after extended periods at 350 °C. The reasons for the discrepancies in performance of different materials is examined through the use of IV curves as well as Auger Electron Spectroscopy (AES) depth profiles. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
First all‐HVPE grown InGaN/InGaN MQW LED structures for 460‐510 nm
Authors: Syrkin A. , Ivantsov V. , Kovalenkov O. , Usikov A. , Dmitriev V. , Liliental‐Weber Z. , Reed M. L. , Readinger E. D. , Shen H. , Wraback M.
Published: April 2008

In this paper we report on first InGaN‐based light emitting structures grown by hydride vapour phase epitaxy (HVPE). InGaN layers and multi layer InGaN/InGaN epitaxial structures were grown on GaN/sapphire template substrates and characterized. InN content in the InGaN layers was varied from 5 to 35 mol.%. Thickness of InGaN layers was controlled from 10 nm to 2 microns. Density of treading dislocations in the InGaN layers was estimated to be in the 109 cm–2 range. X‐ray diffraction measurements and transmission electron microscopy data confirmed a formation of InGaN/InGaN superlattice structures. Light emitting diode epitaxial wafers were fabricated by HVPE deposition of n‐type InGaN layers and multi layer structures on p‐type GaN template substrates. Depending on InN content in the InGaN light emitting regions, peak electroluminescence wavelength varied from 450 to 510 nm. Results of material characterization are reported. Advantages of the proposed upside down LED configuration and future applications of HVPE to grow InGaN layers and structures are discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
InN nanorods and nanowires grown on different substrates
Authors: Liliental‐Weber Z. , Hawkridge M. , Mangum J. , Kryliouk O.
Published: April 2008

Transmission Electron Microscopy was applied to study InN nanorods grown by non‐catalytic, template‐free hydride metal‐organic vapor phase epitaxy (solid‐vapor mechanism) and nanowires grown by a vapor‐liquid‐solid growth (VLS) mechanism in a MOVPE reactor. The nanorods and nanowires were grown on different planes of Al2O3, (0002) GaN/ Al2O3, and (001) Si. The majority of nanorods have a high structural perfection and exhibit abrupt side walls, but some of them show formation of the planar defects. Depend‐ ing on the substrate used, the size, shape and tips of the nanorods vary from hexagonal to pencil‐like. Nanowires, however have very corrugated surfaces along their side‐walls and tips, and depending on the V/III flow ratio these nanowires can have either a constant diameter or taper‐off. Their length can extend up to 100 μm. Bending and branching of nanowires was observed, but this phenomenon was never observed for nanorods. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermal degradation of InGaN/GaN LEDs ohmic contacts
Authors: Meneghini M. , Trevisanello L. , Zehnder U. , Meneghesso G. , Zanoni E.
Published: April 2008

This paper reports an analysis of the high temperature degradation of GaN‐based LEDs. It is shown that exposure to high temperatures implies(i)the decrease of the emitted optical power,(ii)the crowding of the emission profile around the central pad and(iii)the increase of the operating voltage of the devices. Degradation is attributed to the interaction between the PECVD SiN passivation layer and the ohmic contacts at the surface of the devices: by means of the Transmission Line Method the degradation of the p‐side contacts is analyzed in detail. It is shown that high temperature treatment implies the increase of the contact resistivity of the metal/semiconductor (M/S) interface, and a slight variation of the sheet resistance of the semiconductor layer: these processes are responsible for the emission crowding and efficiency decay measured as a consequence of stress on the LEDs. Finally, it is shown that the described degradation process is reversible, after passivation removal and subsequent annealing. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Temperature dependence of the polariton relaxation bottleneck in a GaN microcavity
Authors: Stokker‐Cheregi F. , Vinattieri A. , Colocci M. , Semond F. , Leroux M. , Massies J. , Sellers I. R. , Gurioli M.
Published: April 2008

We present an experimental study aimed to investigate discuss the possible presence of a phonon bottleneck in a GaN bulk microcavity. Clear anticrossing between the lower (LP) and upper polariton (UP) branches has been observed up to room temperature in photoluminescence (PL) by angular measurements with a Rabi splitting of the order of 30 meV. In order to determine the presence of a relaxation bottleneck, angular PL measurements have been performed at different temperatures for negative detuning. At low T the PL shows a clear maximum, at the angle corresponding to the resonance between the exciton and the photon modes, which is an experimental demonstration of the presence of a relaxation bottleneck. The PL enhancement in resonance condition is suppressed with increasing T and it almost disappears at room temperature. We therefore demonstrate that the exciton‐phonon interaction washes out the polariton bottleneck in GaN MCs at room temperature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High‐temperature growth of AlN in a production scale 11 × 2′ MOVPE reactor
Authors: Brunner F. , Protzmann H. , Heuken M. , Knauer A. , Weyers M. , Kneissl M.
Published: April 2008

We report on the growth of high quality AlN films on sapphire by MOVPE in an AIX2400G3‐HT planetary reactor. Specific reactor hardware modifications were conducted to facilitate growth temperatures of up to 1600 °C and to obtain reduced parasitic gas phase reactions. Growth was optimized regarding growth rate and surface morphology as well as optical and structural properties of the AlN layers on sapphire. With increasing growth temperature we observe a transition from an AlN surface with a high density of large pits to a smooth pit‐free morphology. The improvement in material quality with growth temperature is confirmed by X‐ray diffraction, AFM, SIMS and Raman measurements. The impact of residual or intentionally introduced Ga during growth on AlN material properties is discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural features in GaN grown on a Ge(111) substrate
Authors: Zhang Y. , McAleese C. , Xiu H. , Humphreys C. J. , Lieten R. R. , Degroote S. , Borghs G.
Published: April 2008

Using electron microscopy, structural characterisation has been carried out on a GaN epilayer grown directly on a Ge(111) substrate using plasma assisted molecular beam epitaxy (PAMBE) without any intermediate buffer layers. It was determined that a defect with a triangular shape, initially observed with optical microscopy, is essentially a faceted void in the Ge extending from the interface into the substrate. Both hexagonal and cubic phase GaN were observed in the epilayer which may be due to temperature variation during growth. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The role of setback layers on the breakdown characteristics of AlGaAs/GaAs/GaN HBTs
Authors: Lian Chuanxin , Xing Huili Grace
Published: April 2008

Breakdown voltages (VCBO) of AlGaAs/GaAs/GaAs and AlGaAs/GaAs/GaAs‐setback/GaN HBTs have been compared both theoretically and experimentally with respect to setback layer thicknesses and the doping type. VCBO was calculated using a non‐local energy model. The hard breakdown voltage was measured on as‐grown GaAs homojunctions and AlGaAs/GaAs/GaN HBTs formed by direct wafer fusion. The calculation showed an increase of VCBO from ∼ 20 V to ∼ 325 V by replacing the GaAs collector with GaN, and VCBO ∼90 V was indeed measured. The smaller than predicted VCBO is attributed to the large leakage current currently present in the fused junctions. Insertion of a lightly doped GaAs setback layer has resulted in improved current gain of the fused HBTs, but it also degrades the breakdown characteristics. 20‐30 nm setback layers were found to maintain VCBO significantly higher than that of GaAs homojunctions and likely reasonable current gains. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Improvement of the surface morphology of a ‐plane InN using low‐temperature InN buffer layers
Authors: Shikata G. , Hirano S. , Inoue T. , Orihara M. , Hijikata Y. , Yaguchi H. , Yoshida S.
Published: April 2008

We report on the improvement of the surface morphology of a ‐plane InN films grown by RF molecular beam epitaxy. By using low‐temperature (LT) InN buffer layers, we could successfully obtain InN films with a smooth surface. The full width at half maximum values of the x‐ray diffraction (11‐20) rocking curve along the [0001] InN direction were 2870 arcsec and 3410 arcsec for a ‐plane InN samples grown at 500°C with and without LT‐InN buffer layers, respectively. Thus, we could improve also the crystalline quality of a ‐plane InN films by using LT‐InN buffer layers. We observed strong polarization anisotropy in the photoluminescence spectra of a ‐plane InN, which is typical of nonpolar wurtzite III‐nitride films. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Interface characterization of ALD deposited Al2O3 on GaN by CV method
Authors: Ostermaier C. , Lee H.‐C. , Hyun S.‐Y. , Ahn S.‐I. , Kim K.‐W. , Cho H.‐I. , Ha J.‐B. , Lee J.‐H.
Published: April 2008

A high dielectric interface quality is the determining factor for high power GaN metal oxide semiconductor field‐ effect transistor (MOSFET) devices. We characterized 100 Å thick aluminum oxide (Al2O3) films deposited by ALD on MOCVD grown undoped GaN on sapphire. First we measured the leakage current and densification behaviour of the dielectric after annealing at different temperatures up to 900 °C and determined the polycrystalline phase change to be around 800 °C. Further we characterized the interface charges of both films according to the flatband shift, induced by over‐band gap UV light, showing the lowest interface charge density of 1.27 × 1011 cm–2 after thermal treatment at 850 °C. Additionally, we measured the AC conductivity and calculated the interface states density (Dit) of the upper half of the GaN bandgap, showing the lowest Dit of around 2×1010 cm–2 eV–1 at 2 eV above the valence band, while it remains higher around the band edge at 2.8×1011 cm–2 eV–1, after annealing at 750 °C. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simple formulas for improved point‐charge electrostatics in classical force fields and hybrid quantum mechanical/molecular mechanical embedding
Authors: Cisneros G. A. , Tholander S. Na‐Im , Parisel O. , Darden T. A. , Elking D. , Perera L. , Piquemal J.‐P.
Published: April 2008

We present a simple damping scheme for point‐charge electrostatics that could be used directly in classical force fields. The approach acts at the charge (or monopole) level only and allows the inclusion of short‐range electrostatic penetration effects at a very low cost. Results are compared with density functional theory Coulomb intermolecular interaction energies and with several other methods such as distributed multipoles, damped distributed multipoles, and transferable Hermite‐Gaussian densities. Realistic trends in the interactions are observed for atom‐centered Mertz‐Kollman corrected point‐charge distributions. The approach allows increasing the selectivity of parameters in the case of metal complexes. In addition, two QM/MM calculations are presented where the damping function is employed to include the MM atoms located at the QM/MM boundary. The first calculation corresponds to the gas‐phase proton transfer of aspartic acid through water and the second is the first step of the reaction catalyzed by the 4‐oxalocrotonate tautomerase (4OT) enzyme. First, improved agreement is observed when using the damping approach compared with the conventional excluded charge method or when including all charges in the calculation. Second, in the case of 4OT, the damped charge approach is in agreement with previous calculations, whereas including all charges gives a significantly higher energy barrier. In both cases, no reparameterization of the van der Waals part of the force field was performed. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008