bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deconvolution of electrokinetic and chromatographic contributions to solute migration in stereoselective ion‐exchange capillary electrochromatography on monolithic silica capillary columns
Authors: Preinerstorfer Beatrix , Lämmerhofer Michael , Hoffmann Christian V. , Lubda Dieter , Lindner Wolfgang 
Published: April 2008

AbstractA monolithic silica stationary phase functionalized with an enantioselective strong cation exchanger based on an aminosulfonic acid derivative was used for chiral separations of basic test solutes by nonaqueous CEC and capillary LC. The effects of the applied electric field as well as the ionic strength in the eluent on electrokinetic and chromatographic contributions to the overall separation performance in the electrically driven mode were investigated. Hence, under the utilized experimental conditions, i. e., at an electric field strength in the range of ∼︁120–720 V/cm (applied voltages 4–24 kV) and an ionic strength of the counterion between 5 and 25 mM (at constant acid‐to‐base, i. e., co‐ to counterion ratio of 2:1), no deviations from the expected linearity of the EOF were observed. This led to the conclusion that an occurrence of the so‐called electrokinetic effects of the second kind resulting from electric double layer overlap inside the mesopores of the monolithic stationary phase and concentration polarization phenomena were largely negligible. Additional support to this conclusion was inferred from the observed independence of CEC retention factors on the electric field strength across the investigated ionic strength range of the BGE. As a consequence, a simple framework allowing for calculation of the CEC mobilities from the individual separation contributions, viz. electroosmotic and electrophoretic mobilities as well as retention factors, could be applied to model CEC migration. There was a reasonable agreement between calculated and experimental CEC mobility data with deviations typically below 5%. The deconvolution of the individual contributions to CEC migration and separation is of particular value for the understanding of the separation processes in which electrophoretic migration of ionic sample constituents plays a significant role like in ion‐exchange CEC and may aid the optimization procedure of the BGE and other experimental conditions such as the optimization of the surface chemistry of the stationary phase. In combination with the remarkable column performance evident from the low theoretical plate heights observed under CEC conditions for all test solutes (3.5–7.5 μm in the flow rate range of 0.4–1.2 mm/s, corresponding to (130 000–300 000 plates per meter), the presented framework provides an attractive tool as the basis for the assessment of chromatographic selectivities in a miniaturized CEC screening of new selectors and chiral stationary phases (CSPs), respectively, from experimental CEC data and known CE mobilities.
In‐line coupling of a reversed‐phase column to cope with limited chemoselectivity of a quinine carbamate‐based anion‐exchange type chiral stationary phase
Authors: Sardella Roccaldo , Lämmerhofer Michael , Natalini Benedetto , Lindner Wolfgang 
Published: April 2008

AbstractA chiral stationary phase based on tert‐butylcarbamoyl quinine has shown remarkable enantiomer separation capability for the thyroid hormone thyroxine (T4) and its structural analogue triiodothyronine (T3) employing hydroorganic buffered mobile phases (typical RP conditions). To overcome the problem of a somehow limited chemoselectivity for the critical peak pair between adjacent L‐thyroxine (L‐T4) and D‐thyroxine (D‐T4) peaks on the chiral anion‐exchanger CSP when all four compounds need to be analysed simultaneously like in impurity profiling of L‐T4 drug products, an RP column (Gemini C18) was serially coupled with the chiral anion‐exchanger column to add a hydrophobic selectivity increment and to improve thereby the critical resolution between L‐T3 and D‐T4. Various parameters such as organic modifier content, pH, buffer concentration and type, type of achiral column as well as sequence of achiral and chiral column have been investigated with individual and tandem columns. With the optimized conditions and use of the tandem column a significantly improved separation, as compared to the chiral anion‐exchanger column alone, with a critical resolution as high as 3.7 and an almost equal band spacing of the four components of the test mixture could be obtained. The sequence of the columns (achiral–chiral or chiral–achiral) had no significant effect on the separation performance.
Hydrophilic interaction chromatography of small metal species in plants using sulfobetaine‐ and phosphorylcholine‐type zwitterionic stationary phases
Authors: Weber Günther , von Wirén Nicolaus , Hayen Heiko 
Published: April 2008

AbstractHydrophilic interaction chromatography (HILIC) was applied for the separation of small, noncovalent metal species, and free ligands in plants, using two different zwitterionic stationary phases at pH 7.3. Ligands ranged from amino acids and phytosiderophores to organic acids and synthetic chelators like EDTA. Our results confirmed the suitability of zwitterionic stationary phases for the separation of such ligands and their metal complexes. In particular, the chromatographic behavior of phytosiderophore complexes of copper, nickel, and zinc on a sulfobetaine‐type material was compared to that on a phosphorylcholine‐type material under otherwise identical conditions. A compression of the usable retention range for phytosiderophore species on the latter phase was found, which can be traced back to the reversed charge orientation of the zwitterionic functionalities. Differences were also found for the integrity of more labile metal chelates during separation on the two columns. In particular, Ni–malate could only be analyzed on the sulfobetaine phase, and Cu–glutathione, Ni–aspartate, and Ni–citrate complexes were only stable on the phosphorylcholine stationary phase at pH 7.3. Ni–histidine species were only found after lowering the pH to 4–5. The identification of separated species is possible by online ESI‐MS in the negative ionization mode.
Nonlinear surface plasmon polaritonic crystals
Authors: Wurtz G.A. , Zayats A.V. 
Published: April 2008

AbstractWe present an overview of the optical properties of nonlinear surface plasmon polaritonic crystals and their applications to control light with light. Surface plasmon polaritonic crystals are periodically nanostructured metal surfaces or thin metal films that act as two‐dimensional photonic crystals for surface polaritons. Hybritization of such nanostructures with dielectrics exhibiting an optical nonlinear response allows utilization of the electromagnetic field enhancement effects to observe nonlinear effects and bistable behaviour at low light intensities. By changing the geometry of the nanostructured film, the dispersion of the crystal is modified and, thus, electromagnetic mode structure and associated density of states can be controllably tuned in the desired spectral range. This provides enhanced flexibility in engineering the nonlinear optical response of plasmonic crystals in a chosen spectral range for both control and signal wavelengths.
Feasibility of using limited‐population‐based arterial input function for pharmacokinetic modeling of osteosarcoma dynamic contrast‐enhanced MRI data
Authors: Wang Ya , Huang Wei , Panicek David M. , Schwartz Lawrence H. , Koutcher Jason A. 
Published: April 2008

AbstractFor clinical dynamic contrast‐enhanced (DCE) MRI studies, it is often not possible to obtain reliable arterial input function (AIF) in each measurement. Thus, it is important to find a representative AIF for pharmacokinetic modeling of DCE‐MRI data when individual AIF (Ind‐AIF) measurements are not available. A total of 16 patients with osteosarcomas in the lower extremity (knee region) underwent multislice DCE‐MRI. Reliable Ind‐AIFs were obtained in five patients with a contrast injection rate of 2 cc/s and another five patients with a 1 cc/s injection rate. Average AIF (Avg‐AIF) for each injection rate was constructed from the corresponding five Ind‐AIFs. For each injection rate there are no statistically significant differences between pharmacokinetic parameters of the five patients derived with Ind‐AIFs and Avg‐AIF. There are no statistically significant changes in pharmacokinetic parameters of the 16 patients when the two Avg‐AIFs were applied in kinetic modeling. The results suggest that it is feasible, as well as practical, to use a limited‐population‐based Avg‐AIF for pharmacokinetic modeling of osteosarcoma DCE‐MRI data. Further validation with a larger population and multiple regions is desirable. Magn Reson Med 59:1183–1189, 2008. © 2008 Wiley‐Liss, Inc.
3D hyperpolarized He‐3 MRI of ventilation using a multi‐echo projection acquisition
Authors: Holmes James H. , O'Halloran Rafael L. , Brodsky Ethan K. , Jung Youngkyoo , Block Walter F. , Fain Sean B. 
Published: April 2008

AbstractA method is presented for high‐resolution 3D imaging of the whole lung using inhaled hyperpolarized (HP) He‐3 MR with multiple half‐echo radial trajectories that can accelerate imaging through undersampling. A multiple half‐echo radial trajectory can be used to reduce the level of artifact for undersampled 3D projection reconstruction (PR) imaging by increasing the amount of data acquired per unit time for HP He‐3 lung imaging. The point spread functions (PSFs) for breath‐held He‐3 MRI using multiple half‐echo trajectories were evaluated using simulations to predict the effects of T2* and gas diffusion on image quality. Results from PSF simulations were consistent with imaging results in volunteer studies showing improved image quality with increasing number of echoes using up to 8 half‐echoes. The 8‐half‐echo acquisition is shown to accommodate lost breath‐holds as short as 6 sec using a retrospective reconstruction at reduced resolution and also to allow reduced breath‐hold time compared with an equivalent Cartesian trajectory. Furthermore, preliminary results from a 3D dynamic inhalation‐exhalation maneuver are demonstrated using the 8‐half‐echo trajectory. Results demonstrate the first high‐resolution 3D PR imaging of ventilation and respiratory dynamics in humans using HP He‐3 MR. Magn Reson Med 59:1062–1071, 2008. © 2008 Wiley‐Liss, Inc.
Quantitative J‐resolved prostate spectroscopy using two‐dimensional prior‐knowledge fitting
Authors: Lange Thomas , Schulte Rolf F. , Boesiger Peter 
Published: April 2008

AbstractTwo‐dimensional (2D) prior‐knowledge fitting (ProFit) was adapted and applied for the quantification of J‐resolved (JPRESS) spectra acquired at a field strength of 3T from the human prostate in vivo. In contrast to methods based on simple line fitting and peak integration, commonly applied for metabolite quantification in the prostate, ProFit yields metabolite concentration ratios that are independent of sequence and field strength, since it is based on the linear combination of 2D basis spectra. It is demonstrated that ProFit benefits from the increased information content and reduced baseline distortion in JPRESS prostate spectra, in particular for the quantification of coupled metabolites like citrate (Cit), spermine (Spm), and myo‐inositol (mI). The method is validated with 10 repetitive prostate measurements on the same subject. Furthermore, a study carried out on 10 healthy subjects shows that the six prostate metabolites creatine (Cr), total choline (Cho), Cit, Spm, mI, and scyllo‐inositol (sI) can be reliably detected in vivo, some of which—especially total Cho and Cit—have proven to be useful markers for the detection of prostate cancer. Magn Reson Med 59:966–972, 2008. © 2008 Wiley‐Liss, Inc.
Cardiac metabolism measured noninvasively by hyperpolarized 13C MRI
Authors: Golman Klaes , Petersson J. Stefan , Magnusson Peter , Johansson Edvin , Åkeson Per , Chai Chun‐Ming , Hansson Georg , Månsson Sven 
Published: April 2008

AbstractPyruvate is included in the energy production of the heart muscle and is metabolized into lactate, alanine, and CO2 in equilibrium with HCO. The aim of this study was to evaluate the feasibility of using 13C hyperpolarization enhanced MRI to monitor pyruvate metabolism in the heart during an ischemic episode. The left circumflex artery of pigs (4 months, male, 29–34 kg) was occluded for 15 or 45 min followed by 2 hr of reperfusion. Pigs were examined by 13C chemical shift imaging following intravenous injection of 1‐13C pyruvate. 13C chemical shift MR imaging was used in order to visualize the local concentrations of the metabolites. After a 15‐min occlusion (no infarct) the bicarbonate signal level in the affected area was reduced (25–44%) compared with the normal myocardium. Alanine signal level was normal. After a 45‐min occlusion (infarction) the bicarbonate signal was almost absent (0.2–11%) and the alanine signal was reduced (27–51%). Due to image‐folding artifacts the data obtained for lactate were inconclusive. These studies demonstrate that cardiac metabolic imaging with hyperpolarized 1‐13C‐pyruvate is feasible. The changes in concentrations of the metabolites within a minute after injection can be detected and metabolic maps constructed. Magn Reson Med 59:1005–1013, 2008. © 2008 Wiley‐Liss, Inc.
MRI visualization of rodent liver structure and peritoneal adhesion with dialyzate enhancement
Authors: Cheung Jerry S. , Guo Hong , Leung Joseph C.K. , Man Kwan , Lai Kar N. , Wu Ed X. 
Published: April 2008

AbstractThis study investigated the use of peritoneal dialysis fluid (dialyzate) as a MR contrast agent to visualize the liver structure and peritoneal adhesion in rats at 7 T. Intraperitoneal injection of dialyzate (∼0.1 ml/g) yielded excellent and consistent intraperitoneal enhancement that delineated the liver lobular structure in all rats studied (N = 8). It also allowed the MR detection of peritoneal adhesions that were surgically induced. MR measurements of adhesion surface areas correlated well with the postmortem estimations (R = 0.99; N = 6). Dialyzate persisted in the intraperitoneal cavity for up to 2 days. T1 and T2 values of undiluted dialyzate were found to be 3017.5 ± 35.3 ms and 108.4 ± 2.0 ms, respectively. These findings demonstrated dialyzate‐enhanced MRI as a potentially valuable technique to localize certain activities within liver (such as local tumor metastasis), and to monitor therapeutic interventions (e.g., against peritoneal adhesion) in preclinical research using small animal models. Magn Reson Med 59:1170–1174, 2008. © 2008 Wiley‐Liss, Inc.
High‐contrast 3D neonatal brain imaging with combined T1‐ and T2‐weighted MP‐RAGE
Authors: Conklin John , Winter Jeff D. , Thompson R. Terry , Gelman Neil 
Published: April 2008

AbstractOptimization of magnetization‐prepared rapid gradient‐echo (MP‐RAGE) sequence variations for maximum white matter (WM) versus gray matter (GM) contrast in neonates at 3T was investigated. Numerical simulations were applied to optimize and compare three contrast preparation modules and to assess the effect of phase encoding (PE) order on contrast between WM and thin cortical GM layers. Simulations predict that a new sequence, which combines both T1‐ and T2‐weighting into the contrast preparation and utilizes an interleaved elliptical‐spiral PE order, should provide the strongest contrast between neonatal WM and cortical GM. This sequence was compared to a conventional MP‐RAGE acquisition (i.e., T1‐weighted preparation, centric PE order) for in vivo imaging of seven preterm newborn infants. Regional measurements of the contrast‐to‐noise ratio (CNR) between WM and GM demonstrated an increase of 50–70% (depending on GM region) using the new sequence, in good agreement with theoretical predictions. This improved contrast resulted in superior WM versus GM discrimination in intensity‐based brain tissue segmentations. Magn Reson Med 59:1190–1196, 2008. © 2008 Wiley‐Liss, Inc.
Magnetization transfer ratio as a predictor of malignancy in breast lesions: Preliminary results
Authors: Bonini Ruth Helena Morais , Zeotti Denise , Saraiva Luciano Albuquerque Lima , Trad Clovis Simao , Filho Joaquim Moraes Sarmento , Carrara Helio Humberto Angotti , de Andrade Jurandyr Moreira , Santos Antonio Carlos , Muglia Valdair Francisco 
Published: April 2008

AbstractMRI is an important tool for investigating breast cancer. Although recognized as the method of choice for screening high‐risk patients, and for other indications the role of MRI for lesion characterization remains controversial. Recently some authors have advocated the use of morphologic and postcontrast features for this purpose. Quantitative breast MRI techniques have not been applied extensively in breast diseases. Magnetization transfer (MT) is a quantitative MR technique commonly used to investigate neurological diseases. In breast diseases the use of MT has been limited to improving visualization of areas of enhancement in postcontrast images. The purpose of this study was to evaluate the feasibility and utility of MT in discriminating benign from malignant breast lesions. Fifty‐two lesions, BIRADS 4 and 5, from 49 patients, were prospectively evaluated using the MT ratio (MTR). Patients were divided into two groups: benign and malignant lesions. The MTR of fat, pectoralis major muscle, fibroglandular tissue, and breast lesions were calculated. A statistically significant difference was found between MTR from benign and malignant lesions (P < 0.001). Preliminary results suggest that MT can be used to evaluate breast lesions. Further studies are necessary to better define the utility and applicability of this technique. Magn Reson Med 59:1030–1034, 2008. © 2008 Wiley‐Liss, Inc.
High b‐value q‐space diffusion‐weighted MRI of the human cervical spinal cord in vivo: Feasibility and application to multiple sclerosis
Authors: Farrell Jonathan A.D. , Smith Seth A. , Gordon‐Lipkin Eliza M. , Reich Daniel S. , Calabresi Peter A. , van Zijl Peter C.M. 
Published: April 2008

AbstractQ‐space analysis is an alternative analysis technique for diffusion‐weighted imaging (DWI) data in which the probability density function (PDF) for molecular diffusion is estimated without the need to assume a Gaussian shape. Although used in the human brain, q‐space DWI has not yet been applied to study the human spinal cord in vivo. Here we demonstrate the feasibility of performing q‐space imaging in the cervical spinal cord of eight healthy volunteers and four patients with multiple sclerosis. The PDF was computed and water displacement and zero‐displacement probability maps were calculated from the width and height of the PDF, respectively. In the dorsal column white matter, q‐space contrasts showed a significant (P < 0.01) increase in the width and a decrease in the height of the PDF in lesions, the result of increased diffusion. These q‐space contrasts, which are sensitive to the slow diffusion component, exhibited improved detection of abnormal diffusion compared to perpendicular apparent diffusion constant measurements. The conspicuity of lesions compared favorably with magnetization transfer (MT)‐weighted images and quantitative CSF‐normalized MT measurements. Thus, q‐space DWI can be used to study water diffusion in the human spinal cord in vivo and is well suited to assess white matter damage. Magn Reson Med 59:1079–1089, 2008. © 2008 Wiley‐Liss, Inc.
Relaxation‐compensated fast multislice amide proton transfer (APT) imaging of acute ischemic stroke
Authors: Sun Phillip Zhe , Murata Yoshihiro , Lu Jie , Wang Xiaoying , Lo Eng H. , Sorensen A. Gregory 
Published: April 2008

AbstractAmide proton transfer (APT) imaging is a variant form of chemical exchange saturation transfer (CEST) imaging that is based on the magnetization exchange between bulk water and labile endogenous amide protons. Given that chemical exchange is pH‐dependent, APT imaging has been shown capable of imaging ischemic tissue acidosis, and as such, may serve as a surrogate metabolic imaging marker complementary to perfusion and diffusion MRI. In order for APT imaging to properly diagnose heterogeneous pathologies such as stroke and cancer, fast volumetric APT imaging has to be developed. In this study the evolution of CEST contrast after RF irradiation was solved showing that although the CEST steady state is reached by the apparent longitudinal relaxation rate, the decreases of CEST contrast after irradiation is governed by the intrinsic relaxation constant. A volumetric APT imaging sequence is proposed that acquires multislice images immediately after a single long continuous wave (CW) RF irradiation, wherein the relaxation‐induced loss of CEST contrast is compensated for during postprocessing. The proposed technique was verified by numerical simulation, a tissue‐like dual‐pH phantom, and demonstrated on an embolic stroke animal model. In summary, our study has established a fast volumetric pH‐weighted APT imaging technique, allowing further investigation to fully evaluate its diagnostic power. Magn Reson Med 59:1175–1182, 2008. © 2008 Wiley‐Liss, Inc.
Reconstruction of undersampled non‐Cartesian data sets using pseudo‐Cartesian GRAPPA in conjunction with GROG
Authors: Seiberlich Nicole , Breuer Felix , Heidemann Robin , Blaimer Martin , Griswold Mark , Jakob Peter 
Published: April 2008

AbstractMost k‐space‐based parallel imaging reconstruction techniques, such as Generalized Autocalibrating Partially Parallel Acquisitions (GRAPPA), necessitate the acquisition of regularly sampled Cartesian k‐space data to reconstruct a nonaliased image efficiently. However, non‐Cartesian sampling schemes offer some inherent advantages to the user due to their better coverage of the center of k‐space and faster acquisition times. On the other hand, these sampling schemes have the disadvantage that the points acquired generally do not lie on a grid and have complex k‐space sampling patterns. Thus, the extension of Cartesian GRAPPA to non‐Cartesian sequences is nontrivial. This study introduces a simple, novel method for performing Cartesian GRAPPA reconstructions on undersampled non‐Cartesian k‐space data gridded using GROG (GRAPPA Operator Gridding) to arrive at a nonaliased image. Because the undersampled non‐Cartesian data cannot be reconstructed using a single GRAPPA kernel, several Cartesian patterns are selected for the reconstruction. This flexibility in terms of both the appearance and number of patterns allows this pseudo‐Cartesian GRAPPA to be used with undersampled data sets acquired with any non‐Cartesian trajectory. The successful implementation of the reconstruction algorithm using several different trajectories, including radial, rosette, spiral, one‐dimensional non‐Cartesian, and zig–zag trajectories, is demonstrated. Magn Reson Med 59:1127–1137, 2008. © 2008 Wiley‐Liss, Inc.