bluuebunny/crossref_metadata_2025 huggingface dataset:
Propagation Kinetics of Free‐Radical Methacrylic Acid Polymerization in Aqueous Solution. The Effect of Concentration and Degree of Ionization
Authors: Beuermann Sabine , Buback Michael , Hesse Pascal , Kukučková Silvia , Lacık Igor
Published: March 2007

Propagation rate coefficients, kp, of free‐radical methacrylic acid (MAA) polymerization in aqueous solution are presented and discussed. The data has been obtained via the pulsed laser polymerization – size‐exclusion chromatography (PLP‐SEC) technique within extended ranges of both monomer concentration, from dilute solution up to bulk MAA polymerization, and of degree of ionic dissociation, from non‐ionized to fully ionized MAA. A significant decrease of kp, by about one order of magnitude, has been observed upon increasing monomer concentration in the polymerization of non‐ionized MAA. Approximately the same decrease of kp occurs upon varying the degree of MAA ionization, α, at low MAA concentration from α = 0 to α = 1. With partially ionized MAA, the decrease of kp upon increasing MAA concentration is distinctly weaker. For fully ionized MAA, the propagation rate coefficient even increases toward higher MAA concentration. The changes of kp measured as a function of monomer concentration and degree of ionization may be consistently interpreted via transition state theory. The effects on kp are essentially changes of the Arrhenius pre‐exponential factor, which reflects internal rotational mobility of the transition state (TS) structure for propagation. Friction of internal rotation of the TS structure is induced by ionic and/or hydrogen‐bonded intermolecular interaction of the activated state with the molecular environment.
Reverse Iodine Transfer Polymerization (RITP) in Emulsion
Authors: Lacroix‐Desmazes Patrick , Tonnar Jeff , Boutevin Bernard
Published: March 2007

Reverse iodine transfer polymerization (RITP) is a new controlled radical polymerization technique based on the use of molecular iodine I2 as control agent. This paper aims at presenting the basics of RITP and the strategy that we have followed for the development of this process in the past three years, from the validation in homogeneous solution polymerization up to recent results in heterogeneous aqueous polymerization processes. Typical examples of RITP of butyl acrylate in emulsion and RITP of styrene in miniemulsion are discussed.
The entity of young onset primary cervical dystonia
Authors: Koukouni Vasiliki , Martino Davide , Arabia Gennarina , Quinn Niall P. , Bhatia Kailash P.
Published: March 2007

Primary cervical dystonia is typically an adult onset condition with symptom onset usually in the fifth and sixth decade. Young onset (<28 years) is uncommon. We report 76 patients with cervical dystonia as a presenting or predominant feature, with disease onset before the age of 28. Male to female ratio was 1.24:1 and the mean onset age was 21 (3–28) years. A family history of tremor and/or dystonia was noted in 26.3%. Depression and anxiety attacks were present in 23.7%.Prior injury or surgery involving the neck was noted in 17.1%. 23 (30.3%) experienced spontaneous partial or complete remissions within the first 5 years of onset, but all relapsed. Cervical dystonia was predominantly rotational torticollis. 30% developed extra‐nuchal dystonia and tremor affecting contiguous parts but in only one there was spread to affect the legs. All 15 patients tested for the DYT1 gene were negative. 74% responded favorably to botulinum toxin injections, whereas none of the 13 patients treated with L‐Dopa preparations had a beneficial response. The distinctive features of this entity are discussed. © 2007 Movement Disorder Society
Radicular and nonradicular back pain in Parkinson's disease: A controlled study
Authors: Broetz Doris , Eichner Martin , Gasser Thomas , Weller Michael , Steinbach Joachim P.
Published: March 2007

Postural abnormalities and increased muscle tone in Parkinson's disease (PD) may cause back pain. In this controlled study, we analyzed features of back pain in PD patients. The prevalence of back pain was 74% in PD patients (n = 101) when compared with 27% in control patients (n = 132; P < 0.0001, fisher's exact test), but did not correlate with disease severity or duration. The mean back pain intensity (visual analog scale of 0–10) was 4.3 for PD patients, and 1.3 for controls. Both radicular and nonradicular types of back pain were more frequent, and back pain caused more impairment in PD patients. However, it is noteworthy that the PD patients in our study did not receive more pain medication than control patients. This suggests that back pain in PD patients is often neglected and insufficiently treated. Our results argue for the routine evaluation of back pain in every patient suffering from PD. © 2007 Movement Disorder Society
Effect of magnetization transfer on the measurement of cerebral blood flow using steady‐state arterial spin tagging approaches: A theoretical investigation
Authors: McLaughlin Alan C. , Ye Frank Q. , Pekar James J. , Santha Attanagoda K. S. , Frank Joseph A.
Published: March 2007

A simple four‐compartment model for magnetization transfer was used to obtain theoretical expressions for the relationship between regional cerebral blood flow and ΔM, the change in longitudinal magnetization of brain water spins when arterial water spins are perturbed. The theoretical relationship can be written in two forms, depending on the approach used to normalize ΔM. Using the first approach, the calculation of cerebral blood flow requires a knowledge of R1 (ω1, Δω), the longitudinal relaxation rate observed in the presence of continuous off‐resonance RF irradiation. Using the second approach, the calculation of cerebral blood flow requires a knowledge of ℛ1(ω1, Δω), where ℛ1(ω1, Δω) is given by the product of R1(ω1, Δω) and the fractional steady‐state longitudinal water magnetization in the presence of off‐resonance RF irradiation. If the off‐resonance RF irradiation used for arterial tagging does not produce appreciable magnetization transfer effects, ℛ1, (ω1, Δω) can be approximated by the longitudinal relaxation rate measured in the absence of offresonance RF irradiation, R1obs. Theoretical expressions obtained by using the four‐component model for magnetization transfer are compared with equivalent expressions obtained by using two‐compartment models.
The excretion mechanism of the spin label proxyl carboxylic acid (PCA) from the rat monitored by X‐band ESR and PEDRI
Authors: Seimenis Ioannis , Foster Margaret A. , Lurie David J. , Hutchison James M. S. , Whiting Paul H. , Payne Simon
Published: March 2007

Proton electron double resonance imaging (PEDRI) was used for monitoring in vivo the distribution, metabolism and, in particular, the excretion mechanism of the exogenous nitroxide free radical proxyl carboxylic acid (PCA) in the rat. PCA clearance half‐lives through liver, abdominal vessels, and renal tissues were determined from a series of PEDRI images for normal rats (n = 5) and rats treated with probenecid (n = 5), a competitive inhibitor of the tubular secretion process. The approximately doubled renal half‐lives of the treated animals suggest that tubular secretion accounts for about 50% of PCA renal loss in the normal rat and reabsorption is insignificant. PCA binding to bovine serum albumin was investigated by X‐band ESR and the bound fraction was found to be less than 10% of the total PCA. Most probably, PCA binds to hydrophilic sites. Blood PCA concentration investigated by X‐band ESR exhibited biphasic behavior and PEDRI results confirmed the in vivo metabolic reduction of PCA by rat liver cells.
Computational simulation of turbulent signal loss in 2D time‐of‐flight magnetic resonance angiograms
Authors: Siegel John M. , Oshinski John N. , Pettigrew Roderic I. , Ku David N.
Published: March 2007

Time‐of‐flight magnetic resonance (MR) angiography is currently limited in the evaluation of arterial stenoses by flowinduced signal loss. This signal loss has been attributed to phase dispersion and to phase misregistration. We have developed a fluid mechanics model of 2D time‐of‐flight MR angiograms to study the amount of signal loss caused by random turbulence. The simulations were created by stochastic analysis of particle pathlines determined by computational fluid dynamics for turbulent flow. The images obtained by the model compare well to actual MR images of flow in stenoses. By selectively removing the random turbulent motion in the simulation, it can be seen that random phase dispersion is the dominant mechanism of signal loss. Phase misregistration and mean flow phase dispersion act as secondary effects. The MR simulation model recreates accurately the variation of signal loss over a range of echo times. The model can be used further to explore and design new pulse sequences. For example, the current study showed that high slew rate gradient waveforms can significantly reduce poststenotic signal loss. In conclusion, computational modeling of MR angiography can be a useful approach for the analysis of MRA signal loss and the design of improved pulse sequences.
An extended two‐point dixon algorithm for calculating separate water, fat, and B0 images
Authors: Skinner Thomas E. , Glover Gary H.
Published: March 2007

A new algorithm is presented that provides separate water, fat, and B0 images utilizing the in‐phase and opposed‐phase acquisitions of the two‐point Dixon (2PD) method. The accuracy of the extended method (E2PD) compares favorably with the three‐point Dixon (3PD) method, and the acquisition requires 2/3 the 3PD scan time. Slightly increased mismapping may occur in pixels containing an admixture of water and fat due to reduced SNR in the B0 field map compared with the 3PD method.
Improved automatic off‐resonance correction without a field map in spiral imaging
Authors: Man Lai‐Chee , Pauly John M. , Macovski Albert
Published: March 2007

Non‐2DFT k‐space readout strategies are useful in fast imaging but prone to blurring when reconstructed off resonance. Field inhomogeneities or susceptibility variations, coupled with a long readout time, are the major sources of this artifact. Correction methods based on a priori off‐resonance information such as an acquired field map have been proposed in the literature. An alternative approach estimates the spatially varying off‐resonance frequency from the data itself before applying a correction. In this latter approach there is a tradeoff between the extent of correction and the chance of increased artifact due to estimation error. This paper introduces an improved algorithm for field map estimation which is both faster and more robust than the existing method. It uses a multi‐stage estimation of the field map, starting from a coarse estimate both in frequency and space and proceeds towards higher resolution. The new algorithm is applied to phantom and in vivo images acquired with radial and spiral sequences to give sharper images.
The use of active shape models for making thickness measurements of articular cartilage from MR images
Authors: Solloway Stuart , Hutchinson Charles E. , Waterton John C. , Taylor Christopher J.
Published: March 2007

Previously reported studies to quantify articular cartilage have used labor‐intensive manual or semi‐automatic data‐driven techniques, demonstrating high accuracy and precision. However, none has been able to automate the segmentation process. This paper describes a fast, automatic, model‐based approach to segmentation and thickness measurement of the femoral cartilage in 3D T1‐weighted images using active shape models (ASMs). Systematic experiments were performed to assess the accuracy and precision of the technique with in vivo images of both normal and abnormal knees. Segmentation accuracy was determined by comparing the results of the segmentation with the boundaries delineated by a radiologist. The mean error in locating the boundary was 0.57 pixels. To assess the precision of the measurement technique, the mean thickness of the femoral cartilage was calculated for repeated scans of five healthy volunteers. A mean coefficient of variation (CV) of 2.8% was obtained for the thickness measurements.
Determination of deoxymyoglobin changes during graded myocardial ischemia: An in Vivo1H NMR spectroscopy study
Authors: Chen Wei , Zhang Jianyi , Eljgelshoven Marcel H. J. , Zhang Yi , Zhu Xiao‐Hong , Wang Chunshen , Cho Yong , Merkle Hellmut , Uĝcurbil Kǎmil
Published: March 2007

1H NMR spectroscopy was used to detect the proximal histidyl Nδ, proton signal of deoxymyoglobin from canine hearts in vivo during graded myocardial ischemia. The NMR signal intensity provided an indicator of intracellular oxygenation in myocardium. The relationship between the myocardial blood flow and the deoxymyoglobin concentration was successfully measured during resting, partial, and complete coronary artery occlusion conditions. The results demonstrate the feasibility to detect deoxymyoglobin using a 1H NMR spectroscopy technique in living hearts for the first time and the possibility to use this technique for investigating myocardial oxidative metabolism nondestructively and repetitively.
Highly selective water and fat imaging applying multislice sequences without sensitivity to B1 field inhomogeneities
Authors: Schick Fritz , Forster Jürgen , Machann Jürgen , Huppert Peter , Claussen Claus D.
Published: March 2007

Improved selectivity to one chemical shift component was obtained using simultaneous slice‐selective and chemical shift‐selective excitation in sequences with usual spin‐echo refocusing. The new type of sequences can be applied on modern whole‐body units and permits multislice operation. Spatial‐spectral excitation is based on prior research in this field, but the proposed improved version provides off‐center slice excitation by the usual processing of the RF pulse envelopes. In addition, no irregular gradient shapes are necessary. The required B0 homogeneity of the new method is similar to conventional “fat‐sat” techniques. In contrast to fat‐sat methods, selectivity to water is not reduced by unavoidable mis‐adjustments of the transmitter or B1 field inhomogeneities in the newly developed approach. Thus, the reported method has the potential to replace standard frequency selective fat‐sat sequences for most applications.
The distribution of lithium in rat brain and muscle in vivo by 7Li NMR imaging
Authors: Komoroski Richard A. , Pearce John M. , Newton Joseph E. O.
Published: March 2007

The regional distribution of lithium (Li) in vivo was determined on a relative basis in the brain and muscle of rats by 7Li NMR imaging. Both high resolution 7Li NMR spectroscopy and atomic absorption spectrophotometry were performed on extracts of brain and muscle tissue from the same rats. The average in vivo results were generally in good agreement with the corresponding average in vitro results, despite the relatively low signal‐to‐noise ratio of the in vivo images. There was good agreement between the two in vitro methods of analysis, both on average and for individual animals. Significant differences were found in vivo among Li concentration ratios for the various brain regions and muscle by 7Li imaging, as well as by the in vitro methods.
In vivo imaging of a stable paramagnetic probe by pulsed‐radiofrequency electron paramagnetic resonance spectroscopy
Authors: Murugesan Ramachandran , Cook John A. , Devasahayam Nallathamby , Afeworki Mobae , Subramanian Sankaran , Tschudin Rolf , Larsen Janhenrik A. , Mitchell James B. , Russo Angelo , Krishna Murali C.
Published: March 2007

Imaging of free radicals by electron paramagnetic resonance (EPR) spectroscopy using time domain acquisition as in nuclear magnetic resonance (NMR) has not been attempted because of the short spin‐spin relaxation times, typically under 1 μs, of most biologically relevant paramagnetic species. Recent advances in radiofrequency (RF) electronics have enabled the generation of pulses of the order of 10–50 ns. Such short pulses provide adequate spectral coverage for EPR studies at 300 MHz resonant frequency. Acquisition of free induction decays (FID) of paramagnetic species possessing inhomogenously broadened narrow lines after pulsed excitation is feasible with an appropriate digitizer/averager. This report describes the use of time‐domain RF EPR spectrometry and imaging for in vivo applications. FID responses were collected from a water‐soluble, narrow line width spin probe within phantom samples in solution and also when infused intravenously in an anesthetized mouse. Using static magnetic field gradients and back‐projection methods of image reconstruction, two‐dimensional images of the spin‐probe distribution were obtained in phantom samples as well as in a mouse. The resolution in the images was better than 0.7 mm and devoid of motional artifacts in the in vivo study. Results from this study suggest a potential use for pulsed RF EPR imaging (EPRI) for three‐dimensional spatial and spectral‐spatial imaging applications. In particular, pulsed EPRI may find use in in vivo studies to minimize motional artifacts from cardiac and lung motion that cause significant problems in frequency‐domain spectral acquisition, such as in continuous wave (cw) EPR techniques.
Contour‐based registration technique to differentiate between task‐activated and head motion‐induced signal variations in fMRI
Authors: Biswal Bharat B. , Hyde James S.
Published: March 2007

Data acquired using functional magnetic resonance imaging are often contaminated by head motion. As a result, optimal information regarding task‐induced (or resting‐state) signal changes cannot be extracted. Intensity‐based registration methods, including intensity correlation or minimum intensity variance techniques, are widely used to register two or more images. It is shown here that intensity‐based registration cannot accurately register two or more images in the presence of local intensity changes arising from functional magnetic resonance, fMRI, signals. In this paper, we present a contour‐based technique that can be used not only for a more robust registration, but also to help differentiate between task‐induced and motion‐induced signal changes. Results obtained using both phantom and human brain images demonstrate advantages of this technique compared with a conventional intensity registration technique.
Suppression of physiological eye movement artifacts in functional MRI using slab presaturation
Authors: Chen Wei , Zhu Xiao‐Hong
Published: March 2007

Reduction of image‐to‐image signal fluctuations and imaging artifacts is important for fMRI studies. The imaging artifacts caused by respiration, cardiac pulsation, and gross head motion and the suppression of these artifacts have been studied for many years. However, the artifacts caused by eye movement and their effects on fMRI mapping are not well known. It is demonstrated in this report that involuntary eye movements during resting conditions can cause substantial signal fluctuations in the phase‐encoding direction even for a fast echo‐planar imaging sequence. An oblique slab presaturation technique is proposed for saturating the magnetization of eyes and suppressing the artifacts from eye movements with minimal signal loss of other brain tissues. The results show that the technique significantly reduces signal fluctuations and improves fMRI reliability for mapping functional activation in the human brain.
Myocardial infarction in a canine model monitored by two‐dimensional 31p chemical shift spectroscopic imaging
Authors: Farrall Andrew J. , Thompson R. Terry , Wisenberg Gerald , Campbell Constance M. , Drost Dick J.
Published: March 2007

We have developed a closed chest animal model that allows noninvasive monitoring of cardiac high energy phosphate metabolism before, during, and for at least 3 weeks after a myocardial infarction. Ten beagles underwent 2 h of coronary occlusion followed by 3 weeks of reperfusion. Myocardial high energy phosphates from 12‐ml voxels were noninvasively tracked using 31P two‐dimensional chemical shift imaging. Gadolinium enhanced 1H MRI identified the zone at risk, and radioactive microspheres assessed regional blood flow and partition coefficients. Occlusion of the left anterior descending coronary artery produced infarcts that were 13.7 ± 8.8% (mean ± SD) of the left ventricular volume. Rapid changes in the phosphocreatine and inorganic phosphate levels were observed during occlusion, whereas adenosine triphosphate levels decreased more slowly. All metabolites recovered to base‐line levels 2 weeks after occluder release. Multiple inorganic phosphate peaks in the infarct voxel spectra indicated that more than one metabolically compromised tissue zone developed during occlusion and reperfusion. Microsphere data indicating three distinct blood flow zones during ischemia and reperfusion (<0.3, 0.3‐0.75, and >0.75 ml/min/g) supported the grouping of pH values into three distinct metabolic distributions.
Magnetic resonance properties of ex vivo breast tissue at 1.5 T
Authors: Graham Simon J. , Ness Sola , Hamilton Bradford S. , Bronskill Michael J.
Published: March 2007

The magnetic resonance absorption spectrum, T1 and T2 relaxation time distributions, and magnetization transfer properties of ex vivo breast tissue have been characterized at 1.5 T and 37°C. The fraction of fibroglandular tissue within individual tissue samples (n = 31) was inferred from the tissue volumetric water content obtained by integration of resolvable broad‐line fat and water resonances. The spectroscopically estimated water content was strongly correlated with that extracted enzymatically (Pearson correlation coefficient 0.98, P « 0.01), which enabled the assignment of principal relaxation components for fibroglandular tissue (T2 = 0.04 ± 0.01, T1 = 1.33 ± 0.24 s), and for adipose tissue (T2 = 0.13 ± 0.01, T1 = 0.23 ± 0.01 s, and T2 = 0.38 ± 0.03, T1 = 0.62 ± 0.16 s). The relaxation components for fibroglandular tissue exhibited strong magnetization transfer, whereas those for adipose tissue showed little magnetization transfer effect. These results ultimately have applicability to the optimization of clinical magnetic resonance imaging and research investigations of the breast.
Myocardial function in infarcted and remote regions early after infarction in man: Assessment by magnetic resonance tagging and strain analysis
Authors: Marcus J. Tim , Götte Marco J. W. , van Rossum Albert C. , Kuijer Joost P. A. , Heethaar Robert M. , Axel Leon , Visser Cees A.
Published: March 2007

Early after infarction in the perfusion bed of the left anterior descending coronary artery, cine MRI with spatial modulation of magnetization (SPAMM) tagging (7‐mm grid) was used for short‐ and long‐axis cardiac imaging. Two‐dimensional strain analysis of triangular finite elements was performed between end‐diastole and end‐systole. Patients (n = 10) were compared with age‐matched healthy subjects (n = 8). The anteroseptal region at midventricular level was considered representative for “infarcted” and the posterolateral region at basal level was considered “remote”. The left ventricular end‐diastolic volume index was larger in the patients (69 ± 15 ml/m2 versus 56 ± 4 ml/m2, P < 0.05). Short‐axis images showed in the infarcted region a decrease of first principal strain (greatest systolic lengthening: 1.10 ±. 06 versus 1.27 ± 0.04, P < 0.0001), and in the remote region an increase (1.48 ± 0.11 versus 1.36 ± 0.07, P < 0.025). The lateral and inferior ventricular regions at mid‐ and basal levels were found to function normally. Long‐axis images yielded similar results. Early after infarction, regions with dysfunction, normal function, and hyperfunction can be delineated with MR tagging. The compensatory increased contraction in the remote region is possibly triggered by the Frank‐Starling mechanism.
Assessment of quantitative artificial neural network analysis in a metabolically dynamic ex vivo31p NMR pig liver study
Authors: Ala‐Korpela Mika , Changani K. K. , Hiltunen Y. , Bell J. D. , Fuller B. J. , Bryant David J. , Taylor‐Robinson S. D. , Davidson B. R.
Published: March 2007

Quantitative artificial neural network analysis for 1550 ex vivo 31P nuclear magnetic resonance spectra from hypothermically reperfused pig livers was assessed. These spectra show wide ranges of metabolite concentrations and have been analyzed using metabolite prior knowledge based lineshape fitting analysis which had proved robust in its biochemical interpretation. This finding provided a good opportunity to assess the performance of artificial neural network analysis in a biochemically complex situation. The results showed high correlations (0.8655 ≤ R ≤ 0.992) between the lineshape fitting and artificial neural network analysis for the metabolite values, and the artificial neural network analysis was able to fully represent the trends in the metabolic fluctuations during the experiments.
Recording of EEG during fMRI experiments: Patient safety
Authors: Lemieux Louis , Allen Philip J. , Franconi Florence , Symms Mark R. , Fish David K.
Published: March 2007

The acquisition of electroencephalograms (EEG) during functional magnetic resonance imaging (fMRI) experiments raises important practical issues of patient safety. The presence of electrical wires connected to the patient in rapidly changing magnetic fields results in currents flowing through the patient due to induced electromotive forces (EMF), by three possible mechanisms: fixed loop in rapidly changing gradient fields; fixed loop in a RF electromagnetic field; moving loop in the static magnetic field. RF‐induced EMFs were identified as the most important potential hazard. We calculated the minimum value of current‐limiting resistance to be fitted in each EEG electrode lead for a representative worst case loop, and measured RF magnetic field intensity and heating in a specific type of current‐limiting resistors. The results show that electrode resistance should be ≥13 kΩ for our setup. The methodology presented is general and can be useful for other centers.
Measurements of human cerebral GABA at 4.1 T using numerically optimized editing pulses
Authors: Hetherington Hoby P. , Newcomer Bradley R. , Pan Jullie W.
Published: March 2007

The goal of this work was to develop and evaluate a numerically optimized inversion pulse to be used with a homonuclear editing sequence to measure human cerebral GABA 117 vivo at 4.1 T in the occipital lobe. The optimized pulse was constructed using pallindromic symmetry with 30 pulses and 29 delays. The optimized pulse provided greater selectivity than the equivalent bandwidth matched DANTE pulse and sine shaped DANTE. The improved selectivity reduced the co‐editing of the macromolecule resonance, permitting the GABA edited doublet to be resolved in vivo. Using cerebral creatine as a reference, 7.1 mM, the measured GABA level was 1.15 ± 0.13 mM in the occipital lobe.
Differentiation of metabolic concentrations between gray matter and white matter of human brain by in vivo1H magnetic resonance spectroscopy
Authors: Wang Yonker , Li Shi‐Jiang
Published: March 2007

Differentiation of absolute metabolite concentrations between gray and white matter in the occipital region of normal human brain was performed by in vivo localized single‐voxel 1H magnetic resonance spectroscopy at 1.5 Testa with long echo time (136 ms). With the combination of image segmentation between white and gray matter and cerebrospinal fluid, signal compensation of T, and T2 effects, tissue water signal as the internal concentration reference, as well as compensation by different water contents in gray and white matters, it was determined that the levels of N‐acetylaspartate (NAA), creatine and/or phosphocreatine (Cr), and choline‐containing compounds (Cho) in gray matter were significantly higher than in white matter. The averaged NAA, Cr, and Cho concentrations in gray matter were 11.0, 9.7, and 1.9 mM/liter, respectively, in comparison with 7.5, 5.2, and 1.6 mM/liter in white matter. These results suggest that precise composition of white and gray matter and cerebrospinal fluid is necessary to avoid partial voluming effect in a single voxel and to accurately quantify the metabolite concentrations.
A new silent magnetic resonance imaging using a rotating DC gradient
Authors: Cho Z. H. , Chung S. T. , Chung J. Y. , Park S. H. , Kim J. S. , Moon C. H. , Hong I. K.
Published: March 2007

A new approach to silent MR imaging using a rotating DC gradient has been explored and experimentally studied. Acoustic or sound noise has been one of the problems in examining patients, mainly due to the fast gradient pulsings in interaction with the main magnetic field. The sound noise has been noted to be proportionately louder as the magnetic field strength becomes larger. In this report, we describe a new imaging technique using a mechanically rotating DC gradient coil. The rotating DC gradient coil can effectively replace both phase encoding as well as readout gradient pulsings, and data obtained in this manner can provide a set of projection data that later can be used for projection reconstruction. With some interpolation techniques one can also perform conventional two‐dimensional fast Fourier transform image reconstruction. The sound noise intensity compared with the conventional imaging technique, such as the spin‐echo sequence, has been reduced down to about −20.7 dB or 117.5 times with this new technique. The experimental pulse sequence and its principle are described and images obtained by the new silent MR imaging technique are reported.
Sodium TQF NMR and intracellular sodium in isolated crystalloid perfused rat heart
Authors: Schepkin Victor D. , Choy I. Oojin , Budinger Thomas F. , Obayashi Derek Y. , Taylor Scott E. , Decampli William M. , Amartur Sundar C. , Young J. Nilas
Published: March 2007

The feasibility of monitoring intracellular sodium changes using Na triple quantum filtered NMR without a chemical shift reagent (SR) was investigated in an isolated rat heart during a variety of interventions for Ma, loading. Perfusion with 1 mM ouabain or without K+ present in the perfusate for 30 min produced a rise of the Na TQF signal with a plateau of ‐190% and ˜228% relative to the preintervention level, respectively. Stop‐flow ischemia for 30 min resulted in a TQF signal growth of ˜147%. The maximal Na TQF signal increase of 460% was achieved by perfusion without K+/Ca2+, corresponding to an elimination of the Na transmembrane gradient. The observed values of Na NMR TQF growth in the physiological and pathological ranges are in agreement with reported data by other methods and have a linear correlation with intracellular sodium content as determined in this study by Co‐EDTA method and by sucrose‐histidine washout of the extracellular space. Our data indicate that the increase in Na TQF NMR signal is determined by the growth of Nai, and the extracellular Na contribution to the total TQF signal is unchanged at ˜64%. In conclusion, Na TQF NMR without using SR offers a unique and noninvasive opportunity to monitor alterations of intracellular sodium. It may provide valuable insights for developing car‐dioprotective strategies and for observing the effects of pharmaceutical treatments on sodium homeostasis.
Effects of gradient anisotropy in MRI
Authors: Aldefeld Bernd , Börnert Peter
Published: March 2007

A gradient system is anisotropic if the impulse responses of at least two of the gradient channels, x, y, or z, differ from each other. Such an undesired condition may arise, for example, from differences between the gradient channels with respect to eddy currents or from unbalanced time delays in the electronic components. Depending on the degree of anisotropy, the actual gradient then deviates from the nominal, desired gradient under certain oblique orientations during the transient periods of gradient switching. The adverse consequence is degradation of image quality, such as distortion, ghosting, and blurring. In this paper, a theoretical analysis is given of the basic effects. Furthermore, the implications for the MRI process and possible correction methods are described. The effects of anisotropy are shown experimentally for echo‐planar imaging and two‐dimensional selective RF excitation with spiral gradient pulses.
Asymmetric sampling along kslice‐select in two‐dimensional multislice MRI
Authors: Pipe James G.
Published: March 2007

Reduction of the slice‐select refocusing gradient in two‐dimensional multislice imaging results in asymmetry of the k‐space representation of collected data along the slice‐select direction. Standard methods of partial Fourier reconstruction developed for other methods of asymmetric k‐space sampling can be used to reconstruct these data with final through‐plane resolution smaller than the collected slice thickness. This method can be used for reducing scan time in the same manner as asymmetric sampling in the phase‐encoded direction. In addition, the reduced refocusing gradient reduces minimum TE and motion artifacts in the same manner as for asymmetric sampling in the frequency‐encoded direction (fractional echoes). Results using a resolution phantom and a flow phantom illustrate these concepts.
A new multiple quantum filter design procedure for use on strongly coupled spin systems found in vivo: Its application to glutamate
Authors: Thompson Richard B. , Allen Peter S.
Published: March 2007

A numerical procedure is outlined that is appropriate for the design of multiple quantum filter sequences targeted for the strongly coupled, multiple spin systems that occur in metabolites present in brain. The procedure uses numerical methods of solution of the density matrix equations, first, to establish the most appropriate resonance to target with the filter; second, to provide contour plots of a performance index of the filter in terms of critical sequence parameters; and third, to produce the response signals of the target and the background metabolites to the optimized filter. The procedure is exemplified for the AMNPQ spin system of the amino acid glutamate at a field strength of 3 T. The 2.3 ppm peak of the PQ multiplet of glutamate was identified as the target resonance, and the performance of the filter so derived was evaluated experimentally on phantom solutions and in human brain. These experiments clearly demonstrate that a linewidth of £4 Hz is required for full resolution of glutamate from glutamine at 3 T using this double quantum filter. Nevertheless, even at a linewidth of ˜7 Hz in vivo, the 2.3 ppm peak of glutamate dominates the filter response and thereby removes a significant cause of uncertainty in measuring changes in glutamate by eliminating most of the background observed in unedited spectra obtained using PRESS or STEAM.
Influence of aging or left ventricular hypertrophy on the human heart: Contents of phosphorus metabolites measured by 31P MRS
Authors: Okada Mamoru , Mitsunami Kenichi , Inubushi Toshiro , Kinoshita Masahiko
Published: March 2007

Although both aging and hypertrophy are extremely important factors for cardiac performance, their influence on cardiac metabolism, especially that of high‐energy phosphates, has not been fully elucidated as yet. Quantitative measurements of high‐energy phosphates were attempted by comparing myocardial 31P NMR spectra with an external reference using depth‐resolved surface‐coil spectroscopy. The voxel size of the region of interest (ROI) was disk‐shaped with 15‐cm diameter and 25‐mm thickness, but the left ventricular weight actually involved in the ROI was estimated to be between 22 and 66 g using MRI. Myocardial phosphocreatine (PCr) content and adenosine triphosphate (ATP) content for the 30 normal volunteers showed significant age dependence since both decreased in relation to increasing age. Myocardial PCr content and ATP content in patients with hypertension did not differ significantly from the age‐matched control group. PCr content (6.1 ± 2.2 μmol/g wet tissue, n=10) and ATP content (4.1 ±1.3 μmol/g wet tissue) in patients with hypertrophic cardiomyopathy were less than the age‐matched control group (n = 15; PCr: 9.7 ± 2.5 μmol/g wet tissue, P <0.01; ATP: 6.4 ±1.8 μmol/g wet tissue, P <0.05), respectively. These results indicate that quantitative 31P MRS may be valuable in the assessment of changes in high‐energy phosphate metabolism caused by aging or hypertrophy.
Quantitative assessment of bone marrow hematopoiesis using parametric magnetic resonance imaging
Authors: Ballon Douglas , Jakubowski Ann A. , Tulipano Paola K. , Graham Martin C. , Schneider Erika , Aghazadeh Behzad , Chen Qin‐Sheng , Koutcher Jason A.
Published: March 2007

Spatial maps of the percentage cellularity in pelvic bone marrow were calculated at a resolution of 15.6 mm3 from six volunteers and 10 patients treated for documented hematologic disease using a three‐point Dixon MRI pulse sequence. The percentage cellularity calculation was aided by analyzing a two‐dimensional feature space consisting of the apparent water fraction (Wa), and the T2 relaxation time of water (T2w). An extracellular water fraction was assigned to each voxel on the basis of a two‐component T2w algorithm. In six cases, the method was compared to results obtained from core biopsies or aspirates of the posterior iliac crest. The results indicate that segmentation schemes that combine high‐quality phase‐contrast imaging with nuclear relaxation time measurements can potentially identify the true fractional marrow volume occupied by hematopoietic elements in a variety of clinical situations.
Pattern recognition analysis of 1H NMR spectra from perchloric acid extracts of human brain tumor biopsies
Authors: Maxwell Ross J. , Martínez‐Pérez Irene , Cerdán Sebastián , Cabañas Miquel E. , Arús Carles , Moreno Àngel , Capdevila Antoni , Ferrer Enrique , Bartomeus Frederic , Aparicio Alberto , Conesa Gerard , Roda José María , Carceller Fernando , Pascual José María , Howells Siǎn L. , Mazucco Roy , Griffiths John R.
Published: March 2007

Pattern recognition techniques (factor analysis and neural networks) were used to investigate and classify human brain tumors based on the 1H NMR spectra of chemically extracted biopsies (n = 118). After removing information from lactate (because of variable ischemia times), unsupervised learning suggested that the spectra separated naturally into two groups: meningiomas and other tumors. Principal component analysis reduced the dimensionality of the data. A back‐propagation neural network using the first 30 principal components gave 85% correct classification of meningiomas and nonmeningiomas. Simplification by vector rotation gave vectors that could be assigned to various metabolites, making it possible to use or to reject their information for neural network classification. Using scores calculated from the four rotated vectors due to creatine and glutamine gave the best classification into meningiomas and nonmeningiomas (89% correct). Classification of gliomas (n = 47) gave 62% correct within one grade. Only inositol showed a significant correlation with glioma grade.
Magnetic resonance microimaging for noninvasive quantification of myocardial function and mass in the mouse
Authors: Ruff Jan , Wiesmann Frank , Hiller Karl‐Heinz , Voll Sabine , von Kienlin Markus , Bauer Wolfgang R. , Rommel Eberhard , Neubauer Stefan , Haase Axel
Published: March 2007

The purpose of this work was to develop high‐resolution cardiac magnetic resonance imaging techniques for the in vivo mouse model for quantification of myocardial function and mass. Eight male mice were investigated on a 7‐Tesla MRI scanner. High‐quality images in multiple short axis slices (in‐plane resolution 117 μm2, slice thickness 1 mm) were acquired with an ECG‐gated cine sequence. Left ventricular end‐diastolic and end‐systolic volumes and mass were calculated from segmented slice volumes. There was precise agreement of left ventricular mass determined ex vivo and by MRI. lntraobserver (5%) and interobserver (5%) variability of in vivo MR measurements were low.
A spiral volume coil for improved RF field homogeneity at high static magnetic field strength
Authors: Alsop David C. , Connick Thomas J. , Mizsei Gabor
Published: March 2007

Biological samples have a high dielectric constant that can shorten RF wavelengths by a factor of 8 relative to the vacuum. At high field strengths, finite wavelength effects within larger samples are the dominant cause of RF field nonunifor‐mity. A coil design is presented that can reduce and even eliminate this inhomogeneity; 4‐T images in phantoms and in the head of a normal volunteer are presented, which demonstrate improved homogeneity relative to a standard coil. This coil design should aid in realizing the potential advantages of imaging large samples at high field strengths.
Magnetic field changes in the human brain due to swallowing or speaking
Authors: Birn Rasmus M. , Bandettini Peter A. , Cox Robert W. , Jesmanowicz Andrzej , Shaker Reza
Published: March 2007

Variations in the magnetic field in the human brain caused by the processes of swallowing or speaking are measured. In both processes, motion of the pharyngeal muscles, especially the tongue and jaw, alter the susceptibility‐induced magnetic field distribution at the brain slice being imaged. This leads to image warping, compromising the analysis of a time series of images, such as in functional magnetic resonance imaging (fMRI). These dynamic changes are assessed by acquiring a time series of images using a gradient‐echo asymmetric‐spin‐echo sequence (GREASE), a technique in which two images are acquired for each excitation–one during the gradient echo, and one during the latter part of the spin echo. The NMR phase difference between the two images is a measure of the magnetic field distribution. A series of brain images, acquired with this sequence while the subject either swallows or speaks, indicated negative magnetic field changes of up to O.087 ppm in the inferior region of the brain for both speaking and swallowing, and in some speech, additional positive changes of up to O.056 ppm in the frontal region of the brain were indicated.
Integrated analysis of diffusion and relaxation of water in blood
Authors: Li Jonathan G. , Stanisz Greg J. , Henkelman R. Mark
Published: March 2007

Diffusion and T2 relaxation of water both inside and outside red blood cells (RBCs) in human blood were investigated using a hybrid NMR pulse sequence to obtain a more quantitative understanding of the diffusion and relaxation behavior of water in paramagnetic‐doped blood samples. The data were analyzed by both examining the relaxation properties of the system after each diffusion weighting and looking at the diffusion properties at each echo time. The results illustrate how diffusion‐sensitizing gradients affect the T2 spectra of blood and how relaxation weighting changes the curvature of the diffusion curves, thereby demonstrating the close coupling between diffusion and T2 relaxation. A three‐pool model, consisting of RBCs, plasma, and macromolecular protons, was used to model the data from the diffusion‐relaxation hybrid experiments. The model was found to describe all the characteristic features of the experimental data well and was used to evaluate the approximations involved in the conventional analysis methods and elucidate the nature of the relaxing and diffusing components. Compared with the separate diffusion and relaxation experiments, the diffusion‐relaxation hybrid experiments are less time‐consuming, result in better parameter determinations, and may be useful in analyzing diffusion‐T2 coupling in tissues with more complicated multi‐exponential T2 behavior.
Proteomic analysis of Burkholderia cepacia MBA4 in the degradation of monochloroacetate
Authors: Kwok Sui‐Yi , Siu Annie Fung‐Ming , Ngai Sai‐Ming , Che Chi‐Ming , Tsang Jimmy S. H.
Published: March 2007

Burkholderia cepacia MBA4 is a bacterium that degrades 2‐haloacids by removing the halogen and subsequent metabolism of the product for energy. In this study, 2‐DE, MS/MS, and N‐terminal amino acid sequencing were used to investigate the protein expression profiles of MBA4 grown in a 2‐haloacid (monochloroacetate, MCA) and in the corresponding metabolic product (glycolate). Glycolate was used as a control to eliminate the proteins induced by it. Five proteins were found to be up‐regulated and five proteins were down‐regulated in response to MCA. The differentially expressed proteins were examined, seven of them were identified by MS/MS and two of them were sequenced by Edman degradation. Our results definitely provide an insight for understanding the physiology of B. cepacia MBA4 in response to organohalide contaminated site.
Detection of transient protein–protein interactions by bimolecular fluorescence complementation: The Abl‐SH3 case
Authors: Morell Montse , Espargaró Alba , Avilés Francesc X. , Ventura Salvador
Published: March 2007

Protein–protein interactions are essential in most biological processes. Many proteomic approaches have succeeded in the identification of strong and obligatory interactions but the study of weak and transient protein–protein interactions is still a challenge. The aim of the present study was to test the ability of bimolecular fluorescence complementation to detect and discriminate in vivo weak intracellular protein interactions. As a test case, the interaction of the SH3 domain from the c‐Abl tyrosine kinase with both natural and designed targets has been chosen. The reassociation of functional yellow fluorescent protein (YFP) from its fragments requires previous binding between the SH3 domain and its partners; but once this occurs, the complex is trapped, turning transient SH3 interactions into stable, easily detectable ones. The method is very sensitive and can be implemented for proteomic analysis of weak protein interactions using flow cytometry. The fluorescence emission is dependent on the strength of the interaction, in such a way that it can be used, at least qualitatively, to screen for best binding candidates among similar proline‐rich peptides. In addition, it is illustrated how this method can be used to gain structural insights into particular c‐Abl SH3 interactions.
Shotgun immunoproteomics to identify disease‐associated bacterial antigens: Application to human colon cancer
Authors: Tjalsma Harold , Lasonder Edwin , Schöller‐Guinard Marie , Swinkels Dorine W.
Published: March 2007

Circulating antibodies reflect a mirror view of invading antigens that are related to infection and cancer. This was recently exemplified by using serum antibodies to capture Streptococcus bovis antigens followed by MS to generate antigen profiles that were diagnostic for colon cancer. These bacterial antigen profiles have a high potential to aid in the immuno‐diagnosis of this disease, as the magnitude of the immune response to bacterial antigens is, in general, superior to the immune response against tumor (self) antigens. In this study, the identity of individual colon cancer‐associated streptococcal antigens was revealed by enrichment of these “diagnostic” antigens by selected patient antibodies followed by high‐accuracy nanoLC‐MS/MS peptide identification. This showed that both the histone‐like protein HlpA and the ribosomal protein Rp L7/L12 are members of the colon cancer‐associated S. bovis immunome. Both antigens also seem to belong to the group of anchorless surface proteins, like 14 additional proteins that were co‐identified in S. bovis cell wall extracts. Among these were the known streptococcal anchorless surface proteins GAPDH and Enolase. Taken together, these data show that shotgun immunoproteomics, combining immunocapture in‐line with LC MS/MS, is a convenient approach for the rapid identification of disease‐associated bacterial antigens.