bluuebunny/crossref_metadata_2025_split huggingface dataset:
Localized proton NMR spectroscopy in the striatum of patients with idiopathic parkinson's disease: a multicenter pilot study
Authors: Holshouser Barbara A. , Komu Markku , Möller Harald E. , Zijlmans Jan , Kolem Heinrich , Hinshaw David B. , Sonninen Pirkko , Vermathen Peter , Heerschap Arend , Masur Harald , Rinne Urpo K. , Koster Ad De , Tosk Jeffrey M. 
Published: March 2007

AbstractSingle voxel proton MRS was used to study brain metabolism in the striatum of patients diagnosed with idiopathic Parkinson's disease (PD). Peak metabolite ratios in long echo time spectra were evaluated in 151 patient spectra and 97 age‐matched control spectra collected at four participating institutions using identical hardware and clinical protocols. Combining data from all ages (27–83 years old) showed no significant difference between patient and control ratios. However, in an elderly subset of patients (51–70 years old), a significant decrease in striatal N‐acetylaspartate (NAA)/choline (Cho) was observed. Also, a significant decrease in the mean NAA/Cho ratio was observed in patients versus controls for patients not being treated with Sinemet (Du Pont Pharm, Wilmingon, DE) (hereafter referred to as levodopa/carbidopa). This result is consistent with the hypothesis that NAA may provide a reversible spectroscopic marker for neuronal dysfunction, although a prospective follow‐up study will be needed to confirm this. Quantitation of MRS would be useful to exclude the possibility that a change in Cho levels affected the NAA/Cho ratios.
The use of a priori knowledge to quantify short echo in vivo1h mr spectra
Authors: Stanley Jeff A. , Drost Dick J. , Williamson Peter C. , Terry Thompson R. 
Published: March 2007

AbstractIn vivo 1H MR spectra of the prefrontal cortex acquired with the stimulated echo acquisition mode (STEAM) TE = 20 ms sequence were quantified to determine relative levels of cerebral metabolites. A priori knowledge of spectra from individual metabolites in aqueous solution was incorporated into a frequency domain quantification technique. The accuracy and precision of modeling these metabolites were investigated with simulated spectra of varying signal‐to‐noise ratios (SNRs) and relative metabolite levels. The efficacy of modeling in vivo data was tested by quantifying 10 repeated measures of two consecutively acquired in vivo spectra (an 8−cm3 volume of interest (VOI) and a 4−cm3 VOI positioned within the 8−cm3 VOI) on the same normal subject. The differences in levels of glutamate (Glu), phosphocreatine plus creatine (PCr+Cr) and choline‐containing compounds (Cho1 between spectra from the 8− and 4−cm3 VOIs corresponded with the expected differences observed in the proportions of gray matter within the VOIs (estimated from 1H images). Correcting for the T1 and T2 relaxation, the estimated concentrations of N‐acetylaspartate, PCr+Cr, Cho1, Glu, and glutamine were consistent with previous in vivo and in vitro reports.
An roc approach for evaluating functional brain mr imaging and postprocessing protocols
Authors: Constable R. Todd , Skudlarski Pawel , Gore John C. 
Published: March 2007

AbstractA method that can be used to evaluate the performance of MRI methods for detecting discrete regional activations using functional MRI is presented. Computer derived receiver‐operator‐characteristic (ROC) curves have been used to evaluate quantitatively a range of conditions encountered in functional MRI studies. ROC analysis allows multiple acquisition strategies and multiple postprocessing strategies to be quantitatively and objectively compared. The authors first present this analysis technique and then illustrate its use for assessing the relative performances of different functional MRI data acquisition strategies using different gradient echo, echo‐planar imaging protocols. In addition, the authors have used the ROC analysis to evaluate and compare several methods for analyzing functional MRI data to extract regions of activation. This approach to assessing the performance of different methods is of general use and can be applied to evaluate other data acquisition protocols and postprocessing methods.
Limitations of stimulated echo acquisition mode (steam) techniques in cardiac applications
Authors: Fischer Stefan E. , Stuber Matthias , Scheidegger Markus B. , Boesiger Peter 
Published: March 2007

AbstractStimulated echoes are widely used for imaging functional tissue parameters such as diffusion coefficient, perfusion, and flow rates. They are potentially interesting for the assessment of various cardiac functions. However, severe limitations of the stimulated echo acquisition mode occur, which are related to the special dynamic properties of the beating heart and flowing blood. To the well‐known signal decay due to longitudinal relaxation and through‐plane motion between the preparation and the read‐out period of the stimulated echoes, additional signal loss is often observed. As the prepared magnetization is fixed with respect to the tissue, this signal loss is caused by the tissue deformation during the cardiac cycle, which leads to a modification of the modulation frequency of the magnetization. These effects are theoretically derived and corroborated by phantom and in vivo experiments.
Mr geometric distortion correction for improved frame‐based stereotaxic target localization accuracy
Authors: Sumanaweera Thilaka , Glover Gary H. , Hemler Paul F. , Van Elsen Petra A. Den , Martin David , Adler John R. , Napel Sandy 
Published: March 2007

AbstractWe present a method to correct the geometric distortion caused by field inhomogeneity in MR images of patients wearing MR‐compatible Stereotaxic frames. Our previously published distortion correction method derives patient‐dependent error maps by computing the phase‐difference of 3D images acquired at different TEs. The time difference (ΔTE = 4.9 ms at 1.5 T) is chosen such that the water and fat signals are in phase. However, ΔTE is long enough to permit phase wraps in the difference images for frequency offsets greater than 205 Hz. Phase unwrapping techniques resolve these only for connected structures; therefore, the phase difference for fiducial rods may be off by multiples of 2 π relative to the head. We remove this uncertainty by using an additional single 2D phase‐different image with ΔTE = 1 ms (during which time no phase‐wraps are typically expected) to determine the correct multiple of 2m for each rod. We tested our method in a cadaver and in a patient using CT as the gold standard. Targets in the frame coordinates were chosen from CT and compared with their locations in MR. Localizing errors using MR compared with CT were as large as 3.7 mm before correction and were reduced to less than 1.11 mm after correction.
MR gradient coil heat dissipation
Authors: Chu Kenneth C. , Rutt Brian K. 
Published: March 2007

AbstractThe temperature responses of five different gradient coil designs were modeled using simplified engineering equations and measured. The model predicts that the coil temperature approaches a maximum as an inverse exponential, where the maximum temperature is governed by two parameters: a local power density and a cooling term. The power density term is a function of position and is highest where the current paths have minimum widths and are closely packed. The cooling parameter consists of convective, conductive, and radiative components which can be controlled by (1) providing forced cooling, (2) having a coil former with high thermal conductivity and thin walls, and (3) varying the emissivity of the coil surfaces. For a given gradient strength, the average temperature rise is minimized by designing a coil with a small radius and thick copper. The model predicted the local temperature rise, which is also dependent on the current density, to within 5°C of measured values.
Correlation of early reduction in the apparent diffusion coefficient of water with blood flow reduction during middle cerebral artery occlusion in rats
Authors: Mancuso Anthony , Karibe Hiroshi , Rooney William D. , Zarow Gregory J. , Graham Steven H. , Weiner Michael W. , Weinstein Philip R. 
Published: March 2007

AbstractTo determine the relationship between reductions in the apparent diffusion coefficient of water (ADC) and in cerebral blood flow (CBF) during focal ischemia, we used diffusion‐weighted magnetic resonance (D‐MR) imaging and autoradiographic CBF analysis to examine rats subjected to 30 or 90 min of permanent middle cerebral artery (MCA) occlusion. In the 30‐min occlusion group (n = 10), the area with substantially reduced ADC (15% or more below the contralateral level [ADC15]) corresponded best to the area with CBF below 25 ml/100 g/min and was significantly smaller than the area with CBF below 50 ml/100 g/min (CBF50), a level associated with reduced protein synthesis and delayed necrosis (40 ± 13% versus 74 ± 8% of the ischemic hemisphere; P < 0.0001). In the 90‐min occlusion group (n = 6), the ADC15 area corresponded best to the CBF30 to CBF35 area and was again significantly smaller than the CBF50 area (54 ± 13% versus 73 ± 20%, P < 0.05). Thus, the area of substantially reduced ADC at 30 and 90 min represents only 53% and 74%, respectively, of the tissue at risk for infarction. These findings indicate a potential limitation in using early D‐MR imaging to predict stroke outcome.
Phased array detectors and an automated intensity‐correction algorithm for high‐resolution MR imaging of the human brain
Authors: Wald Lawrence L. , Carvajal Lucas , Moyher Susan E. , Nelson Sarah J. , Grant P. Ellen , Barkovich A. James , Vigneron Daniel B. 
Published: March 2007

AbstractTwo‐ and four‐coil phased array detectors were developed to increase the sensitivity and resolution of MR imaging of the human brain cortex, especially for detecting cortical dysplasias in pediatric epilepsy patients. An automated intensity correction algorithm based on an edge‐completed, low‐pass filtered image was used to correct the image intensity for the inhomogenous reception profile of the coils. Seven phased array coils were constructed and tested. The sensitivity of these coils was up to 600% higher at the surface of the cortex than that achieved with a conventional head coil and up to 30% greater at the center of the head. The sensitivity obtained was comparable with that of a conventional small surface coil, but extended over the larger dimensions of the array and previously inaccessible areas such as the top of the head. The advantages of the improved sensitivity are demonstrated with high resolution images of the brain.
Mr contrast due to intravascular magnetic susceptibility perturbations
Authors: Boxerman Jerrold L. , Hamberg Leena M. , Rosen Bruce R. , Weisskoff Robert M. 
Published: March 2007

AbstractA particularly powerful paradigm for functional MR imaging of microvascular hemodynamics incorporates paramagnetic materials that create significant image contrast. These include exogenous (lanthanide chelates) and endogenous (de‐oxygenated hemoglobin) agents for mapping cerebral blood volume and neuronal activity, respectively. Accurate interpretation of these maps requires an understanding of the bio‐physics of susceptibility‐based image contrast. The authors developed a novel Monte Carlo model with which the authors quantified the relationship between microscopic tissue parameters, NMR imaging parameters, and susceptibility contrast in vivo. The authors found vascular permeability to water and the flow of erythrocytes to be relatively unimportant contributors to susceptibility‐induced ΔR2. However, pulse sequence, echo time, and concentration of contrast agent have profound effects on the vessel size dependence of ΔR2. For a model vasculature containing both capillaries and venules, the authors predicted a linear volume fraction dependence for physiological volume changes based on recruitment and dilation, and a concentration dependence that is nonlinear and pulse sequence dependent. Using the model, the authors demonstrated that spin echo functional images have greater microvascular sensitivity than gradient echo images, and that the specifics of the volume fraction and concentration dependence of transverse relaxivity change should allow for robust mapping of relative blood volume. The authors also demonstrated excellent agreement between the predictions of their model and experimental data obtained from the serial injection of superparamagnetic contrast agent in a rat model.
MR Spectroscopic imaging of collagen: Tendons and knee menisci
Authors: Gold Garry E. , Pauly John M. , Macovski Albert , Herfkens Robert J. 
Published: March 2007

AbstractWater molecules associated with collagen have short transverse (T2) relaxation times. Projection‐reconstruction techniques are able to achieve an echo time (TE) much shorter than conventional techniques, allowing imaging of tissues with T2 < 5 ms. Using these techniques, a conventional 1.5‐T MRI human imaging system can directly image collagen‐associated water from knee menisci and tendons in normal volunteers and patients. Long‐T2 suppression improves the contrast between these structures and the surrounding tissue with long‐T2 relaxation times. Spectroscopic imaging provides improved lipid/water registration and information about chemical composition and relaxation times. Direct imaging of tendons and menisci may provide more information about these structures and provide a new way to assess both injury and repair.
Evaluation of muscle diseases using artificial neural network analysis of 31P MR spectroscopy data
Authors: Kari Suresh , Olsen Nancy J. , Park Jane H. 
Published: March 2007

AbstractDermatomyositis is an autoimmune disease characterized by an erythematous rash and severe muscle weakness. 31P Magnetic resonance spectroscopy (MRS) provides quantitative data for longitudinal monitoring of disease status and responses to immunosuppressive therapy. A disease variant, amyopathic dermatomyositis, presents with a typical rash but no clinical muscle weakness. However, metabolic abnormalities in the oxidative capacity of muscles of amyopathic patients during exercise were detected with 31P MRS. Because MRS provided the best quantitative data for evaluating dermatomyositis, the 31P metabolic parameters derived from the MR spectra were further processed using an artificial neural network (XERION). The neural network analyses provided additional clinical information from the weighted correlations of multiple 31P parameters, namely, inorganic phosphate, phos‐phocreatine, ATP, phosphodiesters, and selected ratios. This investigation analyzes the relative importance of the various metabolic parameters for accurate patient characterization and provides insights into the pathogenesis of the disease.
Application of a superparamagnetic iron oxide (Resovis®) for MR imaging of human cerebral blood volume
Authors: Reimer Peter , Schuierer Gerhard , Balzer Thomas , Peters Peter E. 
Published: March 2007

AbstractThe authors describe the feasibility of dynamic MRI using a novel superparamagnetic iron oxide contrast agent. Resovist® was injected as a bolus at doses of 4, 8, and 16 μmol Fe/kg bodyweight in three consented patients participating in a Phase 2 clinical multicenter trial for hepatic MRI. Dynamic images of the brain were obtained with a conventional FLASH sequence. Results were analyzed by evaluation of dynamic images, cerebral blood volume maps, and normalized signal intensity time curves. Resovist® enabled rapid injections and a dose‐dependent strong reduction in gray and white matter signal intensity. The small injection volume and good tolerability may enable Resovist® to serve as a perfusion agent. Dedicated clinical trials are warranted to assess the potentials of Resovist® for perfusion MRI and fMRI.
Imaging myocardial fiber architecture in vivo with magnetic resonance
Authors: Reese Timothy G. , Weisskoff Robert M. , Smith R. Neil , Rosen Bruce R. , Dinsmore Robert E. , Wedeen Van J. 
Published: March 2007

AbstractMethods are presented to image the fiber architecture of the human myocardium in vitro and in vivo. NMR images are obtained of the diffusion anisotropy tensor, indicative of local myofiber orientation. Studies of cardiac necropsy specimens demonstrate classic features of ventricular myoarchitecture including the continuous endocardial to epicardial variation of fiber helix angles (angles to the ventricular circumferential direction) of approximatel ±1.3 to −1.3 radians. Cross‐fiber anisotropy is also observed. In the beating heart, NMR diffusion data must be corrected for the effects of myocardial deformation during the cardiac cycle. This correction can be performed using an independent MRI method to map the strain‐rate tensor field of the myocardium through time. Combining fiber orientation with local myocardial strain rate, local rates of myocardial fiber shortening may be computed.
Size‐restricted cluster formation and cluster maintenance technique for mobile ad hoc networks
Authors: Venkataraman Gayathri , Emmanuel Sabu , Thambipillai Srikanthan 
Published: March 2007

AbstractMobile ad hoc networks may be composed of a large number of nodes and hence a hierarchical cluster‐based structure can be employed to address the scalability issues of the large network. In this paper we propose a size‐restricted, distributed clustering strategy (cluster formation and cluster maintenance) for mobile ad hoc networks. A distributed approach where every node is responsible for the clustering decisions would avoid single‐point bottleneck failures. We use a size restrictionS, for the cluster formation and cluster maintenance. In addition, while forming the cluster we also use a diameter restrictionK. The simulations show that our strategy gives rise to a lesser number of clusters when compared to other clustering algorithms proposed by Gerlaet al., Fernadesset al.and Linet al.This is attributed to the size restriction and cluster merging that we have incorporated. The size restriction helps in better management of resources inside the cluster. Our clustering technique uses a weight‐based cluster head election strategy which results in less change in cluster head and higher cluster head lifetime when compared to the Least Cluster Head Changes (LCC) with lowest ID algorithm. The low change in cluster head and higher cluster head lifetime make our proposed algorithm suitable for high‐mobility situations. The proposed clustering strategy could be used for building the clusters required in a hierarchical structure of the ad hoc network. Copyright © 2007 John Wiley & Sons, Ltd.
Efficient characterization of the random eigenvalue problem in a polynomial chaos decomposition
Authors: Ghanem Roger , Ghosh Debraj 
Published: March 2007

AbstractA new procedure for characterizing the solution of the eigenvalue problem in the presence of uncertainty is presented. The eigenvalues and eigenvectors are described through their projections on the polynomial chaos basis. An efficient method for estimating the coefficients with respect to this basis is proposed. The method uses a Galerkin‐based approach by orthogonalizing the residual in the eigenvalue–eigenvector equation to the subspace spanned by the basis functions used for approximation. In this way, the stochastic problem is framed as a system of deterministic non‐linear algebraic equations. This system of equations is solved using a Newton–Raphson algorithm. Although the proposed approach is not based on statistical sampling, the efficiency of the proposed method can be significantly enhanced by initializing the non‐linear iterative process with a small statistical sample synthesized through a Monte Carlo sampling scheme. The proposed method offers a number of advantages over existing methods based on statistical sampling. First, it provides an approximation to the complete probabilistic description of the eigensolution. Second, it reduces the computational overhead associated with solving the statistical eigenvalue problem. Finally, it circumvents the dependence of the statistical solution on the quality of the underlying random number generator. Copyright © 2007 John Wiley & Sons, Ltd.
What does the hospital diabetic clinic do for you?
Authors: Hartnell V 
Published: March 2007

AbstractThe work of a district's diabetic clinic was audited to assess workload; it focused on patients' reasons for attendance, outcome of their appointment and recording of specified parameters in the notes.Results highlighted the failings of a clinic organised on traditional lines. Most appointments (70%) were for routine follow‐up, all patients were given another appointment and, for at least 27%, this was the only action undertaken. The clinic performed poorly in routine screening and was ineffective, particularly in relationship to skills and services available in primary care.
The epidemic of Indian childhood diabetes in Leicester. Social and cultural differences between cases and control population
Authors: Bodington M J , Burden A C 
Published: March 2007

AbstractWe have provided evidence in favour of an epidemic of childhood onset (<15 years) insulin dependent diabetes in Indian children resident in Leicester, UK. These children either come from, or their forefathers came from, the Indian Subcontinent. The present work examines the hypothesis that the amount of cultural adaption to English life is greater than their non‐diabetic peer. A trained Diabetes Specialist Health Visitor visited each family with a structured questionnaire; to enquire when the diabetes started, where they had lived previously, schooling, friends, diet and living conditions. In total. 32 patients were contacted of the 35. These families have been compared to the Leicester City Indian Census population. They are more likely to have been born in the United Kingdom; to eat meat; to live in detached or semi‐detached housing; to live in an area with few other Indians.The preliminary results suggest that diabetic Indian children are more culturally anglicised than the non‐diabetic; a case control study is urgently required to verify this.
A comparison of the glycaemic and insulinaemic effects of an Asian and a European meal
Authors: Burden ML , Samanta A , Spalding D , Burden AC 
Published: March 2007

AbstractThe glycaemic and insulinaemic effects of an Asian and a European meal were compared. The Asian meal contained 1,439 kcal (14% protein, 45% carbohydrate, 41% fat, 28g dietary fibre), and the European meal 1,370 kcal (18% protein, 25% carbohydrate, 57% fat, 11g dietary fibre). Fifteen normal voiunteers were tested with each meal after an overnight fast, and on consecutive days in random order. There were no differences at fasting or after one hour between either meal. Two hours after the Asian meal, subjects had a higher degree of glycaemia, mean (SE) 5.29 (0.35) vs 4.32 (0.09) mmoI/I (p<0.02) and a higher degree of insulinaemia, mean (SE) 28.17 (6.86)vs 8.06 (1.54) mU/I (p<0.02). These effects were maintained at three hours: plasma glucose 5.12 (0.25) vs 9.84 (2.46) mU/I (p<0.01). The fasting glucose and insulin levels following the Asian meal had not been achieved at three hours so the study was repeated using 11 normal volunteers with a longer follow‐up time of six hours. Only then did the glucose values return to fasting levels, although insulin levels remained slightly elevated. These preliminary results suggest the need for more detailed long‐term observations on the metabolic effects of culturally different meals.