bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of concentrations by time domain fitting of proton nmr echo signals using prior knowledge
Authors: Van Dijk J. E. , Mehlkopf A. F. , Van Ormondt D. , Bovée W. M. M. J. 
Published: March 2007

AbstractA fast and flexible time domain iterative fitting procedure that can be used to fit free induction decays as well as echo‐like signals is described. Damping constants of the first and second part of the echo do not have to be identical. Prior knowledge can be used to diminish the number of parameters to be fitted, which results in an improved accuracy. It is shown how prior knowledge is mathematically incorporated in the Gauss‐Newton method. From proton NMR measurements of model solutions actual prior knowledge is extracted. With this knowledge relative concentrations are determined from a mixture of metabolites. The fitted results agree with the true values within the margins of the noise. After some minor changes the same prior knowledge was successfully used to analyze a series of in vivo rat brain measurements.
A novel method for fat suppression in rare sequences
Authors: Higuchi N. , Hiramatsu K. , Mulkern R. V. 
Published: March 2007

AbstractRapid acquisition relaxation‐enhanced (RARE) sequences (Hennig et al., Magn. Reson. Med. 3, 823 (1986)) utilize one or several Cam‐Purcell–Meiboom–Gill (CPMG) echo trains to sample a number of k‐space lines each repetition time TR. The technique can rapidly generate multislice T2‐weighted images which, as a rule, are strikingly similar in contrast to conventional T2‐weighted spin‐echo (SE) images. An exception to this rule is the appearance of very bright signal from fat in T2‐weighted RARE images as compared to conventional T2‐weighted SE images. To reduce this fat signal, we introduce a time delay, τc, between the 90ox and first 180oy pulse of each echo train such that a phase angle of π/2 develops between fat and the reference (water) line at echo maxima. The technique leads to single‐acquisition fat suppression without the use of frequency‐selective saturation pulses and concomitant loss of slices per TR. A Bloch equation analysis is used to identify two major mechanisms contributing to suppression of off‐resonance spins such that Wτc = π/2. Namely, the CPMG sequence becomes a CP sequence with no self‐correction properties for imperfect 180° pulses leading to enhanced signal decay, and the raw k‐space data matrix become segemented into blocks alternately multiplied by ±i, leading to signal dispersion following Fourier transformation.
Multiexponential proton relaxation processes of compartmentalized water in gels
Authors: Watanabe Tokuko , Murase Norio , Staemmler Martin , Gersonde Klaus 
Published: March 2007

AbstractThe proton relaxation times, T1 and T2, of water in Sephadex gels, exhibiting pores of varying size (i.e., with exclusion limits of molecular weight between l03 and 105) and water contents in the range 30 to 70% (w/w, weight of water to total weight), were measured at 20 MHz in the temperature range 5 to 50°C. Multiexponential analysis of the relaxation curves revealed the existence of two relaxation components in all gel systems. A component with long T1 and T2 (T1,1 and T2,1) is associated with a large water fraction α1,1 and α2,1 and a component with short T1 and T2 (T1,2 and T2,2 with a small water fraction α1,2 and α2,2 An analysis of the temperature behavior of the relaxation components gives insight into the relaxation mechanisms. The relaxation process in water, compartmentalized in the gel matrix, is mainly controlled by dipole‐dipole interactions. In addition, proton exchange processes between hydration water and hydroxyl groups of the matrix chain contribute under specific conditions and lead to a dramatic enhancement of the relaxation rate. In particular, for gels with small pores and with low water content proton exchange is observed. Compartments of water in gels could be models for compartments of water in biological tissues.
Tissue characterization and assessment of preoperative chemotherapeutic response in musculoskeletal tumors by in vivo31p magnetic resonance spectroscopy
Authors: Redmond O. M. , Bell E. , Stack J. P. , Deran P. A. , Carney D. N. , Hurson B. , Ennis J. T. 
Published: March 2007

AbstractThis study investigates the potential of in vivo 31P magnetic resonance spectroscopy (MRS) to characterize musculoskeletal tumors and to determine preoperative levels of histological necrosis, which is an important clinical indicator of patient response. Pretherapy MRS was performed on 28 patients with large musculoskeletal tumors: 13 with osteosarcoma, 3 with chondrosarcoma, 5 with malignant fibrous histiocytoma, 1 with desmoid tumor, 1 with Ewing's, 2 with hemangioendothelioma, 1 with myxoid liposarcoma, 1 with synovial cell sarcoma, and 1 with rhabdomyosarcoma. Fifteen patients had follow‐up MRS examinations after commencement of chemotherapy (mean of five/patient), eight of whom have now had surgery. Elevated levels of PMEs (P < 0.01), Pi (P < 0.01), and PDEs (P < 0.02) as well as elevated tumor pH (P < 0.05) were. observed in all patients. The synovial cell sarcoma was characterized by high levels of PMEs (>20%) and low pH(pH 6.76). This contrasted with the spectra obtained from the malignant fibrous histiocytomas which had high levels of PDEs (17±5%). Reductions in PDE levels postchemotherapy were associated with a high degree of necrosis (>90%) at surgery, while an increase in PDE levels was associated with a low level of histological necrosis. Likewise, reductions in the ratios PDE/NTP and PDE/PCr and an increase in Pi/PDE were also associated with a high level of necrosis.
in vivo identification and monitoring of changes in rat brain glucose by two‐dimensional shift‐correlated 1h nmr spectroscopy
Authors: Peres M. , Fedeli O. , Barrere B. , Gillet B. , Berenger G. , Seylaz J. , Beloeil J‐C. 
Published: March 2007

AbstractIntracerebral glucose resonance was directly detected and resolved in vivo by two‐dimensional shift‐correlated (COSY) 1H NMR spectroscopy in anesthetized rats (n = 4). The relative changes in brain glucose concentration were measured by volume integration of the α‐D‐glucose cross peak in the 2D COSY spectra. This report demonstrates the possibility of monitoring the variations in cerebral glucose following iv injection of glucose.
Real‐time observation of transient focal ischemia and hyperemia in cat brain
Authors: Crespigny A. J. De , Wendland M. F. , Derugin N. , Kozniewska E. , Moseley M. E. 
Published: March 2007

AbstractGradient‐recalled echo‐planar (T2‐weighted) imaging was used to noninvasively monitor regional blood oxygenation state changes in real time during transient episodes of focal ischemia in cat brain. Varying ischemic intervals (12 s to 30 min) were caused by middle cerebral artery occlusion. A rapid signal drop was noted upon occlusion, due to deoxygenation of static blood in the ischemic tissues. Upon successful reperfusion, the signal intensity recovered immediately and increased above (overshot) the baseline level before slowly returning to normal. The “overshoot” response was strongly dependent on the duration of the ischemic interval and is thought to reflect reactive hyperemia.
Determination of Absolute Phosphate Metabolite Concentrations in RIF‐1 Tumors in Vivo by 31P‐1H‐2H NMR Spectroscopy Using Water as an Internal Intensity Reference
Authors: Shungu Dikoma C. , Bhujwalla Zaver M. , Li Shi‐Jiang , Rose Lucy M. , Wehrle Janna P. , Glickson Jerry D. 
Published: March 2007

AbstractThe absolute metabolite quantification method of Thulborn and Ackerman [J. Magn. Reson 55, 357 (1983)] in which the tissue water proton signal is used as an internal intensity standard and its more recent variation in which NMR peak intensities are referenced to that of the natural abundance deuterium signal of water [Li et al., SMRM Abstr. 2, 825 (1988); Song et al, Magn. Reson. Med. 25, 45 (1992) have been implemented to obtain absolute phosphate metabolite concentrations in subcutaneous RIF‐1 tumors during untreated growth and following treatment with 5‐fluorouracil. The equivalence of these two hydrogen isotopes as intensity standards and the validity of their use in the determination of absolute metabolite concentrations in vivo by NMR has been demonstrated. On matched in vivo and extract tumor samples (n = 5), excellent agreement has been obtained between nucleoside triphosphate concentrations determined by NMR and those derived by HPLC analysis for the control tumors. Following 3 days of untreated growth, absolute concentrations of phosphate metabolites in RIF‐1 tumors (n = 10) decreased significantly, except for the Pi concentration which did not vary. For the treated tumors (n = 10) there were no changes in metabolite concentrations except for a decrease in the PCr and, possibly, Pi concentrations. The PCr/Pi ratio in the latter tumors did not change. These observations suggest that changes in absolute metabolite concentrations may be more sensitive indices of response to therapy than changes in metabolite peak amplitude ratios, a parameter commonly used to express in vivo NMR data.© 1992 Academic Press,Inc.
Use of Fluid‐Attenuated Inversion‐Recovery Pulse Sequences for Imaging the Spinal Cord
Authors: White Susan J. , Hajnal Joseph V. , Young Ian R. , Bydder Graeme M. 
Published: March 2007

AbstractFourteen patients with disease of the spinal cord were imaged with fluid‐attenuated inversion‐recovery (FLAIR) sequences in which the inversion time was chosen to substantially reduce or null the signal from CSF. Lesions were seen with greater conspicuity than with conventional contrast‐enhanced and ‐unenhanced T1‐ and T2‐‐weighted sequences in 11 cases.© 1992 Academic Press,Inc.
Distortions from curved flow in magnetic resonance imaging
Authors: Frank Lawrence R. , Buxton Richard B. 
Published: March 2007

AbstractWe present an analysis of how vessel curvature can create distortions in magnetic resonance images of flowing blood. Steady flow in curved vessels produces distortions of the vessel shape and intensity variations in the image due to motion during the interval between phase encoding or slice selection and the echo center. Even with steady flow, vessel curvature produces motion moments higher than velocity (acceleration, etc.), but use of a first order oblique flow compensated phase encoding gradient waveform reduced the distortion in the image. Numerical calculations of image distortions based on simple flow models are in good agreement with experimental results in a phantom.
An assessment of spin‐echo rotating‐frame imaging for spatially localized determination of short T2 relaxation times in vivo
Authors: Dixon Ruth M. , Styles Peter 
Published: March 2007

AbstractThe rotating frame method of localized spectroscopy can be augmented by the inclusion of a refocusing pulse to enable the measurement of T2 relaxation times. This technique is particularly appropriate for determining short relaxation parameters due to the absence of time consuming switched B0 field gradients. We have evaluated the accuracy of this protocol by measuring localized T2s in the range of 1 to 20 ms. Preliminary data obtained from muscle and liver of normal and iron overloaded human subjects are also presented.
Analysis of water‐macromolecule proton magnetization transfer in articular cartilage
Authors: Kim David K. , Ceckler Toni L. , Hascall Vincent C. , Calabro Anthony , Balaban Robert S. 
Published: March 2007

AbstractThese studies were designed to establish which structural elements of cartilage are responsible for proton magnetization transfer between water (Hf) and macromolecules (Hr) observed in MRI studies on articular cartilage. Saturation transfer techniques were used to monitor magnetization transfer in vitro on samples of the two major constituents of cartilage: collagen and proteoglycan. Articular cartilage samples were also evaluated in vitro before and after the removal of the proteoglycan fraction. Isolated hydrated collagen exhibited a significant proton magnetization transfer rate with water. In contrast, proteoglycans exhibited no proton magnetization transfer. Articular cartilage, in vitro, exhibited a high degree of magnetization transfer with water protons consistent with previous MRI studies in vivo. Enzymatic removal of proteoglycan from the cartilage did not alter the magnetization transfer rate between Hr and Hf. These data demonstrate that the structure and concentration of the collagen matrix are the predominant determinants of the magnetization transfer process in articular cartilage with little or no contribution from proteoglycans. This specificity of the magnetization transfer effect may prove useful in the noninvasive evaluation of cartilage composition and structure in vivo.
Magnetization transfer in cross‐linked bovine serum albumin solutions at 200 MHz: A model for tissue
Authors: Koenig Seymour H. , Brown Rodney D. , Ugolini Raphael 
Published: March 2007

AbstractWe report results for proton 1/T1, 1/T2, and K, the rate of magnetization transfer from solvent to solute, for 5 and 10 wt. % solutions of bovine serum albumin, both native and chemically cross‐linked, in undeuterated and ∼50% deuterated water, at 4.7 T (200.1 MHz) and 19°C. At this field, although K > 1/T1 for the cross‐linked samples, magnetization transfer contributes little to 1/T1 directly. Therefore K was measured using off‐resonance irradiation of the protein protons. The data for all the samples can be fit using a theoretical model for magnetization transfer, with three parameters: the intrinsic longitudinal relaxation rates of solute and solvent protons, and K. The magnitude of Kis so large that the newly‐identified, long‐lived (∼1 μs) hydration sites (S. H. Koenig, R. D. Brown III, and R. Ugolini, Magn. Reson. Med., 29, 77 (1993)) must be invoked to account for K, as is necessary to explain the differential effects of cross linking on the magnetic field dependence of 1/T1 of protons and deuterons and the large 1/T1 and 1/T2 values below ∼20 MHz in immobilized systems. Although these sites are few in number, their long resident lifetime becomes the correlation time for magnetization transfer when protein is immobilized, accounting for the large value of K. Recent data from several laboratories have shown that cross‐linked protein, as used here, is a good model for 1/T1 and 1/T2 of tissue, as a function of temperature and magnetic field.
In vitro characterization of lung cancers by the use of 1H nuclear magnetic resonance spectroscopy of tissue extracts and discriminant factor analysis
Authors: Hanaoka Hideto , Yoshioka Yoshichika , Ito Iichiro , Niitu Katuhiro , Yasuda Naoki 
Published: March 2007

AbstractUsing proton magnetic resonance spectroscopy (1H MRS) spectra were obtained in vitro from extracts of four types of lung cancer (squamous cell, adenocarcinoma, large cell, small cell) and normal lung. The hydrophilic phase of the chloroform/methanol‐water extracts yielded several distinct peaks. Among them the peak areas for cholines, creatines, glycine, and alanine, and their ratios were calculated and used as parameters to characterize different lung tissues. The ratios, cholines/alanine and glycine/alanine, were significantly (P < 0.001 to P < 0.05) higher for the normal lung than lung cancers. Creatines/glycine and creatines/cholines generally provided good discrimination (P < 0.001 to P < 0.05) between any two types of lung cancer. When data were further analyzed by discriminant factor analysis, there was 81.5 to 90.7% accuracy in predicting between normal lung and each cancer type, or among the four types of lung cancer. These results suggested that 1H MRS might be useful as an adjunct modality in the differential diagnosis of lung cancers.
Imaging oxygen tension in liver and spleen by 19F NMR
Authors: Holland Scott K. , Kennan Richard P. , Schaub Maria M. , D'Angelo Michael J. , Gore John C. 
Published: March 2007

Abstract19F NMR imaging of the perfluorocarbon emulsion FluosolTM has been used to study regional variations in oxygen tension in rat liver and spleen. We have used the linear dependence of spin lattice relaxation rate (1/T1) on the partial oxygen pressure (pO2) of FluosolTM to determine the oxygen tension in the reticuloendothelial system (RES) of the liver and spleen of male Sprague‐Dawley rats which have serial infusions of FluosolTM. Oxygen tension maps have been computed from 19F NMR images using a calibration obtained for FluosolTM in vitro at 37.5°C. The spatial resolution of the pO2 maps computed using this technique is 1.2 × 1.2 mm in 3‐mm thick slices. Calculations from in vivo pO2 maps indicate an average change in the median pO2 of the RES from 118 to 80 mmHg for (n = 7) rats breathing 95% O2 and 5% CO2 (carbogen) and air, respectively.
MRI gradient waveform design by numerical optimization
Authors: Simonetti Orlando P. , Duerk Jeffrey L. , Chankong Vira 
Published: March 2007

AbstractThis manuscript describes a method of gradient waveform design by nonlinear constrained optimization. Methods of formulation and solution of the waveform optimization problem are briefly described for minimization of root mean squared current and minimization of waveform moments. Waveforms generated using these objectives are presented and compared with those obtained with other objectives. The method uses waveforms which are defined as a set of discrete amplitudes in order to remove artificial constraints on waveform shape imposed by “multilobe” designs. These point‐to‐point amplitudes are the parameters determined in the optimization procedure which includes knowledge of the specific imaging conditions and the specific gradient hardware system. Some beneficial results of this design approach are: a) physically realizable waveforms which optimally achieve specific imaging and motion artifact reduction goals, b) waveforms which are guaranteed to be optimal with respect to one of several possible objective, c) less reliance on the experience of the designer, and d) a potential reduction in waveform design time.
A wireless axial pair resonator
Authors: Maeda Hisatoshi , Toyooka Nobuo , Okawara Hiroshi 
Published: March 2007

AbstractA wireless axial pair resonator consists of two coils coupling inductively with a body coil, which is used as a signal transmitter and receiver. Computer simulations gave signal enhancements of 1.41 and 1.47 for the resonators of 15‐ and 20‐cm diameter, whereas those of phantom studies gave 1.37 and 1.49.
Monocrystalline iron oxide nanocompounds (MION): Physicochemical properties
Authors: Shen Tueng , Weissleder Ralph , Papisov Mikhail , Bogdanov Alexei , Brady Thomas J. 
Published: March 2007

AbstractWe have previously described a novel monocrystalline iron oxide nanocompound (MION), a stable colloid that enables target specific MR imaging. In this study, the physicochemical properties of MION are reported using a variety of analytical techniques. High resolution electron microscopy indicates that a MION consists of hexagonal shaped electron‐dense cores of 4.6 ± 1.2 nm in diameter. This iron oxide core has an inverse spinel crystal structure which was confirmed by x‐ray powder diffraction. Chemical analysis showed that each core has 25 ± 6 dextran molecules (10 kD) attached, resulting in a unimodal hydrodynamic radius of 20 nm by laser light scattering. Because of the flexibillity of the dextran layer, the radius is only 8 nm in nonaqueous reverse micelles. At room temperature, MION exhibit superparamagnetic behavior with an induced magnetization of 68 emu/g Fe at 1.5 T. Mössbauer studies show that the saturation internal magnetic field is 505 KOe, and blocking temperature is at 100 K. The R1 relaxivity of MION is 16.5 (mM‐sec)‐1 and the R2 relaxivity is 34.8 (mM‐sec)‐1 in aqueous solution at 37°C and 0.47 T. In vitro phantom studies show that the detectability of MION in liver tissue is less than 50 nmol Fe/g tissue using gradient echo imaging techniques.
Measurement of capillary permeability to macromolecules by dynamic magnetic resonance imaging: A quantitative noninvasive technique
Authors: Shames David M. , Kuwatsuru Ryohei , Vexler Vladimir , Mühler Andreas , Brasch Robert C. 
Published: March 2007

AbstractA simple, linear kinetic model has been developed for the noninvasive assessment of capillary permeability to macromolecules in the rat by dynamic magnetic resonance imaging using albumin‐Gd‐DTPA. Data required by the model are signal intensity responses from a target tissue and a venous structure such as inferior vena cava before and after bolus intravenous injection of albumin‐Gd‐DTPA. Additional requirements include an early temporal resolution of approximately one image/min and a blood sample for hematocrit. The model does not require measurement of albumin‐Gd‐DTPA concentration in either arterial or venous blood. Pilot experiments suggest that this technique is adequate for estimation of the fractional leak rate of macromolecules from plasma to interstitial water as well as tissue plasma volume, the product of which yields a measure of the permeability surface area product of the tissue if the extraction fraction is modest (<0.2). The technique may be generally applicable to the study of abnormal capillary permeability in humans as well as animals.
Real‐time acquisition, display, and interactive graphic control of NMR cardiac profiles and images
Authors: Hardy Christopher J. , Darrow Robert D. , Nieters Edward J. , Roemer Peter B. , Watkins Ronald D. , Adams William J. , Hattes Neil R. , Maier Josepth K. 
Published: March 2007

AbstractA highly interactive MRI scanner interface has been developed that allows, for the first time, real‐time graphic control of one‐dimensional (1D) and two‐dimensional (2D) cardiac MRI exams. The system comprises a Mercury array processor (AP) in a Sun SPARCserver with two connections to the MRI scanner, a data link that passes the NMR data directly to the AP as they are collected, and a control link that passes commands from the Sun to the scanner to redirect the imaging pulse sequence in real time. In the 1D techniques, a cylinder or “pencil” of magnetization is repeatedly excited using gradient‐echo or spin‐echo line‐scan sequences, with the magnetization read out each time along the length of the cylinder, and a scrolling display generated on the Sun monitor. Rubber‐band lines drawn on the scout image redirect the pencil or imaging slice to different locations, with the changes immediately visible in the display. M‐mode imaging, 1D flow imaging, and 2D fast cardiac imaging have been demonstrated on normal volunteers using this system. This platform represents an operator‐“friendly” way of directing real‐time imaging of the heart.
Measurement of T1 relaxation times of cardiac phosphate metabolites using BIR‐4 adiabatic RF pulses and a variable nutation method
Authors: Sakuma Hajime , Nelson Sarah J. , Vigneron Daniel B. , Hartiala Jaakko , Higgins Charles B. 
Published: March 2007

AbstractT1relaxation times of PCr and β‐ATP in human cardiac and skeletal muscle were evaluated using a variable nutation method. This allows T1measurements with a constant TR and a significant reduction in acquisition time compared with the partial saturation method. Four 1D CSI datasets were obtained using 30°, 45°, 60°, and 90° BIR‐4 adiabatic RF pulses within 40 min. The T1of the phosphate phantom obtained with this method agreed with values obtained with the partial saturation method. The T1s of PCr and β‐ATP in heart are 3.98 = 0.18 s and 1.86 ± 0.16 s (mean = SE). Our results demonstrated that T1 values in heart and skeletal muscle are not significantly different.