bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relaxometry and magnetometry of ferritin
Authors: Brooks Rodney A. , Vymazal Josef , Goldfarb Ron B. , Bulte Jeff W. M. , Aisen Phlip 
Published: March 2007

AbstractBy combining nuclear magnetic relaxometry on 39 ferritin samples with different iron loading with magnetometry, results were obtained that suggest a new interpretation of the core structure and magnetic properties of ferritin. These studies provide evidence that, contrary to most earlier reports, the ferritin core is antiferromagnetic (AFM) even at body temperature and possesses a superparamagnetic (SPM) moment due to incomplete cancellation of antiparallel sublattices, as predicted by Néel's theory. This moment also provides a likely explanation for the anomalous T2 shortening in ferritin solution. However, the number of SPM moments derived from this model is less than the number of ferritin molecules determined chemically, and a similar discrepancy was found by retrospectively fitting previously published magnetometry data. In other words, only a fraction of the ferritin molecules seem to be SPM. The studies also provide evidence for paramagnetic (PM) Curie‐Weiss iron ions at the core surface, where the local Néel temperature is lower; these ions are apparently responsible for the weaker T1 shortening. In fact, the conversion of uncompensated AFM lattice ions to PM ions could explain the small number of SPM particles. The apparent Curie Law behavior of ferritin thus appears to be a coincidental result of different temperature dependences of the PM and SPM components.
Functional Imaging by I0‐ and T2* ‐parameter mapping using multi‐image EPI
Authors: Speck Oliver , Hennig Jürgen 
Published: March 2007

AbstractA new functional imaging method has been developed and used to measure T2*‐ and initial intensity (I0)‐parameter maps of multiple slices during activation of the cortex with high temporal resolution. Multiple echo‐planar images (EPls) are read out after a single excitation of the spin system, leading to several images with increasing effective echo times. Changes induced by primary visual stimulation in T2* and I0 were measured in eight subjects. Although stimulation‐induced increases in I0 only occurred at short repetition times, T2* increased from 57.3 to 60.9 ms on average. The method combines the high stability of a single shot EPI experiment with the high information content of a multiecho acquisition. In addition, stimulation‐induced changes in inflow can be easily separated from true blood oxygenation level dependent (BOLD) signal changes.
A new correlation‐based fuzzy logic clustering algorithm for FMRI
Authors: Golay Xavier , Kollias Spyros , Stoll Gautier , Meier Dieter , Valavanis Anton , Boesiger Peter 
Published: March 2007

AbstractFuzzy logic clustering algorithms are a new class of processing strategies for functional MRI (fMRI). In this study, the ability of such methods to detect brain activation on application of a stimulus task is demonstrated. An optimization of the selected algorithm with regard to dtfferent parameters is proposed. These parameters include (a) those defining the preprocessing procedure of the data set; (b) the definition of the distance between two time courses, considered as p‐dimensional vectors, where p is the number of sequential images in the fMRl data set; and (c) the number of clusters to be considered. Based on the assumption that such a clustering algorithm should cluster the pixel time courses according to their similarity and not their proximity (in terms of distance), cross‐correlation‐based distances are defined. A clear mathematical description of the algorithm is proposed, and its convergence is proven when similarity measures are used instead of conventional Euclidean distance. The differences between the membership function given by the algorithm and the probability are clearly exposed. The algorithm was tested on artificial data sets, as well as on data sets from six volunteers undergoing stimulation of the primary visual cortex. The fMRl maps provided by the fuzzy logic algorithm are compared to those achieved by the well established cross‐correlation technique.
Effects of acceleration, jerk, and field inhomogeneities on vessel positions in magnetic resonance angiography
Authors: Stefansic James D. , Paschal Cynthia B. 
Published: March 2007

AbstractBlood flow and magnetic field inhomogeneities lead to distortions in MR angiography (MRA) images that present added risk for stereotactic neurosurgical applications. These effects are demonstrated in an MRA image of a model of cerebrovas‐culature. Analysis of the effects of velocity, acceleration, jerk, and field inhomogeneities on vessel position is presented; results are used to predict vessel shifts for several cerebral blood vessels. The actual encoded position for flowing spins is shown to be a moment‐weighted average position. Maximum shift of 3.11 mm was reduced to 0.05 mm when velocity compensation was added. Velocity compensation applied specifically in the phase‐encoding direction reduces flow‐dependent shifts to the point that they can be safely ignored even if acceleration and jerk are present. Those prescribing and using MRA images for stereotactic applications must be aware of whether compensation is actually applied along the phase‐encoding axis when a flow‐compensated sequence is used.
Chemically induced analgesic nephropathy in the rat monitored by proton‐electron double‐resonance imaging (PEDRI)
Authors: Seimenis Ioannis , Foster Margaret A. , Lurie David J. , Hutchison James M. S. , Whiting Paul H. , Payne Simon 
Published: March 2007

AbstractProton‐electron double‐resonance imaging (PEDRI) was used to assess renal function by monitoring the flow of the exogenous nitroxide free radical proxyl carboxylic acid (PCA) through normal and injured kidneys in the living rat. Kidney damage was induced by treatment with 2‐bromoethylamine (BEA), which provides a well established model for human analgesic nephropathy. PCA clearance rates for liver, abdominal blood vessels, and renal tissues were determined from serial PEDRI images of normal rats (n = 6) and rats treated with BEA (n = 21). Different groups of BEA‐treated animals were imaged on day 4 (n = 6), day 6 (n = 6), and day 9 (n = 9) after treatment. In BEA‐treated rats, there was an increase in PCA half‐life in all tissues studied. This increase was greatest in the kidney tissues and the effect progressed with time after treatment. The effect is probably due to BEA‐induced damage to the tubules in the renal cortex and may not be related to the primary lesions in the renal medulla.
Intracranial black‐blood MR angiography with high‐resolution 3D fast spin echo
Authors: Alexander Andrew L. , Buswell Henry R. , Sun Yi , Chapman Brian E. , Tsuruda Jay S. , Parker Dennis L. 
Published: March 2007

AbstractThree‐dimensional fast spin‐echo (3DFSE) techniques are promising for black‐blood imaging of cerebral vessels. In this study, flow‐related signal dephasing was demonstrated as the primary mechanism for blood signal attenuation. Parameter optimization of TR (1500 to 3000 ms), receiver bandwidth (25 to 31.25 kHz), effective TE (25.7 to 30.1 ms), and ETL (7 to 8) was accomplished by making measurements of vessel‐totissue contrast‐to‐noise ratios on vessels. A comparison of high‐resolution 3DFSE and 3DTOF magnetic resonance angiography demonstrated that 3DFSE can generate images with equivalent or better small vessel detail than conventional techniques. 3DFSE black‐blood techniques may provide improved sensitivity of small arteries and veins with slow or in‐plane flow and immunity to flow‐related distortions. Future studies with optimized parameters will determine the clinical efficacy of this technique.
Single‐shot, variable flip‐angle slice‐selective excitation with four gradient‐modulated adiabatic half‐passage segments
Authors: Hsu Edward W. , Reeder Scott B. , MacFall James R. 
Published: March 2007

AbstractAdiabatic pulses, although useful in generating uniform spin nutation in the presence of inhomogeneous B1 fields, are limited for NMR imaging applications due to the lack of slice‐selective excitation capability. Selective excitation techniques using gradient modulation have been introduced; however, present methods require either a minimum of two excitations or eight adiabatic segments. Here, a scheme is presented that allows single‐shot, arbitrary flip‐angle, and slice‐selective excitation with only four adiabatic half‐passage segments. The technique is demonstrated via computer simulation and experimental tests on a phantom. Furthermore, issues associated with the implementation of these gradient‐modulated adiabatic pulses are discussed.
Proton spectroscopy without water suppression: The oversampled J‐resolved experiment
Authors: Hurd Ralph E. , Gurr David , Sailasuta Napapon 
Published: March 2007

AbstractA method is introduced for obtaining proton spectra in vivo with all the advantages of a full water signal. The method, based on F1 oversampled J‐resolved spectroscopy, makes it possible to separate metabolite signals from unwanted baseline artifacts. The dominant water resonance is used as a 2D reference signal for the phase‐sensitive reconstruction of the 2D J‐resolved metabolite spectra. The powerful specificity of this method is demonstrated with model compound spectra, phantoms, and in vivo examples.
A theoretical and experimental comparison of continuous and pulsed arterial spin labeling techniques for quantitative perfusion imaging
Authors: Wong Eric C. , Buxton Richard B. , Frank Lawrence R. 
Published: March 2007

AbstractUnder ideal conditions, continuous arterial spin labeling (ASL) techniques are higher in SNR than pulsed ASL techniques by a factor of e. Presented here is a direct theoretical and experimental comparison of continuous ASL and pulsed ASL, using versions of both that are amenable to multislice imaging and insensitive to variations in transit times (continuous ASL with a delay before imaging, and QUIPSS II (Quantitative Imaging of Perfusion Using a Single Subtraction–second version)). Perfusion image quality for comparable imaging time was nearly identical for both single‐slice and multislice imaging. The measured raw signal was approximately 25% higher with continuous ASL, but the SNR per unit time was identical.
Quantitative spectroscopic imaging of the human brain
Authors: Pan Jullie W. , Twieg Donald B. , Hetherington Hoby P. 
Published: March 2007

AbstractA method to provide B1 correction and cerebrospinal fluid (CSF) referencing is developed and applied to spectroscopic imaging of the human brain at 4.1 T using a volume head coil. The B1 image allows rapid determination of the spatially dependent B1 that is then used to compensate for the B1 sensitivity of the spectroscopic sequence. The reference signal is acquired from CSF located in a lateral ventricular position using a point‐resolved echo spectroscopy (PRESS) acquisition. The CSF spectrum is also corrected for B1 dependence. Together with T2 and T1 corrections, this method is used to provide quantitative values of N‐acetylaspartate (NAA), creatine (Cr), and choline (Ch). The metabolite concentrations obtained from a spectroscopic imaging slice through the ventricles in seven normal controls are in good agreement with previously published literature values. This method is applied in a patient with secondary progressive multiple sclerosis, showing separate areas of abnormalities in both NAA and Cr.
Sodium multiple quantum spectroscopy of articular cartilage: Effects of mechanical compression
Authors: Duvvuri Umamaheswar , Kaufman Jonathan H. , Patel Saurabh D. , Bolinger Lizann , Kneeland J. Bruce , Leigh John S. , Reddy Ravinder 
Published: March 2007

AbstractThe effects of mechanical compression on the multiple quantum coherences generated from sodium ions in articular cartilage were investigated. Cartilage samples obtained from bovine patellae were studied during compression at 0.7 MPa (100 psi) for 1 hour. The double quantum filtered spectra showed marked lineshape changes in the compressed samples. Compression did not seem to influence the lineshapes of the single quantum and triple quantum filtered spectra significantly. We found that the residual quadrupolar interaction was reduced in the compressed samples. Changes in the ordering of collagen fibers may be responsible for the observed effect.
Quantitative assessment of improved homogeneity using higher‐order shims for spectroscopic imaging of the brain
Authors: Spielman Daniel M. , Adalsteinsson Elfar , Lim Kelvin O. 
Published: March 2007

AbstractMagnetic field homogeneity is of major concern for in vivo spectroscopy, and with the increased use of volumetric chemical shift imaging (CSI) techniques, the ability to shim over a large volume of tissue is now one of the primary limiting constraints in performing these studies. In vivo shimming is routinely performed using linear shim correction terms, and although many scanners are also equipped with additional resistive shim supplies that can provide second and third‐order shim fields, they are often not used due to the additional effort and scan time required. The question as to how much improvement can be achieved using additional higher‐order shims compared with the linear shims alone was quantitatively addressed. Performance measures for both intervoxel B0 uniformity and intravoxel T2* line broadening were evaluated for 15 normal volunteers. The analysis tools developed in this study, along with the summarized data, can be useful in deciding if a given application warrants the additional time, effort, and expense (if additional hardware needs to be purchased) of Implementing higher‐order shimming routines. For CSI studies of the brain, the use of the higher‐order shims, compared with linear terms alone, yielded approximately 30% greater volume of brain tissue that could be shimmed within typical constraints for intervoxel B0 shifts and intravoxel T2* linebroadening. In addition, a regional analysis shows significant improvement in the homogeneity within specific areas of the brain, particularly those near the skull.
A general kinetic model for quantitative perfusion imaging with arterial spin labeling
Authors: Buxton Richard B. , Frank Lawrence R. , Wong Eric C. , Siewert Bettina , Warach Steven , Edelman Robert R. 
Published: March 2007

AbstractRecently, several implementations of arterial spin labeling (ASL) techniques have been developed for producing MRI images sensitive to local tissue perfusion. For quantitation of perfusion, both pulsed and continuous labeling methods potentially suffer from a number of systematic errors. In this study, a general kinetic model for the ASL signal is described that can be used to assess these errors. With appropriate assumptions, the general model reduces to models that have been used previously to analyze ASL data, but the general model also provides a way to analyze the errors that result if these assumptions are not accurate. The model was used for an initial assessment of systematic errors due to the effects of variable transit delays from the tagging band to the imaging voxel, the effects of capillary/tissue exchange of water on the relaxation of the tag, and the effects of incomplete water extraction. In preliminary experiments with a human subject, the model provided a good description of pulsed ASL data during a simple sensorimotor activation task.
Induction of apoptosis in two mammalian cell lines results in increased levels of fructose‐1,6‐Bisphosphate and CDP‐choline as determined by 31P MRS
Authors: Williams Shane N. O. , Anthony Maria L. , Brindle Kevin M. 
Published: March 2007

AbstractProgrammed cell death or apoptosis was induced in human promyelocytic leukemia (HL‐60) and Chinese hamster ovary (CHO‐K1) cells using several cytotoxic drugs that have different modes of action, including camptothecin, ceramide, chelerythrine, etoposide, farnesol, geranyl geraniol, and hexadecylphosphocholine. The consequent changes in cellular metabolism were monitored using 31P MRS measurements on intact cells and cell extracts. Cells undergoing programmed cell death exhibited characteristic changes in the levels of glycolytic and phospholipid metabolites. The most significant changes were increases in the concentration of the glycolytic intermediate, fructose‐l,6‐bisphosphate and in the concentration of CDP‐choline, which is an intermediate in phosphatidylcholine biosynthesis. In HL‐60 cells, the increase in fructose‐l,6‐bisphosphate levels could be explained by depletion of cellular NAD(H) levels. All of the agents used to induce apoptosis caused the accumulation of CDP‐choline. Since the resonances of this compound occur in a relatively well resolved region of tissue spectra, it could provide a marker for apoptosis that would allow the noninvasive detection of the process in vivo using 31P MRS measurements.
A programmable pre‐emphasis system
Authors: Gach H. Michael , Lowe Irving J. , Madio David P. , Caprihan Arvind , Altobelli Stephen A. , Kuethe Dean O. , Fukushima Eiichi 
Published: March 2007

AbstractMRI systems often use magnetic field gradient and shim pulse‐shaping networks (pre‐emphasis) to correct for magnetic field distortions caused by eddy currents. A pre‐emphasis system that uses up to 16 fixed resistor‐capacitor (RC) time constants per channel with programmable amplitude coefficients is described. The magnetic fields induced by the pre‐emphasis RC time constants serve as a set of basis functions for compensating eddy‐current fields induced by the gradient set. The resultant time‐varying magnetic field gradient accurately reflects the gradient specified by the pulse programmer. Reductions in eddy‐current fields are demonstrated for actively shielded and unshielded gradient sets.
Asymmetric spin‐echo imaging of magnetically inhomogeneous systems: Theory, experiment, and numerical studies
Authors: Stables Lara A. , Kennan Richard P. , Gore John C. 
Published: March 2007

AbstractThe ability of the asymmetric spin‐echo (ASE) pulse sequence to provide different degrees of spin‐echo (SE)‐type and gradient‐echo (GE)‐type contrast when imaging media containing magnetic inhomogeneities is investigated. The dependence of the ASE signal on the size of magnetic field perturbers is examined using theory, computer simulations, and experiment. A theoretical prediction of the ASE signal is obtained using the Anderson‐Weiss mean field theory, the results of which are qualitatively supported by computer simulations and experimental studies. It is shown that the ASE sequence can be used to tune the range of perturber sizes that provide the largest contributions to susceptibility contrast effects.
Ex vivo tissue‐type independence in proton‐resonance frequency shift MR thermometry
Authors: Peters Rober T. D. , Hinks R. Scott , Henkelman R. Mark 
Published: March 2007

AbstractThe temperature sensitivity of the proton‐resonance frequency (PRF) has proven valuable for the monitoring of MR image‐guided thermal coagulation therapy. However, there is significant inconsistency in reported values of the PRF‐thermal coefficient, as measured from experiments encompassing a range of in vivo and ex vivo tissue types and experimental conditions. A method of calibrating the temperature dependence of the PRF is described and results are presented that indicate a tissue‐type independence. To this end, other possible mechanisms for variations in the PRF‐thermal coefficient are suggested, including physiological perturbations and volume magnetic susceptibility effects from geometry and orientation.
In vivo perfusion measurements in the human placenta using echo planar imaging at 0.5 T
Authors: Gowland Penny A. , Francis Susan T. , Duncan Keith R. , Freeman Alan J. , Issa Bashar , Moore Rachel J. , Bowtell Richard W. , Baker Philip N. , Johnson Ian R. , Worthington Brian S. 
Published: March 2007

AbstractThis paper presents the first in vivo measurements of perfusion in the human placenta from 20 weeks gestational age until term, using the non‐selective/selective inversion recovery echo‐planar imaging sequence, in which data is alternately acquired following a selective and non‐selective inversion pulse. Twenty pairs of images were collected, two each at the following inversion times: 20, 310, 610, 910, 1110, 1410, 1910, 2810, 3310, and 4510 ms with the sequence being repeated with a repetition time (TR) of 10 s. The results of these measurements were used to suggest the optimum sequence for future work in terms of the signal to noise ratio in the measured perfusion rate in a given measurement time. The sequence was also analyzed to determine the expected variability in the measurements. In normal pregnancies the average value of perfusion rate was found to be 176 (standard error = ±24) ml/100 mg/min. (n = 16, standard deviation = 96 ml/100 mg/min). The expected variability in the measured parameters due to signal to noise ratio considerations alone was calculated to be 71%. For a maximum scanning time of 400 s, the optimum sequence for measuring placental perfusion was found to require 8 repetitions at each of 10 inversion times which were geometrically spaced (given by a0 a0r0 a0r2 a0r3,…), with a0 = 850 ms, r = 1.073 and TR = 5 s, giving a pixel variability of 38%. Other timing schemes are recommended for measuring perfusion in other anatomical regions with different values of perfusion rate and longitudinal relaxation time.
Reduced circular field‐of‐view imaging
Authors: Scheffler Klaus , Hennig Jürgen 
Published: March 2007

AbstractA rapid dynamic imaging technique based on polar k‐space sampling is presented. A gain in temporal resolution is achieved by angular undersampling. A detailed analysis of the point spread function of angular undersampled polar imaging reveals a reduced diameter of the corresponding circular field of view. Under the assumption that dynamic changes are restricted to a local circular field of view, angular under‐sampled dynamic imaging allows the recording of rapid changes at high temporal and spatial resolution. The theoretical and experimental details of the technique are presented.
ESR spectroscopy for analysis of hippocampal elimination of a nitroxide radical during kainic acid‐induced seizure in rats
Authors: Ueda Yuto , Yokoyama Hidekatsu , Ohya‐Nishiguchi Hiroaki , Kamada Hitoshi 
Published: March 2007

AbstractTo analyze the balance between free radical production and elimination during seizure, techniques were developed to monitor the sequential changes in the level of an exogenous free radical by ESR in the brains of freely moving rats given kainic acid (KA) to induce seizures (n = 6) and control rats given saline (n = 6). The hippocampus of each rat was perfused with a nitroxide radical solution for 120 min by in vivo microdialysis. Then an intraperitoneal injection of KA or the physiological saline was given to each rat, and the perfusate was changed to Ringer's solution. ESR analysis of sequential samples of dialysate taken after injection revealed an exponential decay in signal amplitude. The median half‐life of the nitroxide radical was significantly longer in the KA‐treated group than in the control group (P < 0.01). This finding demonstrates a decreased capacity of the hippocampus to eliminate the nitroxide radical from the extracellular space during seizure and may help clarify the mechanism of neuronal cell vulnerability to free radicals during insult or degeneration.
Partial volume effects on vascular T2 measurements
Authors: Stainsby Jeff A. , Wright Graham A. 
Published: March 2007

AbstractQuantitative, vascular T2 measurements are of interest for applications such as MR oximetry. In the situation of a vessel with long T2 relaxation times embedded in tissue with relatively short T2 values, contamination of the blood signal from the surrounding tissue can bias T2 measurements. Limited data sampling and vessels running obliquely through the imaging slice can cause significant signal contamination. Using a model of these effects to predict the behavior of T2 measurements under a range of conditions, a set of parameters that provides the best combination of measurement accuracy with a signal‐to‐noise ratio as high as possible is proposed.