bluuebunny/crossref_metadata_2025_split huggingface dataset:
In Vivo detection of a boron‐neutron‐capture agent in melanoma by proton observed 1H ‐ 10B double resonance
Authors: Bendel Peter , Zilberstein Judith , Salomon Yoram 
Published: March 2007

AbstractThe Cesium salt of BSSB (Cs4B24H22S2), a common boron‐neutron‐capture‐therapy (BNCT) agent, was injected into M2R mouse melanoma xenografts, and detected in vivo by 1H‐observed, 10B‐edited NMR spectroscopy. The technique of spin‐echo difference spectroscopy, in which a proton spin‐echo is detected following the alternating presence and absence of a 10B 180° pulse was used. This method provides much higher sensitivity than direct 10B NMR detection, and should thus be suitable for in vivo detection in patients about to undergo BNCT treatment, where the infused agents are 95% isotopically enriched in 10B.
Intracellular and extracellular spaces and the direct quantification of molar intracellular concentrations of phosphorus metabolites in the isolated rat heart using 31P NMR spectroscopy and phosphonate markers
Authors: Clarke Kieran , Anderson Russell E. , Nédélec Jean‐François , Foster David O. , Ally Ariff 
Published: March 2007

AbstractTo quantify metabolite and cation concentrations using NMR spectroscopy, the volumes of intracellular and extracellular spaces must be known. We describe a simple 31P NMR spectroscopic method that employs dimethyl methylphosphonate (DMMP) as a marker of total water space and phenylphosphoriate (PPA) as a marker of extracellular space to determine intracellular and extracellular space volumes in the isolated, perfused rat heart. In vivo and in vitro radiolabel studies were used to verify this method. The difference between the total and extracellular water spaces, determined as milliliters/heart, gave the intracellular volume and allowed direct calculation of myocardial creatine phosphate, ATP, and inorganic phosphate concentrations, which were 13.4 mM, 10.1 mM, and 3.4 mM, respectively, for the glucose‐perfused rat heart. The extracellular volume decreased by 84% in hearts subjected to 28 min total, global ischemia and increased by 15% during reperfusion. The method described allows the determination of intracellular energy metabolite concentrations in perfused rat heart directly from a single, fully relaxed 31P NMR spectrum.
Avoiding peripheral nerve stimulation: Gradient waveform criteria for optimum resolution in echo‐planar imaging
Authors: Harvey Paul R. , Mansfield Peter 
Published: March 2007

AbstractAdaptation of Mansfield and Harvey's theory of magnetically induced neural stimulation indicates that, for trapezoidal gradient waveforms and at the relatively low modulation frequencies commonly used in echo‐planar imaging, an increase in rise time even to the point of creating a triangular waveform can prove advantageous over the use of simple sinusoidal modulation. For example, a higher image resolution is in principle possible before the neural stimulation limit is reached. For higher modulation frequencies and fast ramp trapezoidal waveforms, the peak gradient can be lower than that for a sinusoidal waveform by a factor approaching 2/π for equal resolution. This means that by using a multimode resonant gradient drive, the amplifier power requirements are greatly relaxed. The signal sampling bandwidth required is also lower, because, due to the trapezoidal nonlinear sample pattern, sample points are spaced linearly during the waveform plateaus.
Localized two‐dimensional shift correlated spectroscopy in humans at 2 Tesla
Authors: Brereton Ian M. , Galloway Graham J. , Rose Stephen E. , Doddrell David M. 
Published: March 2007

AbstractA method for the acquisition of localized 2D shift‐correlated spectra, based on the combination of the stimulated‐echo volume‐selection and gradient‐enhanced COSY experiments, is described. The sequence can be modified to perform a number of localized experiments including HOHAHA and DQF‐COSY. The method is demonstrated in vivo by presentation of localized COSY and HOHAHA spectra of human tibia marrow, and a localized COSY spectrum of human brain acquired at a field strength of 2 Tesla. Cross peaks corresponding to correlations between coupled groups along the acyl chains of triglycerides are observed in the spectra of marrow. The major cerebral metabolites are represented in the in vivo COSY brain spectrum, including N‐acetylaspartate, glutamate/glutamine, total creatine, aspartate, and myo‐inositol. Difficulties in the implementation of localized shift‐correlation spectroscopy, including water suppression and T2 relaxation, are discussed.
On the field inhomogeneity of a birdcage coil
Authors: Jin Jianming , Shen Gary , Perkins Thomas 
Published: March 2007

AbstractA mathematical model is developed for the numerical analysis of birdcage coils constructed using capacitors having different capacitance. With the aid of this model, it is shown that the deviation of some capacitance introduced by tune, balance, and drive mechanisms can cause inhomogeneity in the B1, field produced by the coil. Useful curves and formulae are developed to provide a guideline for the design of birdcage coils.
Fast volume scanning with frequency‐shifted burst MRI
Authors: Duyn Jeff H. , van Gelderen Peter , Liu Guoying , Moonen Chrit T. W. 
Published: March 2007

AbstractWe introduce a modified BURST imaging technique with reduced saturation effects and improved signal‐to‐noise ratio. The method applies a frequency shift to the RF excitation pulse on successive repetitions. It allows collection of 3D datasets of human brain within a few seconds, on a standard clinical scanner at 1.5 Tesla.
Abstract scoring for the annual SMR program: Significance of reviewer score normalization
Authors: Glover Gary H. , Henkelman R. Mark 
Published: March 2007

AbstractPresently, the scores of three to four reviewers of each abstract are averaged and form a major component of the input for decisions made in choosing papers for oral and poster presentations, and in rejecting others. No normalization is made for differences in either mean or standard deviation between the reviewers of the same abstracts. In this paper, several techniques for normalizing the scores of reviewers are examined, and the consequences of applying such normalization is to several categories of the 1994 abstract submissions are examined. It was found that some alterations in the acceptance and assignments of papers as oral and posters resulted for one of the categories, and the normalized scores were used during the program assembly. It is recommended that future review procedures utilize reviewer normalization.
Assessment of absolute metabolite concentrations in human tissue by31P MRS invivo. Part I: Cerebrum, cerebellum, cerebral gray and white matter
Authors: Buchli Reto , Duc Corinne O. , Martin Ernst , Boesiger Peter 
Published: March 2007

AbstractAbsolute metabolite concentrations were determined in four different brain regions using phosphorus magnetic resonance spectroscopy (31P MRS) on 10 healthy adult volunteers. Localized spectra were collected simultaneously from the cerebellum and the cerebrum and, later, from deep white matter and cortical gray matter by means of a two‐volume lSlS pulse sequence and a Helmholtz‐type RF‐coil. Each brain spectrum was quantified with a calibration spectrum from a head‐shaped simulation phantom. A time‐domain fitting routine was used to process the fully relaxed data. Several metabolite concentrations (mmolAiter) differed significantly between the cerebrum and the cerebellum (PME = 3.2 f 0.3 and 4.0 & 0.6, PC:r = 2.9 & 0.3 and 3.9 f 0.4, NTP = 2.9 f 0.2 and 2.6 & 0.2, respectively) and between cortical gray matter and deep white matter (PME = 3.1 f 0.4 and 4.3 ± 0.8, PDE = 10.1 f 2.5 and 14.2 & 2.6, respectively). The concentration of free magnesium ion was found to be similar in all four brain regions (0.53 ± 0.21 mmol/liter) but the intracellular pH was significantly higher in the cerebellum (7.04 ± 0.03) than in the cerebrum (6.99 ± 0.02).
Transition from lorentzian to gaussian line shape of magnetization transfer spectrum in bovine serum albumin solutions
Authors: Iino Maisaaki 
Published: March 2007

AbstractMagnetization transfer experiments using an off‐resonance irradiation technique were performed on bovine serum albumin solutions by varying the irradiation frequency and the concentration. A transition of the magnetization transfer spectrunr from Lorentzian to Gaussian line shape was observed around the critical concentration of 6.2 mmoles of protein to kg ad solution. Observed magnetizations were well expressed by the rate equations of populations for spins below and above the transition, which yielded the magnetization transfer rates, the intrinsic relaxation rates of both protein and water protons, and the effective tumbling time and the rigid line width of the protein. The result showed that the estimates of the values for magnetization transfer rate do not change once the critical concentration is reached.
The design and test of a new volume coil for high field imaging
Authors: Wen Han , Chesnick Andrew S. , Balaban Robert S. 
Published: March 2007

AbstractA major problem in the development of high field (>100 MHz) large volume (>6000 cm3) MR coils is the interaction of the coil with the subject as well as the radiation loss to the environment. To reduce subject perturbation of the coil resonance modes, a volume coil that uses an array of freely rotating resonant elements radially mounted between two concentric cylinders was designed for operation at 170 MHz. Substantial electromagnetic energy is stored in the resonant elements outside the sample region without compromising the efficiency of the overall coil. This stored energy reduces the effect of the subject on the circuit and maintains a high Q, facilitating the tuning and matching of the coil. The unloaded Q of the coil is 680; when loaded with a head, it was 129. The ratio of 5.3 of the unloaded to loaded Q supports the notion that the efficiency of the coil was maintained in comparison with previous designs. The power requirement and signal‐to‐noise performance are significantly improved. The coil is tuned by a mechanism that imparts the same degree of rotation on all of the elements simultaneously, varying their degree of mutual coupling and preserving the overall coil symmetry. A thin radiofrequency shield is an integral part of the coil to reduce the radiation effect, which is a significant loss mechanism at high fields. MR images were collected at 4T using this coil design with high sensitivity and B1, homogeneity.
Selective saturation in magnetization transfer experiments
Authors: McGowan Joseph C. , Leigh John S. 
Published: March 2007

AbstractThe concept of magnetic saturation in single and binary spin systems is essential to the understanding of magnetization transfer experiments. This paper outlines the requirements for selective magnetic saturation of either of two spin pools contained in a mixture, both having identical chemical shifts. Following a brief discussion of saturation in a homogeneous sample, simple relationships are derived that predict the maximum degree of selective saturation in a two‐spin nonexchanging system. Optimal saturation conditions are described in terms of the intrinsic relaxation parameters as well as the experimental conditions of saturation offset frequency and amplitude. In addition, a novel method is proposed that may be applied to saturate the “free” water as opposed to the “bound” water spins in a magnetization transfer experiment. Saturation in an exchanging system is well approximated by these relationships under some physiologically relevant conditions, examples of which are provided. Application of the relationships presented may be useful in the design of experiments to produce maximum magnetization transfer.
MR gradient echo imaging of intravascular blood oxygenation: T2* determination in the presence of flow
Authors: Chien Daisy , Levin David L. , Anderson Charles M. 
Published: March 2007

AbstractThe T2* relaxation time of blood varies with its oxygen saturation. To evaluate the feasibility of imaging intravascular blood oxygenation in humans using a conventional 1.5T MR system, we have implemented a method to measure T2* of blood despite the presence of pulsatile flow. The method was tested in a) stationary and flow phantoms, b) blood samples at different levels of oxygen saturation, and c) a human hypoxia model. Our results demonstrate the ability of cardiac‐triggered, flow compensated gradient echo imaging to obtain reproducible T2* measurements of flowing blood in vivo.
Water diffusion in the giant axon of the squid: Implications for diffusion‐weighted MRI of the nervous system
Authors: Beaulieu Christian , Allen Peter S. 
Published: March 2007

AbstractTo clarify the result that marked diffusional anisotropy had been found in nonmyelinated nerve, and in completion of an evaluation of the role of all longitudinal axonal structures, we report NMR measurements of water diffusion in the giant axon of the squid, where diffusional anisotropy is determined by the neurofilamentary structure. The diffusion coefficients of water parallel and perpendicular to the long axis of the squid giant axon at 20°C are (1.61 ± 0.06) × 10−5 cm2 s−1 and (1.33 ± 0.09) × 10−5 cm2 s−1, respectively, which yield an anisotropic diffusion ratio of 1.2 2 0.1. Water diffusion in the squid giant axon is therefore quite rapid and nearly isotropic, thus eliminating the possibility of a significant role for the longitudinally oriented neurofilaments in producing diffusional anisotropy within the axoplasm. In conjunction with our work on garfish nerves therefore, only membranes, either as numerous axonal membranes or as myelin (if present), remain to fulfill the role of the primary determinant of anisotropic water diffusion in nerve and in white matter.
Anisotropy of NMR properties of tissues
Authors: Henkelman R. Mark , Stanisz Greg J. , Kim Jae K. , Bronskill Michael J. 
Published: March 2007

AbstractOrientational anisotropy of T2 and T1 relaxation times, diffusion, and magnetization transfer has been investigated for six different tissues: tendon, cartilage, kidney, muscle, white matter, and optic nerve. Relaxation anisotropy was observed for tendon and cartilage, and diffusional anisotropy was measured in kidney, muscle, white matter, and optic nerve. All other NMR measurements of these tissues showed no orientational dependence. This pattern of NMR anisotropies can be interpreted from the underlying geometrical structures of the tissues.
Real‐time motion detection in spiral MRI using navigators
Authors: Sachs Todd S. , Meyer Craig H. , Hu Bob S. , Kohli Jim , Nishimura Dwight G. , Macovski Albert 
Published: March 2007

AbstractA technique has been developed whereby motion can be detected in real time during the acquisition of data. This enables the implementation of an algorithm to accept or reject and reacquire data during a scan. Frames of data with motion are rejected and reacquired on the fly so that by the end of the scan, a complete motion‐free data set has been acquired. The algorithm has been implemented on several different types of sequences. Preliminary in vivo studies indicate that motion artifacts are dramatically reduced.
Quantitative analysis of multi‐slice Gd‐DTPA enhanced dynamic MR images using an automated simplex minimization procedure
Authors: Buckley David L. , Kerslake Robert W. , Blackband Stephen J. , Horsman Anthony 
Published: March 2007

AbstractQuantitative analysis of Gd‐DTPA enhanced dynamic MR images has potential for discriminating lesions, especially because the introduction of clinical fast imaging techniques has enabled good sampling of the relatively rapid Gd‐DTPA wash‐in curves. Analysis of such data requires curve fitting to a nonlinear model, which to date has been performed using a nonlinear least squares (NLLS) fitting procedure. However, this method often fails to converge to the appropriate minima without good initial parameter estimates when multi‐exponential models are involved, making automated analysis of complete multislice or volume data sets problematic. In this report we demonstrate the robust performance of a simplex minimization procedure compared with NLLS, by the method of Marquardt, using a Monte Carlo simulation. Further, we illustrate the applicability of such a technique to the analysis of dynamic contrast enhanced images on a pixel‐by‐pixel basis. As a preliminary example, the technique is applied to a breast lesion but is expected to be suitable for examination of many lesion types.
Detection of apparent restricted diffusion in healthy rat brain at short diffusion times
Authors: Niendorf Thoralf , Norris David G. , Leibfritz Dieter 
Published: March 2007

AbstractThe application of bipolar diffusion sensitizing gradient pulses to significantly reduce the diffusion time is described. This approach is combined with the rapid U‐FLARE imaging sequence. Three diffusion‐sensitized types of experiments are compared and their suitability for detecting restricted diffusion is discussed. Experiments using a modification of the diffusion weighting by varying the diffusion time between 1.6 and 6.0 ms obtained nonmonoexponential signal attenuation curves from both healthy brains and postmortem. This behavior is indicative of restricted diffusion, but as it is detectable only at short diffusion times, in contrast to a restriction due to impermeable barriers, we have termed this “apparent restriction”.
A gradient scheme suitable for localized shimming and in vivo1H/31P STEAM and ISIS NMR spectroscopy
Authors: Yongbi Ngong M. , Payne Geoffrey S. , Leach Martin O. 
Published: March 2007

AbstractA gradient scheme is presented which may be used for STEAM or ISIS localization. One application of the scheme is to perform single‐shot STEAM shimming prior to data acquisition with STEAM and ISIS, using identical gradient amplitudes and durations. Using conventional STEAM to shim for ISIS can produce line‐shape distortions induced by different eddy currents in the two sequences; with this gradient scheme the problem is minimized. Line‐shape improvements of STEAM and ISIS localized data obtained after volume localized shimming with the proposed STEAM sequence are demonstrated. The localization performance of the STEAM and ISIS sequences are demonstrated on phantoms and in vivo for 1H and 31P metabolites.
A strategy for sampling on a sphere applied to 3D selective RF pulse design
Authors: Wong Sam T. S. , Roos Mark S. 
Published: March 2007

AbstractConventional constant angular velocity sampling of the surface of a sphere results in a higher sampling density near the two poles relative to the equatorial region. More samples, and hence longer sampling time, are required to achieve a given sampling density in the equatorial region when compared with uniform sampling. This paper presents a simple expression for a continuous sample path through a nearly uniform distribution of points on the surface of a sphere. Sampling of concentric spherical shells in k‐space with the new strategy is used to design 3D selective inversion and spin‐echo pulses. These new 3D selective pulses have been implemented and verified experimentally.
Breath‐Hold Projection Magnetic Resonance‐Cholangio‐Pancreaticography (MRCP): a New Method for the Examination of the Bile and Pancreatic Ducts
Authors: Laubenberger JÜRg , Büchert Martin , Schneider Britta , Blum Ulrich , Hennig JÜRgen , Langer Mathias 
Published: March 2007

AbstractBreath‐hold MR cholangio‐pancreaticography using the RARE method was evaluated as a noninvasive alternative to direct cholangio‐pancreaticography in 30 healthy volunteers and in 30 patients with various diseases of the respective duct systems. In contrast to 3D MR cholangiography, RARE MRCP generates projection images requiring a 4‐s acquisition time and no postprocessing. Diagnostic information gained from the cholangio‐pancreaticograms was fully equivalent to that of conventional x‐ray imaging by invasive procedures. Additional information was gained whenever endoscopic access was impossible and/or cystic malformations were present.
Echo‐Time Reduction for Submillimeter Resolution Imaging with a 3D Phase Encode Time Reduced Acquisition Method
Authors: Ying K. , Schmalbrock P. , Clymer B. 
Published: March 2007

AbstractTo achieve optimal image quality and highest spatial resolution for inner ear imaging with a 3D gradient echo sequence, it is necessary to minimize susceptibility dephasing effects by using very short TE. Fractional RF pulses and echoes can yield short TE for moderate spatial resolution; however, for voxel size of less than 1 mm, TE is limited by the phase encode gradients. We present a method to obtain very short effective TE by using short triangular shaped phase encode gradients to sample the central portions of k‐space and progressively longer trapezoidal gradients for the outer portions of k‐space. A 3D pulse sequence employing the modified phase encoding scheme for both in‐plane and slice phase encoding directions was implemented and tested on phantoms and in vivo. The effective TE equals the minimal TE used for the central k‐space portions. Submillimeter resolution (0.35 x 0.35 x 0.7 mm3) images of the inner ear were obtained with effective TE of 3.2 ms and were compared with standard 3D images with TE of 8 ms. With this pronounced TE reduction, the susceptibility artifacts at air/fluid interfaces are significantly reduced.
Measurements of Magnetic Field Variations in the Human Brain Using a 3D‐FT Multiple Gradient Echo Technique
Authors: Ericsson Anders , Weis Jan , Hemmingsson Anders , Wikström Mats , Sperber Göran O. 
Published: March 2007

AbstractA magnetic resonance 3DFT multiple gradient‐echo technique was used for measurements of the proton spectrum for each voxel in the measured slice. Water, fat, magnetic field and T2 distributions in the head of a normal volunteer and a patient with intracerebral hematoma were computed. Magnetic field variations caused by the head were calculated after correction for the static magnetic field inhomogeneity. Large local magnetic field variations up to 3 ppm were found in the human brain near interfaces between air or bone and brain tissues and 0.5 ppm between hematoma and brain tissue. Information about magnetic field variations could be useful for shimming procedures in vivo and for correcting artifacts in imaging and spectroscopy.
Magnetic Resonance Imaging and Magnetization Transfer in Experimental Myonecrosis in the Rat
Authors: Mattila Kimmo T. , Lukka Riitta , Hurme Timo , Komu Markku , Alanen Anu , Kalimo Hannu 
Published: March 2007

AbstractExperimental myonecrosi–induced by injection of notexin into rat tibialis anterior muscle–and subsequent regeneration were studied from 1 h to 20 days postinjury with magnetic resonance imaging using conventional and magnetization transfer sequences, and these findings were correlated with histopathology. MR images revealed necrosis within 1 h postinjection. Histopathologically, necrotized fibers enlarged and intercellular spaces widened, indicating intracellular and extracellular edema, which began to decrease after 48 h, whereafter the formation of new myofibers predominated. T2 increased progressively until 7.5 h, while T1 increased until 24 h. Magnetization transfer contrast (MTC) and magnetization transfer rate (Rwm) decreased rapidly postinjection; the decrease in Rwm lasted longer than in MTC (96 h versus 48 h, respectively). Spin echo, inversion recovery and magnetization transfer sequences revealed the lesions equally effectively. MR images and relaxation parameters reflect well the extent of histopathological injury and edema in the acute phase, whereas specific tissue changes in the regenerative phase were not detectable by MRI. MT imaging and especially magnetization transfer rate are as sensitive as conventional T2 contrast to alterations in water imbalance.