bluuebunny/crossref_metadata_2025_split huggingface dataset:
Migration and Accumulation of Silicone in the Liver of Women with Silicone Gel‐Filled Breast Implants
Authors: Pfleiderer Bettina , Garrido Leoncio 
Published: March 2007

Abstract1H NMR localized spectroscopy (STEAM), combined with echocardiography (ECG), respiratory gating, and water and fat suppression, was used to quantify silicone concentrations in the liver of women with silicone gel‐filled breast implants. Localized spectroscopy was performed on 15 patients with silicone gel‐filled breast prostheses and on eight volunteers with no implants. The 1H spectra in the liver of patients showed silicone resonances from 0.3 to −0.8 ppm, attributable to protons in the methyl groups of silicone. The presence of silicone in the liver could first be detected 3–4 years after breast prostheses implantation. No correlation between silicone concentrations and implantation times was observed. However, our results indicated that silicone concentrations may reflect implant integrity: detectable silicone concentrations in the liver appeared to be higher when the implants were ruptured than when the implants appeared intact. Moreover, new resonances in the range of −2.6 to −4 ppm were observed in most patients after long‐term implantation. As these species increase with implantation time, the new resonances may reflect chemically changed silicone (paramag‐netically shifted silicon complexes bound to iron) accumulated over time. The sensitivity of 1H NMR localized spectroscopy is sufficient to detect silicon concentrations as low as 0.20 mM. Results from one patient whose implants had been removed 14 months prior to the NMR examination showed no detectable silicone in the liver, indicating that it may have been excreted via bile or degraded to silica and high coordinated silicon complexes. Quantitative 1H localized spectroscopy of the liver in women with silicone gel‐filled breast implants may provide valuable information concerning silicone accumulation and degradation in vivo, as well as about the kinetics of its elimination from the body after implant removal.
Spatial Encoding and Reconstruction in MRI with Quadratic Phase Profiles
Authors: Pipe James G. 
Published: March 2007

AbstractApplication of a slice‐selective frequency modulated radio‐frequency excitation pulse in a magnetic resonance (MR) imaging experiment creates a quadratic phase profile along the direction of slice selection. This quadratic phase profile inherently localizes the signal contribution to its vertex, which can be shifted with the application of a linear magnetic field gradient. Different methods for reconstruction of the spatial profile are discussed. The point spread functions of these reconstructions are similar to that of conventional Fourier transforms; one important difference is the elimination of aliasing at the expense of MR signal amplitude when performing ‘local,’ or limited, reconstruction. Limited reconstruction together with spatially limited excitation combines some of the advantages of both three‐dimensional phase‐encoded and two‐dimensional multislice techniques in appropriate situations. Applications discussed are three‐dimensional gradient echo experiments applied to time of flight MR angiography and T2‐weighted data collection.
High Speed 1H Spectroscopic Imaging in Human Brain by Echo Planar Spatial‐Spectral Encoding
Authors: Posse Stefan , Tedeschi Gioacchino , Risinger Robert , Ogg Robert , Bihan Denis Le 
Published: March 2007

AbstractWe introduce a fast and robust spatial‐spectral encoding method, which enables acquisition of high resolution short echo time (13 ms) proton spectroscopic images from human brain with acquisition times as short as 64 s when using surface coils. The encoding scheme, which was implemented on a clinical 1.5 Tesla whole body scanner, is a modification of an echo‐planar spectroscopic imaging method originally proposed by Mansfield Magn. Reson. Med. 1, 370–386 (1984), and utilizes a series of read‐out gradients to simultaneously encode spatial and spectral information. Superficial lipid signals are suppressed by a novel double outer volume suppression along the contours of the brain. The spectral resolution and the signal‐to‐noise per unit time and unit volume from resonances such as N‐acetyl aspartate, choline, creatine, and inositol are comparable with those obtained with conventional methods. The short encoding time of this technique enhances the flexibility of in vivo spectroscopic imaging by reducing motion artifacts and allowing acquisition of multiple data sets with different parameter settings.
Proton Transverse Nuclear Magnetic Relaxation in Oxidized Blood: a Numerical Approach
Authors: Gillis Pierre , Petö Stéphane , Moiny Francis , Mispelter Joël , Cuenod Charles‐André 
Published: March 2007

AbstractWhen red blood cells are deoxygenated, hemoglobin, which is then transformed into deoxyhemoglobin or methemoglobin, becomes paramagnetic. The transverse nuclear magnetic relaxation rate of water protons is considerably enhanced by this chemical transformation. A general agreement exists about the origin of the phenomenon—local field inhomogene‐ities induced by paramagnetic centers randomly distributed within the cell—but the localization of the region that dominates the relaxation is unclear. We addressed this problem with a computer simulation devoted to the determination of transverse magnetic relaxation of water protons in the presence of superparamagnetic MRI contrast agent candidates. The simulation confirms an earlier experimental result that shares equitably the responsibility for the observed relaxation between intracellular and extracellular water.
Three‐Point Phase‐Contrast Velocity Measurements with Increased Velocity‐to‐Noise Ratio
Authors: Lee Adrian T. , Bruce Pike G. , Pelc Norbert J. 
Published: March 2007

AbstractWe describe a technique to increase the velocity‐to‐noise ratio (VNR) of phase‐contrast magnetic‐resonance velocity images based on making three measurements/flow encoding axis rather than the usual two. A phase‐aliased high first moment data set and a nonaliased low first moment data set are acquired, and the high‐moment data are phase unwrapped using the low‐moment data. The VNR of the resulting measurement is given by that of the high‐moment measurement and increases linearly with the first moment. A factor of 4 gain in VNR was observed with only a 50% increase in scan time. Thus, this method is a much more efficient way to increase VNR than simple averaging.
Effects of Myocardial Water Exchange on T1 Enhancement during Bolus Administration of MR Contrast Agents
Authors: Judd Robert M. , Atalay Michael K. , Rottman Gerald A. , Zerhouni Elias A. 
Published: March 2007

AbstractInterpretation of first‐pass myocardial perfusion studies employing bolus administration of T1 magnetic resonance (MR) contrast agents requires an understanding of the relationship between contrast concentration and image pixel intensity. The potential effects of myocardial water exchange rates among the intravascular, interstitial, and cellular compartments on this relationship are controversial. We directly studied these issues in isolated, nonbeating canine interventricular septa. Myocardial T1 was measured three times/s during bolus transit of intravascular (albumin‐Gd‐DTPA and poly‐lysine‐Gd‐DTPA) and extracellular (gadoteridol) contrast agents. For polylsine‐Gd‐DTPA, the peak changes in myocardial 1/T1 (ΔR1) scaled nonlinearly with perfusate contrast concentration whereas a linear relationship would be expected for fast water exchange among the vascular, interstitial, and cellular compartments. For all agents, the peak ΔR1 were much smaller than the values expected on the basis of fast myocardial water exchange. The data demonstrate that in isolated myocardial tissue, myocardial T1 enhancement during bolus administration of contrast can be strongly affected by myocardial water exchange for both intravascular and extracellular MR contrast agents.
Anomalous Transverse Relaxation in 1H Spectroscopy in Human Brain at 4 Tesla
Authors: Posse Stefan , Cuenod Charles Andre , Risinger Robert , Bihan Denis Le , Balaban Robert S. 
Published: March 2007

AbstractLongitudinal (T1) and apparent transverse relaxation times (T2) of choline‐containing compounds (Cho), creatine/phospho‐creatine (Cr/PCr), and N‐acetyl aspartate (NAA) were measured in vivo in human brain at 4 Tesla. Measurements were performed using a water suppressed stimulated echo pulse sequence with complete outside volume presaturation to improve volume localization at short echo times. T1‐values of Cho (1.2 ± 0.1 s), Cr (1.6 ± 0.3 s), and NAA (1.6 ± 0.2 s) at 4 Tesla in occipital brain were only slightly larger than those reported in the literature at 1.5 Tesla. Thus, TR will not adversely affect the expected enhancement of signal‐to‐noise at 4 Tesla. Surprisingly, apparent T2‐values of Cho (142 ± 34 ms), Cr (140 ± 13 ms), and NAA (185 ± 24 ms) at 4 Tesla were significantly smaller than those at 1.5 Tesla and further decreased when increasing the mixing interval TM. Potential contributing factors, such as diffusion in local susceptibility related gradients, dipolar relaxation due to intracellular paramagnetic substances and motion effects are discussed. The results suggest that short echo time spectroscopy is advantageous to maintain signal to noise at 4 Tesla.
Solid State Phosphorus‐31 Magnetic Resonance Imaging of Bone Mineral
Authors: Moore James R. , Garrido Leoncio , Ackerman Jerome L. 
Published: March 2007

AbstractChemically selective solid state phosphorus‐31 nuclear magnetic resonance (NMR) imaging of the mineral phase of bone and synthetic calcium phosphate models for bone mineral is demonstrated with microscopy‐scale (about 5 mm field of view) apparatus at 6.0 T magnetic field strength. Pixel‐by‐pixel linear combination of image data from multiple radio frequency (RF) pulse sequences, chosen to develop contrast between chemical constituents of interest in the mineral, generates derived images showing the distribution of individual constituents. The technique combines the noninvasive character of magnetic resonance imaging (MRI) with the ability of solid state NMR spectroscopy to characterize subtle chemical variations in bone mineral, as well as to measure the amount of mineral. These methods are, in principle, extensible to larger dimensional scales suitable for live animal subjects or human limbs.
Optimized Ultra‐Fast Imaging Sequence (OUFIS)
Authors: Zha Leping , Lowe Irving J. 
Published: March 2007

AbstractThe DUFIS sequence can make ultra‐fast images (˜10 ms) without the use of rapidly switched gradients. The RF excitation sequence is spatially selective so that only a small fraction of the magnetization in each imaging pixel is used which produces a poor imaging signal to noise ratio (SNR). We have developed several alternative RF sequences that use RF pulses with multiple phases, and also with just 0° and 180° phases to excite almost all the magnetization in a pixel and greatly improve the SNR. The optimization of these pulse sequences (now called OUFIS) have been conducted both analytically and by numerical searches, with various linear and nonlinear models. Both theoretical and computational methods used in the optimizations are described in detail. Preliminary experimental results are briefly presented with several possible applications of the OUFIS excitation sequences suggested.
Motionless Movies of Myocardial Strain‐Rates using Stimulated Echoes
Authors: Wedeen Van J. , Weisskoff Robert M. , Reese Timothy G. , Beache Garth M. , Poncelet Brigitte P. , Rosen Bruce R. , Dinsmore Robert E. 
Published: March 2007

AbstractWe present methods to acquire and analyze NMR movies of myocardial strain rates in which cardiac motion is suppressed and the histories of strain rates are accurately defined for each voxel of myocardial tissue. By means of stimulated echoes, the myocardial strain‐rate tensor is phase‐encoded at progressive delays in the cardiac cycle while the slice‐select and spatial encoding of the image acquisition are performed at a constant cardiac delay. In these data, every image shows the identical myocardial tissue, and the anatomic configuration of the heart appears motionless. The myocardial strainrate data, however, indicate the state of motion which existed in this slice at the time of the velocity phase‐encoding, and these data evolve with the progressive delay as a movie. Using echo‐planar MRI, motionless movies of myocardial strain rate of four to eight cardiac delays are obtained in a breath‐hold. As an application, a quantitative characterization of cardiac mechanical synchrony is accomplished by principal component analysis (PCA) of the time series of strain rates.
Proton NMR Observation of the Antineoplastic Agent Iproplatin In Vivo by Selective Multiple Quantum Coherence Transfer (Sel‐MQC)
Authors: He Qiuhong , Bhujwalla Zaver M. , Maxwell Ross J. , Griffiths John R. , Glickson Jerry D. 
Published: March 2007

AbstractWe have noninvasively detected the proton signal of an antineoplastic agent Iproplatin in vivo by selective multiple quantum coherence transfer (Sel‐MQC). Without isotopic labeling or chemical modification, the Sel‐MQC method labels Iproplatin by its intrinsic proton multiple quantum coherences and, hence, differentiates the Iproplatin signal from the intensive overlapping resonances of lipid and lactate. This proton NMR method should also be applicable to study other drugs with appropriate spin coupling patterns.
Pharmacokinetic Mapping of the Breast: A New Method for Dynamic MR Mammography
Authors: Hoffmann Ulf , Brix Gunnar , Knopp Michael V. , Heβ Thomas , Lorenz Walter J. 
Published: March 2007

AbstractA dynamic contrast‐enhanced MRI technique for whole breast examinations is presented. The fast kinetics of tissue response during and after constant‐rate intravenous infusion of gadolinium diethylenetriaminopentaacetic acid was resolved using a strongly T1‐weighted saturation recovery TurboFLASH sequence that makes it possible to acquire signal‐time courses sequentially from 15 adjacent slices with a temporal sampling rate of 21 s. On the basis of the mathematically established and experimentally verified linear relationship between the measured saturation recovery TurboFLASH signal variation and the gadolinium diethylenetriaminopentaacetic acid concentration in the tissue, the signal‐time courses were analyzed within the framework of pharmacokinetic modeling. In our study, the tissue response was parameterized adequately using an open linear two‐compartment model. With this approach, the tissue specific information contained in the signal‐time course can be described using only two parameters: an amplitude A, reflecting the degree of MR signal enhancement, and an exchange parameter k21, characterizing vascular permeability and perfusion of the tissue. A clearly arranged representation of the large amount of data (480 saturation recovery TurboFLASH breast images/examination) was accomplished by means of color coding of the computed parameters, resulting in one color‐coded pharmacokinetic parameter map/cross‐section.
A Velocity k‐Space Analysis of Flow Effects in Echo‐Planar and Spiral Imaging
Authors: Nishimura Dwight G. , Irarrazabal Pablo , Meyer Craig H. 
Published: March 2007

AbstractA velocity k‐space formalism facilitates the analysis of flow effects for imaging sequences involving time‐varying gradients such as echo‐planar and spiral. For each sequence, the velocity k‐space trajectory can be represented by kv (k)r; that is, its velocity‐frequency (kr) position as a function of spatial‐frequency (kr) position. In an echo‐planar sequence, kr is discontinuous and asymmetric. However, in a spiral sequence, kr is smoothly varying, circularly symmetric, and small near the kr origin. To compare the effects of these trajectory differences, simulated images were generated by computing the k‐space values for an in‐plane vessel with parabolic flow. Whereas the resulting echo‐planar images demonstrate distortions and ghosting that depend on the vessel orientation, the spiral images exhibit minimal artifacts.
Deuterium Magnetic Resonance Imaging of Rabbit Eye in Vivo
Authors: Obata Takayuki , Ikehira Hiroo , Koga Masahisa , Yoshida Katsuya , Kimura Fukuko , Tateno Yukio 
Published: March 2007

AbstractWe used deuterium magnetic resonance imaging (2H MRI) to visualize water movement in the rabbit eye. Dynamic 2H MRI was obtained every 3.5 min at 2 tesla by FLASH pulse sequence (TR, 300 ms; TE, 10 ms; α = 90°) with a slice thickness of 10 mm using a surface coil (4 cm in diameter). After topical administration (0.2 ml D2O), only the aqueous chamber was imaged, and the signals decreased mono‐exponentially. The flow rate was 0.113/min, in agreement with that already reported. After intravenous administration of deuterated saline (3 ml/kg), the aqueous chamber became visible first during imaging, then by the vitreous body. The signals around the lens were only faintly detected. Thus, deuterium MRI was determined to be useful for visualizing water movement in the eye.
Echo‐Time‐Encoded Burst Imaging (EBI): A Novel Technique for Spectroscopic Imaging
Authors: Jakob Peter M. , Ziegler Anne , Doran Simon J. , Décorps Michel 
Published: March 2007

AbstractA new technique for rapid spectroscopic imaging is presented. The proposed experiment enables a complete mapping of the two‐dimensional reciprocal space kx, ko, and thus the acquisition of a 1D spectroscopic image in a single scan. The properties of the pulse sequence, based on the use of a burst of low flip angle pulses, are analyzed in the framework of linear response theory, and it is shown that chemical shift information may be introduced into the spatially encoded echoes. First experimental results are presented demonstrating that 32 x 32 proton spectroscopic images may be acquired within less than 1 min with a conventional imaging system.
Central nervous system trans‐synaptic effects of acute axonal injury: a 1h magnetic resonance spectroscopy study
Authors: Rango Mario , Spagnoli Diego , Tomei Giustino , Bamonti Fabrizia , Scarlato Guglielmo , Zetta Lucia 
Published: March 2007

AbstractN‐acetylaspartate (NAA) has previously been proposed as a neuronal marker. 1H magnetic resonance spectroscopy (MRS) is able to detect NAA in brain, and decreases of NAA have been documented after brain injury. The reason for this decrease is not fully understood and neuron loss damage and “dysfunction” have all been proposed. It is hypothesized that acute central nervous system (CNS) deafferentation causes a trans‐synaptic NAA decrease and that high resolution 1H MRS is able to detect such a decrease. To test this hypothesis, an experimental model was used in which axonal lesions were obtained by stretch injury in guinea pig right optic nerve (95–99% crossed fibers). The trans‐synaptic concentration of NAA, total creatine (Cr), and the NAA/Cr ratio in lateral geniculate bodies (LGB) and superior colliculi (SC) sample extracts were measured 72 h later by high resolution 1H MRS. In the left LGB/SC, which is where right optic nerve fibers project, reductions of NAA and NAA/Cr were found whereas Cr levels were normal. NAA, NAA/Cr, and Cr values were all normal in the right LGB/SC. Histology and EM findings revealed no abnormalities. At 7 days, left LGB/SC NAA and NAA/Cr values were in the normal range. It was concluded that 1) acute deafferentation in the CNS causes a trans‐synaptic decrease of NAA levels that can be detected by 1H MRS and 2) NAA decrease may be due to changes of NAA metabolism caused by functional neuronal inactivity rather than neuronal loss, injury or “dysfunction.” 1H MRS is a potential tool for the study of functional effect of CNS lesions in vivo.
Magnetostimulation in MRI
Authors: Irnich Werner , Schmitt Franz 
Published: March 2007

AbstractIn national and international bodies, there is active discussion of appropriate safety regulations of levels of magnetic field strength in MRI. Present limits are usually expressed in terms of the switching rate dB/dt, but the validity of this is open to debate. Application of the fundamental law of electrostimulation is well‐established, both on theoretical and experimental grounds. Application of this law, in combination with Maxwell's law, yields a very simple equation that we call the fundamental law of magnetostimulation. This law has the hyperbolic form of a strength‐duration curve and allows an estimation of the lowest possible value of the magnetic flux density capable of stimulating nerves and muscles. Calculations prove that the threshold for heart excitation is much higher than those for nerve and muscle stimulations. Experimental results from us and other authors confirm the correctness of the derived laws for magnetostimulation. In light of these findings, proposed safety limits should be reconsidered.
Fast Three Dimensional Magnetic Resonance Imaging
Authors: Irarrazabal Pablo , Nishimura Dwight G. 
Published: March 2007

AbstractTo reduce the scan time in three‐dimensional (3D) imaging, the authors consider alternative trajectories for traversing k‐space. They differ from traditional 3D trajectories, such as 3DFT, in that they employ time‐varying gradients allowing longer readouts and in turn a reduced scan time. Some of these trajectories reduce by an order of magnitude the number of excitations compared with 3DFT and provide flexibility for trading off signal‐to‐noise ratio for scan time. Other concerns are the minimum echo time and flow/motion properties. As examples, the authors show two applications: A 3D data set of the head (field of view of 30 x 30 x 7.5 cm and resolution of 1.5 x 1.5 x 1.5 mm) acquired in 56 s using a stack of spirals in 3D k‐space; and a 3D movie of the heart (20 x 20 x 20 cm field of view, 2 x 2 x 2 mm resolution, and 16 time frames per cardiac cycle) acquired in 11 min using a cones trajectory.
Proton MRS of Gadolinium‐enhancing MS Plaques and Metabolic Changes in Normal‐Appearing White Matter
Authors: Roser Werner , Hagberg Gisela , Mader Irina , Brunnschweiler Heiner , Radue Ernst Wilhelm , Seelig Joachim , Kappos Ludwig 
Published: March 2007

AbstractLocalized short echo time (TE = 20 ms), stimulated echo acquisition mode, and double spin echo (TE = 135 ms) proton spectroscopy were performed in clearly defined, acute Gadolinium (Gd)‐enhancing multiple sclerosis (MS) plaques of 22 patients with clinically definite MS. The resonances of N‐acetylated metabolites (NA), creatine/phosphocreatine (Cr), choline‐containing compounds (Cho), glycine/myo‐inositol (Ino), and lactate were evaluated. The ratios of NA/Cr and NA/Cho were significantly decreased, Cho/Cr increased, and Ino/Cr remained unchanged. No marker peaks or elevated lactate levels were found. The measured metabolic changes were practically independent of the relative plaque size within the volume of interest (8 ml). Thus, the spectral changes measured with 1H MRS in acute Gd‐enhancing MS plaques originate not only from the lesion as depicted by MRI, but also from the surrounding normal‐appearing white matter.
NMR Relaxometric Investigation on Human Methemoglobin and Fluoromethemoglobin. An Improved Quantitative in Vitro Assay of Human Methemoglobin
Authors: Aime Silvio , Fasano Mauro , Paoletti Silvia , Arnelli Aldo , Ascenzi Paolo 
Published: March 2007

AbstractLongitudinal water proton relaxation rates of methemoglobin solutions show a strong dependence on temperature and pH. The increase of the relaxation rates with temperature is associated with shortened exchange lifetime of the coordinated water molecule. An accurate measurement of the relaxation rate of methemoglobin solutions thus requires careful control of the experimental temperature. This observation prompted the authors to look for an improved version of the relaxometric in vitro determination of methemoglobin. The method is based on transforming methemoglobin into the corresponding fluoromethemoglobin derivative, which shows both a higher relaxivity and a negligible dependence on temperature. The proposed method has been found to be in good agreement with data from spectrophotometric assays.