bluuebunny/crossref_metadata_2025_split huggingface dataset:
MRI contrast enhanced study of cartilage proteoglycan degradation in the rabbit knee
Authors: Bacic Goran , Liu Ke Jian , Goda Fuminori , Hoopes P. Jack , Rosen Gerald M. , Swartz Harold M. 
Published: March 2007

AbstractEarly degeneration of cartilage is accompanied by a loss of proteoglycans and consequent changes in the content of water. Conventional magnetic resonance imaging (MRI) cannot reliably detect this change, since the relaxation properties of the cartilage are dominated by its collagen content. The applicability of a positively charged nitroxide as an MRI contrast agent in detection of the content of the negatively charged proteoglycans within the cartilage was investigated. The results from both MRI and electron paramagnetic resonance (EPR) spectroscopy indicate that the accumulation of the contrast agent reflects the amount of proteoglycans within the cartilage, presumably due to the electrostatic interactions between the negatively charged proteoglycans and the positively charged nitroxide. Such a contrast agent could be useful in the detection and study of early stages of the degeneration of joints.
Multifrequency interpolation for fast off‐resonance correction
Authors: Man Lai‐Chee , Pauly John M. , Macovski Albert 
Published: March 2007

AbstractField inhomogeneities or susceptibility variations produce blurring in images acquired using non‐2DFT k‐space readout trajectories. This problem is more pronounced for sequences with long readout times such as spiral imaging. Theoretical and practical correction methods based on an acquired field map have been reported in the past. This paper introduces a new correction method based on the existing concept of frequency segmented correction but which is faster and the‐oretically more accurate. It consists of reconstructing the data at several frequencies to form a set of base images that are then added together with spatially varying linear coefficients derived from the field map. The new algorithm is applied to phantom and in vivo images acquired with projection reconstruction and spiral sequences, yielding sharply focused images.
Design of adiabatic pulses for fat‐suppression using analytic solutions of the bloch equation
Authors: Rosenfeld Daniel , Panfil Shimon L. , Zur Yuval 
Published: March 2007

AbstractDiscrimination between signals produced by fat and by water is an important issue in MRI. One efficient approach is to perform fat‐suppression by selective inversion. This technique exploits the transition region of a selective RF pulse to invert the longitudinal lipid magnetization while leaving the magnetization of the water protons untouched. The damaging effects of RF field inhomogeneity may be overcome by using pulses based on the adiabatic fast passage principle (AFP). In particular, the well‐known sech/tanh adiabatic pulse is a robust and efficient pulse that is obtained as an analytic solution of the Bloch equation. In this paper, a wider class of analytic solutions of the Bloch equation is presented of which the sech/tanh driving function is merely a particular case. The new pulse exhibits an asymmetric distribution of magnetization with one transition sharper than the other. The sharper transition can be used to perform the required selective discrimination between signals. The resulting pulse features excellent adiabatic behavior. Moreover, the transition width of the new pulse can be reduced by a factor of about 2/3 with respect to an equal‐duration sech/tanh pulse. The performance of the new pulse is compared with a similar sech/tanh pulse with the aid of a practical design example.
Real time monitoring of laser‐induced thermal changes in cartilage in vitro by using snapshot FLASH
Authors: Jakob Peter M. , Hendrich Christian , Breitling Thomas , Schäfer Achim , Berden Astrid , Haase Axel 
Published: March 2007

AbstractSnapshot FLASH imaging has been applied to study the spatial and temporal spreading of thermal changes caused by a Holmium:YAG laser in patella cartilage in vitro at 7 T. The temperature dependence of the proton resonance frequency was used to demonstrate the thermal energy deposition. A series of cartilage images, with a time resolution of 512 ms and a spatial resolution of 400 × 200 μm, showed dynamic changes of the temperature‐related image phase in the regions irradiated by the laser.
MR imaging and spectroscopy using hyperpolarized 129Xe gas: Preliminary human results
Authors: Mugler John P. , Driehuys Bastiaan , Brookeman James R. , Cates Gordon D. , Berr Stuart S. , Bryant Robert G. , Daniel Thomas M. , De Lange Eduard E. , Downs J. Hunter , Erickson Christopher J. , Happer William , Hinton Denise P. , Kassel Neal F. , Maier Therese , Phillips C. Douglas , Saam Brian T. , Sauer Karen L. , Wagshul Mark E. 
Published: March 2007

AbstractUsing a new method of xenon laser‐polarization that permits the generation of liter quantities of hyperpolarized 129Xe gas, the first 129Xe imaging results from the human chest and the first 129Xe spectroscopy results from the human chest and head have been obtained. With polarization levels of approximately 2%, cross‐sectional images of the lung gas‐spaces with a voxel volume of 0.9 cm3 (signal‐to‐noise ratio (SNR), 28) were acquired and three dissolved‐phase resonances in spectra from the chest were detected. In spectra from the head, one prominent dissolved‐phase resonance, presumably from brain parenchyma, was detected. With anticipated improvements in the 129Xe polarization system, pulse sequences, RF coils, and breathing maneuvers, these results suggest the possibility for 129Xe gas‐phase imaging of the lungs with a resolution approaching that of current conventional thoracic proton imaging. Moreover, the results suggest the feasibility of dissolved‐phase imaging of both the chest and brain with a resolution similar to that obtained with the gas‐phase images.
Evidence for 100% 13C NMR visibility of glucose in human skeletal muscle
Authors: Roussel Ronan , Carlier Pierre G. , Wary Claire , Velho Gilberto , Bloch Gilles 
Published: March 2007

AbstractThe accuracy of the measurement of total muscle glucose by in vivo 13C NMR spectroscopy was tested in five normal volunteers during a euglycemic [1‐13C]glucose infusion. The NMR visible concentration calibrated using an external reference was compared with that calculated from plasma glucose concentration, assuming that glucose remained extracellular. The NMR measurement always provided higher values than the calculation from plasma glucose: 0.51 ± 0.035 (mean ± SE) versus 0.38 ± 0.005 mmol/liter of muscle on average. This systematic difference was interpreted as reflecting the presence of muscle glucose‐6‐phospnate, co‐resonating with free glucose. Thus, glucose appeared to be virtually 100% NMR visible in human skeletal muscle.
Quantitative lactate‐specific MR imaging and 1H spectroscopy of skeletal muscle at macroscopic and microscopic resolutions using a zero‐quantum/double‐quantum coherence filter and SLIM/GSLIM localization
Authors: Kmiecik Joseph A. , Gregory Carl D. , Liang Zhi‐Pei , Hrad Daniel E. , Lauterbur Paul C. , Dawson M. Joan 
Published: March 2007

AbstractQuantitative lactate imaging and spectroscopy were performed on phantoms and on electrically stimulated, excised frog skeletal muscle at macroscopic and microscopic resolutions. Lactate selectivity was achieved by use of a zero‐quantum/double‐quantum coherence (ZQC/DQC) lactate filter, which suppressed all signals besides lactate, including water and lipid, to below noise level. Three‐dimensional lactate data sets were acquired in 1–3 h; one of these spatial dimensions was frequency‐encoded and the other two were phase‐encoded. High‐resolution images were reconstructed using the spectral localization by imaging (SLIM) and generalized SLIM (GSLIM) techniques. Lactate quantitation was achieved by employing an external lactate concentration standard and was verified by comparison to quantitative STEAM‐localized and nonlocalized spectra that used total creatine as an internal concentration reference. Additionally, quantitatively accurate behavior of the SLIM and GSLIM techniques as applied to data sets of low signal‐to‐noise ratio and to macroscopically heterogeneous objects was verified using simulations and real muscle lactate data sets with known heterogeneity.
In vivo measurement of regional brain metabolic response to hyperventilation using magnetic resonance: Proton echo planar spectroscopic imaging (PEPSI)
Authors: Posse Stefan , Dager Stephen R. , Richards Todd L. , Yuan Chun , Ogg Robert , Artru Alan A. , Müller‐Gärtner Hans‐Wilhelm , Hayes Cecil 
Published: March 2007

AbstractA new rapid spectroscopic imaging technique with improved sensitivity and lipid suppression, referred to as Proton Echo Planar Spectroscopic Imaging (PEPSI), has been developed to measure the 2‐dimensional distribution of brain lactate increases during hyperventilation on a conventional clincal scanner equipped with a head surface coil phased array. PEPSI images (nominal voxel size: 1.125 cm3) in five healthy subjects from an axial section approximately 20 mm inferior to the intercommissural line were obtained during an 8.5‐min baseline period of normocapnia and during the final 8.5 min of a 10‐min period of capnometry‐controlled hyperventilation (end‐tidal PCO2 of 20 mmHg). The lactate/N‐acetyl aspartate signal increased significantly from baseline during hyperventilation for the insular cortex, temporal cortex, and occipital regions of both the right and left hemispheres, but not in the basal ganglia. Regional or hemispheric right‐to‐left differences were not found. The study extends previous work using single‐voxel MR spectroscopy to dynamically study hyperventilation effects on brain metabolism.
A flexible magnetization transfer line shape derived from tissue experimental data
Authors: Li Jonathan G. , Graham Simon J. , Henkelman R. Mark 
Published: March 2007

AbstractTo summarize and compare magnetization transfer data from biological tissues, a method was developed to extract the average absorption lineshape of the semi‐solid pool directly from magnetization transfer experimental data along with the four other parameters that characterize the two‐pool model of exchange. Magnetization transfer data for several biological tissues were analyzed using this method and the resulting “flexible” lineshapes were compared with super‐Lorentzian and “Kubo‐Tomita” lineshapes. The use of flexible lineshapes noticeably improves the fit of the two‐pool model to the data. The derived flexible lineshapes of all the tissues analyzed are physically realistic and show remarkably consistent behavior.
An MRI method for measuring T2 in the presence of static and RF magnetic field Inhomogeneities
Authors: Yablonskiy Dmitriy A. , Haacke E. Mark 
Published: March 2007

AbstractA magnetic resonance imaging method for measuring the T2 relaxation time constant is proposed. It is based on the assumption that, under very general conditions, the MR signal near a spin echo has a special symmetry arising from the refocusing nature of the 180° RF pulse. A gradient echo sampling of the spin echo (GESSE) sequence is implemented to evaluate T2 by collecting multiple gradient echoes before and after the spin echo. This approach is a modification of the GESFIDE sequence proposed by Ma and Wehrli. However, our approach compares images that are not separated by any RF pulses and, as a result, is insensitive to slice profile imperfections. In addition, the calculated T2 value does not rely on any special assumptions about the MRI signal behavior in the presence of an inhomogeneous static magnetic field and, hence, is insensitive to the presence of static magnetic field inhomogeneities.
Dynamic liver imaging with iron oxide agents: Effects of size and biodistribution on contrast
Authors: Mandeville Joseph B. , Moore John , Chesler David A. , Garrido Leoncio , Weissleder Ralph , Weisskoff Robert M. 
Published: March 2007

AbstractIn vivo effective relaxation rates in normal rat liver were evaluated for four dextran coated iron oxide agents: monocrystal‐line iron oxide nanocolloid (MION) with a mean particle diameter of 3.9 nm, a polycrystalline agent (PION) with a larger mean diameter of 12 nm, and these two agents labeled with the asialofetuin (ASF) protein for high hepatocytic receptor binding affinity (MION‐ASF and PION‐ASF). Using echo planar imaging at 2 Tesla, dose response was measured with high temporal resolution for 3 h after injection of agent, and by comparing with relaxivities in vitro and in brain, dominant in vivo contrast phenomena were elucidated. While transverse relaxivity for PION‐ASF exceeded that for MION‐ASF by almost a factor of 2 in solution, relaxation rates in vivo became equivalent. Liver relaxation using non‐ASF agents was consistent with rapid water exchange between vascular and extravascular compartments, which dominated relaxation as a result of agent accumulation in Kupffer cells.
Guidewire antennas for MR fluoroscopy
Authors: Ladd Mark E. , Erhart Peter , Debatin Jörg F. , Hofmann Eugen , Boesiger Peter , Von Schulthess Gustav K. , McKinnon Graeme C. 
Published: March 2007

AbstractBefore MRI can be used for guiding vascular interventions, the problem of dependably visualizing guidewires must be solved. Ideally, the position and curvature of the tip of the guidewire should be visible to facilitate steering through the vascular system. In this paper, various antennas are described that can be incorporated into a guidewire tip. These antennas allow the guidewire to be visualized with high contrast. Computer simulation and experimental evidence are presented showing the value of adding a passive MR signal source, with a shortT1, internal to the coil. The internal source increases the available signal, narrows the apparent width of the guidewire, and allows the use of fast imaging sequences.
Background suppression with multiple inversion recovery nulling: Applications to projective angiography
Authors: Mani Sanjay , Pauly John , Conolly Steven , Meyer Craig , Nishimura Dwight 
Published: March 2007

AbstractWe have developed a technique to accurately null the longitudinal magnetization (Mz) of background material. This suppression involves first saturating the longitudinal magnetization (Mz) of a region, and then applying several nonselective inversions. The inversions are timed relative to the saturation such that Mz is nulled across a broad range of T1 at a predetermined time after the initial saturation. B1 and B0 inhomogeneity, which could lead to inaccurate suppression, are dealt with by the combination of a multiple tip saturation sequence and four adiabatic inversion pulses. The suppression sequence can be used to form projective angiograms by selectively tagging the imaging region with the saturation pulse. After the inversions are played out, a projection taken through the tag region when Mz is nulled will only contain signal from blood that has flown into the region after the saturation. Since only two dimensions are acquired, the technique can acquire gated projection angiograms in reasonable scan times. Representative inflow MIR angiograms of the carotid arteries and renal arteries show excellent background suppression.
Excitation of arbitrary shapes by gradient optimized random walk in discrete k‐space
Authors: Serša Igor , Macura Slobodan 
Published: March 2007

AbstractA new technique for the excitation of arbitrary shapes is proposed. It is based on a parallel sequence of small tip angle RF pulses and gradient pulses. The small tip angle rotations co‐add yielding a 90° excitation pulse within the selected excitation profile while outside the profile, the rotations cancel each other. A full theory of the completely arbitrary regional volume excitation (CARVE) method is presented and experimentally verified. In CARVE, k‐space is discrete because the RF is applied in pulses. The discrete character of k‐space permits an arbitrary trajectory for the k‐space walk. The optimal random trajectory is found by minimizing the gradient load using simulated annealing. It is shown, both theoretically and experimentally, that such a trajectory is much better than any other systematic or random trajectory in k‐space.
Dispersion in magnetization transfer contrast at a given specific absorption rate due to variations of RF pulse parameters in the magnetization transfer preparation
Authors: Wang Yi , Grist Thomas M. , Mistretta Charles A. 
Published: March 2007

AbstractThe effects of RF pulse parameters on magnetization transfer contrast (MTC) were investigated using a magnetization prepared segmented fast gradient echo sequence. MTC was found not to be uniquely determined by the specific absorption rate (SAR). RF pulse parameters (RF amplitude, number of RF pulses and RF duration) also affect MTC. There can be 40% variation in MTC due to differences in RF parameters at SAR = 1 W/kg for a 70‐kg subject. Increasing the number of RF pulses is a more efficient way to increase MTC than increasing RF amplitude. This phenomenon is likely caused by the fact that the time scale for magnetization transfer between the free and restricted proton pools is on the same order or longer than the duration of the MT pulse. Accordingly, increase in the MT pulse duration by increasing the number of RF pulses in the MT pulse allows more effective magnetization transfer. Such information can be used as a guide to select RF pulse parameters for a magnetization transfer (MT) pulse. An off‐resonance MT pulse designed under this guide for coronary MR angiography improved the depiction of distal vessels.
Functional magnetic resonance imaging of median nerve stimulation in rats at 2.0 T
Authors: Scanley B. Ellen , Kennan Richard P. , Cannan Susan , Skudlarski Pawel , Innis Robert B. , Gore John C. 
Published: March 2007

AbstractAn animal model of sensory activation using fMRI at 2.0 T has been developed, demonstrating that fMRI studies on animals need not be limited to high field magnets. These methods produced reliable image intensity changes of 2% using median nerve stimulation in rats at 3 Hz and propofol as the anesthetic agent. At 6 Hz the activation was slightly but not statistically significantly greater. The feasibility of fMRI studies in animals using propofol suggests that it may be a useful anesthetic for fMRI studies in agitated adult patients or in children.
Gloxy: An oxygen‐sensitive coal for accurate measurement of low oxygen tensions in biological systems
Authors: James Philip E. , Grinberg Oleg Y. , Goda Fuminori , Panz Tomasz , O'Hara Julia A. , Swartz Harold M. 
Published: March 2007

AbstractThis paper describes the characteristics of a new oxygen sensitive, paramagnetic material that has some significant advantages for measurements of tissue pO2 by in vivo EPR. This paramagnetic component of Welsh coal, termed “gloxy” was found to have valuable EPR features that allow accurate measurement of low oxygen tensions in vivo; these include large oxygen‐dependent changes in linewidth, a high number of paramagnetic spin centers (resulting in high signal amplitude), and stability in tissue allowing repeated pO2, measurements to be made in vivo with high precision. Renal pO2 was measured deep in the medulla region of isolated perfused kidneys and found to be lower than that in the cortex (1.7 ± 0.05 and 7.1 ± 0.3 mm Hg, respectively). The quality of the EPR signal obtained from the renal outer medulla and also from tumors in mice was such that the pO2 measurements were obtained with a precision of ±3% of the measured pO2 (Kidney: 1.7 ± 0.05 mmHg; Tumor: 1.37 ± 0.04 mmHg). In vitro tests on the viability of cells and in vivo studies using Gloxy demonstrate the stability and inertness of this oxygen‐sensitive material.
Comparison of blood oxygenattion and cerebral blood flow effect in fMRI: Estimation of relative oxygen consumption change
Authors: Kim Cmrr Seong‐gi , Uĝurbil Kaâmil 
Published: March 2007

AbstractThe most widely‐used functional magnetic resonance imaging (fMRI) technique is based on the blood oxygenation level dependent (BOLD) effect, which requires at least partial uncoupling between cerebral blood flow (CBF) and oxygen consumption changes during increased mental activity. To compare BOLD and CBF effects during tasking, BOLD and flowsensitive alternating inversion recovery (FAIR) images were acquired during visual stimulation with red goggles at a frequency of 8 Hz in an inteerleaved fashion. With the FAIR technique, absolute and relative CBF changes were determined. Relative oxygen consumption changes cdan be estimated using the BOLD and relative CBF changes. In gray matter areas in the visual cortex, absolute and relative CBF changes in humans during photic stimulation were 31 ± 11 SD ml/100 g tissue/min and 43 ± 16 SD % (n =12), respectively, while the relative oxygen consumption change was close to zero. These findings agree extremely well with previouse results using positron emission tomography. The BOLD signal change is not linearly correlated with the relative CBF increase across subjects and negatively correlates with the oxygen consumption change. Caution should be exercised when interpreting the BOLD percent change as a quantitative index of the CBF change, especially in inter‐subject comparisons.
Dynamics of magnetization in hyperpolarized gas MRI of the lung
Authors: Johnson G. Allan , Cates Gordon , Chen X. Josette , Cofer Gary P. , Driehuys Bastiaan , Happer Will , Hedlund Laurence W. , Saam Brian , Shattuck Mark D. , Swartz John 
Published: March 2007

AbstractThe magnetization in hyperpolarized gas (HP) MRI is generated by laser polarization that is independent of the magnet and imaging process. As a consequence, there is no equilibrium magnetization during the image acquisition. The competing processes of gas inflow and depolarization of the spins lead to large changes in signal as one samples k‐space. A model is developed of dynamic changes in polarization of hyperpolarized 3He during infusion and in vivo imaging of the lung and verified experimentally in a live guinea pig. Projection encoding is used to measure the view‐to‐view variation with temporal resolution <4 ms. Large excitation angles effectively sample the magnetization in the early stages of inflow, highlighting larger airways, while smaller excitation angles produce images of the more distal spaces. The work provides a basis for pulse sequences designed to effectively exploit HP MRI in the lung.
Short TE MR Microscopy: Accurate measurement and zonal differentiation of normal hyaline cartilage
Authors: Freeman Dominique M. , Bergman Gabrielle , Glover Gary 
Published: March 2007

AbstractThe purpose of this study was to use MR imaging to accurately measure the thickness of hyaline cartilage and determine the MR contrast parameters for differentiation of cartilage zones in normal human cartilage samples. Cartilage samples were examined using three dimensional spin‐echo MR microscopy at 9.4 T with a voxel size of 31 × 31 × 300 μm. Effects of T2 signal loss, susceptibility, and partial volume on measured thickness of cartilage were investigated. Thickness measurements were obtained on corresponding histological sections for comparison. Optimal contrast parameters for delineation of cartilage zones were evaluated using magnetization transfer, inversion recovery, T1, and T2 contrast. T2 relaxation losses were identified as the primary source of discrepancy between the measured thickness of cortical bone and hyaline cartilage. Good contrast for zonal differentiation was obtained using T1 weighting. We conclude that images obtained using short TE MR microscopy can be used to accurately measure cartilage and bone thickness in human specimens, and can demonstrate zones within normal cartilage.