bluuebunny/crossref_metadata_2025_split huggingface dataset:
Assessing DTI data quality using bootstrap analysis
Authors: Heim S. , Hahn K. , Sämann P.G. , Fahrmeir L. , Auer D.P. 
Published: August 2004

AbstractDiffusion tensor imaging (DTI) is an established method for characterizing and quantifying ultrastructural brain tissue properties. However, DTI‐derived variables are affected by various sources of signal uncertainty. The goal of this study was to establish an objective quality measure for DTI based on the nonparametric bootstrap methodology. The confidence intervals (CIs) of white matter (WM) fractional anisotropy (FA) and Clinear were determined by bootstrap analysis and submitted to histogram analysis. The effects of artificial noising and edge‐preserving smoothing, as well as enhanced and reduced motion were studied in healthy volunteers. Gender and age effects on data quality as potential confounds in group comparison studies were analyzed. Additional noising showed a detrimental effect on the mean, peak position, and height of the respective CIs at 10% of the original background noise. Inverse changes reflected data improvement induced by edge‐preserving smoothing. Motion‐dependent impairment was also well depicted by bootstrap‐derived parameters. Moreover, there was a significant gender effect, with females displaying less dispersion (attributable to elevated SNR). In conclusion, the bootstrap procedure is a useful tool for assessing DTI data quality. It is sensitive to both noise and motion effects, and may help to exclude confounding effects in group comparisons. Magn Reson Med 52:582–589, 2004. © 2004 Wiley‐Liss, Inc.
Semiquantitative fast flow velocity measurements using catheter coils with a limited sensitivity profile
Authors: Volz Steffen , Zuehlsdorff Sven , Umathum Reiner , Hallscheidt Peter , Fink Christian , Semmler Wolfhard , Bock Michael 
Published: August 2004

AbstractFlow measurements can be used to quantify blood flow during MR‐guided intravascular interventional procedures. In this study, a fast flow measurement technique is proposed that quantifies flow velocities in the vicinity of a small RF coil attached to an intravascular catheter. Since the small RF coil receives signal from only a limited volume around the catheter, a spatially nonselective signal reception is employed. To enhance signal from flowing blood, and suppress unwanted signal contributions from static material, a slice‐selective RF excitation is used. At a velocity sensitivity of 150 cm/s, a temporal resolution of 2 × TR = 10.2 ms can be achieved. The flow measurement is combined with an automatic slice positioning to facilitate measurements during interventional procedures. The influence of the catheter position in the blood vessel on the velocity measurement was analyzed in simulations. For blood vessels with laminar flow, the simulation showed a systematic deviation between catheter measurement and true flow between −15% and 80%. In four animal experiments, the catheter velocity measurement was compared with results from a conventional ECG‐triggered 2D phase‐contrast (PC) technique. The shapes of the velocity time curves in the abdominal aorta were nearly identical to the conventional measurements. A relative scaling factor of 0.69–1.19 was found between the catheter velocity measurement and the reference measurement, which could be partly explained by the simulation results. Magn Reson Med 52:575–581, 2004. © 2004 Wiley‐Liss, Inc.
Shim design using a linear programming algorithm
Authors: Ungersma Sharon E. , Xu Hao , Chronik Blaine A. , Scott Greig C. , Macovski Al , Conolly Steven M. 
Published: August 2004

AbstractThe advent of open magnetic resonance imaging (MRI) scanners and dedicated MRI scanners tailored to specific body parts has led to an increasing number of noncylindrical MRI scanner geometries, for which noncylindrical gradients and shims are needed. These new scanner geometries are driving the need for fast, flexible shim design methods that can design shim coils for any geometry. A linear programming (LP) algorithm was developed to design minimum‐power resistive shim coils on an arbitrary surface. These coils can be designed to produce any order shim field over an arbitrarily shaped target region, which can be placed anywhere within the coil. The resulting designs are relatively sparse and can be readily constructed. This algorithm was used to design and construct a seven‐coil cylindrical shim set for a knee imaging magnet with a cylindrical homogeneous region. The algorithm was then used to design shim coils for a biradial head imager with an asymmetrically located spherical target region for brain imaging. Magn Reson Med 52:619–627, 2004. © 2004 Wiley‐Liss, Inc.
Simultaneous1H PFG‐NMR and confocal microscopy of monolayer cell cultures: Effects of apoptosis and necrosis on water diffusion and compartmentalization
Authors: Minard Kevin R. , Holtom Gary R. , Kathmann Loel E. , Majors Paul D. , Thrall Brian D. , Wind Robert A. 
Published: August 2004

AbstractWe induced apoptosis and necrosis in monolayer cultures of Chinese hamster ovary cells using okadaic acid and hydrogen peroxide (H2O2), respectively, and examined the effect on water diffusion and compartmentalization using pulsed‐field‐gradient (PFG)1H‐NMR and simultaneous confocal microscopy. In PFG experiments characterized by a fixed diffusion time (<4.7 ms) and variableb‐values (0–27000 s/mm2),1H‐NMR data collected with untreated cells exhibited multiexponential behavior. Analysis with a slow‐exchange model revealed two distinct cellular water compartments with different apparent diffusion coefficients (ADCs; 0.56, 0.06 × 10−3mm2/s) and volume fractions (0.96 and 0.04). During the first 12 hr of necrosis or apoptosis, the amount of water in the smallest compartment increased twofold before significant changes in cell density or plasma membrane integrity occurred. Over the same period, water content in the largest compartment decreased by a factor of >2 in apoptotic cells, in accordance with observed cell shrinkage, and changed little in necrotic counterparts, where only slight swelling was evident. These results indicate that PFG1H‐NMR serves as a sensitive indicator of early cell death in monolayer cultures, and can be used to distinguish apoptosis from necrosis. Measurements of restricted diffusion and water exchange are presented to elucidate the compartment origins and justify the model assumptions. Magn Reson Med 52:495–505, 2004. © 2004 Wiley‐Liss, Inc.
High‐pass‐low‐pass (HP‐LP) reconstruction of CINE phase‐contrast MRI
Authors: Kerwin W.S. 
Published: August 2004

AbstractA new interpretation of CINE phase‐contrast (PC) MRI is presented in which flowing blood is shown to induce separate high‐ and low‐temporal‐frequency components in the resulting image sequence. The flow velocities can then be extracted from the ratio of these two components, independently of any unknown phase offset. This interpretation leads to new insights into improving temporal resolution, eliminating noise, and reducing acquisition time in PC imaging. A specific example explored in this article uses a technique related to unaliasing by Fourier‐encoding the overlaps using the temporal dimension (UNFOLD) to acquire PC velocity measurements at 54–68 time points in the cardiac cycle, all within a single breath‐hold of <20 s. In experimental studies, these techniques were shown to yield improved signal‐to‐noise ratios (SNRs) in a flow phantom and cerebrospinal fluid (CSF) flow studies, and to resolve the formation of a flow vortex during left ventricular (LV) filling in humans. Magn Reson Med 52:566–574, 2004. © 2004 Wiley‐Liss, Inc.
Pulsatile motion effects on 3D magnetic resonance angiography: Implications for evaluating carotid artery stenoses
Authors: Al‐Kwifi Osama , Kim Jae K. , Stainsby Jeff , Huang Yuexi , Sussman Marshall S. , Farb Richard I. , Wright Graham A. 
Published: August 2004

AbstractIn‐plane carotid artery motion during a 3D MR angiography (MRA) scan can significantly degrade the resulting image resolution. This study characterizes the effect of cardiac pulsatility on 3D contrast‐enhanced (CE) MRA with elliptical centric acquisitions using a point‐spread function (PSF) analysis. Internal carotid artery (ICA) motion was collected from volunteers and patients using both MR and ultrasound (US) scans. After measuring the carotid artery motion displacement, a simulation was performed which calculated the blurring effects for three different protocols: nongated and two different cardiac gating schemes. The motion sensitivity of each protocol was evaluated for different spatial resolutions. The selection of optimal imaging parameters for a given scan time was investigated. The final results showed that cardiac‐gated acquisitions only over a limited region of k‐space high spatial frequencies are more time‐efficient than cardiac gating for the entire k‐space, as it allows for higher resolutions to be achieved and for capturing the arterial phase with low spatial frequencies. Selecting the optimal gating parameters depends directly on the motion characteristics of each individual. Our initial clinical experience is presented, and the need for a real‐time tool that characterizes motion behavior for each individual as a prescan protocol is discussed. Magn Reson Med 52:605–611, 2004. © 2004 Wiley‐Liss, Inc.
Flow‐gated phase‐contrast MRI using radial acquisitions
Authors: Thompson Richard B. , McVeigh Elliot R. 
Published: August 2004

AbstractPhase‐contrast (PC) MRI is a noninvasive method for imaging blood and tissue velocity. PC experiments are typically segmented into many cardiac cycles in order to obtain sufficient spatial and temporal resolution, and thus require a gating signal to properly combine the data from multiple cardiac cycles. Although the surface electrode ECG is the gating waveform of choice for cardiovascular MRI, alternative gating methods are required for fetal cardiac imaging (due to the unavailability of fetal ECG signals) and for cases of ECG contamination via the strong magnetic fields within the MR scanner. This study demonstrates the feasibility of using imaging data from flow‐encoded MRI experiments to derive times for cardiac gating. An undersampled radial k‐space acquisition method is used to measure an image‐derived flow‐gating waveform in real‐time, from which the gating times are derived. These gating times are used to reconstruct a conventional gated‐segmented image series by combining the real‐time data from multiple heartbeats. Flow‐gated PC experiments were performed on five normal volunteers with slice prescriptions in four anatomic regions. The standard deviation (SD) of the difference between the flow‐gating and ECG gating times ranged from 5 ms to 12 ms. Magn Reson Med 52:598–604, 2004. Published 2004 Wiley‐Liss, Inc.
In vivo measurement and imaging of tumor oxygenation using coembedded paramagnetic particulates
Authors: Ilangovan Govindasamy , Bratasz Anna , Li Haiquan , Schmalbrock Petra , Zweier Jay L. , Kuppusamy Periannan 
Published: August 2004

AbstractTumor tissue oxygenation is an important parameter that is positively correlated to the chemo‐ or radiation treatment outcome of certain tumors. Hence, methods to accurately and noninvasively determine the concentration of oxygen (pO2) in tumors will be valuable. In this study, electron paramagnetic resonance (EPR) spectroscopy, utilizing microcrystalline particulates of lithium phthalocyanine (LiPc), was used to perform repeated measurements of pO2 as a function of tumor growth. We permanently embedded the particulates in the tumor by coimplanting them with RIF‐1 tumor cells during inoculation in mice. This procedure enabled repeated measurements of oxygen concentration in the tumor to be obtained for >2 weeks during its growth phase. The particulates were stable and nontoxic to the tumor cells. Both an in vitro clonogenic assay and an in vivo tumor growth rate examination in C3H mice showed no apparent effect on cell proliferation or tumor growth rate. The measurements indicated that the pO2 of the tumor decreased exponentially with tumor growth and reached hypoxic levels (∼4 mmHg) within 4 days after inoculation of the tumor cells. Spatial EPR imaging revealed a nonuniform distribution of the embedded particulates, which were localized mainly in the middle of the tumor volume. Oxygen mapping of the tumor, obtained by spectroscopic EPR imaging, showed significant variation of pO2 within the tumor. In summary, EPR spectroscopy and imaging with an embedded oximetry probe enabled accurate and repeated measurements of pO2 to be obtained in growing tumors under nonperturbing conditions. Magn Reson Med 52:650–657, 2004. © 2004 Wiley‐Liss, Inc.
Persistent contrast enhancement by sterically stabilized paramagnetic liposomes in murine melanoma
Authors: Bertini Ivano , Bianchini Francesca , Calorini Lido , Colagrande Stefano , Fragai Marco , Franchi Alessandro , Gallo Oreste , Gavazzi Cinzia , Luchinat Claudio 
Published: August 2004

AbstractIn the present research, we investigated the use of paramagnetic liposomes as contrast agents (CAs) for the detection of solid tumors. The liposomes were sterically stabilized by a polyethylene glycol (PEG) coating, and their size was constrained to ∼100 nm. Dimyristoyl‐sn‐glycero‐3‐phosphoethanolamine‐N‐diethylene‐triaminepentaacetate (DMPE‐DTPA) was used as the gadolinium‐carrying fatty acid chain. The relaxation properties were characterized through nuclear magnetic relaxation dispersion (NMRD) measurements, and analyzed with the use of theories and computer programs that are adequate for slowly rotating systems. Their relaxivity at 1.5 T was found to be acceptable for in vivo use. We then tested the liposomes against B16‐F10 murine melanomas using standard T1‐weighted schemes at 1.5 T, and concentrations corresponding to 0.03 mmol/kg of gadolinium (i.e., three to six times lower than the concentration of the small gadolinium complexes in clinical use). The blood half‐life was found to be 120 ± 20 min. The experiments show a good contrast enhancement in the tumor (33% ± 22%) 2 hr after administration, a further increase (43 ± 27%) 20 hr after administration, and a decrease (25% ± 14%) 54 hr after administration. High persistence of the CA was also observed in the liver and intestine, as expected in a hepatobiliar excretion pathway. Magn Reson Med 52:669–672, 2004. © 2004 Wiley‐Liss, Inc.
Three‐dimensional diffusion tensor microscopy of fixed mouse hearts
Authors: Jiang Yi , Pandya Kumar , Smithies Oliver , Hsu Edward W. 
Published: August 2004

AbstractThe relative utility of 3D, microscopic resolution assessments of fixed mouse myocardial structure via diffusion tensor imaging is demonstrated in this study. Isotropic 100‐μm resolution fiber orientation mapping within 5.5° accuracy was achieved in 9.1 hr scan time. Preliminary characterization of the diffusion tensor primary eigenvector reveals a smooth and largely linear angular rotation across the left ventricular wall. Moreover, a higher level of structural hierarchy is evident from the organized secondary and tertiary eigenvector fields. These findings are consistent with the known myocardial fiber and laminar structures reported in the literature and suggest an essential role of diffusion tensor microscopy in developing quantitative atlases for studying the structure–function relationships of mouse hearts. Magn Reson Med 52:453–460, 2004. © 2004 Wiley‐Liss, Inc.
Simultaneous magnetoencephalography and SQUID detected nuclear MR in microtesla magnetic fields
Authors: Volegov Petr , Matlachov Andrei N. , Espy Michelle A. , George John S. , Kraus Robert H. 
Published: August 2004

AbstractA system that simultaneously measures magnetoencephalography (MEG) and nuclear magnetic resonance (NMR) signals from the human brain was designed and fabricated. A superconducting quantum interference device (SQUID) sensor coupled to a gradiometer pickup coil was used to measure the NMR and MEG signals. 1H NMR spectra with typical Larmor frequencies from 100–1000 Hz acquired simultaneously with the evoked MEG response from a stimulus to the median nerve are reported. The single SQUID gradiometer was placed approximately over the somatosensory cortex of a human subject to noninvasively record the signals. These measurements demonstrate, for the first time, the feasibility of simultaneous MRI and MEG. NMR in the microtesla regime provides narrow linewidths and the potential for high spatial resolution imaging, while SQUID sensors enable direct measurement of neuronal activity with high temporal resolution via MEG. Magn Reson Med 52:467–470, 2004. © 2004 Wiley‐Liss, Inc.
Perturbation method for magnetic field calculations of nonconductive objects
Authors: Jenkinson Mark , Wilson James L. , Jezzard Peter 
Published: August 2004

AbstractInhomogeneous magnetic fields produce artifacts in MR images including signal dropout and spatial distortion. A novel perturbative method for calculating the magnetic field to first order (error is second order) within and around nonconducting objects is presented. The perturbation parameter is the susceptibility difference between the object and its surroundings (for example, ∼10 ppm in the case of brain tissue and air). This method is advantageous as it is sufficiently accurate for most purposes, can be implemented as a simple convolution with a voxel‐based object model, and is linear. Furthermore, the method is simple to use and can quickly calculate the field for any orientation of an object using a set of precalculated basis images. Magn Reson Med 52:471–477, 2004. © 2004 Wiley‐Liss, Inc.
Effects of inductive coupling on parallel MR image reconstructions
Authors: Ohliger Michael A. , Ledden Patrick , McKenzie Charles A. , Sodickson Daniel K. 
Published: August 2004

AbstractTheoretical arguments and experimental results are presented that characterize the impact of inductive coupling on the performance of parallel MRI reconstructions. A simple model of MR signal and noise reception suggests that the intrinsic amount of spatial information available from a given coil array is unchanged in the presence of inductive coupling, as long as the sample remains the dominant source of noise for the coupled array. Any loss of distinctness in the measured coil sensitivities is compensated by information stored in the measured noise correlations. Adjustments to the theory are described to account for preamplifier noise contributions. Results are presented from an experimental system in which preamplifier input impedances are systematically adjusted in order to vary the level of coupling between array elements. Parallel image reconstructions using an array with four different levels of coupling and an acceleration factor up to six show average SNR changes of −7.6% to +7.5%. The modest changes in overall SNR are accompanied by similarly small changes in g‐factor. These initial results suggest that moderate amounts of inductive coupling should not have a prohibitive effect on the use of a given coil array for parallel MRI. Magn Reson Med 52:628–639, 2004. © 2004 Wiley‐Liss, Inc.
Visualization of β‐amyloid plaques in a transgenic mouse model of Alzheimer's disease using MR microscopy without contrast reagents
Authors: Lee Sang‐Pil , Falangola Maria F. , Nixon Ralph A. , Duff Karen , Helpern Joseph A. 
Published: August 2004

AbstractThe visualization of β‐amyloid plaque deposition in brain, a key feature of Alzheimer's disease (AD), is important for the evaluation of disease progression and the efficacy of therapeutic interventions. In this study, β‐amyloid plaques in the PS/APP transgenic mouse brain, a model of human AD pathology, were detected using MR microscopy without contrast reagents. β‐Amyloid plaques were clearly visible in the cortex, thalamus, and hippocampus of fixed brains of PS/APP mice. The distribution of plaques identified by MRI was in excellent agreement with those found in the immunohistological analysis of the same brain sections. It was also demonstrated that image contrast for β‐amyloid plaques was present in freshly excised nonfixed brains. Furthermore, the detection of β‐amyloid plaques was achieved with a scan time as short as 2 hr, approaching the scan time considered reasonable for in vivo imaging. Magn Reson Med 52:538–544, 2004. © 2004 Wiley‐Liss, Inc.
Susceptibility weighted imaging (SWI)
Authors: Haacke E. Mark , Xu Yingbiao , Cheng Yu‐Chung N. , Reichenbach Jürgen R. 
Published: August 2004

AbstractSusceptibility differences between tissues can be utilized as a new type of contrast in MRI that is different from spin density, T1‐, or T2‐weighted imaging. Signals from substances with different magnetic susceptibilities compared to their neighboring tissue will become out of phase with these tissues at sufficiently long echo times (TEs). Thus, phase imaging offers a means of enhancing contrast in MRI. Specifically, the phase images themselves can provide excellent contrast between gray matter (GM) and white matter (WM), iron‐laden tissues, venous blood vessels, and other tissues with susceptibilities that are different from the background tissue. Also, for the first time, projection phase images are shown to demonstrate tissue (vessel) continuity. In this work, the best approach for combining magnitude and phase images is discussed. The phase images are high‐pass‐filtered and then transformed to a special phase mask that varies in amplitude between zero and unity. This mask is multiplied a few times into the original magnitude image to create enhanced contrast between tissues with different susceptibilities. For this reason, this method is referred to as susceptibility‐weighted imaging (SWI). Mathematical arguments are presented to determine the number of phase mask multiplications that should take place. Examples are given for enhancing GM/WM contrast and water/fat contrast, identifying brain iron, and visualizing veins in the brain. Magn Reson Med 52:612–618, 2004. © 2004 Wiley‐Liss, Inc.
Intracellular manganese ions provide strong T1 relaxation in rat myocardium
Authors: Nordhøy Wibeke , Anthonsen Henrik W. , Bruvold Morten , Brurok Heidi , Skarra Sissel , Krane Jostein , Jynge Per 
Published: August 2004

AbstractThe efficacy of manganese ions (Mn2+) as intracellular (ic) contrast agents was assessed in rat myocardium. T1 and T2 and Mn content were measured in ventricular tissue excised from isolated perfused hearts in which a 5‐min wash‐in with 0, 30, 100, 300, or 1000 μM of Mn dipyridoxyl diphosphate (MnDPDP) was followed by a 15‐min wash‐out to remove extracellular (ec) Mn2+. An inversion recovery (IR) analysis at 20 MHz revealed two T1 components: an ic and short T1‐1 (650–251 ms), and an ec and longer T1‐2 (2712–1042 ms). Intensities were about 68% and 32%, respectively. Tissue Mn content correlated particularly well with ic R1‐1. A two‐site water‐exchange analysis of T1 data documented slow water exchange with ic and ec lifetimes of 11.3 s and 7.5 s, respectively, and no differences between apparent and intrinsic relaxation parameters. Ic relaxivity induced by Mn2+ ions in ic water was as high as 56 (s mM)−1, about 8 times and 36 times higher than with Mn2+ aqua ions and MnDPDP, respectively, in vitro. This value is as high as any reported to date for any synthetic protein‐bound metal chelate. The increased rotational correlation time (τR) between proton and electron (Mn2+) spins, and maintained inner‐sphere water access, might make ic Mn2+ ions and Mn2+‐ion‐releasing contrast media surprisingly effective for T1‐weighted imaging. Magn Reson Med 52:506–514, 2004. © 2004 Wiley‐Liss, Inc.