bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fat‐suppressed steady‐state free precession imaging using phase detection
Authors: Hargreaves Brian A. , Vasanawala Shreyas S. , Nayak Krishna S. , Hu Bob S. , Nishimura Dwight G. 
Published: June 2003

AbstractFully refocused steady‐state free precession (SSFP) is a rapid, efficient imaging sequence that can provide diagnostically useful image contrast. In SSFP, the signal is refocused midway between excitation pulses, much like in a spin‐echo experiment. However, in SSFP, the phase of the refocused spins alternates for each resonant frequency interval equal to the reciprocal of the sequence repetition time (TR). Appropriate selection of the TR results in a 180° phase difference between lipid and water signals. This phase difference can be used for fat–water separation in SSFP without any increase in scan time. The technique is shown to produce excellent non‐contrast‐enhanced, flow‐independent angiograms of the peripheral vasculature. Magn Reson Med 50:210–213, 2003. © 2003 Wiley‐Liss, Inc.
Spatial normalization of diffusion tensor fields
Authors: Xu Dongrong , Mori Susumu , Shen Dinggang , van Zijl Peter C.M. , Davatzikos Christos 
Published: June 2003

AbstractA method for the spatial normalization and reorientation of diffusion tensor (DT) fields is presented. Spatial normalization of tensor fields requires an appropriate reorientation of the tensor on each voxel, in addition to its relocation into the standardized space. This appropriate tensor reorientation is determined from the spatial normalization transformation and from an estimate of the underlying fiber direction. The latter is obtained by treating the principal eigenvectors of the tensor field around each voxel as random samples drawn from the probability distribution that represents the direction of the underlying fiber. This approach was applied to DT images from nine normal volunteers, and the results show a significant improvement in signal‐to‐noise ratio (SNR) after spatial normalization and averaging of tensor fields across individuals. The statistics of the spatially normalized tensor field, which represents the tensor characteristics of normal individuals, may be useful for quantitatively characterizing individual variations of white matter structures revealed by DT imaging (DTI) and deviations caused by pathology. Simulated experiments using this methodology are also described. Magn Reson Med 50:175–182, 2003. © 2003 Wiley‐Liss, Inc.
Robust myelin water quantification: Averaging vs. spatial filtering
Authors: Jones Craig K. , Whittall Kenneth P. , MacKay Alex L. 
Published: June 2003

AbstractThe myelin water fraction is calculated, voxel‐by‐voxel, by fitting decay curves from a multi‐echo data acquisition. Curve‐fitting algorithms require a high signal‐to‐noise ratio to separate T2 components in the T2 distribution. This work compared the effect of averaging, during acquisition, to data postprocessed with a noise reduction filter. Forty regions, from five volunteers, were analyzed. A consistent decrease in the myelin water fraction variability with no bias in the mean was found for all 40 regions. Images of the myelin water fraction of white matter were more contiguous and had fewer “holes” than images of myelin water fractions from unfiltered echoes. Spatial filtering was effective for decreasing the variability in myelin water fraction calculated from 4‐average multi‐echo data. Magn Reson Med 50:206–209, 2003. © 2003 Wiley‐Liss, Inc.
Simple analytic variable density spiral design
Authors: Kim Dong‐hyun , Adalsteinsson Elfar , Spielman Daniel M. 
Published: June 2003

AbstractVariable density spirals have been proposed in a variety of applications, including MR fluoroscopy, cardiac imaging, and MR spectroscopic imaging. In this work, a simple analytic solution for designing a flexible set of variable density spiral trajectory waveforms is presented. The method enables real‐time waveform prescription on scanners with limited computational power. Both slew rate‐limited and amplitude‐limited regimes are incorporated in the design process. Magn Reson Med 50:214–219, 2003. © 2003 Wiley‐Liss, Inc.
MRI detection of weak magnetic fields due to an extended current dipole in a conducting sphere: A model for direct detection of neuronal currents in the brain
Authors: Konn Daniel , Gowland Penny , Bowtell Richard 
Published: June 2003

AbstractTo investigate the feasibility of direct MR detection of neuronal activity in the brain, neuronal current flow was modeled as an extended current dipole located in a conducting sphere. The spatially varying magnetic field induced within the sphere by such a dipole was calculated, including its form close to and within the current source. The predicted field variation was experimentally verified by measurements of the variation in phase of the MR signal in a sphere containing a model dipole. The effects of the calculated magnetic field distributions on the phase and magnitude of the signal in MR images were explored. The minimum detectable dipole strength under normal experimental conditions was calculated to be about 4.5 nAm, which is similar in magnitude to dipole strengths from evoked neuronal activity, and is an order of magnitude smaller than dipole strengths expected from spontaneous activity. This minimum detectable dipole strength increases with increasing spatial extent of the primary current distribution. In the experimental work, the effects of a field of [1.1 ± 0.5] × 10–10 T strength were detected, corresponding to the maximum net field caused by a dipole of 6.3 nAm strength with a spatial extent of 3 × 3 × 2 mm3. Magn Reson Med 50:40–49, 2003. © 2003 Wiley‐Liss, Inc.
Parallel spectroscopic imaging with spin‐echo trains
Authors: Dydak Ulrike , Pruessmann Klaas P. , Weiger Markus , Tsao Jeffrey , Meier Dieter , Boesiger Peter 
Published: June 2003

AbstractA reduction in scan time in spectroscopic imaging (SI) can be achieved by both fast and reduced k‐space sampling. This work presents an ultrafast SI technique that combines the two approaches. The synergy of multiple spin‐echo (MSE) acquisition and sensitivity encoding (SENSE) enables high‐resolution SI to be performed within a clinically acceptable scan time. MSE‐SENSE‐SI with echo train lengths ranging from one to four echoes is evaluated with respect to SNR and spatial response function by means of in vitro experiments. It is shown that acquiring two spin‐echoes (SEs) per acquisition yields a good practical trade‐off among scan time, SNR, and spatial response. The clinical feasibility of the technique is demonstrated in a patient with an astrocytoma, and SI data are obtained with an image matrix of 24 × 24 in just over 2 min. Magn Reson Med 50:196–200, 2003. © 2003 Wiley‐Liss, Inc.
Textural analysis of contrast‐enhanced MR images of the breast
Authors: Gibbs Peter , Turnbull Lindsay W. 
Published: June 2003

AbstractTexture analysis was applied to high‐resolution, contrast‐enhanced (CE) images of the breast to provide a method of lesion discrimination. Significant differences were seen between benign and malignant lesions for a number of textural features, including entropy and sum entropy. Using logistic regression analysis (LRA), a diagnostic accuracy of Az = 0.80 ± 0.07 was obtained with a model requiring only three parameters. By initially dividing the patient data into training and test datasets, reasonable model robustness was also established. On combining features obtained using textural analysis with lesion size, time to maximum enhancement, and patient age, a diagnostic accuracy of Az = 0.92 ± 0.05 was demonstrated. Magn Reson Med 50:92–98, 2003. © 2003 Wiley‐Liss, Inc.
Developmental and regional changes in the neurochemical profile of the rat brain determined by in vivo 1H NMR spectroscopy
Authors: Tkáč Ivan , Rao Raghavendra , Georgieff Michael K. , Gruetter Rolf 
Published: June 2003

AbstractSixteen metabolites were quantified from 11–24 μl volumes in three different brain regions (hippocampus, striatum, and cerebral cortex) during postnatal development. Rat pups from the same litter were repeatedly measured on postnatal days 7, 10, 14, 21, and 28 using a completely noninvasive and longitudinal study design. Metabolite quantification was based on ultra‐short echo‐time 1H NMR spectroscopy at 9.4 T and LCModel processing. Most of the brain metabolites were quantified with Cramer‐Rao lower bounds (CRLB) less than 20%, which corresponded to an estimated concentration error <0.2 μmol/g. Taurine and total creatine were quantified with CRLB ≤ 5% from all 114 processed spectra. The resulting high reliability and reproducibility revealed significant regional and age‐related changes in metabolite concentrations. The most sensitive markers for developmental and regional variations between hippocampus, striatum, and cerebral cortex were N‐acetylaspartate, myo‐inositol, taurine, glutamate, and choline compounds. Absolute values of metabolite concentrations were in very good agreement with previously published in vitro results based on chromatographic measurements of brain extracts. The current data may serve as a reference for studies focused on developmental defects and pathologies using neonatal rat models. Magn Reson Med 50:24–32, 2003. © 2003 Wiley‐Liss, Inc.
In vivo trans‐synaptic tract tracing from the murine striatum and amygdala utilizing manganese enhanced MRI (MEMRI)
Authors: Pautler Robia G. , Mongeau Raymond , Jacobs Russell E. 
Published: June 2003

AbstractSmall focal injections of manganese ion (Mn2+) deep within the mouse central nervous system combined with in vivo high‐resolution MRI delineate neuronal tracts originating from the site of injection. Previous work has shown that Mn2+can be taken up through voltage‐gated Ca2+channels, transported along axons, and across synapses. Moreover, Mn2+is a paramagnetic MRI contrast agent, causing positive contrast enhancement in tissues where it has accumulated. These combined properties allow for its use as an effective MRI detectable neuronal tract tracer. Injections of low concentrations of MnCl2into either the striatum or amygdala produced significant contrast enhancement along the known neuronal circuitry. The observed enhancement pattern is different at each injection site and enhancement of the homotopic areas was observed in both cases. Ten days postinjection, the Mn2+had washed out, as evidenced by the absence of positive contrast enhancement within the brain. This methodology allows imaging of neuronal tracts long after the injection of the ion because Mn2+concentrates in active neurons and resides for extended periods of time. With appropriate controls, differentiation of subsets of neuronal pathways associated with behavioral and pharmacological paradigms should be feasible. Magn Reson Med 50:33–39, 2003. © 2003 Wiley‐Liss, Inc.
Measurement of reduced glutathione (GSH) in human brain using LCModel analysis of difference‐edited spectra
Authors: Terpstra Melissa , Henry Pierre‐Gilles , Gruetter Rolf 
Published: June 2003

AbstractThe concentration of reduced glutathione (GSH), an antioxidant, may be altered in various brain diseases. MEGA‐PRESS was used to edit for the 1H NMR signal from GSH in the occipital lobe of 12 normal humans. In all studies, GSH was clearly detected with a spectral pattern consistent with spectra acquired from a phantom containing GSH. Retention of singlet resonances in the subspectra, a key advantage of this difference‐editing technique, provided an unambiguous reference for the offset and phase of the edited signal. Linear combination model (LCModel) analysis provided an unbiased means for quantifying signal contribution from edited metabolites. GSH concentration was estimated from the in vivo spectra as 1.3 ± 0.2 μmol/g (mean ± SD, n = 12). Magn Reson Med 50:19–23, 2003. © 2003 Wiley‐Liss, Inc.
High‐resolution MRI with cardiac and respiratory gating allows for accurate in vivo atherosclerotic plaque visualization in the murine aortic arch
Authors: Wiesmann Frank , Szimtenings Michael , Frydrychowicz Alex , Illinger Ralf , Hunecke Andreas , Rommel Eberhard , Neubauer Stefan , Haase Axel 
Published: June 2003

AbstractGenetically engineered mouse models provide enormous potential for investigation of the underlying mechanisms of atherosclerotic disease, but noninvasive imaging methods for analysis of atherosclerosis in mice are currently limited. This study aimed to demonstrate the feasibility of MRI to noninvasively visualize atherosclerotic plaques in the thoracic aorta in mice deficient in apolipoprotein‐E, who develop atherosclerotic lesions similar to those observed in humans. To freeze motion, MR data acquisition was both ECG‐ and respiratory‐gated. T1‐weighted MR images were acquired with TR/TE ∼1000/10 ms. Spatial image resolution was 49 × 98 × 300 μm3. MRI revealed a detailed view of the lumen and the vessel wall of the entire thoracic aorta. Comparison of MRI with corresponding cross‐sectional histopathology showed excellent agreement of aortic vessel wall area (r = 0.97). Hence, noninvasive MRI should allow new insights into the mechanisms involved in progression and regression of atherosclerotic disease. Magn Reson Med 50:69–74, 2003. © 2003 Wiley‐Liss, Inc.
Centering the projection reconstruction trajectory: Reducing gradient delay errors
Authors: Peters Dana C. , Derbyshire J. Andrew , McVeigh Elliot R. 
Published: June 2003

AbstractThe projection reconstruction (PR) trajectory was investigated for the effect of gradient timing delays between the actual and requested start time of each physical gradient. Radial trajectories constructed with delayed gradients miss the center of k‐space in an angularly dependent manner, causing effective echo times to vary with projection angle. The gradient timing delays were measured in phantoms, revealing delays on the x, y, and z gradients which differed by as much as 5 μsec. Using this one‐time calibration measurement, the trajectories were corrected for gradient delays by addition of compensatory gradient areas to the prephasers of the logical x and y readout gradients. Effective projection‐to‐projection echo time variability was reduced to less than 1 μsec for all imaging orientations. Using corrected trajectories, artifacts were reduced in phantom images and in volunteer studies. This correction should potentiate greater clinical use of the PR trajectory. Magn Reson Med 50:1–6, 2003. Published 2003 Wiley‐Liss, Inc.
Measuring the effects of indomethacin on changes in cerebral oxidative metabolism and cerebral blood flow during sensorimotor activation
Authors: St. Lawrence K.S. , Ye F.Q. , Lewis B.K. , Frank J.A. , McLaughlin A.C. 
Published: June 2003

AbstractThe work presented here uses combined blood oxygenation level‐dependent (BOLD) and arterial spin tagging (AST) approaches to study the effect of indomethacin on cerebral blood flow (CBF) and oxygen consumption (CMRO2) increases during motor activation. While indomethacin reduced the CBF increase during activation, it did not significantly affect the CMRO2 increase during activation. The ratio of the activation‐induced CBF increase in the presence and absence of indomethacin was 0.54 ± 0.08 (±SEM, n = 8, P < 0.001), while the ratio of the CMRO2 increase in the presence and absence of the drug was 1.02 ± 0.08 (±SEM, N = 8, ns). Potential difficulties in estimating CMRO2 changes from combined BOLD/AST data are discussed. Magn Reson Med 50:99–106, 2003. Published 2003 Wiley‐Liss, Inc.
Accuracy and uniqueness of three in vivo measurements of atherosclerotic carotid plaque morphology with black blood MRI
Authors: Luo Ying , Polissar Nayak , Han Chao , Yarnykh Vasily , Kerwin William S. , Hatsukami Thomas S. , Yuan Chun 
Published: June 2003

AbstractHigh‐resolution MRI provides unique information about morphology of atherosclerotic carotid plaque. In this study, the accuracy and precision of measurements of carotid plaque burden and lumen narrowing were determined for in vivo black blood MRI assessment with respect to ex vivo MRI in a group of 37 atherosclerosis patients who underwent carotid endarterectomy (CEA). Three different plaque measures were compared between paired in vivo and ex vivo MR images: maximum wall area (MWA), minimum lumen area (mLA), and wall volume (WV). MWA and WV are measures of plaque burden, while mLA is a measure of lumen narrowing. The matched in vivo and ex vivo measurements showed good agreement (the correlation coefficients for in/ex vivo WV, MWA, and mLA were 0.92, 0.91, 0.90, respectively) with predictable bias. This study indicates that in vivo black blood MRI can be used to directly estimate the morphology of the plaque. Comparison of the three plaque measures showed that mLA and MWA or WV provide different information regarding the atherosclerotic lesions (the correlation coefficients between mLA and MWA or WV were less than 0.3). Black blood MRI technique is a potentially powerful clinical tool to characterize the severity of atherosclerotic plaque. It can provide accurate measurements on different aspects of the plaque, from plaque burden to lumen narrowing. Magn Reson Med 50:75–82, 2003. © 2003 Wiley‐Liss, Inc.
Peripheral nerve stimulation properties of head and body gradient coils of various sizes
Authors: Zhang Beibei , Yen Yi‐Fen , Chronik Blaine A. , McKinnon Graeme C. , Schaefer Daniel J. , Rutt Brian K. 
Published: June 2003

AbstractPeripheral nerve stimulation (PNS) caused by time‐varying magnetic fields has been studied both theoretically and experimentally. A human volunteer study performed on three different body‐size gradient coils and one head‐size gradient coil is presented in this work. The experimental results were used to generate average PNS threshold parameters for the tested gradient systems. It was found that the average stimulation threshold increases while gradient‐region‐of‐uniformity size decreases. In addition, linear relationships between PNS parameters and diameter of homogeneous gradient spherical volume (DSV) were discovered: SRmin and ΔGmin both vary inverse linearly with DSV. More importantly, the chronaxie value was found to vary inversely linearly with the DSV. This finding indicates that, contrary to the general understanding, the parameter “chronaxie” in the commonly accepted simple stimulation models cannot be considered to be a single‐value, nerve‐specific constant. A modified linear model for gradient‐induced PNS based on these results was developed, which may permit, for the first time, the general prediction of nerve stimulation properties for gradient coils of arbitrary linear region dimension. Magn Reson Med 50:50–58, 2003. © 2003 Wiley‐Liss, Inc.
Real‐time imaging of two‐dimensional cardiac strain using a harmonic phase magnetic resonance imaging (HARP‐MRI) pulse sequence
Authors: Sampath Smita , Derbyshire J. Andrew , Atalar Ergin , Osman Nael F. , Prince Jerry L. 
Published: June 2003

AbstractThe harmonic phase (HARP) method provides automatic and rapid analysis of tagged magnetic resonance (MR) images for quantification and visualization of myocardial strain. In this article, the development and implementation of a pulse sequence that acquires HARP images in real time are described. In this pulse sequence, a CINE sequence of images with 1‐1 spatial modulation of magnetization (SPAMM) tags are acquired during each cardiac cycle, alternating between vertical and horizontal tags in successive heartbeats. An incrementing train of imaging RF flip angles is used to compensate for the decay of the harmonic peaks due to both T1 relaxation and the applied imaging pulses. The magnitude images displaying coarse anatomy are automatically reconstructed and displayed in real time after each heartbeat. HARP strain images are generated offline at a rate of four images per second; real‐time processing should be possible with faster algorithms or computers. A comparison of myocardial contractility in non‐breath‐hold and breath‐hold experiments in normal humans is presented. Magn Reson Med 50:154–163, 2003. © 2003 Wiley‐Liss, Inc.
Evaluation of systematic quantification errors in velocity‐selective arterial spin labeling of the brain
Authors: Duhamel Guillaume , de Bazelaire Cédric , Alsop David C. 
Published: June 2003

AbstractVelocity‐selective (VS) sequences potentially permit arterial spin labeling (ASL) perfusion imaging with labeling applied very close to the tissue. In this study the effects of cerebrospinal fluid (CSF) motion, radiofrequency (RF) field imperfections, and sequence timing parameters on the appearance and quantitative perfusion values obtained with VS‐ASL were evaluated. Large artifacts related to CSF motion were observed with moderate velocity weighting, which were removed by inversion recovery preparation at the cost of increased imaging time. Imperfect refocusing and excitation pulses resulting from nonuniform RF fields produced systematic errors in the ASL subtraction images. A phase cycling scheme was introduced to eliminate these errors. Quantitative perfusion images were obtained with CSF suppression and phase cycling. Gray matter blood flow of 27.7 ml 100 g–1 min–1, approximately half the value reported in studies using spatially‐selective ASL, was measured. Potential sources for this underestimation are discussed. Magn Reson Med 50:145–153, 2003. © 2003 Wiley‐Liss, Inc.
MR microscopy of magnetically labeled neurospheres transplanted into the Lewis EAE rat brain
Authors: Bulte Jeff W.M. , Ben‐Hur Tamir , Miller Bradley R. , Mizrachi‐Kol Rachel , Einstein Ophira , Reinhartz Etti , Zywicke Holly A. , Douglas Trevor , Frank Joseph A. 
Published: June 2003

AbstractStem cell transplantation is being explored as a new paradigm for the treatment of demyelinating diseases. Magnetically labeled multipotential neural precursor cells were transplanted into the ventricles of rats with acute experimental allergic encephalomyelitis (EAE) and high‐resolution (microscopic) MR images were obtained ex vivo. Migration patterns of live cells into periventricular white matter structures could be easily visualized, with a good correlation of the corresponding histopathology. The present results confirm that MR cell tracking can be used to guide the development of successful transplantation protocols. Magn Reson Med 50:201–205, 2003. © 2003 Wiley‐Liss, Inc.
Density of organic matrix of native mineralized bone measured by water‐ and fat‐suppressed proton projection MRI
Authors: Wu Yaotang , Ackerman Jerome L. , Chesler David A. , Graham Lila , Wang Yan , Glimcher Melvin J. 
Published: June 2003

AbstractWater‐ and fat‐suppressed projection MR imaging (WASPI) utilizes the large difference between the proton Ts of the solid organic matrix and the fluid constituents of bone to suppress the fluid signals while preserving solid matrix signals. The solid constituents include collagen and some molecularly immobile water and exhibit very short T. The fluid constituents include mobile water and fat, with long T. In WASPI, chemical shift selective low‐power π/2 pulses excite mobile water and fat magnetization which is subsequently dephased by gradient pulses, while the magnetization of collagen and immobile water remains mostly in the z‐direction. Additional selective π pulses in alternate scans further cancel the residual water and fat magnetization. Following water and fat suppression, the matrix signal is excited by a short hard pulse and the free induction decay acquired in the presence of a gradient in a 3D projection method. WASPI was implemented on a 4.7 T MR imaging system and tested on phantoms and bone specimens, enabling excellent visualization of bone matrix. The bone matrix signal per unit volume of bovine trabecular specimens was measured by this MR technique and compared with that determined by chemical analysis. This method could be used in combination with bone mineral density measurement by solid state 31P projection MRI to determine the degree of bone mineralization. Magn Reson Med 50:59–68, 2003. © 2003 Wiley‐Liss, Inc.