bluuebunny/crossref_metadata_2025_split huggingface dataset:
A comparison of fast MR scan techniques for cerebral activation studies at 1.5 Tesla
Authors: Yang Yihong , Glover Gary H. , van Gelderen Peter , Patel Anand C. , Mattay Venkata S. , Frank Joseph A. , Duyn Jeff H. 
Published: March 2007

AbstractTo evaluate the sensitivity of fast, gradient‐echo MR scan techniques in their ability to detect blood oxygenation level dependent (BOLD) signal changes in task activation studies, three dedicated fast scan techniques, each with whole‐brain coverage, were compared during a 3‐min finger tapping paradigm on nine normal volunteers on a clinical 1.5 T scanner. Multislice (2D) single‐shot spiral, 3D spiral, and multislice (2D) single‐shot EPI scan techniques were done with similar temporal and spatial resolutions on each of the volunteers in random order. After image registration and statistical analysis, the sensitivity to detect activation was evaluated for the techniques by calculatingtscores and number of activated voxels in predetermined regions of interest, including the contralateral primary sensorimotor cortex, the premotor region, the parietal region, the supplementary motor area, and the ipsilateral cerebellum. Baseline images acquired with the three techniques were qualitatively comparable and had a similar effective spatial resolution of around 5 × 5 × 5 mm3, as determined from autocorrelation analysis. The anatomical coverage was somewhat reduced (4 less slices per volume) with EPI at the identical temporal resolution of 1.76 s for all techniques. The use of multislice 2D spiral scan for motor cortex fMRI experiments provided for a superior overall temporal stability, and an increased sensitivity compared with multislice 2D EPI, and 3D spiral scan. The difference in sensitivity between multislice 2D spiral and EPI scans was small, in particular in the case of a ramp‐sampled version of EPI. The difference in performance is attributed mainly to the difference in scan‐to‐scan stability.
Three‐dimensional spiral fMRI technique: A comparison with 2D spiral acquisition
Authors: Lai Song , Glover Gary H. 
Published: March 2007

AbstractA comparison study was performed of 3D and 2D spiral k‐space fMRI techniques using BOLD contrast with a 4.25‐min finger‐tapping task paradigm. The 3D sequence uses the conventional 2D spiral technique in conjunction with Fourier phase encoding in the slice select direction. Characteristics that were compared included image appearances, signal‐to‐noise ratio (SNR), fluctuation noise, functional contrast‐to‐noise ratio (fCNR), detected activation areas, inflow effect, and large vessel involvement. The results showed that, with constant total scan time, the 3D spiral acquisition has higher SNR and fCNR despite its slightly higher fluctuation noise. The capability for thin‐slice incoherent averaging is a further advantage of 3D over 2D. With these advantages as well as its intrinsic ability for contiguous slices and image reformatting, the 3D spiral fMRI technique may be superior to its 2D counterpart.
Imaging lungs using inert fluorinated gases
Authors: Kuethe Dean O. , Caprihan Arvind , Fukushima Eiichi , Waggoner R. Allen 
Published: March 2007

AbstractRat lungs were imaged by 19F projection MRI of hexafluoroethane, mixed with 20% oxygen to form the inhaled gas. The 3D image had 700 μm resolution, and the data took 4.3 h to acquire. Free induction decays were collected in the presence of steady magnetic field gradients in 686 different directions. To take advantage of fast relaxation (T1 = 5.9 ± 0.2 ms), the repetition time was 5 ms. To eliminate signal loss from magnetic field inhomogeneities, data were collected within 2 ms of spin excitation (from 80 μs to 2 ms after the 42‐μs π/2 pulses). The singular value decomposition of the transform from frequency to time domain was used to obtain projections despite the absence of data during and immediately after the RF pulses. Inert fluorinated gas imaging may be less expensive than polarized noble gas imaging and is appropriate for imaging steadystate rather than transient gas concentrations.
Mapping of lateral geniculate nucleus activation during visual stimulation in human brain using fMRI
Authors: Chen Wei , Kato Toshinori , Zhu Xiao‐Hong , Strupp John , Ogawa Seiji , Uǧurbil Kǎmil 
Published: March 2007

AbstractFunctional magnetic resonance imaging has been successfully used to map the activation in the lateral geniculate nucleus (LGN) in both hemispheres as well as the primary visual cortex (V1) during a checkerboard visual stimulation. The average blood oxygenation level dependent (BOLD) change in LGN was less than that in V1. However, the BOLD temporal responses were similar between LGN and V1. The activation in the pulvinar nucleus during visual perception was also detected, and its activated location could be separated from LGN in 3D images. The LGN activation between intersubject and intrasubject multiple trials was compared. The results demonstrate that fMRI can reliably and robustly detect small subcortical nucleus activation in the human brain.
Bilateral imaging using separate interleaved 3D volumes and dynamically switched multiple receive coil arrays
Authors: Greenman Robert L. , Lenkinski Robert E. , Schnall Mitchell D. 
Published: March 2007

AbstractMultiple receive coil arrays are often designed for unilateral imaging of anatomy having bilateral symmetry. A technique is described for extending the utility of such arrays to simultaneously image both bilaterally symmetric anatomical features. A separate, complete multiple receive coil array is placed at each location. Two separate, noncontiguous 3D volumes are then acquired, one at each location, in an interleaved fashion. High‐impedance blocking networks are alternately activated and deactivated to minimize coupling between the arrays. It is demonstrated that there is no degradation in image quality when compared to a unilateral exam. A general method for analyzing the interactions between separate multiple coil arrays is presented.
Right ventricular regional function using MR tagging: Normals versus chronic pulmonary hypertension
Authors: Fayad Zahi A. , Ferrari Victor A. , Kraitchman Dara L. , Young Alistair A. , Palevsky Harold I. , Bloomgarden Daniel C. , Axel Leon 
Published: March 2007

AbstractRight ventricular (RV) regional function, in both normal and diseased states, is not well characterized. Using 1D MR myocardial tagging, RV and septal intramyocardial segmental shortening was noninvasively measured in ten healthy subjects and in seven patients with chronic pulmonary hypertension. The normal RV free wall regional shortening was not uniform. A pattern of increasing RV free wall short‐axis shortening was found from the RV outflow tract to the RV apex, and a more complex pattern of RV free wall long‐axis shortening was observed. Both regional short‐ and long‐axis shortening were globally reduced in pulmonary hypertension patients, with the greatest decreases in the RV outflow tract and in the basal septal wall region. Regional RV function can be quantitatively evaluated using MR tagging to determine the impact of chronic pulmonary hypertension on RV performance.
Off‐resonance experiments and contrast agents to improve magnetic resonance imaging
Authors: Bertini Ivano , Luchinat Claudio , Parigi Giacomo , Quacquarini Gea , Marzola Pasquina , Cavagna Friedrich M. 
Published: March 2007

AbstractThe effect of off‐resonance irradiation on the water proton NMR signal intensity has been investigated as follows: (a) in the presence of a paramagnetic probe like manganese(II); (b) in the presence of bovine serum albumin (BSA) and two gadolinium(III) complexes, Gd‐DTPA and Gd‐BOPTA; (c) in the presence of cross‐linked BSA and the two above‐mentioned gadolinium(III) complexes. The experimental data have been rationalized on the basis of the available theoretical models. The effectiveness of the two complexes as contrast agents for MRI has been predicted. It is shown that contrast agents providing comparable longitudinal and transverse relaxation rate enhancements are those of general interest for off‐resonance magnetization transfer‐MRI.
Probabilistic analysis of functional magnetic resonance imaging data
Authors: Frank Lawrence R. , Buxton Richard B. , Wong Eric C. 
Published: March 2007

AbstractProbability theory is applied to the analysis of fMRI data. The posterior distribution of the parameters is shown to incorporate all the information available from the data, the hypotheses, and the prior information. Under appropriate simplifying conditions, the theory reduces to the standard statistical test, including the general linear model. The theory is particularly suited to handle the spatial variations in the noise present in fMRI, allowing the comparison of activated voxels that have different, and unknown, noise. The theory also explicitly includes prior information, which is shown to be critical in the attainment of reliable activation maps.
Quantitation of dexfenflurainine/d‐norfenfluramine concentration in primate brain using 19F NMR spectroscopy
Authors: Christensen James D. , Babb Suzann M. , Cohen Bruce M. , Renshaw Perry F. 
Published: March 2007

AbstractFluorine (19F) magnetic resonance spectroscopy (MRS) was used to quantify the combined concentration of the anorectic drug dexfenfluramine (DF) and its active metabolite d‐norfenfluramine (dNF) in rhesus monkey brain. The accuracy of the MRS technique was assessed by comparison with gas chromatography. Brain 19F MRS signals were converted to brain DF + dNF concentrations after correction for signal relaxation losses and drug distribution in nonbrain tissue. Gas chromatography (GC) was used to assay brain DF and dNF concentrations following MRS evaluation. DF + dNF concentrations measured by 19F MRS averaged 104 ± 36 μM (mean ± SD) and GC measurements averaged 71 ± 12 μM. Correction for the distribution of DF and its metabolites in nonbrain tissue yielded a DF + metabolite brain concentration that was within one standard deviation of the GC‐derived value. The concentration of DF plus dNF measured by 19F MRS was similar to or greater than the value obtained by GC, which indicates that DF and its active metabolite dNF are fully detected by 19F MRS in primate brain in vivo. The application of these techniques to human subjects should enable the measurement of low micromolar‐range brain concentrations of DF and other fluorinated drugs.
Determination of the intracellular sodium concentration in perfused mouse liver by 31P and 23Na magnetic resonance spectroscopy
Authors: Colet Jean‐Marie , Makos Janice D. , Malloy Craig R. , Sherry A. Dean 
Published: March 2007

AbstractA combination of 31P and 23Na NMR spectroscopy has been used to quantify the concentration of intracellular sodium, [Na]IC in the isolated and perfused mouse liver. The 31P resonances of dimethyl methylphosphonate and LaDOTP5−, markers of total tissue space and extracellular space, respectively, were used to determine the intracellular liver volume. For a mean wet weight of 1.7 ± 0.3 g, the intracellular liver volume as measured by 31P NMR averaged 1.2 ± 0.2 ml. The amount of intracellular sodium was measured from the baseline‐resolved intracellular 23Na resonance during perfusion of the shift reagent, TmDOTP5−. These two measurements resulted in an NMR‐determined value for [Na]IC of 29.0 ± 5.2 mM. Separate measurement of total tissue Tm and Na by atomic absorption spectroscopy on the same samples provided an AAS‐determined value for [Na]Ic of 32.1 ± 7.4 mM. These results indicate that intracellular sodium in the isolated, perfused liver is 100% visible by 23Na NMR spectroscopy.
Measurement of changes in cerebral blood volume in spontaneously hypertensive rats following L‐arginine Infusion using dynamic susceptibility contrast MRI
Authors: Caramia Francesca , Yoshida Tazuka , Hamberg Leena M. , Huang Zihong , Hunter George , Wanke Isabel , Zaharchuk Greg , Moskowitz Michael A. , Rosen Bruce R. 
Published: March 2007

AbstractTo understand whether the NO‐dependent vasodilator L‐arginine was effective upon a chronically hypertensive cerebral capillary endothelium, dynamic susceptibility contrast MRI was used to measure the relative cerebral blood volume (rCBV) changes in nonischemic spontaneously hypertensive rats (SHRs). rCBV was measured in 11 rats at 4.7 T using fast gradient echo imaging with intravenous injection of Gd‐DTPA. Images were acquired before, immediately after, and up to 90 min after the infusion of 300 mg/kg L‐arginine (n = 7) or of an equivalent volume of saline (n = 4). L‐arginine increased rCBV in cortex beginning 10 min after infusion and reached significance after 30 min (P < 0.01), reached a peak of 1.24 ± 0.06 (mean ± SEM) times pre‐injection level after 50 min, and was sustained throughout the 90 min observation period. In contrast, the rCBV in the deeper gray matter (striatum) showed no statistically significant change over the 90 min observation period. While this is consistent with previous studies showing that L‐arginine infusion can directly modulate vascular tone and cerebral hemodynamics, it demonstrates that the effect is present only in cortex, and that it can occur also in the setting of a disturbed capillary endothelium.
Homonuclear J coupling effects in volume localized NMR spectroscopy: Pitfalls and solutions
Authors: Yablonskiy Dmitriy A. , Neil Jeffrey J. , Raichle Marcus E. , Ackerman Joseph J. H. 
Published: March 2007

AbstractIt has been observed that the signal amplitude of multiplet resonances such as the 1H doublet resonance of lactate varies with pulse sequence timing when echo‐driven volume selective methods such as point resolved spectroscopy are used. Herein a standard vectorial description is presented for the mechanism of this artifact, which results from the chemical shift between homonuclear scalar‐coupled (i.e., J coupled) nuclei. The chemical shift causes the extent of a signal phase modulation to vary for different spatial regions of the excited voxel. This variation results in spatial interference effects that can lead to marked loss of signal intensity as well as corruption of the size and shape of the voxel from which signal is obtained. The phenomenon is substantial at an imaging field of 1.5 T and becomes especially pronounced at higher field strengths. Several strategies to avoid the artifact are provided.
Functional MRI using steady‐state arterial water labeling
Authors: Talagala S. Lalith , Noll Douglas C. 
Published: March 2007

AbstractFlow‐sensitive functional MRI (fMRI) was performed using steady‐state arterial water labeling (SS‐AWL). Arterial water labeling was accomplished by flow induced adiabatic fast passage. The signal intensity of the visual cortex in arterial water labeled images decreased by ˜1.4% during visual stimulation of the brain. Acquisition of arterial water unlabeled and labeled images allows measurement of relative cerebral blood flow increase during brain activation. During visual stimulation, cerebral blood flow in the visual cortex increased by 17 to 35% as measured by SS‐AWL. Quantitation of brain activation in terms of a physiological parameter using SS‐AWL will facilitate comparative fMRI studies under different conditions.
Identification of different lipid phases and calcium phosphate deposits in human carotid artery plaques by MAS NMR spectroscopy
Authors: Guo Wen , Morrisett Joel D. , Lawrie Gerald M. , DeBakey Michael E. , Hamilton James A. 
Published: March 2007

AbstractAccumulation of lipids in atherosclerotic plaques causes progressive narrowing of the arterial lumen, often followed by thrombosis and ischemia. Currently several different methods, most requiring disruption of the plaque, are used to study the physical properties of lipids accumulated in plaques, and lipid composition is typically determined by chemical analysis of completely disrupted plaques. In this study, 13C magic angle spinning NMR spectroscopy (MAS NMR) was used to determine in situ the lipid composition and molecular organization of all lipid phases in human carotid artery plaques (ex vivo). Protocols were developed to observe signals from one lipid phase without interference from other phases. In addition, 31P MAS NMR detected calcification in plaques by the signals from inorganic phosphate complexed to calcium. Together, 13C and 31P MAS NMR comprise a powerful nondisruptive approach for determining the quantity and phase state of components in arterial plaques.
Effects of endotoxin lung injury on NMR T2 relaxation
Authors: Cutillo Antonio G. , Chan Pei H. , Ailion David C. , Watanabe Suetaro , Albertine Kurt H. , Durney Carl H. , Hansen Christopher. B. , Laicher Gernot , Scheel Randall. F. , Morris Alan H. 
Published: March 2007

AbstractThe effects of endotoxin injury on lung NMR relaxation times (T1, CPMG T2, and Hahn decay constant (Hahn T2)) were studied in excised unperfused rat lungs. Blinded histologic examination showed no clear‐cut separation between endotoxin and control lungs. Morphometric lung tissue volume density and gravimetric lung water content did not differ significantly between the two groups. In contrast, the values of the fast, intermediate, and slow T2 components, obtained by multiexponential analysis of the CPMG decay curve, increased markedly after endotoxin administration, with minimal overlap between endotoxin and control values. The response of Hahn T2 was, in general, in the same direction as that of CPMG 72; however, Hahn T2 may be more affected by measurement errors and may be less sensitive to the presence of lung injury. t1 showed minimal changes after injury. The present data suggest that CPMG 72 measurements can consistently detect the presence of lung injury even when conventional histologic, morphometric, and gravimetric studies provide negative or equivocal results, and that the CMPG T2 method is superior, in this respect, to the Hahn decay method. T1 does not appear to be sensitive to lung injury in the absence of significant lung water accumulation.
A prospective approach to correct for inter‐image head rotation in FMRI
Authors: Lee Christine C. , Grimm Roger C. , Manduca Armando , Felmlee Joel P. , Ehman Richard L. , Riederer Stephen J. , Jack Clifford R. 
Published: March 2007

AbstractGlobal head motion occurring between successive image acquisitions during a functional MRI time series can corrupt the signal of physiologic brain activation, potentially invalidating interpretation of the final activation map from that particular fMRI time series. By approximating the head as a rigid body, multiaxial global head motion can be decomposed into orthogonal linear and rotational components. This paper describes a method using orbital navigator echoes to provide prospective correction for both through–plane and in–plane inter–image head rotation in functional MRI. The dynamic detection and correction of rotation can be performed in <100 ms. Phantom experiments demonstrate accurate correction of rotational motion over a range of ±0.36° to ±12°. Imaging studies in volunteers document the feasibility of real–time prospective correction of rotational motion in vivo. Using a modified receiver operating characteristic method, motion–corrected functional MRI sensorimotor studies incorporating deliberate head rotations are shown to be superior to functional MRI time series acquired under similar conditions but without motion correction.
Improvement of spatial resolution of keyhole effect images
Authors: Oesterle Claudia , Hennig Jürgen 
Published: March 2007

AbstractAn algorithm is proposed which improves the spatial resolution of difference or effect images acquired with a keyhole sampling strategy. This new reconstruction algorithm uses a priori information about sharp structures in the observed signal changes from a high resolution reference scan. The potential of this algorithm even being able to deal with noisy effect images is illustrated by application to functional MRI data.
Variable TE gradient and spin echo sequences for in Vivo MR microscopy of short T2 species
Authors: Song Hee Kwon , Wehrli Felix W. 
Published: March 2007

AbstractCollagen‐rich tissues such as skin or fibrous cartilage have very short T2 and thus, in order to be visible, demand a commensurate reduction in echo time. Whereas short echo time for imaging of humans is straightforward at large fields of view with currently available whole body gradient hardware, the problem is more challenging in the microscopic resolution regime (<100μm). In this work a simple approach consisting of shortening the echo time dynamically toward the lower spatial frequencies is described for three–dimensional partial flip‐angle gradient and spin‐echo sequences. Microimages obtained in vivo at 50 μm resolution on a 1.5 T whole body scanner are shown to afford a signal‐to‐noise gain of over 100% in the dermis of the human skin. A point–spread function analysis indicates that the variable echo time gradient–echo sequence produces a unique not previously reported off‐resonance artifact in the phase–encoding direction. The artifact results from the phase modulation occurring during the variable echo time and can manifest as both blurring and intensity fluctuations, as well as shifts of boundaries in the phase–encoding direction. However, for the on‐resonance condition, the images are free from these artifacts and exhibit significantly improved signal‐to‐noise ratio.
High‐resolution in vivo measurements of transverse relaxation times in rats at 7 Tesla
Authors: Crémillieux Yannick , Ding Shujun , Dunn Jeff F. 
Published: March 2007

AbstractA multi‐echo imaging sequence suitable for high‐resolution and accurate in vivo transverse relaxation time (T2) mapping has been implemented. The sequence was tested on phantoms and was used to measure T2 values in vivo in the rat brain, muscle, and fat at 7 T. Brain T2 maps are shown and regional variations in brain T2 are reported (41.8 ms in cortex, 47.9 ms in hippocampus). Results are compared to literature values obtained at lower field in vivo as well as high‐field T2 measurements on excised rat tissues. The reported T2 values are generally smaller compared to lower‐field‐strength literature values. A discussion of the possible causes of these field effects on T2 is included (dipolar interaction, fast chemical exchange, and diffusion in susceptibility gradients).
Identification of a high concentration of scyllo‐inositol in the brain of a healthy human subject using 1H‐ and 13C‐NMR
Authors: Seaquist Elizabeth R. , Gruetter Rolf 
Published: March 2007

AbstractThe peak at 3.35 ppm in the 1H‐NMR spectrum characteristic for scyllo‐inositol may be a marker for cerebral pathology, although it has a well‐known constant concentration relative to myo‐inositol. Such a peak was observed with an intensity at least 300% above normal in the brain of a healthy volunteer. The scyllo‐inositol signal was assigned based on the detection of a corresponding peak at 74.5 ppm in the 13C‐NMR spectrum and on the demonstration of singlet characteristics of the proton signal. The presence of substantial brain concentrations of scyllo‐inositol suggests that scyllo‐inositol metabolism may be regulated independently from myo‐inositol and that such concentrations are compatible with normal health.
Correction for variations in MRI scanner sensitivity in brain studies with histogram matching
Authors: Wang Liqun , Lai H‐Ming , Barker Gareth J. , Miller David H. , Tofts Paul S. 
Published: March 2007

AbstractQuantitative comparisons of abnormalities in MRI scans between patients or within patients serially are affected by variations in MR scanner performance. A histogram matching method is proposed to correct for variation in scanner sensitivity. It is demonstrated that this histogram matching method reduced the variation in white matter intensities across normal subjects from 7.5 to 2.5% and provided a method to remove the threshold dependency in lesion volume measurement with global thresholding in patients with multiple sclerosis (MS). The effectiveness of the method was compared with three other possible correction schemes. The histogram matching method was shown to be 2 to 5 times better.