bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phospholipid composition of postmortem schizophrenic brain by 31P NMR spectroscopy
Authors: Pearce John M. , Komoroski Richard A. , Mrak Robert E. 
Published: December 2008

AbstractCell membrane abnormalities due to changes in phospholipid (PL) composition and metabolism have been implicated in schizophrenia pathogenesis. That work has generally assessed membrane phospholipids from nonneural tissues such as erythrocytes and platelets. High‐resolution 31P NMR spectroscopy was used to characterize PLs of gray matter in postmortem brain for 20 schizophrenics, 20 controls, and 7 patients with other mental illnesses (psychiatric controls). Tissues from frontal, temporal, and occipital cortices were extracted with hexane–isopropanol, and 31P NMR spectra were obtained in an organic–solvent system to resolve the major PL classes (based on headgroups) and subclasses (based on linkage at the sn − 1 position). Surprisingly, repeated‐measures multivariate analysis of variance revealed no overall differences among the groups. There were no significant differences (P < .05) among the three groups for any individual PL subclass, including lysophospholipids. The sum of all phosphatidylethanolamine headgroups was significantly lower for schizophrenics than for controls or psychiatric controls in the frontal cortex. The present results are minimally correlated with previous results for aqueous PL metabolites on these same samples. The metabolite changes measured by in vivo 31P MRS in schizophrenia do not appear to reflect PL concentration changes. The present results offer very little support for the phospholipid hypothesis of schizophrenia. Magn Reson Med 61:28–34, 2009. © 2008 Wiley‐Liss, Inc.
Calibration of RF transmitter voltages for hyperpolarized gas MRI
Authors: Bashir Adil , Conradi Mark S. , Woods Jason C. , Quirk James D. , Yablonskiy Ddmitriy A. 
Published: December 2008

AbstractMRI with hyperpolarized gases, 3He, 129Xe, 13C, and others, has the potential to become an important diagnostic technique for clinical imaging. Due to the nonreversible loss of magnetization in hyperpolarized gas imaging, the choice of the flip angle is a major factor that influences the signal intensity, and hence, the signal‐to‐noise ratio. Conventional automated radiofrequency (RF) calibration procedures for 1H imaging are not suitable for hyperpolarized gas imaging. Herein, we have demonstrated a simple procedure for RF calibration for magnetic resonance imaging (MRI) with hyperpolarized gases that is easily adaptable to clinical settings. We have demonstrated that there exists a linear relationship between the RF transmitter voltages required to obtain the same nutation angle for protons (V1H) and hyperpolarized gas nuclei (V3He). For our 1H and 3He coils we found that V3He = 1.937 · V1H with correlation coefficient r2 = 0.97. This calibration can be done as a one‐time procedure during the routine quality assurance (QA) protocol. The proposed procedure was found to be extremely robust in routine scanning and provided an efficient method to achieve a desired flip angle, thus allowing optimum image quality. Magn Reson Med 61:239–243, 2009. © 2008 Wiley‐Liss, Inc.
Spin‐echo MRI using π/2 and π hyperbolic secant pulses
Authors: Park Jang‐Yeon , Garwood Michael 
Published: December 2008

AbstractFrequency‐modulated (FM) pulses have practical advantages for spin‐echo experiments, such as the ability to produce a broadband π rotation, with an inhomogeneous radiofrequency (RF) field. However, such use leads to a nonlinear phase of the transverse magnetization, which is why FM pulses like the hyperbolic secant (HS) pulse are not commonly used for multislice spin‐echo magnetic resonance imaging (MRI). Here, a general theory and methods are described for conventional spin‐echo imaging using a π HS pulse for refocusing. Phase profiles produced by the HS pulse are analytically described. The analysis is extended to yield the specific relationships between pulse parameters and gradients, which must be satisfied to compensate the nonlinear phase variation produced with a spin‐echo sequence composed of π/2 and π HS pulses (the π/2 HS − π HS sequence). The latter offers advantages for multislice spin‐echo MRI, including excellent slice‐selection and partial compensation for RF inhomogeneity. Furthermore, it can be implemented with a shorter echo time and lower power deposition than a previously described method using a pair of π HS pulses. Magn Reson Med 61:175–187, 2009. © 2008 Wiley‐Liss, Inc.
Quantitative magnetization transfer characteristics of the human cervical spinal cord in vivo: Application to Adrenomyeloneuropathy
Authors: Smith Seth A. , Golay Xavier , Fatemi Ali , Mahmood Asif , Raymond Gerald V. , Moser Hugo W. , van Zijl Peter C.M. , Stanisz Greg J. 
Published: December 2008

AbstractMagnetization transfer (MT) imaging has assessed myelin integrity in the brain and spinal cord; however, quantitative MT (qMT) has been confined to the brain or excised tissue. We characterized spinal cord tissue with qMT in vivo, and as a first application, qMT‐derived metrics were examined in adults with the genetic disorder Adrenomyeloneuropathy (AMN). AMN is a progressive disease marked by demyelination of the white matter tracts of the cervical spinal cord, and a disease in which conventional MRI has been limited. MT data were acquired at 1.5 Tesla using 10 radiofrequency offsets at one power in the cervical cord at C2 in 6 healthy volunteers and 9 AMN patients. The data were fit to a two‐pool MT model and the macromolecular fraction (Mob), macromolecular transverse relaxation time (T2b) and the rate of MT exchange (R) for lateral and dorsal column white matter and gray matter were calculated. Mob for healthy volunteers was: WM = 13.9 ± 2.3%, GM = 7.9 ± 1.5%. In AMN, dorsal column Mob was significantly decreased (P < 0.03). T2b for volunteers was: 9 ± 2 μs and the rate of MT exchange (R) was: WM = 56 ± 11 Hz, GM = 67 ± 12 Hz. Neither T2b nor R showed significant differences between healthy and diseased cords. Comparisons are made between qMT, and conventional MT acquisitions. Magn Reson Med 61:22–27, 2009. © 2008 Wiley‐Liss, Inc.
Calculation of susceptibility through multiple orientation sampling (COSMOS): A method for conditioning the inverse problem from measured magnetic field map to susceptibility source image in MRI
Authors: Liu Tian , Spincemaille Pascal , de Rochefort Ludovic , Kressler Bryan , Wang Yi 
Published: December 2008

AbstractMagnetic susceptibility differs among tissues based on their contents of iron, calcium, contrast agent, and other molecular compositions. Susceptibility modifies the magnetic field detected in the MR signal phase. The determination of an arbitrary susceptibility distribution from the induced field shifts is a challenging, ill‐posed inverse problem. A method called “calculation of susceptibility through multiple orientation sampling” (COSMOS) is proposed to stabilize this inverse problem. The field created by the susceptibility distribution is sampled at multiple orientations with respect to the polarization field, B0, and the susceptibility map is reconstructed by weighted linear least squares to account for field noise and the signal void region. Numerical simulations and phantom and in vitro imaging validations demonstrated that COSMOS is a stable and precise approach to quantify a susceptibility distribution using MRI. Magn Reson Med 61:196–204, 2009. © 2008 Wiley‐Liss, Inc.
Quantifying hepatic glycogen synthesis by direct and indirect pathways in rats under normal ad libitum feeding conditions
Authors: Soares Ana F. , Viega Francisco J. , Carvalho Rui A. , Jones John G. 
Published: December 2008

AbstractHepatic glycogen synthesis from intact hexose (direct pathway) relative to that from gluconeogenic precursors (indirect pathway) was quantified in ad libitum‐fed rats. Following 2H2O administration and overnight feeding, the livers were removed and glycogen 2H‐enrichment was measured by 2H NMR. Six controls and six rats rendered hyperglycemic by streptozotocin (STZ; fasting blood glucose = 385 ± 31 mg/dl) were studied. The indirect pathway contribution, estimated as glycogen hydrogen 5 relative to hydrogen 2 enrichment, was 54% ± 4% for control rats—similar to values from healthy, meal‐fed humans. In STZ‐treated rats, the indirect pathway contribution was significantly higher (68% ± 4%, P < 0.05 vs. controls), similar to that of Type 1 diabetic (T1D) patients. In conclusion, sources of hepatic glycogen synthesis in rats during ad libitum nocturnal feeding were quantified by analysis of glycogen enrichment from 2H2O. STZ caused alterations resembling the pathophysiology of hepatic glycogen synthesis in T1D patients. Magn Reson Med 61:1–5, 2009. © 2008 Wiley‐Liss, Inc.
Lung imaging under free‐breathing conditions
Authors: Oechsner Markus , Pracht Eberhard D. , Staeb Daniel , Arnold Johannes F.T. , Köstler Herbert , Hahn Dietbert , Beer Meinrad , Jakob Peter M. 
Published: December 2008

AbstractRespiratory motion and pulsatile blood flow can generate artifacts in morphological and functional lung imaging. Total acquisition time, and thus the achievable signal to noise ratio, is limited when performing breath‐hold and/or electrocardiogram‐triggered imaging. To overcome these limitations, imaging during free respiration can be performed using respiratory gating/triggering devices or navigator echoes. However, these techniques provide only poor gating resolution and can induce saturation bands and signal fluctuations into the lung volume. In this work, acquisition schemes for nonphase encoded navigator echoes were implemented into different sequences for morphological and functional lung imaging at 1.5 Tesla (T) and 0.2T. The navigator echoes allow monitoring of respiratory motion and provide an ECG‐trigger signal for correction of the heart cycle without influencing the imaged slices. Artifact free images acquired during free respiration using a 3D GE, 2D multislice TSE or multi‐Gradient Echo sequence for oxygen‐enhanced T quantification are presented. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.
The tensor distribution function
Authors: Leow A. D. , Zhu S. , Zhan L. , McMahon K. , de Zubicaray G. I. , Meredith M. , Wright M. J. , Toga A. W. , Thompson P. M. 
Published: December 2008

AbstractDiffusion weighted magnetic resonance imaging is a powerful tool that can be employed to study white matter microstructure by examining the 3D displacement profile of water molecules in brain tissue. By applying diffusion‐sensitized gradients along a minimum of six directions, second‐order tensors (represented by three‐by‐three positive definite matrices) can be computed to model dominant diffusion processes. However, conventional DTI is not sufficient to resolve more complicated white matter configurations, e.g., crossing fiber tracts. Recently, a number of high‐angular resolution schemes with more than six gradient directions have been employed to address this issue. In this article, we introduce the tensor distribution function (TDF), a probability function defined on the space of symmetric positive definite matrices. Using the calculus of variations, we solve the TDF that optimally describes the observed data. Here, fiber crossing is modeled as an ensemble of Gaussian diffusion processes with weights specified by the TDF. Once this optimal TDF is determined, the orientation distribution function (ODF) can easily be computed by analytic integration of the resulting displacement probability function. Moreover, a tensor orientation distribution function (TOD) may also be derived from the TDF, allowing for the estimation of principal fiber directions and their corresponding eigenvalues. Magn Reson Med 61:205–214, 2009. © 2008 Wiley‐Liss, Inc.
Single‐shot magnetic resonance spectroscopic imaging with partial parallel imaging
Authors: Posse Stefan , Otazo Ricardo , Tsai Shang‐Yueh , Yoshimoto Akio Ernesto , Lin Fa‐Hsuan 
Published: December 2008

AbstractA magnetic resonance spectroscopic imaging (MRSI) pulse sequence based on proton–echo‐planar‐spectroscopic‐imaging (PEPSI) is introduced that measures two‐dimensional metabolite maps in a single excitation. Echo‐planar spatial–spectral encoding was combined with interleaved phase encoding and parallel imaging using SENSE to reconstruct absorption mode spectra. The symmetrical k‐space trajectory compensates phase errors due to convolution of spatial and spectral encoding. Single‐shot MRSI at short TE was evaluated in phantoms and in vivo on a 3‐T whole‐body scanner equipped with a 12‐channel array coil. Four‐step interleaved phase encoding and fourfold SENSE acceleration were used to encode a 16 × 16 spatial matrix with a 390‐Hz spectral width. Comparison with conventional PEPSI and PEPSI with fourfold SENSE acceleration demonstrated comparable sensitivity per unit time when taking into account g‐factor–related noise increases and differences in sampling efficiency. LCModel fitting enabled quantification of inositol, choline, creatine, and N‐acetyl‐aspartate (NAA) in vivo with concentration values in the ranges measured with conventional PEPSI and SENSE‐accelerated PEPSI. Cramer–Rao lower bounds were comparable to those obtained with conventional SENSE‐accelerated PEPSI at the same voxel size and measurement time. This single‐shot MRSI method is therefore suitable for applications that require high temporal resolution to monitor temporal dynamics or to reduce sensitivity to tissue movement. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.
Phase labeling using sensitivity encoding (PLUS): Data acquisition and image reconstruction for geometric distortion correction in EPI
Authors: Techavipoo Udomchai , Lackey John , Shi Jianrong , Leist Thomas , Lai Song 
Published: December 2008

AbstractGeometric distortion caused by magnetic field inhomogeneity is generally an inevitable tradeoff for fast MRI acquisitions using echo‐planar imaging. Most of the existing distortion‐correction techniques require separate scans for field maps in order to correct the distortion contained in a measurement. A drawback of these current techniques is that the field map scans and the measurement can capture different patient positions, which invalidates the stationary condition. A new method was developed in this work to correct geometric distortion by using local phase shifts derived directly from the measurement itself, without the need of extra field map scans. This self‐sufficient method takes advantage of parallel imaging and k‐space trajectory modification to produce multiple images from a single acquisition. The measurement is also used to derive sensitivity maps for parallel imaging reconstruction. The derived phase shifts are retrospectively applied to the measurement for correction of geometric distortion in the measurement itself. The proposed method was successfully demonstrated using experimental data from a phantom and a human brain. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.
On the measurement of absolute cerebral blood volume (CBV) using vascular‐space‐occupancy (VASO) MRI
Authors: Uh Jinsoo , Lewis‐Amezcua Kelly , Varghese Rani , Lu Hanzhang 
Published: December 2008

AbstractRecently, a vascular‐space‐occupancy (VASO) MRI technique was developed for quantitative assessment of cerebral blood volume (CBV). This method uses the T1‐shortening effect of gadolinium diethylenetriamine pentaacetic acid (Gd‐DTPA) with imaging parameters chosen that null the precontrast blood magnetization but allow the postcontrast blood magnetization to recover to equilibrium. A key advantage of VASO CBV estimation is that it provides a straightforward procedure for converting MR signals to absolute physiologic values. However, as with other T1‐based steady‐state approaches, several important factors need to be considered that influence the accuracy of CBV values obtained with VASO MRI. Here, the transverse relaxation (T2/T) effect in VASO MRI was investigated using multiecho spin‐echo and gradient‐echo experiments, resulting in underestimation of CBV by 14.9% ± 1.1% and 16.0% ± 2.5% for spin echo (TE = 10 ms) and gradient echo (TE = 6 ms), respectively. In addition, the influence of contrast agent clearance was studied by acquiring multiple postcontrast VASO images at 2.2‐min intervals, which showed that the concentration of Gd‐DTPA in the first 14 min (single dose) was sufficient for the blood magnetization to fully recover to equilibrium. Finally, the effect of vascular Gd‐DTPA leakage was assessed for scalp tissue, and signal extrapolation as a function of postinjection time was demonstrated to be useful in minimizing the associated errors. Specific recommendations for VASO MRI acquisition and processing strategies are provided. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.
High‐field diffusion MR histology: Image‐based correction of eddy‐current ghosts in diffusion‐weighted rapid acquisition with relaxation enhancement (DW‐RARE)
Authors: Tyszka J. Michael , Frank Lawrence R. 
Published: December 2008

AbstractHigh‐resolution, diffusion‐weighted (DW) MR microscopy is gaining increasing acceptance as a nondestructive histological tool for the study of fixed tissue samples. Spin‐echo sequences are popular for high‐field diffusion imaging due to their high tolerance to B0 field inhomogeneities. Volumetric DW rapid acquisition with relaxation enhancement (DW‐RARE) currently offers the best tradeoff between imaging efficiency and image quality, but is relatively sensitive to residual eddy‐current effects on the echo train phase, resulting in encoding direction‐dependent ghosting in the DW images. We introduce two efficient, image‐based phase corrections for ghost artifact reduction in DW‐RARE of fixed tissue samples, neither of which require navigator echo acquisition. Both methods rely on the phase difference in k‐space between the unweighted reference image and a given DW image and assume a constant, per‐echo phase error arising from residual eddy‐current effects in the absence of sample motion. Significant qualitative and quantitative ghost artifact reductions are demonstrated for individual DW and calculated diffusion tensor images. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.
MR elastography of the human heart: Noninvasive assessment of myocardial elasticity changes by shear wave amplitude variations
Authors: Sack Ingolf , Rump Jens , Elgeti Thomas , Samani Abbas , Braun Jürgen 
Published: December 2008

AbstractMany cardiovascular diseases and disorders are associated with hemodynamic dysfunction. The heart's ability to contract and pump blood through the vascular system primarily depends on the elasticity of the myocardium. This article introduces a magnetic resonance elastography (MRE) technique that allows noninvasive and time‐resolved measurement of changes in myocardial elasticity over the cardiac cycle. To this end, low‐frequency shear vibrations of 24.3 Hz were induced in the human heart via the anterior chest wall. An electrocardiograph (ECG)‐triggered, steady‐state MRE sequence was used to capture shear oscillations with a frame rate of eight images per vibration cycle. The time evolution of 2D‐shear wave fields was observed in two imaging planes through the short axis of the heart in six healthy volunteers. Correlation analysis revealed that wave amplitudes were modulated in synchrony to the heartbeat with up to 2.45 ± 0.18 higher amplitudes during diastole than during systole (interindividual mean ± SD). The reduction of wave amplitudes started at 75 ± 9 ms prior to changes in left ventricular diameter occurring at the beginning of systole. Analysis of this wave amplitude alteration using a linear elastic constitutive model revealed a maximum change in the myocardial wall stiffness of a factor of 37.7 ± 10.6 during the cardiac cycle. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.
Quantification of myocardial perfusion using free‐breathing MRI and prospective slice tracking
Authors: Pedersen Henrik , Kelle Sebastian , Ringgaard Steffen , Schnackenburg Bernhard , Nagel Eike , Nehrke Kay , Kim Won Yong 
Published: December 2008

AbstractQuantification of myocardial perfusion using first‐pass magnetic resonance imaging (MRI) is hampered by respiratory motion of the heart. Prospective slice tracking (PST) potentially overcomes this problem, and may provide an attractive alternative or supplement to current breath‐hold techniques. This study demonstrates the feasibility of patient‐adapted 3D PST on a 3.0 Tesla MR system. Eight patients underwent free‐breathing studies of myocardial perfusion, simultaneously collecting data with and without PST. On average, PST reduced residual in‐plane motion by a factor of 2, compared to the noncorrected images, resulting in a fourfold improvement of perfusion measurements. In addition, a comparison of perfusion measurements performed with and without PST showed that through‐plane motion can contaminate measurements of myocardial perfusion. However, the quality of the navigator echoes on this field strength constituted a major source of error and needs further improvement to increase the accuracy and robustness of the method. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.
Rigid‐body motion correction with self‐navigation MRI
Authors: Mendes Jason , Kholmovski Eugene , Parker Dennis L. 
Published: December 2008

AbstractThe use of phase correlation to detect rigid‐body translational motion is reviewed and applied to individual echotrains in turbo‐spin‐echo data acquisition. It is shown that when the same echotrain is acquired twice, the subsampled correlation provides an array of delta‐functions, from which the motion that occurred between the acquisitions of the two echotrains can be measured. It is shown further that a similar correlation can be found between two sets of equally spaced measurements that are adjacent in k‐space. By measuring the motion between all adjacent pairs of k‐space subgroups, the complete motion history of a subject can be determined and the motion artifacts in the image can be corrected. Some of the limiting factors in using this technique are investigated with turbo‐spin‐echo head and hand images. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.
Three‐dimensional spatial and temporal temperature control with MR thermometry‐guided focused ultrasound (MRgHIFU)
Authors: Mougenot Charles , Quesson Bruno , de Senneville Baudouin Denis , de Oliveira Philippe Lourenco , Sprinkhuizen Sara , Palussière Jean , Grenier Nicolas , Moonen Chrit T.W. 
Published: December 2008

AbstractHigh‐intensity focused ultrasound (HIFU) is an efficient noninvasive technique for local heating. Using MRI thermal maps, a proportional, integral, and derivative (PID) automatic temperature control was previously applied at the focal point, or at several points within a plane perpendicular to the beam axis using a multispiral focal point trajectory. This study presents a flexible and rapid method to extend the spatial PID temperature control to three dimensions during each MR dynamic. The temperature in the complete volume is regulated by taking into account the overlap effect of nearby sonication points, which tends to enlarge the heated area along the beam axis. Volumetric temperature control in vitro in gel and in vivo in rabbit leg muscle was shown to provide temperature control with a precision close to that of the temperature MRI measurements. The proposed temperature control ensures heating throughout the volume of interest of up to 1 ml composed of 287 voxels with 95% of the energy deposited within its boundaries and reducing the typical average temperature overshoot to 1°C. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.