bluuebunny/crossref_metadata_2025_split huggingface dataset:
Detection of Residual Quadrupolar Interaction in Human Skeletal Muscle and Brain in vivo via Multiple Quantum Filtered Sodium NMR Spectra
Authors: Reddy Ravinder , Bolinger Lizann , Shinnar Meir , Noyszewski Elizabeth , Leigh John S. 
Published: March 2007

AbstractUsing sodium multiple quantum filtered methods, we have, for the first time, demonstrated the presence of residual quadrupolar interaction in human skeletal muscle and brain in vivo. Surface coils were used in both skeletal muscle and brain studies on healthy human volunteers. Theoretical analysis shows that even with arbitrary flip angles the double quantum filter retains filtering capability; it passes even rank two quantum coherence more efficiently than odd rank two quantum coherence. Multiple quantum filtered spectra were obtained from the gastrocnemius muscle in the leg and from the parietal lobe region of the brain. In double quantum filtered spectra, we observed different proportions of narrow and broad components with preparation time, while the line shape of triple quantum filtered spectra remained similar to the one observed in isotropic environment. These results suggest that, in human skeletal muscle and brain, sodium ions are bound to some ordered structures.
Ultra‐Rapid Gradient Echo Imaging
Authors: Heid Oliver , Deimling M. , Huk W. J. 
Published: March 2007

AbstractA novel ultra‐rapid gradient echo (URGE) NMR imaging technique is introduced, which is capable of continuous high resolution 3D scanning while neither subject to fast gradient switching nor excessive RF power deposition. Sampling free induction decays instead of creating spin echoes enables maintaining a workable steady state magnetization. Due to segmented k‐space acquisition, chemical shift, diffusion, and field inhomogeneity effects do not present major problems. We report on implementations acquiring from 32 x 64 x 64 partial‐Fourier image sets in 0.72 s, allowing for single‐shot magnetization‐prepared 3D imaging, to 128 x 128 x 128 image sets in 13.3 s and 21.5 s on a standard MRI scanner.
Block Regional Interpolation Scheme for k‐Space (BRISK): A Rapid Cardiac Imaging Technique
Authors: Doyle Mark , Walsh Edward G. , Blackwell Gerald G. , Pohost Gerald M. 
Published: March 2007

AbstractWe introduce an acquisition method, “block regional interpolation scheme for k‐space” (BRISK), to reduce the acquisition time for cardiac imaging. The method exploits the high degree of correlation that exists between time‐resolved cardiac images. For representative k‐space data sets, Fourier analysis was applied along the cardiac phase dimension to reveal that different regions of k‐space can be effectively sampled at different rates. A reduced sampling strategy was implemented, and unsampled points were generated by Fourier interpolation. Time savings of up to 75% are quite feasible and 25% BRISK scans compare well with 100% scans. Simulations and acquisitions using a normal volunteer and patients are presented.
Multi‐Slice MRI of Rat Brain Perfusion During Amphetamine Stimulation Using Arterial Spin Labeling
Authors: Silva Afonso C. , Zhang Weiguo , Williams Donald S. , Koretsky Alan P. 
Published: March 2007

AbstractWhen a single coil is used to measure perfusion by arterial spin labeling, saturation of macromolecular protons occurs during the labeling period. Induced magnetization transfer contrast (MTC) effects decrease tissue water signal intensity, reducing the sensitivity of the technique. In addition, MTC effects must be properly accounted for in acquiring a control image. This forces the image to a single slice centered between the labeling plane and the control plane. In this work, a two‐coil system is presented as a way to avoid saturation of macromolecular spins during arterial spin labeling. The system consists of one small surface coil for labeling the arterial water spins, and a head coil for MRI, actively decoupled from the labeling coil by using PIN diodes. It is shown that no signal loss occurs due to MTC effects when the two‐coil system is used for MRI of rat brain perfusion, enabling three‐dimensional perfusion imaging. Using the two‐coil system, a multi‐slice MRI sequence was used to study the regional effects of amphetamine on brain perfusion. Amphetamine causes significant increases in perfusion in many areas of the brain including the cortex, cingulate, and caudate putamen, in agreement with previous results using deoxyglucose uptake to monitor brain activation.
Phased Array Coils for Upper Extremity MRA
Authors: Monroe James W. , Schmalbrock Petra , Spigos Dimitrios G. 
Published: March 2007

AbstractA phased array coil was constructed for imaging the upper extremity vasculature for patients undergoing dialysis treatment. The phased array coil exhibits improved signal‐to‐noise ratio (SNR) over the body coil and allows imaging of the entire upper extremity. SNR as a function of depth was measured on a homogeneous phantom with the arm coil and compared with the body coil. Near the coil there is an improvement of a factor of 7 and at a depth of approximately 6–7 cm, there is an improvement of factor 2. In vivo SNR measurements resulted in similar improvements. Images of the upper extremity vasculature of healthy volunteers were generated using 2D‐time‐of‐flight (2DTOF) angiography. Blood flow velocity was assessed in a CINE‐phase contrast study.
Barbiturate‐Reversible Reduction of Water Diffusion Coefficient in Flurothyl‐Induced Status Epilepticus in Rats
Authors: Zhong Jianhui , Petroff Ogen A. C. , Prichard James W. , Gore John C. 
Published: March 2007

AbstractRat brains (n = 17) with flurothyl‐induced status epilepticus (SE) have been imaged with a gradient‐echo diffusion‐weighted imaging sequence at 2.0 T. The apparent water diffusion coefficient (ADC) decreased during seizure discharges. The magnitude of the ADC reduction correlated well with the duration of flurothyl exposure. A 17% reduction in the water ADC compared with preseizure condition was observed in rats with the longest flurothyl exposure time. In 13 rats, pentobarbital was used to arrest the electrographic seizure activity. ADC values began to return to normal a few minutes after the injection. In four rats with no pentobarbital administration, ADC values remained depressed up to 1 h after seizure onset. The results suggest that diffusion‐weighted MR imaging may be useful for mapping recent intense seizure activity in human patients with medically intractable epilepsy.
3D 31P Spectroscopic Imaging of the Human Heart at 4.1 T
Authors: Hetherington Hoby P. , Luney Derek J. E. , Thomas Vaughan J. , Pan Jullie W. , Ponder Steven L. , Tschendel Otmar , Twieg Donald B. , Pohost Gerald M. 
Published: March 2007

AbstractHigh field (4 Tesla) spectroscopic imaging offers the advantages of increased signal‐to‐noise ratio and the possibility of acquiring high resolution metabolite images. We have applied a three dimensional spectroscopic imaging sequence using a sparse Gaussian sampling method to acquire phosphocreatine (PCr) images of the human heart with 8‐cc voxels. PCr images enabled observation of the septum, left ventricular free wall, apex, and skeletal muscle. Quantitative evaluation of the 50 myocardial voxels acquired from 10 studies of healthy adults revealed a PCr/adenosine triphosphate (ATP) ratio of 1.80 ± 0.32 after correction for saturation effects. Due to the small size of the voxels and the ability to choose the location of the volumes to minimize inclusion of blood, no correction for blood pool ATP was required. The calculated PCr/ATP ratio is in agreement with other studies at 1.5 and 4.0 T.
A Model for Magnetization Transfer in Tissues
Authors: Morrison Clare , Mark Henkelman R. 
Published: March 2007

AbstractMagnetization transfer in several tissues is measured and successfully modeled using a two‐pool model of exchange. The line shape for the semi‐solid pool is characterized by a superLorentzian and the liquid pool by a Lorentzian. The tissues investigated were white and gray matter, optic nerve, muscle, and liver. All tissues the authors studied are characterized by the same model but differ in the parameter values of the model. Blood and cerebral spinal fluid (CSF) were also investigated. The two‐pool model with a Lorentzian line shape for both the semi‐solid and liquid pools modeled the magnetization transfer in blood. In CSF, as expected, there is no measurable exchange of magnetization. The T2B associated with the semi‐solid pool was short (˜10 μ) for all tissues indicating a fairly rigid semi‐solid pool. In addition characterization of the line shape as superLorentzian indicates molecules such as integral membrane proteins or lipids in membranes are likely molecules participating in the exchange. Conversely, in blood large globular proteins are indicated due to the Lorentzian nature of the semi‐solid pool and a T2B ≈ 300 μs.
Quantitative Combined Phosphorus and Proton PRESS of the Brains of Newborn Human Infants
Authors: Cady Ernest B. 
Published: March 2007

AbstractTechniques for quantitative, combined phosphorus and proton, point‐resolved spectroscopy (PRESS) studies of newborn‐infant brain have been developed. Phosphorus PRESS advantages include: voxel‐shimming; rapid transmitter‐pulse setting; novel use of brain‐water as a localized quantitation reference; and reduced broad components. Proton spectra from 1‐ml voxels and phosphorus spectra can both be acquired quantitatively within acceptable time. Cerebral lactate was consistently detected by proton PRESS and the normal concentration (˜ 3 mmol/kg wet weight) may be higher than in adult brain. Phosphorus PRESS provided metabolite peak‐area ratios and concentrations comparable with those obtained using ISIS.
The effects of isoflurane and halothane on blood flow and 31P NMR spectra in murine RIF‐1 tumors
Authors: Zhao Ming , Fortan Ludwig G. , Evelhoch Jeffrey L. 
Published: March 2007

AbstractThe principal aim of these studies was to evaluate the utility of isoflurane and halothane for NMR investigations of tumor physiology. In vivo 31P and 2H NMR were used to examine RIF‐1 tumors before, during, and (for 31P) after anesthesia. In tumors, halothane decreases blood flow, [PCR]:[NTP], and pH indicated by the P1 chemical shift (pHnmr), while it increases [P1:[NTP]; effects consistent with well‐established cardiovascular effects of halothane. Isoflurane does not affect tumor blood flow or [PCr]:[NTP], but increases tumor [P1:[NTP] and decreases tumor pHnmr. In vivo 31P NMR measurements of normal mouse liver (upper abdomen) indicate that isoflurane has a similar effect in the liver. Although the mechanism for these effects is unknown, observation of a split P1 peak during isoflurane anesthesia suggests that a pool of P1 in a lower pH environment may become evident under isoflurane anesthesia. Regardless of the cause for increased [P1:[NTP] and decreased pHnmr the utility of isoflurane anesthesia for 31P NMR studies of energy metabolism is limited.
Pulses with fixed magnitude and variable phase response profiles
Authors: Pickup Stephen , Ding Xiaoning 
Published: March 2007

AbstractThe Shinnar‐Le Roux (SLR) method of pulse envelope design provides for the generation of nearly arbitrary magnitude response profiles with such great efficiency that the pulse envelopes may often be calculated at the time of sequence initiation. A significant limitation of the method is that it provides only limited control of the phase of the response profile. In the current manuscript it is demonstrated that the phase of the response profile can be modulated without affecting the magnitude profile by replacement of some of the roots of the SLR polynomials with one over their complex conjugate. This method allows interactive tailoring of the phase profile to the user's needs. Although the method does not allow for the optimization of arbitrary phase profiles, a variety of pulses, which are of general utility, have been generated. Some of these pulses and their response profiles are presented.
Spatial‐Frequency‐Tuned Markers and Adaptive Correction for Rotational Motion
Authors: Korin Hope W. , Felmlee Joel P. , Riederer Stephen J. , Ehman Richard L. 
Published: March 2007

AbstractA common type of motion present in clinical magnetic resonance imaging examinations is rotational motion, such as that due to voluntary motion during head examinations. The correction scheme presented in this work offers a method for eliminating the effects of rotations within the imaging plane. Integral to the implementation of this technique is the concept and design of spatial‐frequency‐tuned markers, which are used to track the rotational motion. These studies showed that it is possible to accurately track the motion, measuring both axis and angle of rotation, and use this information to retrospectively correct the acquired images. These markers can also provide information about any translational motion present. The resulting images show a marked decrease in artifacts and improved clarity.
Respiratory Motion of the Heart: Kinematics and the Implications for the Spatial Resolution in Coronary Imaging
Authors: Wang Yi , Riederer Stephen J. , Ehman Richard L. 
Published: March 2007

AbstractRespiratory motion is a major limiting factor in improving image resolution and signal‐to‐noise ratio in MR coronary imaging. In this work the effects of respiration on the cardiac position were studied quantitively by imaging the heart during diastole at various positions of tidal respiration with a breath‐hold segmented fast gradient echo technique. It was found that during tidal breathing the movement of the heart due to respiration is dominated by superior‐inferior (SI) motion, which is linearly related to the SI motion of the diaphragm. The motion of the heart due to respiration is approximately a global translation. These results provide motivation for employing adaptive motion correction techniques to reduce image blurring in nonbreath‐hold coronary MR imaging.
Measurement of Water Diffusion in Hormone‐Treated Rat Uteri by Diffusion‐Weighted Magnetic Resonance Imaging
Authors: Yang Yihong , Xu Su , Joan Dawson M. 
Published: March 2007

AbstractIn this study, apparent water diffusion coefficients in hormone‐treated rat uteri were measured by diffusion‐weighted NMR imaging. Four groups of ovariectomized, mature young rats were treated with estrogen, progesterone, estrogen plus progesterone, or saline (as control). It was found that water diffusion is anisotropic in the myometrium, but not in the endometrium, and that it depends on hormonal conditions in the endometrium, but not in the myometrium. The anisotropy of water diffusion can be exploited to improve image contrast among the various uterine tissue types. The hormonal response suggests that diffusion imaging of human uterus may be useful in detecting endometrial pathology.
Discrimination of Large Venous Vessels in Time‐Course Spiral Blood‐Oxygen‐Level‐Dependent Magnetic‐Resonance Functional Neuroimaging
Authors: Lee Adrian T. , Glover Gary H. , Meyer Craig H. 
Published: March 2007

AbstractA technique is described for discriminating blood‐oxygen‐level‐dependent (BOLD) signal changes originating from large venous vessels and those that arise from the cortical parenchyma based on examining the temporal delay of each pixel's response. Photic stimulation experiments were performed with a conventional 1.5 T scanner and correlated each pixel's time‐course with sine and cosine functions at the frequency of the stimulus. It was found that the signal in pixels anatomically associated with gray matter was delayed between 4 and 8 s compared with the stimulus, whereas the signal in pixels correlated with visible vessels and sulci was generally delayed from 8 to 14 s. This larger delay is consistent with the longer time required for blood to reach the larger vessels. Finally, stimulus‐induced NMR phase changes were observed for the largest vessels, which are attributed to bulk susceptibility shifts.
Motion Induced Phase Shifts in MR: Acceleration Effects in Quantitative Flow Measurements—A Reconsideration
Authors: Kouwenhoven Marc , Hofman Mark B. M. , Sprenger Michiel 
Published: March 2007

AbstractMagnetic resonance phase difference techniques are commonly used to study flow velocities in the human body. Acceleration is often present, either in the form of pulsatile flow, or in the form of convective acceleration. Questions have arisen about the exact time point at which the velocity is encoded, and also about the sensitivity to (convective) acceleration and higher order motion derivatives. It has become common practice to interpret the net phase shifts measured with a phase difference velocity technique as being the velocity at a certain (Taylor) expansion time point, chosen somewhere between the RF excitation and the echo readout. However, phase shifts are developed over the duration of the encoding magnetic field gradient wave form, and should therefore be interpreted as a more or less time‐averaged velocity. It will be shown that the phase shift as measured with a phase difference velocity technique represents the velocity at the “gravity” center of the encoding bipolar gradient (difference) function, without acceleration contribution. Any attempt to interpret the measured phase shift in terms of velocity on any other time point than the gradient gravity point will automatically introduce acceleration sensitivity.
In Vivo Validation of Magnetic Resonance Blood Volume Flow Measurements with Limited Spatial Resolution in Small Vessels
Authors: Hofman Mark B. M. , Visser Frans C. , Van Rossum Albert C. , Vink Ger Q. M. , Sprenger Michiel , Westerhof Nico 
Published: March 2007

AbstractThe accuracy of magnetic resonance phase contrast volume flow measurements in small blood vessels is expected to be smaller than in large vessels, because of partial volume effects at the vessel boundary. Accuracy was validated in the dog femoral artery, diameter 3.5 ± 0.7 mm, using an ultrasonic transit‐time flowmeter (TT). The number of pixels per vessel diameter (ND) ranged from 1.6 to 4.8. The vessel cross‐section was determined using a threshold in the magnitude image. Between the two methods the correlation coefficient was 0.95 (range 10–200 ml/min). The proportional difference (PD), (QTT – QMR/1/2(QTT + QMR), was 0.8%, showing no systematic difference between the methods. The PDs standard deviation was 27%, and 19% for flow rates above 30 ml/min. Only a significant decrease of the PDs variance was found at the highest ND values, suggesting other sources of error than partial volume effects. It is concluded that with an ND value of about 3, accurate blood volume flow rates can be determined.
NMR Microscopy of Single Neurons Using Spin Echo and Line Narrowed 2DFT Imaging
Authors: Bowtell Richard W. , Peters Andrew , Sharp Jonathan C. , Mansfield Peter , Hsu Edward W. , Aiken Nanci , Horsman Anthony , Blackband Stephen J. 
Published: March 2007

AbstractNMR microimages of single neural cells were acquired at 500 MHz using a conventional spin echo pulse sequence and a line‐narrowing sequence that eliminates susceptibility effects. The data show that any contribution to the measuredT2relaxation rate arising from diffusion in local field inhomogeneities using spin echo sequences at high fields and high spatial resolution is relatively small. We conclude that the measuredT2difference between the nucleus and cytoplasm in these cells represents primarily a trueT2relaxation effect arising from the interactions of water with macromolecules in the two compartments and does not result from microsusceptibility differences. These observations have implications regarding water compartmentation in single cells and the interpretation of the MR characteristics of tissuesin vivo.
Accuracy of Oxygen Measurements in T2 (Line Width) EPR Oximetry
Authors: Smirnova Tatyana I. , Smirnov Alex I. , Clarkson Robert B. , Linn Belford R. 
Published: March 2007

AbstractEPR oximetry is used for in vivo and in vitro measurements of oxygen in biological systems, including experimental animals. The accuracy of oxygen measurements in T2 (line width) EPR oximetry is significantly improved if least‐squares simulation is used to extract the line width parameters. The oxygen effect on the EPR spectra of nitroxide solutions and aqueous suspensions of fusinite can be described as an additional homogeneous broadening that modifies the EPR spectrum of the oxygen‐free probe. This allows one to use a one‐parameter line width model in most cases. The simulations were carried out with the use of a fast‐convolution algorithm followed by Levenberg‐Marquardt optimization. The validity of error estimates provided by this method was tested on sets of experimental spectra taken under common conditions. It is shown that the accuracy of oxygen measurements in line width (T2) oximetry is determined not only by the probe sensitivity (rate of line width change versus oxygen concentration), but also by the signal‐to‐noise ratio, inhomogeneous contribution to the line shape (e.g., unresolved proton superhyperfine structure), and the spectral window. The accuracy of oxygen measurements is compared for aqueous solutions of two nitroxide radicals with different superhyperfine structure and for aqueous suspensions of fusinite.
A Nyquist Modulated Echo‐to‐View Mapping Scheme for Fast Spin‐Echo Imaging
Authors: Keller Paul J. , Heiserman Joseph E. , Fram Evan K. , Rand Scott D. , Drayer Burton P. 
Published: March 2007

AbstractA new scheme for assignment of echoes to views in fast spin‐echo imaging was developed. The scheme places early and late echoes in alternating lines of the periphery of k‐space; continued alternation of echoes arising closer to the middle of the echo train encodes the central portion of k‐space. The scheme has two effects: a) The echo‐to‐echo signal decay that usually gives rise to multiple faint ghosts, now yields a single Nyquist ghost that is removed by phase over‐sampling. b) Mapping earlier echoes (and thus more energy) to the periphery of k‐space yields sharper edges.
Design of Matching Networks for Low Noise Preamplifiers
Authors: Reykowski Arne , Wright Steven M. , Porter Jay R. 
Published: March 2007

AbstractThis paper discusses matching networks that minimize inductive coupling between the antennas within an array while simultaneously insuring minimum noise contributions from preamplifiers. Typical low noise preamplifier designs require a strong mismatch between the source impedance and the amplifier input impedance (reflection coefficient close to one) to achieve optimal noise performance. This is in contrast to the familiar impedance match known from communication theory where input and source impedances have complex conjugate values for maximizing the power transfer from source to amplifier. The high input reflection coefficient of low noise amplifiers can be exploited to reduce antenna currents by using lossless impedance transformations to create a high impedance at the coil terminals while simultaneously maintaining a low noise figure for the amplifier. The networks presented here constitute an improvement over previous work because they give additional freedoms regarding the values of the network components and the amplifier input impedance. The technique has been formalized and coded in MathCadTM, making the design of realizable networks a simple process.