bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bsh distributions in the canine head and a human patient using 11b mri
Authors: Bradshaw Kenneth M. , Schweizer Martin P. , Glover Gary H. , Rock Hadley J. , Tippets Richard , Tang Peng‐Peng , Davis Wayne L. , Peter Heilbrun M. , Johnson Suzanne , Ghanem Tamer 
Published: March 2007

AbstractA 3D projection reconstruction (3DPR) method was used to obtain in vivo 11B images in a large canine brain tumor model and in a human infused with borocaptate sodium (BSH). Studies were performed in dogs with and without gliosarcomas implanted and grown to a size of 2–3 cm. The 3DPR method demonstrates a signal‐to‐noise ratio (SNR) that allows qualitative kinetic studies of the boron compound in normal and tumor tissue of the head. The measurements indicate initial uptake of the BSH compound in tumor to be less than that in muscle with no uptake in normal brain tissue. Moreover, uptake of BSH in tissue was found to lag the boron concentration in blood with delays that depend on tissue type. In addition, the first human boron images were obtained on a patient who underwent surgical resection and volumetric debulking of a large (7 cm) glioblastoma multiforme. BSH was readily taken up in residual tumor tissue, while diffusion into the resection volume was slower.
Correction for geometric distortion in echo planar images from B0 field variations
Authors: Jezzard Peter , Balaban Robert S. 
Published: March 2007

AbstractA method is described for the correction of geometric distortions occurring in echo planar images. The geometric distortions are caused in large part by static magnetic field inho‐mogeneities, leading to pixel shifts, particularly in the phase encode direction. By characterizing the field inhomogeneities from a field map, the image can be unwarped so that accurate alignment to conventionally collected images can be made. The algorithm to perform the unwarping is described, and results from echo planar images collected at 1.5 and 4 Tesla are shown.
Increased flexibility in GRASE imaging by k space‐banded phase encoding
Authors: Feinberg David A. , Johnson Glyn , Kiefer Berthold 
Published: March 2007

AbstractGRASE (GRadient and Spin Echo) is an echo train imaging technique that combines gradient and RF refocusing. Although overall signal decay is with T2 and field inhomogeneity phase errors do not accumulate, the small residual phase errors are periodic with echo number. The echo order described previously eliminates the phase error periodicity in k space but instead creates periodicity in the T2 modulation function that can also cause artifacts. In addition, with this order, the effective TE must be half the echo train time, and asymmetric Fourier sampling is difficult to implement. A new method is described that greatly reduces artifacts due to T2 decay, permits greater control of T2 contrast, and lends itself to asymmetric Fourier sampling. Different time segments of the echo train are encoded with different bands of spatial frequency in k space (hence “k banding”). Both computer simulations and experimental results demonstrate improvements in GRASE images acquired by this method.
Modulation of water diffusion during gonadotropin‐induced ovulation: nmr microscopy of the ovarian follicle
Authors: Tempel Catherine , Schiffenbauer Yael S. , Meir Gila , Neeman Michal 
Published: March 2007

AbstractThe preovulatory rat follicle reaches a diameter of 1 mm with no internal blood vessels. Nutrient supply to the enclosed oocyte depends solely on passive diffusion across the follicular wall and the follicular fluid. Spin‐echo and stimulatedecho NMR microscopy experiments were applied here for studying modulations in water diffusion during gonadotropin‐induced maturation of perfused rat ovarian follicles (32°C). Two diffusion compartments were observed for the follicular wall. The intracellular water diffusion coefficient, measured at a short diffusion time (9 ms) was 0.28 x 10−5 cm2/s. Diffusion at long diffusion times was restricted to 16 μm, the size of cells in the follicular wall, and did not change during maturation. In the follicular fluid a transient 26% decrease in the diffusion coefficient was observed 4–7 h after gonadotropin stimulation, a change that is bound to affect the metabolic balance of the oocyte before ovulation.
Homonuclear J‐refocused spectral editing technique for quantification of glutamine and glutamate by 1H NMR spectroscopy
Authors: Lee Heung K. , Yaman A. , Nalcioglu Orhan 
Published: March 2007

AbstractQuantification of the excitatory amino acid of glutamine and glutamate is extremely important partly because, when in excessive amounts, they can produce neuronal damage. However, quantification of such metabolites seems to be not straightforward owing to a large number of metabolic signals, particularly between the 2.0– and 3.0−ppm chemical shift range. The authors investigated a quantification method by using a homonuclear J‐refocused spectral editing technique, namely the J‐refocused PRESS (JPRESS), using both 1.5− and 4‐T whole body NMR systems. At first, the J‐coupling modulation of each metabolite at different TE values using the PRESS and JPRESS pulse sequences was compared. The suppression of J modulations with the JPRESS is well demonstrated on condition that TE values are less than 1/4 J. Then, the accuracy of glutamate quantification after subtracting the two spectra obtained at two different echo times and integrating the difference spectral area at different concentrations was evaluated. The results exhibit an excellent linear relationship between the actual concentration versus the difference spectral peak area at both 1.5 and 4 T. The achievable minimum voxel size was also considered and a 1‐ml voxel size seems to be possible at the typical glutamate concentration in vivo at a field strength of 4 T.
Development of a phased‐array coil for the lower extremities
Authors: Alley Marcus T. , Grist Thomas M. , Swan J. Shannon 
Published: March 2007

AbstractA phased‐array coil was developed to facilitate imaging the vasculature of the lower extremities. The array consists of four surface coils placed in a Plexiglas “I‐beam” frame that are configured to allow bilateral studies with up to a 40‐cm field of view (FOV). Data from phantoms indicate an increase in signal‐to‐noise ratio (SNR) in the regions of interest by an average factor of 2.8 ± 0.9 over that of the body coil. Preliminary in vivo data have also been obtained from n = 8 subjects and demonstrate significant improvements in image quality. The coil design described here should lead to reduced scan times through the ability to image both legs simultaneously with less need for patient repositioning.
A computer simulation of the static magnetic field distribution in the human head
Authors: Li Shizhe , Williams Gerald D. , Frisk Timothy A. , Arnold Blake W. , Smith Michael B. 
Published: March 2007

AbstractDistortion of the static magnetic field inside the human head is dependent on regional tissue susceptibility variations and geometrical shape. These effects result in resonance line broadening and frequency shifts and consequently, intensity and spatial errors in both magnetic resonance imaging (MRI) and magnetic resonance (MR) spectroscopy. To calculate the field distortion due to the susceptibility's geometry, two dimensional (2D) finite element analysis was applied to simulate the field distribution in a 2D model of the human head, placed in a uniform magnetic field. The model contains air‐filled cavities and sinuses, and the remainder is treated as water. The magnetic field deviation was evaluated using gray scale plots and histograms of the magnetic field. The shifts in parts/ million and broadening of the histograms correspond to the NMR of the sampled region. The field distribution of the human head was also experimentally mapped using the DANTE tagging sequence. The calculated and experimental field maps are in good agreement. Thus, geometric considerations with uniform susceptibilities are sufficient to explain most of the static magnetic field distribution in the human head.
A magnetization‐driven gradient echo pulse sequence for the study of myocardial perfusion
Authors: Judd Robert M. , Reeder Scott B. , Atalar Ergin , Mcveigh Elliot R. , Zerhouni Elias A. 
Published: March 2007

AbstractA T1‐weighted imaging pulse sequence for contrast‐based studies of myocardial perfusion is presented and evaluated in phantoms and in vivo. The sequence is similar to spoiled gradient‐recalled echo equences except that nonselective preparatory RF pulses drive magnetization to steady state prior to image acquisition. Steady state is thus obtained in both tissue and blood resulting in a stable, homogeneous, and dark pre‐contrast baseline. Tip angles and timings are chosen so that pixel intensity approximates a linear relation to 1/T1. The dynamic range of signal response to contrast agent concentration is greater than that of an inversion‐recovery fast low angle shot sequence. The sequence proposed should be useful for myocardial perfusion studies.
Quantification of relative cerebral blood flow change by flow‐sensitive alternating inversion recovery (FAIR) technique: Application to functional mapping
Authors: Kim Seong‐Gi 
Published: March 2007

AbstractRelative cerebral blood flow changes can be measured by a novel simple blood flow measurement technique with endogenous water protons as a tracer based on flow‐sensitive alternating inversion recovery (FAIR). Two inversion recovery (IR) images are acquired by interleaving slice‐selective inversion and nonselective inversion. During the inversion delay time after slice‐selective inversion, fully magnetized blood spins move into the imaging slice and exchange with tissue water. The signal enhancement (FAIR image) measured by the signal difference between two images is directly related to blood flow. For functional MR imaging studies, two IR images are alternatively and repeatedly acquired during control and task periods. Relative signal changes in the FAIR images during the task periods represent the relative regional cerebral blood flow changes. The FAIR technique has been successfully applied to functional brain mapping studies in humans during finger opposition movements. The technique is capable of generating microvascular‐based functional maps.
In Vivo localized proton NMR spectroscopy of thiamine‐deficient rat brain
Authors: Lee Haakil , Tarter James , Holburn George E. , Price Ronald R. , Weinstein David D. , Martin Peter R. 
Published: March 2007

AbstractThiamine deficiency (TD) in rats produces lesions similar to those found in humans suffering from Wernicke's encephalopathy, an organic mental disorder associated with alcoholism. Male Sprague‐Dawley rats (n = 29) were deprived of thiamine via a regimen of thiamine‐deficient chow and daily intraperitoneal injections of the thiamine antagonist pyrithiamine hydrobromide. Spectra were obtained by using the STEAM sequence. No significant change occurred in the ratio of Cr/NAA, while the ratio of Cho/NAA declined significantly (60 ± 11%) on Day 14. Eleven rats received intraperitoneal injections of thiamine hydrochloride at the end of 12 days, and dose‐dependent recovery in Cho/NAA was observed.
Evaluation of protective effects of prostaglandin E1 on ischemic liver damage with in vivo31P‐MR spectroscopy
Authors: Nabeshima Motoshige , Moriyasu Fuminori , Nishikawa Koji , Hamato Noriyuki , Fujimoto Masazumi , Nada Takayuki , Okuma Minoru , Morikawa Shigehiro , Inubushi Toshiro 
Published: March 2007

AbstractThe cytoprotective effect of prostaglandins (PG) was evaluated by in vivo 31P MR spectroscopy. Twenty rabbits were divided into two groups; the control group given physiological saline, and the PG group given prostaglandin E1 (0.5 μg/kg/min). Each solution was infused for 8 min, after which complete hepatic ischemia was induced for 20 min, followed by reperfusion for 40 min. During ischemia, β‐ATP decreased to 23.6% and 42.3%, phosphomonoester increased to 260% and 200% of their initial values in the control and the PG groups, respectively. Inorganic phosphate also increased. After reperfusion, β‐ATP recovered to 65.2% and 96.5%, phosphomonoester to 130% and 110%, inorganic phosphate to 140% and 120% in the control and PG groups, respectively. The changes during ischemia were significantly smaller and the recoveries during reperfusion were more complete in the PG group. These results may confirm the cytoprotective effect of prostaglandins by in vivo 31P‐MR spectroscopy.
Spiral imaging on a small‐bore system at 4.7t
Authors: Spielman Daniel M. , Pauly John M. 
Published: March 2007

AbstractSpiral imaging has a number of advantages for ultrafast data acquisition. However, implementation on high‐field small‐bore systems requires carefully addressing the issues of in‐homogeneity‐induced blurring and gradient hardware constraints. In this paper, spiral imaging on a 40‐cm‐bore 4.7T CSI Omega System (Bruker Instruments) is discussed. A constant‐voltage gradient waveform design algorithm is developed to reduce readout times as well as minimize waveform distortions due to gradient amplifier nonlinearities. Residual errors are then measured and taken into account in the image reconstruction procedure. Multiple spiral interleaves as well as a multifrequency reconstruction algorithm are used to decrease blurring of off‐resonance spins. Both phantom and in vivo images demonstrate the performance of the resulting pulse sequences.
A computer simulation program for mr imaging: application to rf and static magnetic field imperfections
Authors: Olsson Magnus B. E. , Wirestam Ronnie , Persson Bertil R. R. 
Published: March 2007

AbstractA computer simulation program capable of demonstrating various artifacts, such as image distortion caused by metallic implants in MR imaging, is presented. The structure of the program allows for the implementation of various imaging situations as long as spins only experience weak interaction, i.e., the Bloch equations are obeyed. The raw data are obtained by repeatedly applying the Bloch equations to the magnetization vector of each point of the simulated object, throughout the pulse sequence. With only a limited number of spins in each voxel, the effects of intravoxel dephasing and rephasing require special attention, and algorithms for this have been implemented.
A time encoding method for single‐shot imaging
Authors: Elizabeth Meyerand M. , Wong Eric C. 
Published: March 2007

AbstractA new 2D single‐shot imaging technique is introduced that uses only one dimension of Fourier encoding. The second dimension is encoded in time, rather than using phase encoding. The data is acquired in the form of a closely spaced echo train with each echo produced from a different physical line in the object. A 1D Fourier transform is applied to each echo for image reconstruction. Because only the desired lines are excited, there can be no aliasing in the time encoding direction even when the object is much larger than the field of view. This technique is also very insensitive to motion, as motion‐related artifacts do not propagate in the time encoding direction.
Validation of 19f‐magnetic resonance determination of myocardial blood volume
Authors: Rottman Gerald A. , Judd Robert M. , Yin Frank C. P. 
Published: March 2007

AbstractThe use of perfluorochemical (PFC) emulsions to study the myocardial circulation by means of 19F NMR requires that the biodistribution of the PFC be known. The authors tested the hypothesis that PFC particles remain within the myocardial vascular space by infusing rats with both a PFC emulsion and 125I‐albumin. Measurement of myocardial vascular volume by 19F NMR and by standard radiotracer analysis of the same tissue yielded concordant values by the two methods, establishing the PFC emulsion as an intravascular agent in this tissue. Perfluorochemical emulsions should be useful for the noninvasive study of myocardial vascular physiology by magnetic resonance.
Reduction of phase error ghosting artifacts in thin slice fast spin‐echo imaging
Authors: Wan Xin , Parker Dennis L. , Lee James N. , Buswell Henry R. , Gullberg Grant T. 
Published: March 2007

AbstractFast spin‐echo (FSE) imaging techniques are very sensitive to the relative phase between the 90° (excitation) RF pulse and the 180° (refocusing) RF pulses. In this paper, it is demonstrated that a phase shift can be created between the excitation and refocusing pulses in such a manner that the received signal is divided into two components of distinctly different phase shifts. The nature of these two components is reviewed. It is demonstrated that ghosting artifacts will occur when images are reconstructed from this received signal. The ghosting is shown to be object dependent. A correction technique is presented which calculates the phase errors among different echoes based on measurements from a single echo train acquired without phase encoding gradients. The results in both phantom and human studies show that this method is capable of reducing the ghosting artifact in thin slice FSE images.
Estimation of average flow in ungated 3D phase contrast angiograms
Authors: Maier Stephan E. , Cline Harvey E. , Jolesz Ferenc A. 
Published: March 2007

AbstractThree dimensional (3D) phase contrast angiograms contain velocity data, which is discarded after the reconstruction of the projections. In extension to earlier work on velocity quantification with ungated 2D phase data, this paper shows that a useful estimate of the average velocity and flow rate can be extracted from ungated 3D phase contrast angiograms. Simulations and experiments in a phantom and in vivo were performed. For pulsatile flow and strong spin saturation, an over‐estimation of the flow rate at the net in‐flow end of the imaging volume and underestimation at the net out‐flow end was observed. Imaging at lower RF tip angles yielded flow rates close to the correct value within the entire imaging volume. In contrast to ungated 2D experiments, the flow rates determined by repeated 3D experiments showed no variation.
In vivo measurement of partial oxygen pressure in large vessels and in the reticuloendothelial system using fast 19F‐MRI
Authors: Nöth Ulrike , Morrissey Sean P. , Deichmann Ralf , Adolf Holger , Schwarzbauer Christian , Lutz Joachim , Haase Axel 
Published: March 2007

AbstractQuantitative in vivo 19F‐MRI was performed in a rat model to monitor partial oxygen pressure (pO2) using a perfluorocarbon (PFC) emulsion as contrast agent. On Days 1, 4, and 8 postin‐jection of the PFC emulsion, transaxial T1 and pO2 maps were acquired of the abdomen of rats that were consecutively ventilated with pure oxygen, air, and a mixture of 10% oxygen and 90% nitrogen. The images had a resolution of 0.75 mm x 0.75 mm x 2 mm and a total acquisition time of 24 min. In these images it was possible to distinguish between different vessels and hepatic and splenic tissue in the selected imaging plane. Serial 19F‐MRI measurements on the different days postinjection of the PFC allowed to determine separately the pO2 of arterial and venous blood and the intracellular pO2 in macrophages of the liver and spleen.
Continuous radial data acquisition for dynamic MRI
Authors: Rasche Volker , Boer Ruud W. De , Holz Dietrich , Proksa Roland 
Published: March 2007

AbstractSince image acquisition times in MRI have been reduced considerably over recent years, several new important application areas of MRI have appeared. In addition to pure static anatomic information, the evolution of a dynamic process may be visualized by a sequence of temporal snapshots of the process acquired within a short time period. This makes applications like interactive or interventional MRI as well as the acquisition of additional functional information feasible. For high temporal resolution, all these applications require a quasi real‐time image acquisition during the time the interaction or dynamic process evolves. We present an approach to realtime imaging using a continuous radial acquisition scheme. The intrinsic advantages of radial or projection reconstruction (PR) techniques are used to minimize motion‐related image distortions. Modifications of the acquisition scheme as well as dedicated reconstruction techniques are used to further reduce the temporal blurring due to the finite acquisition time of one entire data set in our approach. So far we have used this technique for the visualization of active joint motion.
Shielded gradient coils on hyperbolic surfaces of revolution
Authors: Carlson Joseph W. , Roos Mark S. 
Published: March 2007

AbstractA formalism for the calculation of fields generated by current distributions on hyperbolic surfaces of revolution is presented and used to generate designs for shielded gradient coils. One application is the development of small, insertable coils suitable for head imaging while allowing clearance for shoulders. This technique demonstrates that efficient designs that offer substantial advantages over conventional cylindrical designs are possible.
A Methodology for co‐registering abdominal MR images over multiple breath‐holds
Authors: Feinberg David A. , Johnson G. 
Published: March 2007

AbstractPrevious studies have demonstrated that the SNR of abdominal MR images can be increased by averaging images obtained in different breath‐hold acquisitions. In this note, the authors present a simple new methodology for ensuring that images acquired in multiple breath‐hold periods are accurately co‐registered. Within each breath‐hold, a quick coronal scout scan is followed by a longer axial scan. The scout is used to position the axial slices in a fixed position relative to the organ under examination. This MR technique can, in principle, be automated so as to add less than 1 s to the imaging time of the axial scan. The method can be used to increase SNR by signal averaging or to co‐register images acquired during, for example, uptake of contrast agents. SNR improvement with negligible blurring is demonstrated in liver images acquired by this method from healthy volunteers.
Increased noe enhancement in 1h decoupled 31p mrs
Authors: Sluis Robert Van , Payne Geoffrey S. , Leach Martin O. 
Published: March 2007

Abstract1H decoupling using the WALTZ‐4 decoupling scheme is a popular means of improving spectral resolution in 31P NMR spectroscopy. At the same time, sensitivity in the proton decoupled 31P spectra is enhanced by the nuclear Overhauser effect. The authors show that when using WALTZ‐4 decoupling in a uniform decoupler RF field, the degree of sensitivity enhancement is critically dependent on whether the decoupling interval contains an odd or an even number of WALTZ decoupling elements. This effect is demonstrated both in phantoms and in vivo.
The rician distribution of noisy mri data
Authors: Gudbjartsson HáKon , Patz Samuel 
Published: March 2007

AbstractThe image intensity in magnetic resonance magnitude images in the presence of noise is shown to be governed by a Rician distribution. Low signal intensities (SNR < 2) are therefore biased due to the noise. it is shown how the underlying noise can be estimated from the images and a simple correction scheme is provided to reduce the bias. the noise characteristics in phase images are also studied and shown to be very different from those of the magnitude images. Common to both, however, is that the noise distributions are nearly Gaussian for SNR larger than two.