bluuebunny/crossref_metadata_2025_split huggingface dataset:
MR imaging of coronary artery flow in isolated and in vivo hearts
Authors: Burstein Deborah 
Published: March 2007

AbstractMethods for imaging flow in coronary arteries with magnetic resonance (MR) imaging techniques are demonstrated in isolated heart preparations and live animal models. Coronary artery flow was first imaged with a flow‐compensated gradient‐echo pulse sequence in isovolumic and working perfused rat hearts and then in vivo. A bolus tracking technique was used to measure flow velocity in the coronary arteries. Ultrafast gradient‐echo imaging techniques were then applied, with high resolution obtained by combining the information from several cardiac cycles. A stimulated‐echo pulse sequence was demonstrated as a method for performing coronary angiography by flow tagging in isovolumic perfused hearts. This report describes the results of coronary flow MR imaging in isolated rat hearts and live mice and rats. The general approach has proved useful in evaluating new methods for coronary MR angiography and should permit wellcontrolled studies of pathologic conditions. This ability to image coronary flow in isolated hearts and in small animals should permit integrated MR studies of coronary flow, myocardial perfusion, myocardial metabolism, and cellular ionic status.
Measurement of abdominal fat with T1‐weighted MR images
Authors: Lancaster Jack L. , Ghiatas Abraham A. , Alyassin Abdalmajeid , Kilcoyne Ray F. , Bonora Enzo , Defronzo Ralph A. 
Published: March 2007

AbstractThe cross‐sectional area of visceral and subcutaneous fat in the abdomen was measured with T1 weighted spin‐echo images acquired with a 1.5‐T magnetic resonance (MR) imager. Four axial images centered on L‐4 were acquired in each patient. Outline regions of interest (ROIs) were drawn manually for subcutaneous and visceral fat. The subcutaneous fat cross‐sectional area was calculated from the ROIs drawn around the outer and inner margins of subcutaneous fat. Several adaptive processing methods were evaluated for measuring fat in the complex structure of the viscera. These methods were compared with an existing MR imaging measurement method for abdominal fat in 18 patients. The adaptive method that uses the valley between the fat and nonfat distributions in the average histogram curve was judged best for research evaluations because it reduces the effects of volume averaging while using a more natural division between fat and nonfat data. Another adaptive method that yielded comparable measurements was thought to be more suitable for clinical applications. Cross‐sectional area measurements of abdominal fat were compared in 18 nonobese and 17 obese women to illustrate the utility of these measurements.
Evaluation of functional positions of tongue and soft palate with MR imaging: Initial clinical results
Authors: Wein Berthold B. , Drobnitzky Matthias , Klajman Stanislaw , Angerstein Wolfgang 
Published: March 2007

AbstractMagnetic resonance imaging was used to analyze functional positions of the tongue and soft palate in 10 patients and 10 healthy volunteers. The patients had velopharyngeal insufficiency and/or dysfunction of the tongue. With snapshot FLASH (fast low‐angle shot) sequences (data acquisition time, <1 second), malpositions of the articulatory apparatus were imaged and recorded for follow‐up documentation.
Right‐side aortic arch with aneurysm of aberrant left subclavian artery: MR imaging appearance
Authors: Benedikt Richard A. , Jelinek James S. , Schaefer Paul S. , Edwards Fred , Ghaed Victor 
Published: March 2007

AbstractReports of aneurysms of the subclavian artery in both normal and anomalous aortic arches have been rare. The authors describe a patient with a right‐side aortic arch and an aneurysm of the aberrant left subclavian artery, which, to the authors' knowledge, is a previously unreported association. At presentation, the aneurysm appeared as a calcified left superior mediastinal mass. Magnetic resonance imaging enabled preoperative diagnosis and guided surgical planning.
Interventricular differences in myocardial T2 measurements: Experimental and clinical studies
Authors: Scholz Thomas D. , Fisher David J. , Ehrhardt James C. , Skorton David J. 
Published: March 2007

AbstractThe goal of this study was to determine the accuracy, the reproducibility, and some of the tissue determinants of image‐based myocardial T2 measurements. Image‐based T2 calculations for the free walls of the right ventricle (RV) and left ventricle (LV), in vitro T2 determination (at 0.47 T), and water, fat, and collagen content analyses were performed in ex vivo hog hearts. T2 values of the RV and LV free walls were also determined from spin‐echo images of 14 healthy human subjects. Preliminary reproducibility studies were performed with 10 sets of images acquired from a single subject. For both in vitro and image‐based T2 values of hog hearts, RV T2 was significantly longer than LV T2. Water content was the only tissue factor to significantly correlate with in vitro and image‐based T2 values. For the 14 human subjects studied, image‐based T2 values calculated from the first‐ and third‐echo images demonstrated a significant difference between LV and RV. The difference was not significant when the first‐ and second‐echo images were used. Image‐based T2 measurements of a single subject showed a coefficient of variation of 6.8% for the LV and 9.1% for the RV. The authors conclude that image‐based T2 measurements of normal myocardium can be made with sufficient precision to identify differences of the magnitude of those found between RV and LV T2 values. Image‐based T2 values of myocardium may provide useful data to aid in patient treatment.
Multipoint dixon technique for water and fat proton and susceptibility imaging
Authors: Glover Gary H. 
Published: March 2007

AbstractExtensions to a previously described three‐point Dixon magnetic resonance imaging technique are presented that use alternative water/fat phase‐encoding strategies. The technique is generalized to phase encoding of (−θ,0,θ) or (0,θ,2θ) radians, and the signal‐to‐noise ratio (S/N) performance is evaluated. It was found that a θ of 2π/3 radians has optimal S/N but that a θ of π radians is a good compromise and that phase encoding of (O,π, 2π) radians offer an advantage over the previous method, which used (−π, O, π) increments, in that a T2′ (intravoxel susceptibility dephasing) image may be obtained in addition to the usual water, fat, and B0 images. A new four‐point method with phase encoding of (O, π, 2π, 3π) radians that can also provide a measure of the spectral width of the fat resonance is suggested. The disadvantages of the method are the extra imaging time and low S/N efficiency.
Visualization of MR angiographic data with segmentation and volume‐rendering techniques
Authors: Hu Xiaoping , Alperin Noam , Levin David N. , Tan Kim K. , Mengeot Michel 
Published: March 2007

AbstractNovel image processing and computer graphics techniques were developed to create three‐dimensional (3D) models of vasculature from magnetic resonance (MR) angiographic images of the head or neck. Region growing was used to produce a mask that isolated the vascular signal in the MR angiographic data. The masked images were subjected to gradient‐shaded volume rendering to create 3D views of the vasculature. The computer‐derived model of intracranial vasculature was then merged with a 3D model of brain parenchyma derived from a set of MR images. The combined display of vascular and gyral anatomy may be useful for neurosurgical planning.
Significance of the point of expansion in interpretation of gradient moments and motion sensitivity
Authors: Simonetti Orlando P. , Wendt Richard E. , Duerk Jeffrey L. 
Published: March 2007

AbstractThe relationship between magnetic field gradient waveform moments and the motion sensitivity of magnetic resonance imaging was explored analytically and by computer simulation. The analysis and simulations revealed several key points. In general, waveform time moments define sensitivity to the time derivatives of position of moving material only at a single time point: the time about which the moments are computed. A Taylor series description of instantaneous position is expanded about this same time point to compute the phase acquired due to specific derivatives of position. A moment is proportional to phase sensitivity to a particular derivative of position throughout the waveform only when sensitivity to all lower‐order derivatives is zero. Under restricted conditions of waveform symmetry and motion characteristics, the phase due to motion may be expressed in terms of the average value of a derivative of position over the duration of the waveform. The choice of the moment center, or point of expansion, adds a degree of freedom that may be used advantageously in the design of motion‐compensating and motion phase‐encoding gradient waveforms. These results facilitate a more complete understanding of the effects of motion through a magnetic field gradient.
Acoustic pressure wave generation within an MR imaging system: Potential medical applications
Authors: Jolesz Ferenc A. , Jakab Peter D. 
Published: March 2007

AbstractThe static magnetic field of a magnetic resonance (MR) imaging system was used as a component of an electromagnetic transducer for generating acoustic pressure waves. To permit limited focusing, the transducer was constructed from a conductive thin plate shaped like a section of a sphere. The plate was placed within the static field of the MR unit (B0 = 1.5 T), and current pulses with a rise time of 73 nsec and amplitude of 1.0 kA were applied to it. Hydrophonic recording demonstrated a shock wave with a peak pressure of 4.8 MPa at the approximated focal point. MR guidance of lithotripsy would be particularly useful to limit undesirable soft‐tissue damage. It is also suggested that the integration of an acoustic pressure wave generator with MR imaging and control provides a novel technology for the treatment of solid soft‐tissue tumors.
Serial P‐31 MR spectroscopy after fructose infusion in patients with chronic hepatitis
Authors: Sakuma Hajime , Itabashi Kenji , Takeda Kan , Hirano Tadanori , Kinosada Yasutomi , Nakagawa Tsuyoshi , Yamada Masao , Nakano Takeshi 
Published: March 2007

AbstractSerial changes in phosphorus metabolites after intravenous administration of fructose were compared between five healthy volunteers and five patients with chronic hepatitis by means of phosphorus‐31 magnetic resonance (MR) spectroscopy. P‐31 spectra were obtained every 5 minutes after intravenous drip infusion of 20% fructose at a dose of 0.5 g/kg of body weight. In the healthy volunteers, phosphomonoesters (PME) increased to 338% ± 76% of the preadministration value at 15‐20 minutes. Inorganic phosphate (Pi) was depleted in the first 15 minutes, then rebounded to 260% ± 67% of the initial value. β‐adenosine triphosphate decreased to less than 50% of its initial value and then gradually recovered. In patients with chronic hopatitis, the increase of PME at 15‐20 minutes (151% ± 49% of the preadministration value) was significantly less than that in healthy volunteers (p <.05). In addition, the rebound of pi at 35‐40 minutes (126% ± 42%) was significantly less than that in healthy volunteers (P <.05). IN conclusion, P‐31 MR Spectroscopy with fructose administration is valuable in the fuctional evaluation of diffuse liver diseases.
Phase‐constrained data extrapolation method for reduction of truncation artifacts
Authors: Amartur Sundar , Liang Zhi‐Pei , Boada Fernando , Haacke E. Mark 
Published: March 2007

AbstractThe authors present an improvement to a sigma‐filter extrapolation method for the reconstruction of magnetic resonance (MR) images from symmetric discrete Fourier data. By making use of the phase information in the image data, the proposed method can overcome the data inconsistency problem of the original method for handling MR image data with large phase variations, such as those obtained in gradientecho pulse sequences. Reconstruction results show that its performance is comparable with that of the modified complex sigma‐filter method proposed previously to handle the inconsistency problem. However, the new approach has the advantage of reducing computation time by a factor of two with use of a sigma filter applied to real instead of complex images. It is expected that this method will be more practical for use in clinical MR imaging systems.
Ionic versus nonionic MR imaging contrast media: Operational definitions
Authors: Allen Chang C. , Sieving Paul F. , Watson Alan D. , Dewey Torin M. , Karpishin Timothy B. , Raymond Kenneth N. 
Published: March 2007

AbstractAn experimental rationale is provided to differentiate between the terms ionic and nonionic for magnetic resonance (MR) imaging contrast media such as gadodiamide and gadopentetate dimeglumine. Four independent types of physical measurements (electric conductivity, osmolality, elec‐trophoresis, and ion exchange) were performed on a range of test compounds, including D‐glucose, iohexol, gadopentetate dimeglumine, and gadodiamide. Iohexol, D‐glucose, and gadodiamide are shown to be nonionic species at physiologic pH (7.4), not measurably dissociating in solution. A range of gadopentetate salts behave as electrolytes, dissociating into constituent charged ions in aqueous media. Operational definitions for the terms ionic and nonionic are provided, and the terms neutral and net zero charge are compared with nonionic for accuracy. The nomenclature nonionic and ionic is deemed appropriate for differentiating MR imaging contrast media.
Temperature monitoring during MR imaging: Comparison of fluoroptic and standard thermistors
Authors: Taber Katherine H. , Hayman L. Anne 
Published: March 2007

AbstractTemperature readings from standard wire lead thermistor probes and a fluoroptic temperature probe were compared before, during, and after exposure to a spin‐echo imaging sequence at 2.35 T. All the probes were placed in saline‐filled vials (1‐mL capacity) surrounded by dense foam rubber to isolate and preserve local heating effects. There were no consistent differences in the temperatures recorded by the various probes. The authors conclude that wire lead thermistor probes do not exhibit substantial heat deposition when exposed to a standard spin‐echo imaging sequence at 2.35 T.
Visualizing three‐dimensional flow with simulated streamlines and three‐dimensional phase‐contrast MR imaging
Authors: Napel Sandy , Lee Donald H. , Frayne Richard , Rutt Brian K. 
Published: March 2007

AbstractThree‐dimensional (3D) velocity maps acquired with 3D phase‐contrast magnetic resonance (MR) imaging contain information regarding complex motions that occur during imaging. A technique called simulated streamlines, Which facilitates the display and comprehension of these velocity data, is presented. Single or multiple seed points may be identified within blood vessels of interest and tracked through the velocity field. The resulting trajectories are combined with a 3D MR angiogram and displayed with 3D volume visualization software. Mathematical analysis highlights potential applications and pitfalls of the technique, which was implemented both in phantoms and in vivo with excellent results. For example, single streamlines reveal helical flow patterns in aneurysms, and multiple streamlines seeded in the common carotid artery reveal branch filling‐time relationships and slow filling of the carotid bulb. The technique is helpful in understanding these complex flow patterns.
Dynamic signal intensity changes in liver with superparamagnetic MR contrast agents
Authors: Reimer Peter , Kwong Kenneth K. , Weisskoff Robert , Cohen Mark S. , Brady Thomas J. , Weissleder Ralph 
Published: March 2007

AbstractThe dynamic effects of three different superparamagnetic magnetic resonance (MR) contrast agents on liver signal were evaluated with an echo‐planar imaging technique. The contrast agents were (a) USPIO (ultrasmall superparamagnetic iron oxide), which has a long blood half‐life and was developed for MR imaging of lymph nodes and bone marrow; (b) AG (arabinogalactan)‐USPIO, an asialoglycoprotein receptor directed iron oxide with hepatocyte uptake; and (c) AMI‐25, a conventional reticuloendothelial iron oxide agent. Dynamic liver signal intensity (SI) curves reflect different uptake mechanisms for the different agents. Receptor blocking experiments indicate that intracellular redistribution or clustering of the AG‐USPIO (known to occur from electron microscopy studies) does not contribute to the decrease in liver SI. Monitoring liver SI over time with echo‐planar imaging may provide a better understanding of the kinetics of the growing number of MR contrast agents and allow optimization of imaging protocols to exploit peak enhancement.
In vivo relationship between marrow T2* and trabecular bone density determined with a chemical shift—selective asymmetric spin‐echo sequence
Authors: Majumdar Sharmila , Genant Harry K. 
Published: March 2007

AbstractMaguetic field inhomogeneities due to differences in susceptibility between trabecular bone and bone marrow result in a reduction in T2*. The authors previously quantified the relationship between the relaxation rate enhancement per unit change in bone density, Δ*, using dried, excised vertebral bodies immersed in saline. In the present study, they investigated the precision and reproducibility of such measurements in vitro and found that the short‐term precision ranges from 2% to 11%, while the longterm precision error, which may be governed by the placement of the region of interest, can vary up to 50%. A chemical shift—selective asymmetric spin‐echo sequence was used to assess T2* changes in the saturated fat component of bone marrow in vivo. It was shown that the marrow fat relaxation rate increases as the surrounding trabecular bone density increases and that the Δ* of the marrow fat component was 0.20 sec −1/mg/cm3. The results also indicate that the distribution of T2* varies with image resolution. Both in vitro and in vivo, characteristics of the relaxation time distribution such as the mean, standard deviation, and skewness decrease as image resolution decreases, the degree of variation depending on the density of the surrounding trabecular network.
Policies, guidelines, and recommendations for MR imaging safety and patient management
Authors: Kanal Emanuel , Shellock Frank G. ,   SMRI Safety Committee
Published: March 2007

AbstractThe following are policies, guidelines, and recommendations from the Safety Committee of the Society for Magnetic Resonance Imaging (SMRI) concerning various issues related to magnetic resonance (MR) imaging safety and patient management. These policies, guidelines, and recommendations were developed to provide standardized and consistent information for use by health practitioners involved in clinical MR imaging.
Analysis of flow effects in echo‐planar imaging
Authors: Butts Kim , Riederer Stephen J. 
Published: March 2007

AbstractThe effects on the phase of spins moving during echo‐planar imaging (EPI) acquisition were studied. Standard single‐shot and interleaved multishot blipped EPI acquisitions were considered, assuming either high gradient strength and slew rates or standard gradient strength and slew rates. A spiral k‐space trajectory was also considered. Flow components in the section‐select and phase‐ and frequency‐encoding directions were analyzed separately. While the effect of flow in the section‐select direction is identical to that in a standard two‐dimensional Fourier transform (2DFT) acquisition, flow in the phase‐ or frequency‐encoding directions can have substantial effects on the image, different from that in 2DFT imaging. The magnitude of these effects, which include displacement, distortion, and/or ghosting of vascular structures, is analyzed and predicted for a given velocity and direction of flow, the specific acquisition sequence, and the strength and slew rate of the gradients. For example, 50‐cm/sec flow along the phase‐encoding direction can cause a blurring of 1.25 cm full width at half maximum for blipped EPI with high‐strength gradients, assuming a 40‐cm field of view and 64 × 64 matrix.
Mitral and aortic valvular flow: Quantification with MR phase mapping
Authors: Sondergaard Lars , Thomsen Carsten , Stahlberg Freddy , Gymoese Erik , Lindvig Knud , Hildebrandt Per , Henriksen Ole 
Published: March 2007

AbstractWhen magnetic resonance phase mapping is used to quantitate valvular blood flow, the presence of higher‐order‐motion terms may cause a loss of phase information. To overcome this problem, a sequence with reduced encoding for higher‐order motion was used, achieved by decreasing the duration of the flow‐encoding gradient to 2.2 msec. Tested on a flow phantom simulating a severe valvular stenosis, the sequence was found to be robust for higher‐order motion within the clinical velocity range. In eight healthy volunteers, mitral and aortic volume flow rates and peak velocities were quantified by means of phase mapping and compared with results of the indicator‐dilution technique and Dop‐pler echocardiography, respectively. Statistically significant correlations were found between phase mapping and the other two techniques. Similar studies in patients with valvular disease indicate that phase mapping is also valid for pathologic conditions. Phase mapping may be used as a noninva‐sive clinical tool for flow quantification in heart valve disease.
Pelvic imaging with phased‐array coils: Quantitative assessment of signal‐to‐noise ratio improvement
Authors: Hayes Cecil E. , Dietz Mark J. , King Bernard F. , Ehman Richard L. 
Published: March 2007

AbstractThe signal‐to‐noise ratios (S/Ns) of two different pelvic magnetic resonance (MR) imaging phased arrays were compared with that of the body coil. Each array consisted of two coils placed anteriorly and two posteriorly, oriented transversely in one array and longitudinally in the other. S/N measurements were obtained in an adjustable water‐filled phantom that simulated the shape and radio‐frequency loading effects of various‐size patients. Depending on the simulated anterior‐posterior thickness of the patient, the S/N produced by the longitudinal array ranged from 2.3 to 3.1 times higher than that of the body coil. The S/N of the transverse array was 3.1 to 3.4 times higher. The increased coil sensitivity permits imaging with shorter acquisition times, smaller fields of view, finer resolution, and/or thinner sections. Two examples in patients demonstrate the enhanced imaging capability of the phased arrays.
Centric phase‐encoding order in three‐dimensional MP‐RAGE sequences: Application to abdominal imaging
Authors: Bampton Anna E. H. , Riederer Stephen J. , Korin Hope W. 
Published: March 2007

AbstractThree‐dimensional (3D) magnetization‐prepared rapid gradient‐echo imaging has been proposed as a method for improving signal‐to‐noise ratio (S/N) and contrast‐to‐noise ratio (C/N) in rapid abdominal imaging. Originally, a standard sequential phase‐encoding order was proposed. In the present study, two approaches to a 3D centric phase‐encoding order are presented: (a) application of the two‐dimensional (2D) centric order to one of the 3D encoding directions, and (b) an interleaved square spiral order, which is the segmented 3D analog of the 2D centric order. With use of simulation, phantom, and volunteer results, the proposed 3D centric methods are compared in terms of S/N, C/N, and artifacts to the 3D sequential method and 2D magnetization‐prepared methods. The second centric approach was found to be superior to the first; however, in general, the 3D technique was found to be inferior to the 2D technique for abdominal imaging because of motion artifact in the 3D image set caused by misregistration among the multiple breath holds required.