bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of joint position and ligament tension on the MR signal intensity of the cruciate ligaments of the knee
Authors: Smith Kevin L. , Daniels John L. , Arnoczky Steven P. , Dodds Julie A. , Cooper Thomas G. , Gottschalk Alexander , Shaw Daniel A. 
Published: March 2007

AbstractSix cadaveric lower extremities were imaged with T1‐weighted spin‐echo pulse sequences with the knees extended and flexed to 90°. Magnetic resonance signal intensities of the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) were compared. Changing from extension to flexion resulted in decreased signal intensity in six of six ACLs and five of six PCLs. Two of the knees were then imaged with and without tension applied to the ACL. Both specimens showed a decrease in signal intensity with tension, followed by an increase in signal intensity with release of the tension. Finally, in three of the limbs the ACL was surgically reconstructed and then imaged with and without tension applied to the tension graft. Signal intensity decreased with tension and increased with release of the tension in all three specimens. Thus, joint position and changes in ligament tension affect the signal intensity of the ACL and PCL, generally resulting in a signal intensity decrease with tension.
MR measurement of pulsatile pressure gradients
Authors: Urchuk Steven N. , Plewes Donald B. 
Published: March 2007

AbstractA magnetic resonance (MR) imaging method for evaluating pulsatile pressure gradients in laminar blood flow is presented. The technique is based on an evaluation of fluid shear and inertial forces from cardiac‐gated phase‐contrast velocity measurements. The technique was experimentally validated by comparing MR and manometer pressure gradient measurements performed in a pulsatile flow phantom. Analyses of random noise propagation and sampling error were performed to determine the precision and accuracy of the method. The results indicate that a precision of 0.01–0.03 mmHg/cm and an accuracy of better than 8% can be achieved by using standard clinical pulse sequences in tubes exceeding 6 mm in diameter. The authors conclude that MR measurement of pressure gradients is feasible and that additional hemodynamic information may be derived from conventional phase‐contrast imaging studies.
Effects of physiologic waveform variability in triggered MR imaging: Theoretical analysis
Authors: Lauzon M. Louis , Holdsworth David W. , Frayne Richard , Rutt Brian K. 
Published: March 2007

AbstractOne of the assumptions inherent in most forms of triggered magnetic resonance (MR) imaging is that the pulsatile waveform (be it cardiac, respiratory, or some other) is purely periodic. In reality, the periodicity condition is rarely met. Physiologic waveform variability may lead to image artifacts and errors in velocity or volume flow rate estimates. The authors analyze the effects of physiologic waveform variability in triggered MR imaging. They propose that this variability be treated as a modulation of the underlying motion waveform. This report concentrates on amplitude modulation of the velocity waveform, which results in amplitude and phase modulation of the transverse magnetization. Established Fourier and modulation theory and the recently described principles of (k, t)‐space were used to derive the appearance of physiologic waveform variability artifacts in triggered MR images and to predict errors in time‐averaged and instantaneous velocity estimates that may result from such motion effects, including effects such as ghost overlap. Simulations and experimental results are provided to confirm the theory.
Characterization of a gadolinium‐labeled cholesterol derivative as an organ‐specific contrast agent for adrenal MR imaging
Authors: Muhler Andreas , Platzek Johannes , Radüchel Bernd , Frenzel Thomas , Weinmann Hanns‐Joachim 
Published: March 2007

AbstractThe purpose of the study was to determine if derivatization of cholesterol with a paramagnetic label could result in an organ‐specific contrast agent for magnetic resonance imaging of the adrenal glands. Gadolinium‐DO3A‐labeled cholesterol was synthesized and the relaxivities in water and blood plasma determined at 0.47 T and 40°C. Organ distribution was measured at 2 (n = 2) and 24 (n = 2) hours after intravenous injection of a 50 μmol/kg dose of Gd‐DO3A‐cholesterol in rats weighing 220–240 g. T1‐weighted spin‐echo images were acquired at 2 T before and after injection of 50 μmol/kg Gd‐DO3A‐cholesterol (n = 2) and Gd‐DTPA (diethylenetriaminepentaacetic acid)‐albumin (n = 2). More than 99% of the Gd‐DO3A‐cholesterol was found to be protein bound in bovine serum. High T1 and T2 relaxivities were found in water and plasma. High tissue concentrations of Gd‐DO3A‐cholesterol were found only in adrenal glands and liver. At 24 hours, adrenal gadolinium concentrations were about 10 times higher than in blood. At 2 hours after injection of Gd‐DO3A‐cholesterol. enhancement was 162% in adrenal glands and 146% in liver. With Gd‐DTPA‐albumin, enhancement values were 57% and 56%. respectively.
Quantitative mr imaging data in the evaluation of hepatic metastases during systemic chemotherapy
Authors: Giovagnoni Andrea , Paci Enrico , Terilli Filippo , Cellerino Riccardo , Piga Andrea 
Published: March 2007

AbstractTo identify changes induced by chemotherapy in hepatic metastases, 34 patients with metastases underwent magnetic resonance (MR) imaging before the start of systemic chemotherapy and monthly thereafter. The number, size, and morphologic patterns of the lesions and changes in quantitative parameters (signal‐to‐noise ratio [S/N], contrast‐to‐noise ratio, and signal intensity ratio) were evaluated and correlated with response to treatment and prognosis. After treatment, seven patients showed a partial response, 18 had stable disease, and nine had progressive disease. No relevant changes in the patterns of the lesions were observed. Quantitative data showed that patients with a good prognosis had an increase in S/N on T1‐weighted images and a relative decrease on T2‐weighted images; patients with a poor prognosis showed a decrease in S/N on T1‐weighted images and an increase on T2‐weighted images. The differences between patient groups were significant for both T1‐ and T2‐ weighted images. This study demonstrates the value of MR imaging in follow‐up of liver metastases and suggests the usefulness of quantitative MR imaging data.
Hybrid dante and phase‐contrast imaging technique for measurement of three‐ dimensional myocardial wall motion
Authors: Perman William H. , Creswell Lawrence L. , Wyers Stephan G. , Moulton Michael J. , Pasque Michael K. 
Published: March 2007

AbstractCharacterization of myocardial stress and strain is necessary for a complete understanding of myocardial function. The precise quantification of regional myocardial strain is complicated by its time‐varying pattern and regional variation resulting from the anisotropy of the myocardium and by complex torsional and shortening motions of the heart during the cardiac cycle. The authors have developed a technique for point‐specific tracking of myocardial motion along all three axes in a constant selected section of myocardium by combining prospective section selection with in‐plane DANTE (delays alternating with nutations for tailored excitation) tissue tagging and phase‐contrast detection of motion perpendicular to the image plane. With this technique, it is possible to determine point‐specific myocardial strain values in vivo.
Analysis of on‐ and off‐resonance magnetization transfer techniques
Authors: Hua Jianmin , Hurst Gregory C. 
Published: March 2007

AbstractThree methods of performing magnetization transfer (MT) MR imaging ere emlyzed: (a) off‐resonance continuous wave, (b) off‐rceonance shaped pulses, end (c) on‐resonance binomial pulses. With two‐pool Bloch‐model simulations., signal levels from “MT active” spin systems were calculated. with reference to direct saturation of “MT inactive” systems. allowing calculation of contrast due to MT. Simulations demonstrate several trends with variation of excitation amplitude and Offret fiequency for the off‐resoname methods and with variation of excitation emplitude end pulse shape „order”︁ for binomial pulses. The simulations show that nominally optimized versions of each of these approaches provide essentially equivalent contrast at a given level of applied MT power, contrary to previous claims. Experiments with an MT‐inactive phentom, with a whole‐body syetem, show results with off‐ rewnence pulses to be in good agreement with simulations. whereas binomiel‐ pulse experiments show anomalously large direct saturation.
A complex‐difference phase‐contrast technique for measurement of volume flow rates
Authors: Polzin Jason A. , Alley Marcus T. , Korosec Frank R. , Gristn Thomas M , Wang Yi , Mistretta Charles A. 
Published: March 2007

AbstractMagnetic resonance (MR) phase‐difference methods work well for measuring volumetric flow rates when the vessel diameter is large compared with the in‐plane voxel dimensions. For small vessels (eg, coronary arteries), partial‐volume effects introduce substantial errors in the measured volume flow rate. To correctly measure flow rates through a voxel, both the fraction of the voxel containing moving spins and the phase shift imparted to those spins must be known. The authors propose a flow measurement method that combines information obtained with both the complex‐difference and phase‐difference processing techniques and thereby provides the fractional volume occupied by the moving spins and the phase of those spins. The complex‐difference flow map method proposed results in improved accuracy of MR phase‐contrast flow measurements in the presence of partial‐volume effects.
Correction of partial‐volume effects in phase‐contrast flow measurements
Authors: Tang Chao , Blatter Duane D. , Parker Dennis L. 
Published: March 2007

AbstractBecause of the relatively small size of vessels and limited magnetic resonance (MR) imaging resolution, the accuracy of volume flow rate measurements is limited. A technique that corrects the partial‐volume effect in volume flow rate measurements is presented. The technique uses small‐phase‐shift approximation, with the assumption that blood flow in the voxels at the boundary of the vessel is slow. With the proposed correction technique, the volume flow rate in partially occupied voxels is corrected on a voxel‐by‐voxel basis and the accuracy of flow measurements increases. Results are shown analytically and for MR phantom data.
Separation of fat and water in fast spin‐echo MR imaging with the three‐point dixon technique
Authors: Hardy Peter A. , Hinks R. Scott , Tkach Jean A. 
Published: March 2007

AbstractA method for suppressing fat in fast spin‐echo imaging with the three‐point Dixon technique is described. The method differs from the three‐point Dixon method used in conventional spin‐echo imaging in that the readout gradient instead of a radio‐frequency pulse is shifted. This method preserves the Carr‐Purcell‐Meiboom‐Gill nature of the fast spin‐echo sequence and hence is less sensitive to magnetic field inhomogeneities and resonance frequency mistiming. As in the original three‐point Dixon technique used in conventional spin‐echo imaging, three acquisitions are required to estimate the field inhomogeneity and completely separate fat and water. The extra time required is not excessive considering that the fast spin‐echo method is frequently applied with multiple signal acquisition. Also, this technique achieves an expected signal‐to‐noise ratio comparable to 2.67 signal acquisitions, which is approximately 94% of the signal‐to‐noise ratio obtained with three signal acquisitions. The method is demonstrated with applications to phantoms and a human volunteer.
Hepatic tumors: Magnetization transfer MR imaging with gadolinium enhancement
Authors: Onaya Hiroaki , Yoshioka Hiroshi , Itai Yuji , Niitsu Mamoru , Anno Izumi , Okumura Toshiyuki 
Published: March 2007

AbstractThirty patients with 15 hepatocellular carcinomas, 10 metastases, four hemangiomas, and one cholangiocarcinoma underwent magnetic resonance imaging at 1.5 T with T1‐weighted, T2‐ weighted spin‐echo (SE) images, gradient‐echo (GRE) magnetization transfer (MT) images, and gadolinium‐enhanced T1‐weighted SE and MT‐ GRE images. The MT effect and lesion‐liver contrast‐to‐noise ratio (C/N) were calculated and visual assessment (qualitative analysis) performed for unenhanced and enhanced MT‐GRE images and enhanced Tl‐weighted SE images. The C/N values for hepatic adenocarcinomas (seven metastases and one cholangiocarcinoma) and hemangiomas were larger for enhanced MT‐GRE images (adenocarcinoma, 8.4 ± 2.3 [P < 0.01); hemangioma, 24 ± 2.1 [P < 0.05]) than for enhanced GRE images (5.0 ± 1.9 and 18 ± 2.7, respectively).These enhancing tumors had the highest scores in the qualitative analysis. Enhanced MT‐GRE images showed no advantage for depiction of hepatocellular carcinomas relative to the other images.
Cardiac‐gated MR angiography of pulsatile flow: K‐space strategies
Authors: Franck Anders , Selby Katharine , van Tyen Rem , Nordell Bo , Saloner David 
Published: March 2007

AbstractSignal strength in time‐of‐flight magnetic resonance (MR) anglograpny of pulsatile flow is modulated by the time‐varying intraluminal magnetization strength. The specific appearance of MR angiographlc images therefore depends on the relationship of different phase‐encoding steps to the pulsatile flow waveform. Cardiac‐phase gating can be applied with phase‐encoding reordering to acquire different regions of k‐space during the desired phases of the cardiac cycle. The authors have developed a simulation program for evaluating the merits of different encoding strategies for pulsatile flow. The model was validated with phantom studies. High signal intensity relative to that in conventional MR anglographic studies can be attained with strategies that impose relatively small penalties in total acquisition time.
Fast three‐dimensional time‐of‐flight MR angiography of the intracranial vasculature
Authors: Talagala S. Lalith , Jungreis Charles A. , Kanal Emanuel , Meyers Steven P. , Foo Thomas K. F. , Rubin Richard A. , Applegate Gregory R. 
Published: March 2007

AbstractMagnetic resonance angiography is most commonly performed with the three‐dimensional (3D) time‐of‐flight (TOP) technique. As currently practiced, this requires long image acquisition times (5–10 minutes). The authors show that the acquisition time of 3D TOP images can be reduced to less than 1 minute by using a very short TR (<10msec). Under normal flow conditions, the major vessels of the circle of Willis were consistently well demonstrated on these fast 3D TOP images. Signal saturation was observed in studies of patients with abnormal blood flow. In those cases, it was demonstrated that serial acquisition of fast 3D TOP data during and after contrast agent administration could be used to overcome the saturation effects. Time‐resolved fast 3D TOP imaging during and after contrast agent administration can also provide qualitative assessment of flow and may depict other features that cannot be observed in TOP studies with long imaging times.
Tracking of cyclic motion with phase‐contrast cine MR velocity data
Authors: Pelc Norbert J. , Drangova Maria , Pelc Lorie R. , Zhu Yudong , Noll Douglas C. , Bowman Brett S. , Herfkens Robert J. 
Published: March 2007

AbstractA method of computing trajectories of objects by using velocity data, particularly as acquired with phase‐contrast magnetic resonance (MR) imaging, is presented. Starting from a specified location at one time point, the method recursively estimates the trajectory. The effects of measurement noise and eddy current‐induced velocity offsets are analyzed. When the motion is periodic, trajectories can be computed by integrating in both the forward and backward temporal directions, and a linear combination of these trajectories minimizes the effect of velocity offsets and maximizes the precision of the combined trajectory. For representative acquisition parameters and signal‐to‐ noise ratios, the limitations due to measurement noise are acceptable. In a phantom with reciprocal rotation, the measured and true trajectories agreed to within 3.3%. Sample trajectory estimates of human myocardial regions are encouraging.
Biopsy needles and devices: Assessment of ferromagnetism and artifacts during exposure to a 1.5‐T MR system
Authors: Moscatel Marleigh A. , Shellock Frank G. , Morisoli Stacy M. 
Published: March 2007

AbstractForty‐eight biopsy devices (needles, stylets, guide wires, biopsy guns, etc) were evaluated for ferro‐magnetism (n=48) and artifacts (n=43) in a 1.5‐T magnetic resonance (MR) system, with previously described techniques. Forty‐five of the 48 devices were found to be ferromagnetic. Artifacts varied, depending on the type and size of the component material(s) of the device. Most of the commercially available biopsy devices are not useful for MR imaging‐guided biopsy procedures because of the presence of ferromagnetism and associated artifacts.
Single breath‐hold volumetric imaging of the heart using magnetization‐prepared 3‐dimensional segmented echo planar imaging
Authors: Wielopolski Piotr A. , Manning Warren J. , Edelman Robert R. 
Published: March 2007

AbstractWe show the feasibility of single breath‐hold volumetric imaging of the heart using a three‐dimensional (3D) segmented echo planar Imaging (EPI) pulse sequence. Fifteen healthy subjects were evaluated using three magnetization preparation schemes: (a) a driven equilibrium T2‐weighted preparation for bright blood and dark myocardium; (b) a STEAM magnetization preparation for dark blood; and (c) fat suppression for coronary artery Imaging. An interleaved EPI trajectory encoding six echoes per Interleave with a 1090 Hz/pixel readout bandwidth was used to collect a 126 × 256 matrix in 22 heartbeats with data acquisition windows per cardiac cycle of 71–285 msec for 8–32 sections. Multiplanar reconstructions could be used if thin (1–3 mm) sections were acquired. Breath‐hold volumetric imaging with 3D segmented EPI holds promise for rapid volumetric evaluation of cardiac anatomy.
Variablemangle uniform signal excitation (vuse) for threel dimensional time‐of‐flight MR angiography
Authors: Priatna Agus , Paschal Cynthia B. 
Published: March 2007

AbstractA spatially asymmetric RF pulse that improves the uniformity of blood signal intensity and vascular contrast in three‐dimensional (3D) MR angiorpgphy [MRA] is presented. The pulse, called variable‐angle uniform signal excitation (VUSE), was designed to provide uniform signal response and improved contrast for blood flowing through a 3D imagine volume during a FLASH sequence. The VUSE excitation proffle was optimized on the bash of the number of pulses seen by the blood, which varied with the velocity of through‐plane flow, repetition time, and slab thickness with the maximum flip angle at the flow udt constrained at 90°. The theoretical results show that the optimal RF pulse gives more uniformity for flow signal than does a linear ramp excitation proffle or a Gaussian pulse combined with a presaturation pulse. After truncation and ffltering of the VUSE pulse in the time domain, the general shape of the VUSE RF excitation profile is maintained. but the maximum flip angle is reduced. The arteries of the neck in a healthy volunteer were imaged with the VUSE pulse, a constant flip angle (flat) pulse, and a linear ramp pulse in flow‐compensated 3D MRA requences. The WSE pulse produced the most uniform signal as evidenced by the lowest relative dispersion of signal along the left vertebral artery (18.0 versus 26.4 to 23.6 for the other studies). F‐distribution tests also showed that the signal distribution obtained with the VUSE pulse in a 3D FLASH sequence was statistically different from that for the flat and the linear ramp pulses.
Partial volume effects in volume localized phased‐array proton spectroscopy of the temporal lobe
Authors: Strauss Wayne L. , Tsuruda Jay S. , Richards Todd L. 
Published: March 2007

AbstractMRS techniques can aide in confirming the location of seizure foci in temporal lobe epilepsy. N‐acetyl aspartate (NAA). creatine plus phosphocreatine. choline‐containing compounds, and lactate arc most often the clinically relevant metabolites in these studies. We examined the importance of partial volume effects from tissue heterogeneity in temporal lobe spectroscopy on the metabolite ratios. Our study shows that localized spectroscopy, using three different voxel slzes. centered on the anterior body of the hippocampus. produces significantly different values for the NAA to the creatine ratio. The spectroscopy was performed at 1.5 T wing the PRESS pulse sequence and a phased‐array coil system specifically designed for the temporal lobe. The data exhibits a clear trend of increasing NM to creatine ratios with increasing voxel size. This trend demonstrates that partial volume effects can contribute to variation of NAA to creatine ratios in healthy subjects.
Artifacts in functional magnetic resonance imaging from gaseous oxygen
Authors: Bates Sandra , Yetkin Zerrin , Jesmanowicz Andre , Hyde James S. , Bandettini Peter A. , Estkowski Lloyd , Haughton Victor M. 
Published: March 2007

AbstractUnexpectedly large fluctuations in signal intensity wen identified in the functional MRI (FMRI) of normal subjects breathing pure oxygen intermittently. To test the hypothesis that the signal changes were due to fluctuating concentrations of gaseous (paramagnetic) oxygen in the magnetic field, echo planar gradient echo images were acquired of a phantom contiguous to an oxygen mask through which pure oxygen was administered intermittently via plastic tubing. As a control, room air was administered intermittently or oxygen continuously in the same experimental protocol. Signal intensity changes of up to 60% temporally correlated with the administration of oxygen were produced in the phantom. In functional images prepared from the echo planar images, the signal intensity changes resulted in artifacts especially at interfaces in the phantom. The intermittent administration of pure oxygen during acquisition of data for FMRI may produce signal intensity changes that simulate or obscure function.
Comparison of t2 relaxation in blood, brain, and ferritin
Authors: Brooks Rodney A. , Vymazal Josef , Baumgarner Charles D. , Tran Vu , Bulte Jeff W. M. 
Published: March 2007

AbstractT2 was measured in samples of human blood and monkey brain over a field range of 0.02–1.5 Tesla, with variable interecho times, and was compared with previous data on ferritin solutions (taken with the same apparatus). 1/T2 in deoxygenated blood increased quadratically with field strength, as noted previously, but in brain gray matter the increase was linear, as also was the case in ferritin solution. In both deoxygenated blood and gray matter, 1/T2 increased with interecho time, but appeared to level off at times around 50 msec, as expected from the theory of diffusion through magnetic gradients. Diffusion times estimated by using the chemical exchange approximation were 3.4 msec for deoxygenated blood and 5.7 msec for the globus pallidus. The quadratic field dependence in blood is consistent with this same theory, but the linear dependence in brain tissue and in ferritin solutions remains unexplained.