bluuebunny/crossref_metadata_2025_split huggingface dataset:
Coronary flow and coronary flow reserve measurements in humans with breath‐held magnetic resonance phase contrast velocity mapping
Authors: Davis Clarence P. , Liu Pei‐Fang , Hauser Markus , Göhde Susanne C. , Von Schulthess Gustav K. , Debatin Jörg F. 
Published: March 2007

AbstractObjective evidence for coronary lesion significance can be obtained with ischemic stress testing. Since flow‐limiting stenoses have already undergone compensatory vasodilatation to maintain flow, the response to vasoactive stimulation is dampened. The degree of response limitation is reflected by the coronary flow reserve (CFR). Absolute volume flow rates can be accurately and noninvasively measured with MRI techniques. The purpose was to assess the ability to measure coronary volume flow rate noninvasively, and characterize the effect of pharmacologic stress on coronary flow quantitatively by using ultrafast, breath‐held segmented k‐space phasecontrast‐MR imaging (PC‐MRI). Ten healthy volunteers were examined by using ultrafast breath‐held PC‐MRI. Coronary volume flow rates were measured in the anterior descending coronary artery (LAD) at rest and following intravenous administration of dipyridamole. CFR was determined based on these data. Mean LAD volume flow rates increased from 38 ± 11 ml/min before application of dipyridamole to 169 ± 42 ml/min. The mean CFR amounted to 5.0 ± 2.6 (median = 4.15). This study demonstrates the feasibility of breath‐held PC‐MRI to noninvasively quantify coronary volume flow rates over the cardiac cycle. Pharmacologically induced changes in volume flow rate and thus CFR can be quantitated.
Slice location dependence of aortic regurgitation measurements with MR phase velocity mapping
Authors: Chatzimavroudis George P. , Walker Peter G. , Oshinski John N. , Franch Robert H. , Pettigrew Roderic I. , Yoganathan Ajit P. 
Published: March 2007

AbstractAlthough several methods have been used clinically to assess aortic regurgitation (AR), there is no “gold standard” for regurgitant volume measurement. Magnetic resonance phase velocity mapping (PVM) can be used for noninvasive blood flow measurements. To evaluate the accuracy of PVM in quantifying AR with a single imaging slice in the ascending aorta, in vitro experiments were performed by using a compliant aortic model. Attention was focused on determining the slice location that provided the best results. The most accurate measurements were taken between the aortic valve annulus and the coronary ostia where the measured (Y) and actual (X) flow rate had close agreement (Y = 0.954 × + 0.126, r2 = 0.995, standard deviation of error = 0.139 L/min). Beyond the coronary ostia, coronary flow and aortic compliance negatively affected the accuracy of the measurements. In vivo measurements taken on patients with AR showed the same tendency with the in vitro results. In making decisions regarding patient treatment, diagnostic accuracy is very important. The results from this study suggest that higher accuracy is achieved by placing the slice between the aortic valve and the coronary ostia and that this is the region where attention should be focused for further clinical investigation.
Steady state effects in fast gradient echo magnetic resonance imaging
Authors: Duyn Jeff H. 
Published: March 2007

AbstractFourier methodology is applied to analyze steady state effects in fast gradient echo imaging. Simulations and MR imaging experiments on phantoms demonstrate the effectiveness of existing schemes under different experimental conditions, and modifications are introduced which result in reduced sensitivity to slow object motion as compared to conventional phase modulation schemes. In addition, phase modulation schemes are introduced which more than double temporal signal stability in human brain scans, at flip angles well above the Ernst angle and TR >> T1, T2. Application of phase modulation to the measurement of higher order signals shows increased sensitivity, particularly for the highest order signals.
RARE spiral T2‐weighted imaging
Authors: Block Walter , Pauly John , Nishimura Dwight 
Published: March 2007

AbstractSpiral imaging has a number of advantages for fast imaging, including an efficient use of gradient hardware. However, inhomogeneity‐induced blurring is proportional to the data acquisition duration. In this paper, we combine spiral data acquisition with a RARE echo train. This allows a long data acquisition interval per excitation, while limiting the effects of inhomogeneity. Long spiral k‐space trajectories are partitioned into smaller, annular ring trajectories. Each of these annular rings is acquired during echoes of a RARE echo train. The RARE refocusing RF pulses periodically refocus off‐resonant spins while building a long data acquisition. We describe both T2‐weighted single excitation and interleaved RARE spiral sequences. A typical sequence acquires a complete data set in three excitations (32 cm FOV, 192 × 192 matrix). At a TR = 2000 ms, we can average two acquisitions in an easy breath‐hold interval. A multifrequency reconstruction algorithm minimizes the effects of any off‐resonant spins. Though this algorithm needs a field map, we demonstrate how signal averaging can provide the necessary phase data while increasing SNR. The field map creation causes no scan time penalty and essentially no loss in SNR efficiency. Multiple slice, 14‐s breath‐hold scans acquired on a conventional gradient system demonstrate the performance.
Detection of glutamate/glutamine resonances by 1H magnetic resonance spectroscopy at 0.5 tesla
Authors: Prost Robert W. , Mark Leighton , Mewissen Mark , Li Shi‐Jiang 
Published: March 2007

AbstractMidfield proton magnetic resonance spectroscopy (MRS) provides a noninvasive method to monitor glutamate and glutamine (Glx) levels in vivo. Experiments to detect the γ and β resonances of Glx have been performed by using commercial 0.5 T and 1.5 T MR scanners on seven patients with elevated blood ammonia and eight normal volunteers. Compared with the spectral sensitivity obtained on an otherwise identical system operating at 1.5 T, the singlet resonance of N‐acetyl aspartate (NAA) was decreased by a factor of 1.48, which is significantly less than expected using the ratio of Boltzman populations at the two field strengths. However, the resonances of Glx at 0.5 T increased in signal‐to‐noise ratio (SNR) by a factor of 2. The increased SNR of Glx is principally due to improved B 0 main‐field homogeneity and collapse of the strongly J ‐coupled Glx resonances. Our preliminary results suggest that midfield proton MRS will provide significant clinical utility in the detection of Glx levels in human brain.
Use of voigt lineshape for quantification of in vivo1H spectra
Authors: Marshall Ian , Higinbotham John , Bruce Stephen , Freise Andreas 
Published: March 2007

AbstractQuantification of NMR visible metabolites by spectral modeling usually assumes a Lorentzian or Gaussian lineshape, despite the fact that experimental lineshapes are neither. To minimize systematic fitting errors, a mixed Lorentzian‐Gaussian (Voigt) lineshape model was developed. When tested with synthetic FIDs, the Voigt lineshape model gave more accurate results (maximum error 2%) than either Lorentzian (maximum error 20%) or Gaussian models (maximum error 12%). The three lineshape models gave substantially different peak areas in an in vitro experiment, with the Voigt model having a much lower X2 (2.1 compared with 5.2 for the Lorentzian model and 6.2 for the Gaussian model). In a group of 10 healthy volunteers, fitting of 1H spectra from cerebral white matter gave significantly different peak areas between the methods. Even when area ratios were taken, the Lorentzian model gave higher values (+5% for NAA/choline and +2% for NAA/creatine) than the Voigt lineshape model, whereas the Gaussian model gave lower values (−2% and −1%, respectively).
Theory of heterogeneous relaxation in compartmentalized tissues
Authors: Barsky Daniel , Pütz Benno , Schulten Klaus 
Published: March 2007

AbstractA new model of compartmentalized relaxation—that which occurs for spins (protons) exchanging between compartments of different relaxation rates—is presented. This model generalizes previous ones by allowing spatially dependent relaxation within compartments. Solutions for the diffusion‐Bloch equations are found via an efficient numerical technique known as the generalized moment expansion, and they agree well with the solutions to the standard two‐site exchange equations (TSEE) for many typical situations. Specific models are developed for liposomes, red blood cells, capillaries, and arteries with respect to applied contrast agents. A parameter derived from tissue characteristics is introduced to predict the nature of the solutions. A new method is proposed for using contrast agents to detect capillaries, which exploits their high surface‐to‐volume ratio relative to the other elements of the vasculature.
Different effects of exercise and edema on T2 relaxation in skeletal muscle
Authors: Ploutz‐Snyder Lori L. , Nyren Sven , Cooper Thomas G. , Potchen E. James , Meyer Ronald A. 
Published: March 2007

AbstractThe hypothesis that increased muscle T2 after exercise is caused by increased extracellular fluid volume was tested by comparing the effects of exercise versus external leg negative pressure on muscle T2 relaxation in normal human subjects. T2 in lower leg muscles was measured by echo‐planar imaging at 63 echo times from 24 to 272 ms, and the relaxation spectrum was calculated by using a non‐negative least squares algorithm. T2 relaxation in anterior leg muscle before exercise was characterized by a single component with mean T2 = 29.3 ± 0.7 (SE, n = 5). After ankle dorsiflexion exercise, this single component broadened, and mean T2 increased to 38.3 ± 0.7 ms. In contrast, after leg negative pressure, which increased the total leg muscle cross‐sectional area by 21% (range 12–32% n = 6), there was a variable appearance of much slower‐relaxing components (60–500 ms). The results suggest that increased extracellular fluid can account for only a minor portion of the increase in muscle T2 observed during exercise.
Global cardiac function using fast breath‐hold MRI: Validation of new acquisition and analysis techniques
Authors: Bloomgarden Daniel C. , Fayad Zahi A. , Ferrari Victor A. , Chin Bennett , St. John Sutton Martin G. , Axel Leon 
Published: March 2007

AbstractCalculation of global cardiac function parameters has been validated using fast, segmentedk‐space, breath‐hold, gradient‐echo, magnetic resonance images. Images of phantoms, experimental animals, normal volunteers, and patients were acquired with a 1.5 T clinical scanner. Humans were imaged using two phased‐array surface coils in multicoil mode. Myo‐cardial contours were extracted using a new interactive, semi‐automated method based on the active contour model method. Images were acquired in the short‐axis orientation, and, using a new imaging and analysis strategy, in rotating plane long‐axis orientations, to provide better definition of the valve planes and the apex, and also to reduce the number of slices (compared with the short‐axis method) required to sample the whole heart. Validation was accomplished through calculation of the volumes of phantoms and left and right ventricular masses of animal hearts. Functional parameters from MRI were compared with those from echocardiograms and radionuclide angiograms in normal volunteers and patients, respectively.
Fast three dimensional sodium imaging
Authors: Boada Fernando E. , Gillen Joseph S. , Shen Gary X. , Chang Sam Y , Thulborn Keith R. 
Published: March 2007

AbstractAn efficient scheme for fast three dimensional acquisition of sodium MR images is described. This scheme relies on the use of three dimensional k‐space trajectories with constant sample density to achieve significant (60–70%) reductions in total data acquisition time over conventional projection imaging schemes. The performance of this data acquisition scheme is demonstrated with acquisition of sodium data sets on phantoms and normal human volunteers at 1.5 and 3.0 Tesla. The experimental results demonstrate that high quality three dimensional sodium images (0.2 cc voxel size, 10:1 signal‐to‐noise ratio) can be acquired at clinical field strengths (1.5 Tesla) in under 10 min.
Relaxation of solvent protons by solute Gd3+‐chelates, revisited
Authors: Kellar Kenneth E. , Henrichs P. Mark , Spiller Marga , Koenig Seymour H. 
Published: March 2007

AbstractThe magnetic field dependence (NMRD profile) of 1/T1, of solvent protons in an aqueous solution of Gd(DTPA)2− was remeasured at 5,15,25,30, and 35°C. The data were reanalyzed with the usual low‐field theory, using recently published values for TM, the residence lifetime of the single inner‐coordinated waters of solute Gd(DTPA)2−. (These TM values are significantly longer than earlier estimates). Values were obtained for three dynamic parameters: TR, the rotational relaxation time of solute ions, and TSO and TV, the low‐field relaxation time of the Gd3+ magnetic moment and the related correlation time. These Gd(DTPA)2+ values, together with recent results for TM for Gd(DTPA‐BMA) — a nonionic structural analog of Gd(DTPA)2− with an unusually long TM — were used to calculate NMRD profiles at 5 and 35°C. These profiles agree very well with new data given here for a solution of Gd(DTPA‐BMA). This reaffirms the importance of knowing the temperaturedependent values of TM a priori in order to obtain unambiguous quantitative theoretical analyses of NMRD profiles of chelates of known structure. Additionally, the theory of inner sphere relaxation is extended to high fields, at which the magnetic energy of a solute moment is greater than its thermal energy.
31P NMR saturation transfer study of the creatine kinase reaction in human skeletal muscle at rest and during exercise
Authors: Goudemant Jean‐François , Francaux Marc , Mottet Isabelle , Demeure Roger , Sibomana Merence , Sturbois Xavier 
Published: March 2007

AbstractThe creatine kinase reaction has been studied by 31P NMR in exercising human calf muscle. Quantitative analysis of high energy phosphates and saturation transfer study of the creatine kinase flux in the direction of ATP synthesis (Vfor) were performed at rest and during exercise. As expected, exercise induced a [PCr] decrease (from 28.5 ± 0.9 to 21.9 ± 1.5 mM, P < 0.01) matched by a P1, increase (from 4.5 ± 0.2 to 8.9 ± 1.8 mM,P = 0.06). pHi and [ATP] remained unchanged. Vfor did not change from rest (12.4 ± 0.9 mM s−1) to moderate exercise and decreased at the highest exercise level (8.4 ± 1.4 mM s−1, P = 0.006). This observation differs from the prediction of the creatine kinase rate equation, showing an increase in the flux with exercise intensity. Computations suggest that this discrepancy arises from metabolite compartmentalization and/or from the reaction kinetics of a dead end complex stabilized by planar anions.
Multicoil array for high resolution imaging of the breast
Authors: Insko Erik K. , Connick Thomas J. , Schnall Mitchell D. , Orel Susan G. 
Published: March 2007

AbstractAn RF multicoil array for high resolution imaging of the breast is presented. The RF multicoil is incorporated into a dedicated breast imaging apparatus that holds either breast in gentle compression during imaging. Simulations and imaging experiments demonstrate the high sensitivity and RF homogeneity of the multicoil array. Direct comparisons are made between the multicoil and a surface coil. In vivo images are presented to demonstrate the homogeneity of the RF field of the multicoil over the entire breast. An in vivo image of both high temporal and spatial resolution is shown, which demonstrates the sensitivity of the RF multicoil array that may be achieved in a practical imaging experiment.
Phosphorus J‐coupling constants of ATP in human brain
Authors: Jung Wulf‐Ingo , Staubert Andreas , Widmaier Stefan , Hoess Thomas , Bunse Michael , van Erckelens Franz , Dietze Günther , Lutz Otto 
Published: March 2007

AbstractProton decoupled 31P NMR spectroscopy of the occipital brain of healthy volunteers was performed with a 1.5 T whole‐body imager. By use of two‐dimensional chemical‐shift imaging in combination with slice‐selective excitation well resolved localized spectra (38 ml) were obtained within 34 min from which the homonuclear 31P‐31P J‐coupling constants of ATP could be determined: Jαβ = 16.1 Hz ± 0.2 Hz and Jαβ = 16.3 Hz ± 0.1 Hz (mean ± SEM, n = 14). Both, the J‐coupling constants and the chemical‐shift difference between α‐ and β‐ATP (δαβ = 8.61 ppm ± 0.01 ppm) were used to calculate the concentration of intracellular free magnesium. The concentrations are 0.39 mM ± 0.09 mM by using the average of both coupling constants of each spectrum, which is in fair agreement with 0.32 mM ± 0.01 mM obtained from the chemical shift of α and β phosphate resonances, which is the more accurate result.
Intracellular volume and apparent diffusion constants of perfused cancer cell cultures, as measured by NMR
Authors: Pilatus Ulrich , Shim Hyunsuk , Artemov Dmitri , Davis Delphine , Van Zijl Peter C. M. , Glickson Jerry D. 
Published: March 2007

AbstractDiffusion NMR spectroscopy was used to study intracellular volume and apparent water diffusion constants in different cell lines (DU145, human prostate cancer; AT3, rat prostate cancer; MCF‐7, human breast cancer; RIF‐1, mouse fibrosacroma). The cells were grown on various matrices (collagen sponge, collagen beads, polystyrene beads) which enabled continuous growth in perfused high density cell culture suitable for NMR studies. In perfused cell systems, the attenuation of the water signal versus the squared gradient strength was fitted by the sum of two decaying exponentials. For the slowly decaying component the apparent water diffusion constant at 37°C was 0.22 (±0.02) × 10−9 s/m2 for all cell lines at diffusion times > 100 ms. It continuously increased up to 0.47(±0.05) × 10−9 s/m2 when the diffusion time was decreased to 8 ms, indicating restricted diffusion. No significant effect of the matrices was observed. The fractional volume of the slow component as determined from the biexponential diffusion curve correlated with the relative intracellular volume, as obtained from the cell density in the sample and the cell size as measured by light microsocopy. Therefore, this simple NMR approach can be used to determine intracellular volume in perfused cell cultures suitable for NMR studies. Using this information in combination with spectroscopic data, changes in intracellular metabolite concentration can be detected even when the cellular volume is changing during the experiment. The apparent diffusion constant for the fast diffusing component varied with growth matrix, cell density and cell type and also showed the typical characteristics of restricted diffusion (increase of apparent diffusion constant with time).
Effect of brain, body, and magnet bore temperatures on energy metabolism during global cerebral ischemia and reperfusion monitored by magnetic resonance spectroscopy in rats
Authors: Shimizu Hiroaki , Chang Lee‐Hong , Litt Lawrence , Zarow Gregory , Weinstein Philip R. 
Published: March 2007

AbstractTo record brain temperature for comparison with rectal and temporalis muscle temperatures in preliminary studies before MR spectroscopy experiments, a thermistor was inserted into the basal ganglia in eight anesthetized, ventilated, and physiologically monitored rats. The rats were placed in an MR spectrometer and subjected to 60 min of global cerebral ischemia and 2 h of reperfusion without radiofrequency (RF) pulsing. Body temperature was maintained at 37.5–38.0°C (normothermia) or 36.5–37.0°C (mild hypothermia). Brain temperature during ischemia, which dropped to 31.9 ± 0.3 (hypothermia) and 33.6 ± 0.5±C (normothermia), correlated with temporalis muscle temperature (r2 = 0.92) but not with body or magnet bore temperature measurements. Ischemia reduced brain temperature approximately 1.7°C in rats subjected to mild hypothermia (1° reduction of body temperature). Parallel MR spectroscopy experiments showed no significant difference in energy metabolites between normothermic and hypothermic rats during ischemia. However, the metabolic recovery was more extensive 20–60 min after the onset of reperfusion in hypothermia rats, although not thereafter (P < 0.05). Mild hypothermia speeds metabolic recovery temporarily during reperfusion but does not retard energy failure during global ischemia in rats.
Evaluation of the early response in fMRI in individual subjects using short stimulus duration
Authors: Hu Xiaoping , Le Tuong Huu , Uǧurbil Kǎmil 
Published: March 2007

AbstractOptical imaging studies have provided evidence of an initial increase in deoxyhemoglobin following the onset of neuronal stimulation/activation and demonstrated that this initial increase could be spatially more specific to the site of neuronal activity. These studies also raised the possibility of improving the specificity of fMRI by selective mapping of this early response. Previous MR studies reported the observation of this early response but were limited in scope and not in full agreement. This paper presents a more extensive study that (a) demonstrates the initial signal decrease in individual subjects and (b) examines its dependence on stimulus duration and subject. Binocular visual stimulation experiments were performed on 14 subjects using echo‐planar imaging (EPI) with high temporal resolution. An initial signal decrease was consistently observed in regions that were more localized than those displaying the delayed positive response. In agreement with previous fMRI and optical imaging findings, the maximum signal decrease was 1–2% and occurred at approximately 2 s after the onset of the stimulus, depending on the subject. For stimulus longer than 3.0 s, the temporal dynamics and the amount of signal change of the early response was essentially independent of the stimulus duration, while the delayed response and the post‐stimulus undershoot increased both in terms of magnitude and rise time as the duration of the stimulus increased; this observation is concordant with the recent optical imaging study.
Physiologic basis for BOLD MR signal changes due to hypoxia/hyperoxia: Separation of blood volume and magnetic susceptibility effects
Authors: Kennan Richard P. , Scanley B. Ellen , Gore John C. 
Published: March 2007

AbstractAn NMR method is presented for separating blood volume and magnetic susceptibility effects in response to respiratory challenges such as hypoxia and hyperoxia. The technique employs high susceptibility contrast agents to enhance blood volume induced signal changes. The results show that for a rat model the dominant source of signal variation upon changing breathing gas from 100% oxygen to 10% oxygen/90% nitrogen is the change in blood magnetic susceptibility associated with the BOLD effect. The results imply that signal changes associated with respiratory challenges can be regarded as indicators of local blood oxygenation in vivo.
Mechanism and echo time dependence of the fast response in FMR
Authors: Dymond Rosemary C. , Norris David G. 
Published: March 2007

AbstractThe fast response (FR) is an early reduction in the amplitude of the fMR signal occurring shortly after the onset of stimulation. Owing to its potential advantages in terms of temporal and spatial resolution, it may be of considerable significance in functional experiments. A model for the mechanism of the FR was developed which accounts for the fMRS finding that the amplitude of the dip decreases with increasing echo time. Two computer simulations that confirmed the predictions of the model and showed that it is possible to select optimal echo times for the detection of the FR were performed.