bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling and observation of temperature changes in Vivo using MRI
Authors: Young Iain R. , Hand Jeffrey W. , Oatridge Angela , Prior Michael V. 
Published: March 2007

AbstractModels have been developed for the signal changes occurring in human peripheral muscle after thermal stress for some methods of measuring temperature in vivo. These include the dependency of T1, on temperature, observed by both direct, and magnetization transfer, experiments, and the temperature sensitivity of the diffusion coefficient and the chemical shift of the water proton line. Results show the relative complexity of the T1‐dependent models when there are significant variations in, possibly amongst other things, tissue perfusion, and how the predictions made using them match the behavior of the practical values quite well. Using changes in the diffusion coefficient appears less problematic, although there can still be significant errors in temperature calibrations. The problems with this approach are likely to be due to the consequences of anisotropy in tissue.
Analysis and correction of motion artifacts in diffusion weighted imaging
Authors: Anderson Adam W. , Gore John C. 
Published: March 2007

AbstractFor diffusion‐weighted magnetic resonance imaging and under circumstances where patient movement can be modeled as rigid body motion, it is shown both theoretically and experimentally that translations and rotations produce phase errors which are zero‐ and first‐order, respectively, in position. Whlile a navigator echo can be used to correct the imaging data for arbitrary translations, only when the diffusion gradient is applied in the phase encode direction is there sufficient information to correct for rotations around all axes, and therefore for general rigid body motion. Experiments in test objects and human brain imaging confirm theoretical predictions and demonstrate that appropriate corrections dramatically improve image quality in vivo.
In vivo 31P NMR studies of orientation effects upon rat brain metabolism during mild hypoxia
Authors: Chen Meng , Stolk Jacob A. , Olsen Jay I. , Schweizer Martin P. 
Published: March 2007

AbstractEnergy metabolites in rat brain under the same level of hypoxia were monitored by 31P NMR in both horizontal and vertical magnets. The changes in PCr, P|, and pHI in the vertical setting toward the end of hypoxia were significantly larger and the recovery in the horizontally held animals was more complete. The results demonstrated quantitatively that the stress of the alignment is superimposed on the stress of hypoxia in the vertical magnet.
Assessment of absolute metabolite concentrations in human tissue by 31P MRS in vivo. Part II: Muscle, liver, kidney
Authors: Buchli Reto , Meier Dieter , Martin Ernst , Boesiger Peter 
Published: March 2007

AbstractAbsolute metabolite concentrations were assessed in the muscle, the liver, and the kidney of healthy human volunteers by 31P MRS. Fully relaxed in vivo spectra were acquired with a surface coil and were localized with an adiabatic lSlS pulse sequence. The spectra were quantified with a subsequent measurement of a calibration phantom and were processed iteratively in the time domain. The following mean metabolite concentrations (mmollliter) were measured in the resting male calf muscle (n = 9), in the fasting liver (n = 12), and in the orthiotopic kidney (n= 5): [PME] = 2.0 ± 0.6, 3.8 ± 0.7, and 2.6 ± 0.9, [Pi] = 2.9 ± 0.3, 1.8 ± 0.3, and 1.6 ± 0.4, [PDE] = 3.8 ± 0.8, 9.7 ± 1.5, and 4.9 ± 1.1, [PCr] = 22.0 ± 1.2, 0, and 0, [NTP] = 5.7 ± 0.4, 2.9 ± 0.4, and 2.0 ± 0.3, respectively. Several interesting findings are to be emphasized: The concentrations of Pi, PCr, and NTP were 20% lower in the muscle of women than of men. In addition, the pH, was significantly lower in female muscle (6.99 ± 0.03) than in male muscle (7.05 ± 0.03). The pH, in the liver (7.12 ± 0.09) and in the kidney (7.09 ± 0.08) were higher than in the muscle of both genders. The free magnesium concentration (mmollliter) was higher in the lliver (1.40 ± 0.64) than in the kidney (0.79 ± 0.39) and in the muscle (0.52 ± 0.10).
A four‐channel time domain multiplexer: A cost‐effective alternative to multiple receivers
Authors: Porter Jay R. , Wright Steven M. , Famili Nader 
Published: March 2007

AbstractThe concept of simultaneous image acquisition as originally conceived by Hyde has been implemented by Roemer et al. using a multiple receiver system. This article describes an alternative technique that uses time domain multiplexing (TDM) to acquire simultaneous images using a single receiver channel. This method requires few modifications to the existing receiver and has been shown to be equivalent to a true four channel receiver in most applications. The multiplexing technique was implemented and tested on a standard commercial scanner that has also been equipped with a four channel receiver. Signal‐to‐noise results demonstrate that four independent images can be multiplexed through a single receiver channel with no degradation in image quality. Additionally, spine images that were obtained from a normal volunteer with both a multiplexed single channel receiver and a true four channel receiver system are presented.
2D 1H spectroscopic imaging of the human brain at 4.1 T
Authors: Hetherington Hoby P. , Pan Jullie W. , Mason Graeme F. , Ponder Steven L. , Twieg Donald B. , Deutsch Georg , Mountz James , Pohost Gerald M. 
Published: March 2007

AbstractA two‐dimensional spectroscopic imaging sequence consisting of an inversion recovery pulse, a plane selective prefocused pulse, and a semiselective water suppression pulse has been used to create 1H spectroscopic images of the human brain with nominal voxels of 0.5 cc. Due to the excellent lipid suppression provided by the inversion recovery pulse and subsequent delay, only planar volume selection is required enabling the entire brain within the slice to be imaged without contamination from extracerebral lipids in the brain voxels. The use of a semiselective refocusing pulse for water suppression permits any echo evolution time to be used, minimizing J‐modulation and T2 losses, while retaining full sensitivity in the lactate resonance. Using this sequence we have visualized the lactate elevation in the peri‐infarct region about a 6‐week‐old stroke.
Phase errors in multi‐shot echo planar imaging
Authors: Feinberg David A. , Oshio Koichi 
Published: March 2007

AbstractField inhomogeneity related phase errors in multi‐shot echo planar imaging (EPI) are directly visualized and analyzed in the spatial frequency domain data or ‘k‐space’. The echo time shift (ETS) technique incrementally moves the position of the echo train and improves the phase error function by redistributing phase discontinuities away from the center of k‐space.
31P NMR and triple quantum filtered 23Na NMR studies of the effects of inhibition of Na+/H+ exchange on intracellular sodium and pH in working and ischemic hearts
Authors: Navon Gil , Werrmann Jeffrey G. , Maron Ron , Cohen Sheila M. 
Published: March 2007

AbstractThe triple quantum filtered 23Na NMR method is applied here to measure the effects of EIPA, a specific inhibitor of the Na+/H+antiporter, on relative intracellular sodium concentrations in isolated working hearts at baseline, during ischemia, and at subsequent reperfusion. In analogy to the spectrophotometric isosbestic point, an approach is developed that defines a value of τ at which the effect of the relaxation times on the TQF signal intensities is minimized, and the signals are proportional to the sodium concentration for both ischemic and working hearts. EIPA at 1.5 μ significantly inhibited (P < 0.01) the influx of intracellular Na+ during 20 min of ischemia at 36.2°C in this rat heart model. In parallel31P NMR studies, EIPA had no effect on either the development of acidosis during ischemia or on the recovery of pH, during reperfusion despite its profound effect on intracellular Na+ influx. Thus, under our conditions the Na+/H+ antiporter did not play a critical role in the maintenance of intracellular pH. EIPA treatment resulted in improved recovery (P < 0.005) of mechanical function after 20 min of ischemia. [ATP] was higher in treated hearts during ischemia and reperfusion.
Dynamic contrast‐enhanced MR imaging of the upper abdomen: Enhancement properties of gadobutrol, gadolinium‐DTPA‐polylysine, and gadolinium‐DTPA‐cascade‐polymer
Authors: Adam Gerhard , Neuerburg Jörg , Spüntrup Elmar , Mühler Andreas , Scherer Kira , Günther Rolf W. 
Published: March 2007

AbstractThe enhancement properties of gadobutrol (40 and 80 μmol/kg body weight, 550 daltons), gadolinium‐DTPA‐polylysine (20 μmol/kg body weight, 53,000 daltons) and gadolinium‐DTPA‐cascade‐polymer (20 μmol/kg body weight, < 30,000 Daltons) were investigated in abdominal MR imaging using a pig model (n = 24). Signal intensities before and after contrast media application were assessed using a fast single slice FLASH sequence. Measurements were made every 4 s within the first 116 s, every minute between 4 and 10 min and after 15,20,30,40, 50,60,90, and 120 min after contrast media injection. Injection of gadobutrol resulted in typical signal intensity curves characterizing it as an extracellular agent similar to gadopentetate dimeglumine. Significant enhancement was found in all tissues except the trunk muscles when the lower dose was administered. Gadolinium‐DTPA‐polylysine injection resulted also in significant enhancement of the liver, the pancreas, and the renal cortex, but not of the trunk muscle, reflecting its blood pool properties known also from other macromolecular contrast agents. The signal intensity curves obtained after gadolinium‐DTPA‐cascade‐polymer injection were similar to those obtained after polylysine injection, stressing the blood pool character of this new type of blood pool agent.
A new T2 preparation technique for ultrafast gradient‐echo sequence
Authors: Parrish Todd , Hu Xiaoping 
Published: March 2007

AbstractThe T2, contrast in images obtained with driven equilibrium (90°x−180°x−90°x) prepared ultrafast gradient‐echo sequences is compromised by the longitudinal magnetization build‐up after the second 90°x pulse, which does not carry T2 information. This paper describes a new T2 contrast preparation technique for ultrafast gradient‐echo sequence that suppresses the signal arising from the build‐up. By dephasing in the preparation and rephasing in the acquisition of the gradient echoes, the new technique eliminates signals that are not dictated by the T2 contrast in a driven‐equilibrium approach. Consequently, it generates an image that is essentially T2‐weighted. Phantom and in vivo experiments were conducted to validate the technique and to demonstrate its clinical utility. These studies indicate that the technique works properly and can be used for in vivo studies.
Reduced power selective excitation radio frequency pulses
Authors: Shinnar Meir 
Published: March 2007

AbstractA pulse synthesis algorithm is described that allows for the synthesis of selective radio frequency pulses requiring less peak power. The pulses thus synthesized have the same duration, total energy, and frequency response as those synthesized by the standard algorithm. Their phase function is, however, different. The power reduction is typically on the order of 60–70%. This modification will increase the utility of optimized selective pulses.
Experimental encephalomyelitis modulates inositol and taurine in the spinal cord of biozzi mice
Authors: Preece Nicholas E. , Amor Sandra , Baker David , Gadian David G. , O'Neill Janet K. , Urenjak Jutta 
Published: March 2007

AbstractIn this high resolution magnetic resonance spectroscopic study of experimental allergic encephalomyelitis (EAE) and Semliki Forest virus (SFV) infection of the Bioui AB/H mouse, marked increases in the initially low levels of N‐trimethyl compounds in the spinal cord were observed during probable demyelinating episodes. There was also a pronounced and reproducible modulation of the levels of taurine and myo‐inositol during acute and again during chronic relapsing EAE. The ratio of N‐acetyl‐aspartate to creatine in the spinal cord of mice infected with the mutant M9 strain of SFV decreased to approximately 70% of that seen in normal mice.
q‐Space imaging of the brain
Authors: King Martin D. , Houseman John , Roussel Simon A. , Van Bruggen Nicholas , Williams Stephen R. , Gadian David G. 
Published: March 2007

Abstractq‐Space imaging (Callaghan, J. Magn. Reson. 88,493 (1990)) has been used to obtain mouse brain water displacement profiles. These profiles take the form of a unidirectional incoherent‐displacement probability density distribution. Two groups of mice were studied, a normal group and one in which surgery had been performed to reduce the supply of blood to the forebrain. In the normal group the incoherent displacement of water was reducedpostmortem. Four of the surgically treated mice yielded displacement profiles that resembled those obtained postmortem; the remaining two were near normal. This study demonstrates the feasibility of in vivo q‐space imaging. The displacement profile changes that occur subsequent to an interruption of the forebrain blood supply are consistent with the hyperintensity changes seen in diffusion‐weighted imaging.
Measurement of vascular volume fraction and blood‐tissue permeability constants with a pharmacokinetic model: Studies in rat muscle tumors with dynamic Gd‐DTPA enhanced MRI
Authors: Su Min‐Ying , Jao Jo‐Chi , Nalcioglu Orhan 
Published: March 2007

AbstractWe propose a compartmental model to explain the signal enhancement curves following the bolus injection of Gd‐DTPA. The model incorporates vascular volume fraction contribution, and the possibility of having different transport constants between the plasma and extravascular components. A Walker 256 carcinoma grown in rat muscle was used to demonstrate the capability of this model. Several different types of tissues were included in the measurements: normal, quickly enhanced, slowly enhanced, and necrotic tissues. Blood volume and blood‐tissue permeability information can be derived from the dynamic contrast‐enhanced MRI study employing the proposed model. In the tissue contrast enhancement curve, the initial rising slope after injection is related to the blood volume (or, vascular volume fraction), the maximum enhancement ratio is related to the uptake of tissue, and the decay rate is related to the clearance of tracer from tissue. The measured permeability constant is not the conventional permeability; instead they are contrast agents uptake and clearance rates, which are limited by the blood perfusion. These parameters can be used to characterize different enhancement patterns.
Magnetization transfer, cross‐relaxation, and chemical exchange in rotationally immobilized protein gels
Authors: Zhou Dawei , Bryant Robert G. 
Published: March 2007

AbstractWater proton spin‐lattice relaxation rates are reported as a function of the magnetic field strength for cross‐linked bovine Serum albumin samples. The relaxation dispersion profile is analyzed using a relaxation model where the solid components have the magnetic field dependence proportional to v−0.5 which may result from a defect diffusion model with two degrees of freedom. If the cross‐linking agent concentration is not sufficiently high, the relaxation dispersion curve may have significant contributions from freely rotating protein. The magnetic field dependence of the relaxation rates studied as a function of the proton mole fraction in the sample show that approximately 30% of the magnetization transfer rate is directly proportional to the proton mole fraction. This contribution is identified with the magnetization transfer from exchange of whole water molecules with buried binding sites on the protein. The second order magnetization transfer rate constant is 388 s−1 assuming unit water spin concentration. The solid component relaxation obeys an Arrhenius activation law, but the overall temperature dependence of the crossrelaxation is complicated by chemical exchange processes which enter with opposite sign.
Initial feasibility studies using single‐shot EPI for the detection of focal liver lesions
Authors: Reimer Peter , Ladebeck Ralph , Rummeny Ernst J. , Repp Heinz , Schmitt Franz , Bongartz Georg , Schuierer Gerhard , Lange Thomas , Peters Peter E. 
Published: March 2007

AbstractEcho planar MR imaging (EPI) has been developed to completely eliminate motion artifacts and is currently being prepared for implementation into clinical MR systems. Thus, the purpose of this study was to evaluate the clinical utility of EPI in the detection of focal liver lesions and to compare EPI with contrast‐enhanced CT. EPI studies were performed on an experimental 1.0 Tesla whole body system using fat‐suppressed single‐shot spin echo (SE) and inversion recovery (IR) pulse sequences. A total of 26 liver tumors in 12 patients scheduled for liver resection were prospectively examined and correlated with intraoperative ultrasound, surgery, and pathology as the gold standard. Quantitative analysis of EPI was performed by means of liver signal‐to‐noise and tumorliver contrast‐to‐noise calculations. Diagnostic performance compared with contrast‐enhanced CT was assessed by means of ROC analysis. Lesion‐liver contrast was highest with EPI SE at a TE‐time of 70 ms and this technique showed best lesion detectability as measured by area under curve (AUC) values. Among EPI techniques, the IR sequence with an inversion time of 300 ms to null the liver signal showed high lesion‐liver contrast but all four reviewers reported problems assessing liver anatomy. Improved EPI techniques may prove useful for screening of focal liver lesions.
Theory of NMR signal behavior in magnetically inhomogeneous tissues: The static dephasing regime
Authors: Yablonskiy Dmitriy A. , Haacke E. Mark 
Published: March 2007

AbstractThis paper is devoted to a theory of the NMR signal behavior in biological tissues in the presence of static magnetic field inhomogeneities. We have developed an approach that analytically describes the NMR signal in the static dephasing regime where diffusion phenomena may be ignored. This approach has been applied to evaluate the NMR signal in the presence of a blood vessel network (with an application to functional imaging), bone marrow (for two specific trabecular structures, asymmetrical and columnar) and a ferrite contrast agent. All investigated systems have some common behavior. If the echo timeTEis less than a known characteristic timetcfor a given system, then the signal decays exponentially with an argument which depends quadratically onTE. This is equivalent to an R2* relaxation rate which is a linear function ofTE. In the opposite case, whenTEis greater thantc, the NMR signal follows a simple exponential decay and the relaxation rate does not depend on the echo time. For this time interval, R2* is a linear function of a) volume fraction ζ occupied by the field‐creating objects, b) magnetic field B0or just the objects' magnetic moment for ferrite particles, and c) susceptibility difference Δχ between the objects and the medium.
Detection of propan‐1,2‐diol in neonatal brain by in vivo proton magnetic resonance spectroscopy
Authors: Cady Ernest B. , Lorek Ann , Penrice Juliet , Reynolds E. Osmund R. , Iles Richard A. , Burns Shamus P. , Coutts Glyn A. , Cowan Frances M. 
Published: March 2007

AbstractCerebral in vivo proton magnetic resonance spectroscopy of 13 newborn infants displaying seizures and receiving phenobarbitone, in one case supplemented by phenytoin, showed signals from propan‐1,2‐diol (the injection vehicle for both these anticonvulsants). Subsequent in vitro spectroscopy of cerebro spinal fluid (CSF) from one of these infants also showed signals from this substance. The estimated in vivo propan‐1,2‐diol concentration (∼3 mM) was less than that measured in the CSF sample (14.4 mM). These observations suggest that propan‐1,2‐diol may accumulate in cerebral tissue and misidentification of its signals in both in vivo and in vitro proton spectra may confuse diagnoses of metabolic or other disorders.
Proton Magnetic Resonance Spectroscopy and Gadolinium‐DTPA Perfusion Imaging of Asymptomatic MRI White Matter Lesions
Authors: Oppenheimer Stephen M. , Nick Bryan R. , Conturo Thomas E. , Soher Brian J. , Preziosi Thomas J. , Barker Peter B. 
Published: March 2007

AbstractIn the elderly, asymptomatic white matter hyperintensities are common on T2‐weighted magnetic resonance imaging (MRI). In symptomatic patients, such MRI appearances correlate with varied postmortem findings including demyelination or stroke. What structural correlates underlie the T2 hyperintensities in patients whose lesions are asymptomatic is controversial. Therefore, in order to investigate the underlying metabolism and perfusion in white matter lesions (exhibiting T2 hyperintensity), 13 patients underwent proton magnetic resonance spectroscopy and dynamic gadolinium‐DTPA perfusion‐weighted MR imaging. N‐acetyl aspartate (NA) levels were reduced in the lesions compared with age‐matched controls (P = 0.031), implying neuronal/axonal loss. Creatine levels were also reduced (P = 0.001). Choline levels were unchanged in the lesions. Lactate was identified in the lesions of 5 of the 13 patients. Although not statistically significant, perfusion studies exhibited a trend toward lower cerebral blood volumes in patients with high grade extracranial carotid stenosis and lactate‐containing lesions. These findings suggest that neuronal/axonal loss underlies the majority of T2‐weighted asymptomatic lesions in the older population, and in many cases these changes may be due to chronic ischemia.
Calculation of Sensitivity Correction Factors for Surface Coil MRS
Authors: Doyle Victoria L. , Buil Michiel , Payne Geoffrey S. , Leach Martin O. 
Published: March 2007

AbstractQuantification of MRS signals obtained with surface coils is difficult due to the inhomogeneous response of these coils. This inhomogeneity results in the measured signal from a defined volume of interest (VOI) being spatially dependent. To account for the sensitivity variation with position from the surface coil, we have developed a method of calculating correction factors for defined VOIs based on an experimentally obtained 3D sensitivity coil map. These factors may then be applied to spectra obtained from these VOIs to accurately take into consideration the varying coil sensitivity resulting in a reduction of measured signal. This method is demonstrated here to be able to correct for the inhomogeneity of surface coils over a range of two coil radii to within 4% accuracy.
Cerebral White Matter in the Centrum Semiovale Exhibits a Larger N‐acetyl Signal than Does Gray Matter in Long Echo Time 1H‐Magnetic Resonance Spectroscopic Imaging
Authors: Tedeschi Gioacchino , Righini Andrea , Bizzi Alberto , Barnett Alan S. , Alger Jeffry R. 
Published: March 2007

AbstractLong echo time (272 ms) 1H magnetic resonance spectro‐scopic imaging was used to measure the relative magnitudes of the N‐acetylaspartate (NAA) signal in a variety of anatomically defined brain structures (centrum semiovale, thalamus, medial frontal cortex, and genu of the corpus callosum) composed primarily of gray matter or white matter. Six normal young adult humans aged 30–40 were studied. With a 95% level of statistical confidence, the white matter in the centrum semiovale (CSO) produced a more intense NAA signal than did the gray matter in the thalamus and the frontal cortex. Differences between the white matter regions were also noted. The CSO white matter's NAA signal yielded a larger NAA signal than did the white matter of the genu of the corpus callosum. Possible reasons for the anatomical variation in the cerebral NAA signal intensity are discussed.