bluuebunny/crossref_metadata_2025_split huggingface dataset:
NMR relaxation of water in hydrogel polymers: A model for tissue
Authors: Gore John C. , Brown Mark S. , Zhong Jianhui , Mueller K. Fritz , Good William 
Published: March 2007

AbstractThe NMR relaxation rates ofa class of hydrated polymers (hydrogels) have been investigated over a wide range of frequencies (0.01 to 60 MHz) and compositions. The gels comprise long chains of polytetramethylene oxide diol crosslinked by copolymers of dimethylacrylamide and methylmethacrylate. The longitudinal relaxation rate dispersion curves of these materials are very similar to those shown by human tissues and they can be altered in flexible fashion by changing the polymer content. By substitution of the water by deuterium oxide, the contribution of intermolecular cross‐relaxation effects has been shown to account for two‐thirds the total water relaxation rate. With their close similarity to tissue relaxation behavior, hydrogels of differing compositions are particularly well‐suited to MRI phantoms and test objects. © 1989 Academic press, Inc.
MRI detection of myocardial perfusion changes by gadolinium‐DTPA infusion during dipyridamole hyperemia
Authors: Miller D. Douglas , Holmvang Godtfred , Gill John B. , Dragotakes Donna , Kantor Howard L. , Okada Robert D. , Brady Thomas J. 
Published: March 2007

AbstractTo detect abnormal regional myocardial coronary flow reserve, serial spin‐echo MR tomograms of four control dogs and six with a partial balloon occlusion of the left anterior descending (LAD) coronary artery were acquired before and after dipyridamole infusion and during the paramagnetic effect of a bolus plus infusion of gadolinium‐DTPA. Microsphere myocardial blood flow was measured for correlation with serial regional changes in MR signal intensity. Significant difference in gadolinium‐enhanced MR signal intensity existed between the hypoperfused LAD and the hyperemic left circumflex perfusion beds (46 ± 22% vs 78 ± 29% above baseline, respectively; P < 0.05). The percentage changes in gadolinium‐enhanced MR signal and microsphere myocardial blood flow were significantly correlated (r2 = 0.93). © 1989 Academic Press, Inc.
Characterization of normal brain tissue using seven calculated MRI parameters and a statistical analysis system
Authors: Hyman Timothy J. , Levy George C. , Kurland Robert J. , Shoop Jon D. 
Published: March 2007

AbstractA statistical analysis system for classifying normal brain tissue has been applied to the analysis of MRI scans on 45 volunteers. The Bayes Maximum Likelihood method was used to achieve a discrimination accuracy of 84% for 13 tissue types among three age group sets, with classification accuracies for individual regions ranging from 50 to 100%. In order to attain this level of discrimination a set of seven derived relaxation‐type parameters was used to categorize the tissue types. Values for these experimentally estimated parameters were derived from the MRI intensities of eight images in the following pulse sequences: (1) a Carr‐Purcell‐Meiboom‐Gill (CPMG) four‐echo train, (2)a single‐echo inversion recovery, and (3) three single‐echo sequences with varying repetition times, TR, and echo delays, TE. The T2 values derived from ratios of single‐echo intensities showed better discrimination power than those from the four‐echo CPMG train. The general precision of the seven estimated parameters was excellent, with percentage stan‐ dard deviations ranging from 4 to 18% for the various regions studied. The tissue discrimination achieved by use of just three relaxation parameters, T1, T2, and proton density, calculated from intensities of images from a four‐echo sequence, an inversion recovery sequence, and a short TR single‐echo sequence, was not as good, being only 55%. © 1989 Academic Press. Inc.
Magnetic resonance imaging of estrogen‐induced pituitary hypertrophy in rats
Authors: Van Nesselrooij Joop H. J. , Szeverenyi Nikolaus M. , Ruocco Martin J. 
Published: March 2007

AbstractEstrogen‐induced pituitary hypertrophy has been studied using magnetic resonance imaging in a group of 15 control and 30 experimental rats. Following the subcutaneous implantation of an estrogen pellet, differences in the anatomical appearance of the pituitary gland of the implanted rats can be detected in as little as 16 days, when compared to the control animals. The gland in the experimental animals appears diffusely enlarged with rounded margins, when viewed in sagittal T 1‐weighted magnetic resonance images. Additionally, a uniform signal intensity is not detected in the hypertrophic pituitary glands of estrogen‐implanted rats, while in the control rats this is a common finding. A satellite study of 300 animals (treated in a manner identical to that in the imaging study) demonstrates that the weights of excised pituitaries in estrogen‐treated rats increases to a statistically significant level in the interval 18 to 35 days. Changes in the appearance and volume of the pituitary gland observed with magnetic resonance imaging seem to have promise for the early detection of pituitary lesions in rats. © 1989 Academic Ress. Inc.
A liposomal MRI contrast agent: Phosphatid ylethanolamine‐DTPA
Authors: Grant Chris W. M. , Karlik Stephen , Florio Eugene 
Published: March 2007

AbstractThe chelating agent, diethylenetriaminepentaacetic acid (DTPA), was attached via one‐COOH group to the amino headgroup of phosphatidylethanolamine to produce a phospholipid which is also a powerful chelating agent. It readily assembles into the walls of lipid bilayer structures as a liposome‐associated camer of cations for MR contrast or radioisotope studies. Freeze‐etch electron microscopy showed that phosphatidylethanolamine‐DTPA formed satisfactory sonicated vesicles when mixed with natural phospholipids at up to 50 wt%. The resultant structures with bound gadolinium effectively shortened T1 and T2 of surrounding water protons. When sonicated liposomes bearing chelating agent with bound 111In3+ were injected intravenously into rats, uptake was primarily by liver and spleen. By 24 h postinjection there was biliary excretion of this material. Phosphatidylethanolamine‐DTPA may have some general utility as an amphiphilic liposomal chelating agent for polyvalent cations.
Diagnosis and assessment of mitral and aortic valve disease by cine‐flow magnetic resonance imaging
Authors: Mitchell Leslie , Jenkins Jeremy P. R. , Watson Yvonne , Rowlands Derek J. , Isherwood Ian 
Published: March 2007

AbstractSeventy‐six aortic and mitral valves, in 44 patients and 5 normal volunteers, were studied by Cine‐Flow MRI (on a 0.26‐T superconducting magnet system), utilizing compound oblique imaging planes and a Field Echo Even Rephasing sequence. All patients had had cardiac catheterization and echocardiography. All patients with valvular stenosis and aortic sclerosis (n = 45) showed complete signal loss distal to the respective valve. Length of signal loss distal to the aortic valve in those in whom it was measured (n = 15) allowed differentiation of aortic stenosis (n = 9) from sclerosis (n = 6). This also permitted grading of stenosis with highly significant correlation ( T = 0.86; P < 0.002) with pressure gradient measurement. In mitral stenosis (n = 12) calculation of the area of signal loss distal to the mitral valve as a percentage of left ventricular cross‐sectional area showed a highly significant correlation (T = 0.77; P = 0.001) with pressure gradient measurement. Clinically significant valvular regurgitation was graded by size and duration of signal loss proximal to the valve with concordance with angiocardiography. It is concluded that Cine‐Flow MRI has a clinical role in the diagnosis and assessment of valvular heart disease. © 1989 Academic Press, Inc.
Volume‐selective determination of the spin‐lattice relaxation time in the rotating frame, T1ρ, and T1ρ, imaging
Authors: Rommel E. , Kimmich R. 
Published: March 2007

AbstractA method for the volume‐and resonance line‐selective determination of the longitudinal relaxation time in the rotating frame, T1ρ, is described. The spin‐lock pulse intrinsic to the T1ρ sequence simultaneously replaces the first slice‐selective pulse of the VOSY method for localized spectroscopy. This is a further parameter suitable for the local characterization of tissue. On the same basis, T1ρ, can be used as a new contrast parameter for biomedical imaging purposes. An appropriate pulse sequence for T1ρ imaging is presented. Test experiments which promise some striking advantages compared with conventional magnetic resonance imaging are reported. © 1989 Academic Press, Inc.
Echo‐planar high‐resolution flow velocity mapping
Authors: Firmin D. N. , Klipstein R. H. , Hounsfield G. L. , Paley M. P. , Longmore D. B. 
Published: March 2007

AbstractA technique for the very rapid measurement of blood flow with high spatial resolution is described. The method combines the previously validated technique of phase velocity mapping and echo‐planar principles. The relatively small diameter of blood vessels enables a high‐resolution echo‐planar flow measurement to be made with as few as 16 echoes such that the method can be incorporated into a near standard NMR scanner. Two sequence variations are tested and validatedin vitroand one is used to demonstratein vivoblood flow measurement. The results are shown to compare well with a previously validated less rapid method. The technique should enhance the potential of NMR flow imaging by enabling sudden changes in flow to be studied. It should also simplify the measurement of blood flow in small mobile vessels such as the coronary arteries. © 1989 Academic Press, Inc.
Cerebral metabolite dynamics during temporary complete ischemia in rats monitored by time‐shared 1h and 31p nmr spectroscopy
Authors: Chang L.‐H. , Shirane R. , Weinstein P. R. , James T. L. 
Published: March 2007

AbstractThe changes in cerebral phosphorus metabolites, intracellular pH, and lactate during 30 min of complete global ischemia and 2 h of reperfusion were monitored by time‐shared 1H and 31P in vivo NMR spectroscopy in rats. After the induction of ischemia, intracellular pH decreased from 7.14 ± 0.01 to 6.32 ± 0.10, and lactate concentration increased from 1.6 ± 0.4 to 15.8 ± 2.5 μmol/g; ATP and phosphocreatine were totally depleted, while inorganic phosphate increased 715 ± 47%. Within 1 h after blood flow was restored, high‐energy phosphates and lactate levels had recovered close to baseline levels. The changes in intracellular pH and lactate levels during ischemia and reperfusion correlated Well.
Magnetic relaxation in blood and blood clots
Authors: Bryant Robert G. , Marill Keith , Blackmore Craig , Francis C. 
Published: March 2007

AbstractNuclear magnetic relaxation rates are measured for whole blood, blood plasma, whole blood clots, and plasma clots in vitro. Relaxation rates are linear in the hematocrit and transverse relaxation rates are significantly greater than longitudinal relaxation rates. Longitudinal relaxation rates measured from 0.01 to 42 MHz for proton Larmor frequencies are found to decline monotonically with increasing magnetic field strength; however, the dispersion curves do not follow a simple Lorentzian behavior, which is anticipated in a suspension of particles in a solution of proteins having a distribution of molecular weights. The transverse relaxation rate is a function of the acquisition parameters, in particular, the choice of TE in either Hahn echo experiments or in echo‐train experiments. The origin of this dependence of T2 on TE or the interpulse spacing in an echo train is identified with the exchange of water from inside the red blood cell to the outside and is only an important relaxation mechanism in the case where the blood cell membrane is intact and the cell contains deoxygenated hemoglobin. The dependence of the apparent transverse relaxation rate on the interpulse spacing in a Meiboom‐Gill‐Carr‐Purcell pulse sequence provides the estimate that the mean residence time of water inside the blood cell is about 10 ms. These data provide a sound basis for understanding the dependence of magnetic images on magnetic field strength and the choices of the image acquisition parameters, TE and TR.
Spectral baseline correction using clean
Authors: Mckinnon G. C. , Burger C. , Boesiger P. 
Published: March 2007

AbstractBaseline distortion in NMR spectroscopy, caused by the “dead time” between signal excitation and detection, makes quantitative interpretation difficult and is aesthetically displeasing. Here the use of the CLEAN algorithm for deconvolving the effect of signal dead time to produce a distortionless baseline is discussed. Unlike other nonlinear spectral estimation techniques, CLEAN is easy to program, easy to use, quite robust, and fast.
Quantitative studies of hydrodynamic effects and cross‐relaxation in protein solutions and tissues with proton and deuteron longitudinal relaxation times
Authors: Zhong Jianhui , Gore John C. , Armitage Ian M. 
Published: March 2007

AbstractLongitudinal relaxation times T1 of water protons were measured in 5% protein solutions at different static magnetic fields (0.47, 2, and 7 T), for proteins with molecular weight ranging between 1.4 and 480 kDa and in solvents of varying degrees of deuteration. T1, values were also obtained for rat liver soaked with Krebs‐Ringer solutions of varying degrees of deuteration at the above fields. For the samples containing D2O, T1 for deuterium was also measured at fields 2 and 7 T. The deuterium measurements were used to estimate water rotational correlation times which were in turn used to estimate the contribution of so‐called “hydrodynamic effects” of macromolecules to proton relaxation. The proton relaxation rates at full deuteration were compared with those in protonated solvent (water) to obtain a second, direct measurement of this effect. Both measurements provide quantitation of the hydrodynamic effects, free from the contributions of other effects that are transparent to deuteration, and results from both measurements agree with each other reasonably well. The cross‐relaxation rate between solute and solvent protons, and the contribution of paramagnetic impurities in the samples were also obtained from the proton T1studies. The experimental results show that the hydrodynamic effects (intramolecular and intermolecular water‐water interactions) are about the same magnitude in all the proteins studied as well as in rat liver. However, the cross‐relaxation rate generally increases with increasing protein molecular weight. Measurements in soaked rat liver indicate that the cross‐relaxation rate per unit mass of solute is much higher in tissues than in simple solutions of proteins of similar mean molecular weight. The results challenge the prevailing concept that the relaxation properties of biological tissues may be treated as a simple superposition of the properties of their Constituents.
Echo‐planar imaging of the human fetus in utero
Authors: Stehling M. K. , Mansfield P. , Ordidge R. J. , Coxon R. , Chapman B. , Blamire A. , Gibbs P. , Johnson I. R. , Symonds E. M. , Worhington B. S. , Coupland R. E. 
Published: March 2007

AbstractWe have demonstrated that echo‐planar imaging can be used to produce high‐quality snapshot images of the human fetus in utero in a fraction of a second. These images are free of motional artifact or blurring and allow detailed depiction of fetal structures in normal and pathological pregnancies.
A continuously variable field of view surface coil
Authors: Duensing R. , Fitzsimmons J. , Sanford D. , Vazquez J. 
Published: March 2007

AbstractA new type of surface coil is described which allows the user to continuously vary the size of the field of view. This utilizes a modified radiofrequency trombone for size adjustment that results in a stable frequency over a wide range of dimensions. Results show that the coil may be increased in area by as much as 60% while maintaining frequency stability to ca. 1 MHz at 63.5 MHz. Images of the human spine are presented to demonstrate the clinical utility of the new design.
NMR studies in experimental allergic encephalomyelitis: Factors which contribute to T1 and T2 values
Authors: Karlik S. J. , Gilbert J. J. , Wong C. , Vandervoort M. K. , Noseworthy J. H. 
Published: March 2007

AbstractTo determine the factors which may alter NMR relaxation times in multiple sclerosis (MS) lesions we measured the proton T1 and T2, specific gravity (SG), and histology in the central nervous system (CNS; 13–19 levels per animal) in the myelin basic protein (MBP) and CNS‐induced acute and relapsing EAE models in 44 juvenile Hartley guinea pigs. In the MBP model, T1 is unchanged but T2 is prolonged before symptoms and pathological changes occur. T2 remains prolonged during the acute phase of MBP‐in‐duced EAE. In the acute CNS model, T1 and T2 were not different from control despite advanced pathological changes of inflammation and demyelination and changes in specific gravity, indicating a marked change in tissue water content. No single variable, pathological or SG, could predict TI or T2 values in the CNS‐induced model. In active disease in the MBP model, when edema occurs in the presence or absence of parenchymal infiltration, T2 values are increased. However, as the factors which influence tissue NMR characteristics are complex in these MS models, it is likely difficult to infer specific pathological events from MRI findings in patients with MS. © 1990 Academic Press, Inc.
Oxygenation‐sensitive contrast in magnetic resonance image of rodent brain at high magnetic fields
Authors: Ogawa Seiji , Lee Tso‐Ming , Nayak Asha S. , Glynn Paul 
Published: March 2007

AbstractAt high magnetic fields (7 and 8.4 T), water proton magnetic resonance images of brains of live mice and rats under pentobarbital anesthetization have been measured by a gradient echo pulse sequence with a spatial resolution of 65 × 65‐μm pixel size and 700‐μm slice thickness. The contrast in these images depicts anatomical details of the brain by numerous dark lines of various sizes. These lines are absent in the image taken by the usual spin echo sequence. They represent the blood vessels in the image slice and appear when the deoxyhemoglobin content in the red cells increases. This contrast is most pronounced in an anoxy brain but not present in a brain with diamagnetic oxy or carbon monoxide hemoglobin. The local field induced by the magnetic susceptibility change in the blood due to the paramagnetic deoxyhemoglobin causes the intra voxel dephasing of the water signals of the blood and the surrounding tissue. This oxygena‐tion‐dependent contrast is appreciable in high field images with high spatial resolution. © 1990 Academic Press, Inc.
Tm(DOTP)5−: A 23Na+ shift agent for perfused rat hearts
Authors: Buster Douglas C. , Castro M. Margarida C. A. , Geraldes Carlos F. G. C. , Malloy Craig R. , Sherry A. Dean , Siemers Timothy C. 
Published: March 2007

AbstractTm(DOTP)5−, the thulium(III) complex of 1,4,7,10‐tetraazacyclododecane N,N′,N″,N‴tetra(methylenephosphonate), is introduced as a 23Na1 shift agent for use in discrimination of the NMR resonances of intra‐ and extracellular 23Na+ ions in perfused rat hearts. The novel shift agent is directly compared to the widely used Dy(TTHA)3‐ (dysprosium(III) triethylenetetraminehexaacetate). © 1990 Academic Press, Inc.
Influence of global ischemia on intracellular sodium in the perfused rat heart
Authors: Malloy Craig R. , Buster Douglas C. , Margarida Castro M. C. A. , Geraldes Carlos F. G. C. , Jeffrey F. Mark H. , Sherry A. Dean 
Published: March 2007

AbstractIntracellular [Na+], [H+], and [ATP] and mechanical performance were measured in the isovolumic perfused rat heart during ischemia. The concentration of intracellular sodium, [Na+]i, was determined by atomic absorption spectroscopy under control conditions, and [Na+] was monitored by 23Na NMR spectroscopy at 1‐min intervals under control conditions and during global ischemia. [ATP], [H+], and [Pi] were measured by 31PNMR in a separate group under identical conditions. The control [Na+]i measured by atomic absorption was 30.7 ± 3.3 mM(mean ± SD, n = 6), and [Na+]i measured by NMR was 6.2 ± 0.5 mM(n = 3). Brief ischemia (10 min) was associated with a 54% increase in [Na+]i which reversed completely with reperfusion. Developed pressure also returned to control values upon reperfusion. Prolonged ischemia (30 min) produced continuous further accumulation of sodium (0.53 mM/min, r2 = 0.99). [H+] also increased approximately linearly early in ischemia (0.084 μM/min, r2 = 0.97). The rate of increase in [Na+]i was more than 4000 times greater than the increase in [H+] on a molar basis. Nevertheless, [H+]/[Na+] increased early in ischemia because the proportional change in [H+] was greater than that in [Na+] i. These results indicate that (1) intracellular sodium measured by NMR in the functioning heart is about 20% of total intracellular sodium; (2) intracellular acidosis and accumulation of sodium develop simultaneously during global ischemia; (3) increased intracellular sodium content is not in itself an indicator of irreversible injury; and (4) recovery of mechanical performance is associated with return of [Na+] (measured by NMR) to baseline after brief ischemia. The mechanism of the increase in sodium content detected by NMR is unknown. © 1990 Academic Press, Inc.
Measurement of cerebral blood flow in rat brain by 19F‐NMR detection of trifluoromethane washout
Authors: Detre John A. , Eskey Clifford J. , Koretskyp Alan P. 
Published: March 2007

AbstractThe washout of trifluoromethane (CHF3) from rat cerebral cortex was monitored by 19F NMR. After 15 min of inhalation of 67% CHF3/33% O2 the fluorine signal detected was in a steady state. The CHF3 was switched off rapidly at the endotracheal tube and the washout detected with 12‐s time resolution. Two models were used to extract flow information, a simple exponential fit and a model which accounts for arterial CHF3 recirculation. In both cases, a two‐compartment model fit the data significantly better than a one‐compartment model. In both models, the faster time component varied with increasing pCO2, but no significant change in the slow component was detected. At control values of pCO2, there was a small difference in washout rate constants derived from the two models. At high pCO2, when tissue washout was comparable to arterial washout of CHF3, the model which accounted for arterial recirculation gave higher flows. Using this two‐compartment model with correction for recirculation, a control flow (pCO2 = 35 mm Hg) of 0.73 ± 0.04 ml/min/g was measured. Increasing plasma pCO2 increased the apparent flow six‐ to sevenfold with a 4.4% increase in flow per millimeter of Hg change in CO2. These results are qualitatively in agreement with results found by others using the washout of 133Xe. However, this method yields values for flow that are lower than those obtained using 133Xe washout, probably because of diffusion limitations of CHF3. © 1990 Academic Press, Inc.