摘要:

AbstractAbnormal cardiac energy metabolism has been postulated as a mechanism for adriamycin induced cardiotoxicity. This study was designed to determine high energy phosphate stores at rest and with hemodynamic stress in perfused rat hearts after animals had been chronically exposed to adriamycin (2 mg/kg weekly for 14 weeks). Morphologic and hemodynamic changes were mild in this model. Phosphorus‐31 NMR determined intracellular pH and levels of inorganic phosphate (Pi) and ATP were comparable in treated and control hearts. Phosphocreatine (PCr) levels were markedly decreased in treated hearts (0.89 ± 0.07 units/g versus 1.7 ± 0.13 units/g,p<0.001). The PCr/Pi ratio decreased in both groups during hemodynamic stress. It recovered earlier in controls and there was a marked overshoot after cessation of rapid pacing in this group which was not present in adriamycin treated hearts. These results suggest that metabolic regulation in response to hemodynamic stress is impaired after chronic adriamycin exposure. PCr depletion and delayed metabolic recovery after hemodynamic stress appear to be potentially useful markers for the effect of adriamycin on the heart. © 1991 Academic Press,

ISSN:0740-3194    

DOI:10.1002/mrm.1910170112

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractLocalized proton NMR spectroscopy using stimulated echoes (STEAM) has been used to study metabolites in different proximal skeletal muscles of normal volunteers at rest. Single scan water‐suppressed proton NMR spectra obtained at 1.5 and 2.0 T (Siemens Magnetom) from a 64‐ml volume‐of‐interest (VOI) yield resonances due to triglycerides, phosphocreatine plus a minor contribution from creatine, and betaines comprising carnitine and choline‐containing compounds. The observation of the pH‐dependent resonances of carnosine required multiple acquisitions and echo times as short as 20 ms.T1andT2relaxation times of muscle metabolites were obtained by varying the repetition time and echo time of the STEAM sequence, respectively. Although rather longT2values such as 180 ms for (phospho‐) creatine correspond to natural resonance line widths of only 2 Hz, the observed line widths of typically 10‐12 Hz are entirely determined by the shortT2relaxation times (25‐30 ms) of the water protons used for shimming. The spectroscopic results from 24 muscle studies on 17 young male volunteers show remarkable intra‐ and interindividual differences in the absolute signal intensities of mobile lipids. Further metabolic variations were observed for the relative concentrations of betaines (by a factor of 2) and carnosine (by a factor of 3) when total creatine is assumed to be constant. © 1991

ISSN:0740-3194    

DOI:10.1002/mrm.1910170113

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper describes a new MR imaging technique termed Modified Stejskal Tanner versus Flow Compensation (MST/FC) for the separation of diffusion and microcirculatory flow. The theory behind the sequence is explained, along with a five‐component model of microcirculation applicable to any “perfusion” imaging technique. Phantom data is presented showing that (1) diffusion effects can be matched between MST and FC (suggesting the possibility of flow‐compensated diffusion imaging), and (2) the technique is a quantitative method of separating diffusion and slow (<0.25 mm/s) tortuous flow through a Sephadex column. Furthermore, animal images show the technique to be feasible and quantitative in measuring rat brain microcirculation under normal, vasodilated (hypercarbia), and no‐flow (post mortem) conditions. © 1991 Academic

ISSN:0740-3194    

DOI:10.1002/mrm.1910170114

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractClinicians typically obtain high‐resolution clinical MR images in an effort to avoid the truncation artifacts that often arise in Fourier transform reconstruction of limited data. A method for reducing these artifacts in MR images, at the reconstruction stage, would allow for reduced imaging times, through the collection of fewer phase encode steps and increased signal‐to‐noise ratios, through increased pixel size. The approach to reducing truncation artifacts in MR images is developed and a simple algorithm is presented which significantly reduces truncation artifacts in images with as few as 96 phase encode steps. The algorithm is compared with a more sophisticated method of reconstructing truncation‐free images and is shown to be equivalently effective. Three clinical examples are shown illustrating the Success of the method. © 1991 Academic Pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910170115

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractWe report a new micromanometer‐tip catheter to record high‐fidelity pressures during cine‐gated gradient echo NMR imaging in an intact animal model. Of the various metals and alloys tested for use in its construction, brass produced the smallest NMR artifact with minimal magnification. With the use of this new catheter design, there was little signal loss and no distortion of endocardial borders during imaging. © 1991 Academic Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910170116

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe performance of current, flow‐based sequences for imaging vasculature using MR is severely restricted in regions with inherently slow flow. We address this problem with a flow‐independent imaging method. Specifically, we generate projection images of blood in the limbs while suppressing signal from all other tissues (primarily skeletal muscle, bone marrow, and subcutaneous fat) using a flow‐compensated, water‐selective, short TI inversion recovery sequence with a long echo time. We experimentally evaluate the effectiveness of this sequence and presentin vivoresults clearly demonstrating the method's potential. © 1991 Academic Pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910170117

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractNMRD profiles, the magnetic field dependence of the water proton longitudinal relaxation rates, have been acquired for two new diphosphonate‐modified GdDTPA complexes currently under evaluation as relaxation agents for the MRI detection of soft‐tissue calcifications. Fresh dilute solutions show profiles identical to that of unmodified GdDTPA, which remain unchanged for up to 9 weeks. Solutions containing Gd species at MRI significant concentrations, 100 to 500 mM, show the presence of oligomers (n= 5 or more) upon aging, with much higher high‐field relaxivities. Aggregation is attributed to the interactions between a gadolinium center and the phosphonate terminus of a neighboring molecule, and is prevented by esterification of the phosphonate terminus. Oligomers are also easily disrupted by dilution with phosphate‐buffered saline, where the exogenous phosphate ions compete with the phosphonate. Other nucleophiles such as are present in protein side chains of bovine serum albumin also compete with the phosphonate in these associations, the result being species with even higher relaxivities. © 1991 Academic Pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910170118

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe eddy currents in nuclear magnetic resonance (NMR) imaging are analyzed from the solutions of Maxwell's equations and their effects are examined over various experimental conditions from whole‐body diagnostic imaging to recently developed NMR microscopy. The analysis is focused mainly on the frequency characteristics and intensity variations of the eddy‐current‐induced field which depends on the overall system size, ratio of the gradient coil size to the magnet bore diameter, and the pulse‐sequence‐dependent parameters such as input current waveform and repetition time. From the analysis, the frequency response of the eddy‐current‐induced field is that of a high‐pass filter whose cutoff frequency is inversely proportional to the square of the overall system size. The intensity ratio of the generated field to the induced field is not affected by the overall system size, but is sensitively related to the ratio of the gradient coil size to the magnet bore diameter. © 1991 Aca

ISSN:0740-3194    

DOI:10.1002/mrm.1910170119

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractBinding of potential blood pool and hepatobiliary paramagnetic iron(III) contrast agents,rac‐ and Meso‐Fe(5‐Br‐EHPG)−(iron(III) N,N′‐ethylenebis[(5‐bromo‐2‐hydroxyphenyl)glycinate]) and Fe(5‐Br‐HBED)−(iron(III) N,N′‐bis‐(5‐bromo‐2‐hydroxybenzyl)ethylenediaminediacetic acid) to human serum albumin (HSA) has been studied using the proton relaxation enhancement (PRE) effect on solvent protons. These chelates bind avidly to multiple sites on HSA with binding constants on the order of 104to 105M−1. Interestingly, binding results in a decrease in the diamagnetic component of the water relaxivity due to HSA, while the expected enhancement of the paramagnetic component of water proton relaxation rates occurs due to the increase in the rotational correlation times of the protein‐bound agents. These relaxation enhancements are variable, depending upon the site on the protein to which these chelates are bound, and can be as high as ∼7 mM−1s−1at 5°C and ∼5 mM−1s−1at 37°C at 20 MHz (enhancements of ∼2−5). Change of temperature from 5 to 37°C also appears to switch the relative affinities of these chelates for their primary and secondary binding sites. It is found that the important HSA binding site for the heme breakdown product, bilirubin‐IXα, is a target for these agents and is the site of hi

ISSN:0740-3194    

DOI:10.1002/mrm.1910170120

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe effect of homonuclearJmodulation on19F spin‐echo images is evidenced by a substantial reduction in signal when the echo time, TE, approaches 1 /2J, with a subsequent increase in signal at longer TEs. Suppression of theJ‐modulation effect is demonstrated using chemical Shift‐Selective 180° refocusing pulses. © 1991 Academic Pre

ISSN:0740-3194    

DOI:10.1002/mrm.1910170121

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY