ISSN:0740-3194    

DOI:10.1002/mrm.1910290102

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

年代:1993

数据来源: WILEY

摘要:

AbstractIn theory, multidimensional pulses can be designed to be selective in any number of dimensions. In practice, available gradient power has enforced a limit to two dimensions. We show here that three‐dimensional π pulses are feasible on commercial imaging machines provided that the range of offresonance frequencies are limit

ISSN:0740-3194    

DOI:10.1002/mrm.1910290103

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

年代:1993

数据来源: WILEY

摘要:

AbstractIn order to assess the influence of longitudinal relaxation on previously reported variations in31P NMR signals during brain development, we used an accelerated two‐point technique to determineT1at 2.35 Tesla in 8 min. Comparison between 10 normal neonates (age range 37–46 weeks postconception) and 10 healthy infants (age range 80–157 weeks postconception) indicated thatT1does not vary substantially during the first year of life, except in the phosphomonoester (PME) region of the spectra.T1of total PME decreases with age which we could explain by its variable multicomponent nature: The signal from (unresolved) components at the downfield shoulder of PME (attributed mostly to phosphorylethanolamine at 6.72 ppm) with aT1of at least 6.4 s decreases with age relative to contributions from other phosphomonoester compounds resonating predominantly at the upfield side of the peak (approximately 6.3 ppm), withT1below 2.9 s. Because theT1heterogeneity of PME may depend on its relative composition, quantitative31P NMR spectroscopy may require an assessment of the influence of longitudinal relaxation on the signal amplitudes in each measur

ISSN:0740-3194    

DOI:10.1002/mrm.1910290104

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe concentration of oxygen within cells is important in many physiological and pathological processes, but such oxygendependent phenomena are generally studied as a function of the concentration of extracellular oxygen, due to a lack of suitable methods. Electron parmamagnetic resonance (EPR) oximetric techniques offer an attractive alternative to make such measurements. Previous EPR oximetric studies of extracellular‐intracellular oxygen gradients have been hindered, however, by the fact that separate samples, prepared in slightly different ways, were required for individual measurements of extracellular and intracellular oxygen concentrations. In this study we demonstrate a technique that allows simultaneous measurement of intracellular and extracellular oxygen concentrations in a single sample: extracellular measurement is achieved using positively charged nitroxides encapsulated in liposomes, while intracellular oxygen is determined using a membrane‐permeable nitroxide along with an extracellular broadening agent. Application of this system to the measurement of oxygen concentrations in suspensions of rat myoblast cells gave results which are consistent with nonsimultaneous measurements and which show substantial extracellular‐intracellular oxygen gradients in these rapidly respiring

ISSN:0740-3194    

DOI:10.1002/mrm.1910290105

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

年代:1993

数据来源: WILEY

摘要:

AbstractTwo theories have been proposed to explain the multiexponential transverse relaxation of muscle water protons: “anatomical” and “chemical” compartmentation. In an attempt to obtain evidence to support one or the other of these two theories, interstitial and intracellular macromolecular preparations were studied and compared with rat muscle tissue by proton NMR transverse relaxation (T2) measurements. All macromolecule preparations displayed monoexponential T2 decay. Membrane alteration with DMSO/glycerin did not eliminate the biexponential T2 decay of muscle tissue. Maceration converted biexponential T2 decay of muscle tissue to single exponential decay. It is concluded that the observed two component exponential T2 decay of muscle represents anatomical compartmentation of tissue water, probably intracellular versus extrac

ISSN:0740-3194    

DOI:10.1002/mrm.1910290106

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

年代:1993

数据来源: WILEY

摘要:

AbstractStrong, extensive magnetic fringe fields are a significant problem with magnetic resonance imaging magnets. This is particularly acute with 4‐T, whole‐body research magnets. To date this problem has been addressed by restricting an extensive zone around the unshielded magnet or by placing external unsaturated iron shielding around the magnet. This paper describes a solution to this problem which uses superconducting coils closely integrated with fully saturated iron elements. A 4‐T, 30‐cm‐bore prototype, based on this design principle, was built and tested. The 5 G fringe field is contained within 1 meter of the magnet bore along thezaxis. Homogeneity of the raw magnetic field is 10 ppm over 30% of the magnet's diameter after passive shimming. Compared with an unshielded magnet, 20% less superconductor is required to generate the magnetic field. Images and spectra are presented to demonstrate the magnet's viability for magnetic resonance imaging and spe

ISSN:0740-3194    

DOI:10.1002/mrm.1910290107

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

年代:1993

数据来源: WILEY

摘要:

AbstractHuman peripheral blood mononuclear cells (PBMCs) were incubated with large unilamellar vesicles (LUV) containing encapsulated dextran‐magnetite particles (DMP). This resulted in an efficient incorporation of DMP. Electron microscopy revealed the presence of DMP in cells mainly in phagosomes and secondary lysosomes. DMP‐labeled PBMCs showed a strong increase of the transverse relaxation rate (up to 16.6 s−1for 5 x 107cells/ml) and, accordingly, a great loss of signal intensity in MR imaging. The fraction of DMP containing PBMCs could be enriched by magnetic cell separation. The major population of the DMP containing cells proved to be monocytes. When PBMCs depleted of monocytes were used for labeling, DMP uptake was observed also in the peripheral blood lymphocytes. The labeling of PBMCs presented here may be used in future studies of selective MR imaging ofin vivocell migration in a variety of immunologically compromised tissue states, e.g., tumors, transplantations, and absc

ISSN:0740-3194    

DOI:10.1002/mrm.1910290108

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

年代:1993

数据来源: WILEY

摘要:

AbstractCitrate is a secretory product of the normal prostate, a lack of citrate in prostate tissue is expected to be pathognomonic for adenocarcinoma. In the present study proton AB‐signal characteristics of citrate at low field strength of 1.5 T were investigated byvolume selective spectroscopic and theoreticalmethods. The nonappearance of fast phase modulation of the J‐coupled system at low field strengthin vivois verified by measurements of sodium citrate solution.In vivolocalized spectroscopy of small volume elements of (2 cm)3with the double spin‐echo method within the prostatic gland provides citrate signal reception even using a Helmholtz coil with 170‐mm diameter. Volume selective proton spectra with different echo times are presented which are comparable to spectra acquired by former authors with endorecta

ISSN:0740-3194    

DOI:10.1002/mrm.1910290109

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

年代:1993

数据来源: WILEY

摘要:

AbstractAn MR imaging technique that simultaneously acquires Fourier velocity encoded data from multiple stations is described. The technique employs a comb excitation rf pulse that excites an arbitrary number of slices. As the Fourier velocity phase encoding gradient pulse is advanced, the phase of each slice is the comb is advanced by a unique amount. This causes the signals from the spins in a particular slice to appear at a position in the phase encoding direction, which is the sum of the spin velocity and an offset arising from the phase increment given to that excitation slice. Acquisition of spin velocity information occurs simultaneously for all slices, permitting the calculation of wave velocities arising from pulsatile flow. These wave velocities can then be used to determine vessel distensibility.

ISSN:0740-3194    

DOI:10.1002/mrm.1910290110

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe bioenergetics of paralyzed muscles of spastic paraplegic patients under functional electrical stimulation (FES) was studiedin vivousing31P NMR. The protocol included rest, 3 min of induced tetanic isometric contraction through surface electrodes and 40 min of recovery. The continuous stimulation, the force recording and the31P NMR measurements were sampled simultaneously inside the whole body imager. Normal values were found for the phosphorous metabolite ratios at rest. During contraction, prominent changes were detected including: a) accumulation of inorganic phosphate (P) accompanied by an unusually strong signal in the phosphomonoester (PME) region, b) phosphocreatine (PCr) decline, and c) a decrease in the intracellular pH. In the following recovery period the physiological state of the muscle was monitored and quantitated by31P NMR. No metabolic and mechanical irreversible damage was detected in the paraplegics' muscles activated by FES under our experimental conditions.

ISSN:0740-3194    

DOI:10.1002/mrm.1910290111

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

年代:1993

数据来源: WILEY