摘要:

AbstractDetermination of the chemical shift and integral of the myocardial intracellula inorganic phosphate (Pi) resonance by31P magnetic resonance spectroscopy (MRS) is often precluded due to a large overlapping signal from 2,3‐diphosphoglycerate (2,3‐DPG) from chamber and myocardial blood. This report demonstrates the use of radiofrequency (RF) magnetic field gradient echoes (RFGE) to eliminate signals from 2,3‐DPG in flowing blood, while retaining signals from intracellular myocardialPi, ATP, and phosphocreatine (PCr). The ECG‐triggered31P spectra were acquired from the myocardium of open chest pigs using a Philips Gyroscan 2‐T magnetic resonance spectrometer. A 2.5‐cm‐diameter surface coil attached to the myocardium was used to provide the RF gradient as well as for excitation and detection of signals. Optimal performance of the RFGE pulse sequence was obtained when the RF gradient pulses were centered at peak diastole or peak systole. Under these conditions, 2, 3‐DPG signals were completely suppressed, and sensitivity was usually sufficient to allow detection of a well‐resolvedPisignal. Myocardial pH determined from RFGE experiments was 7.16 ± 0.10, and the ratio of the integrals of thePiand ATP resonances (Pi/ATP) was 0.24. The mean signal‐to‐noise ratio (S/N) for PCr in control spectra acquired in 4 min was 19/1, while the meanS/Nfor PCr in RFGE‐edited spectra acquired in 15 min was 11/1, demonstrating that the present implementation of the RFGE method results in significant loss in sensitivity. These experiments demonstrate that RFGE‐editing allows accurate determination of the chemical shift and integral of thePiresonance in blood‐perfused myocardiumin situ

ISSN:0740-3194    

DOI:10.1002/mrm.1910200202

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe level of intracellular sodium (Nai) is maintained at approximately 14 mMin healthy myocytes. When myocytes are damaged, Naiincreases and therefore the level of Naimay be a means of evaluating myocardial cell integrity. A particularly useful method to monitor Nailevels is23Na NMR spectroscopy. However, because of the isochronous nature of the extracellular sodium (Nao) and NaiNMR signals, paramagnetic lanthanide shift reagents (LSR), such as dysprosium triphosphate, Dy(PPP)72, have been used to shift the Naosignal. This reveals the unshifted Naisignal and allows the NMR monitoring of Naiin isolated perfused hearts and other systems. A major shortcoming of this method (the “shift‐only” method) is in the need to minimize the Naosignal by not submerging the perfused hearts in Na+‐containing buffer. An equally undesirable alternative is the utilization of relatively high concentrations of LSR to shift a large Naosignal sufficiently to enable reasonable resolution and quantitation of Nai. We present here a method, the “shiftrelaxation” method, which is a combination of using a mixture of Dy(PPP)72, a shift reagent, and gadolinium triphosphate, Gd(PPP)72, a relaxation agent, with data acquisition using an inversion‐recovery (IR) pulse sequence. This combination allows differentiation between Naoand Naiby the difference in their respectiveT1values in addition to the shift between them. With this technique we can selectively minimize the extracellular signal and therefore minimize the need for a large Dy‐induced shift, as well as allow data acquisition on a heart submerged in Na+‐containing perfusate. The resulting improved discrimination between Naiand Naoat relatively low levels of LSR should be helpful for ultimatein vivoapplication and potential clinical applications, where a lower dose of LSR also means a decreased possibility of physiologically deleterious effects. Also included in this paper is a method for the quick determination of an accurate 180° pulse which is required for the optimization of the IR method. © 1991

ISSN:0740-3194    

DOI:10.1002/mrm.1910200203

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

年代:1991

数据来源: WILEY

摘要:

AbstractWater proton relaxation measurements obtained from model cellular systems composed of red blood cell (RBC) ghosts are presented. The purpose of the investigation was to evaluate hypotheses concerning the possible sources of multiple exponential components in similar relaxation measurements made on tissue. Both laboratory frame transverse and longitudinal relaxation rates, as well as rotating frame relaxation rates, were measured in preparations of RBC ghosts and “extracellular fluid” that were, (a) uniformly mixed or (b) compartmentalized by layering, as the concentration of serum albumin was varied in the “extracellular fluid.” The data show that although transmembrane exchange is too fast to give rise to multiexponential relaxation, multiple components can result from compartmentalization at the level of the cellular organization and do not necessarily require different tissue types. In addition, the data clearly demonstrate the importance of protein adsorption to cellular membranes as a determinant of the concentration of freely mobile solute protein molecules in tissue fluids. © 1991 Academic Pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910200204

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

年代:1991

数据来源: WILEY

摘要:

AbstractBiological systems exhibit heterogeneity at many different levels, leading to the expectation of multiple relaxation time components for water protons in tissue samples. Traditional methods which fit the relaxation data to an a priori number of discrete components are open to observer bias in their interpretation of this data, and moreover, are intutively less realistic for heterogeneous systems than methods which produce continuous relaxation time distributions. Previous validations of continuous distribution techniques have been made on simulated data assuming uniform Gaussian noise. In the current work we have investigated the ability of one particular linear inverse theory technique to reproduce known relaxation time distributions from the data on a controllable model system. Furthermore, using the experience gained on the model system, we have applied this same technique to the analysis ofin vitrorelaxation time measurements on excised brain tissue and found for water protons in white matter, four reproducible components for the transverse relaxation, whereas gray matter gave rise to only two. The lougitudinal relaxation displayed only one component in either white matter or gray matter. © 1991 Academic Press, Inc

ISSN:0740-3194    

DOI:10.1002/mrm.1910200205

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

年代:1991

数据来源: WILEY

摘要:

AbstractWe report methods for quantitative NMR imaging of the primate uterus and the application of these methods of measuring the response of the monkey (Macaca nemestrina) uterus (endometrial volume. myometrial volume,T2values, myometrial junction zone) to estrogen stimulation. High‐gield (2.35 T), fat‐suppressed,T2‐weighted (TE50) oblique methods were used, Slice thickeness, location, and angle were varied on each examination to obtain six contiguous slices between the cervix and fundus, regardles of size or orientation of the uterus. Basal endometrial and myometrial volumes were 0.05± 0.01 cm3and 1.31 ± 0.23 cm3in chronically ovariectomized animals. These increased by 15.7 ± 3.6‐fold and 3.1 ± 0.4 fold, respectively, during 7 days of estrogen stimulation (estradiol benzoate, 5 ųg/kg sc daily) while myometrialT2increased from 52 ± 1 to 67 ± 4 ms. These changes reversed following menstrual bleeding. © 1991 Acad

ISSN:0740-3194    

DOI:10.1002/mrm.1910200206

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe behavior of the lithium (Li) ion in normal human erythrocytes has been studied by7Li NMR. The uptake of Li into the cells was followed as a function of solution conditions, temperature, hematocrit, and blood age using dysprosium tripolyphosphate shift reagent. Under our conditions the uptake of Li increases with increasing hematocrit and blood age. For packed cells the extracellular7Li spin‐lattice relaxation time was only slightly longer than the intracellular relaxation time. Thus,T1may not be useful for separate observation of intra‐and extracellular Liin vivo. The intra‐ and extracellularT2s were substantially shorter than the correspondingT1s. Also, the intracellularT2was considerably shorter than that for the extracellular compartment, suggesting thatT2may provide a noninvasive handle for observation of intracellular Li. Nuclear Overhauser enhancements could be observed for both extra‐and intracellular7Li, confirming that dipolar coupling to1H is a contributing relaxation mechanism. The7Li NMR visibility was esentially 100% at high Li concentrations, decreasing to about 84% at 1 mMLi. Based on time course studies of the invisibility, and a comparison of NMR and inductively coupled plasma results, it appears that the invisibility of the intra‐ and extracellular compartments for packed cells in the same. Although a23Na double‐quantum signal could be observed for red blood cells, no double‐quantum signal was observed for7Li. © 1991 Acade

ISSN:0740-3194    

DOI:10.1002/mrm.1910200207

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

年代:1991

数据来源: WILEY

摘要:

AbstractWe studied tumor tissue oxygenation in the BA1112 rhabdomyosarcoma using microelectrode pO2measurements, optical spectrophotometry, analyses of cell survival after irradiation, and31P magnetic resonance spectroscopy (MRS). Studies were carried out in WAG/Rij/Y rats breathing normoxic, hypoxic, and hyperoxic gas mixtures with and without iv administration of perfluorochemical. Significant changes in tissue oxygenation and metabolic status were found when pO2values, optical measurements of hemoglobin saturation and cytochrome a, a3reduction‐oxidation, radiation cell survival determinations, and MRS measurements of phosphometabolite ratios were obtained in rats breathing different gas mixtures. Inhalation of 100% O2caused increases in tumor pO2, hemoglobin saturation, cytochrome a, a3oxidation, tumor radiosensitivity, and PCr/Pi,NTP/Pi, and PDE/Piratios. Such changes were augmented by pretreatment with iv perfluorochemicals. Inhalation of hypoxic gas mixtures resulted in reductions in the above paramenters. These results indicate that tissue oxygenation can be manipulated reproducibly in the BA1112 rhabdomyosarcoma and suggest that31P MRS can be used to monitor changes in tumor oxygenation in this model syste

ISSN:0740-3194    

DOI:10.1002/mrm.1910200208

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

年代:1991

数据来源: WILEY

摘要:

AbstractWe propose methods for the spatial and temporal characterization of time‐dependent magnetic fields generated by eddy currents after switching gradients. For an on‐line determination of the temporal variations of the fields, we extract two terms from the unresolved signal of an extended sample, describing the time evolution of a frequency shift γΔBz(t) and of a decay constantk(t). This procedure allows us to optimize interactively the multiexponential pre‐emphasis as well as any spectral volume selection method with respect to eddy currents, Additionally, we suggest an imaging sequence which allows us to determine the spatial distribution of eddy current fields at a chosen time‐point after any gradient sequence to be tested. Expansion of these eddy currents fields into spherical harmonic functions proves the existence of a higher order terms, which cannot be corrected by a standard pre‐emphasis device, where time constants and amplitudes are adjusted on theX, Y, ZandZ0 coils. The proposed numerical analysis gives a tool to characterize any magnet/ gradient system quantitatively with respect to eddy current performance. © 1991 Academi

ISSN:0740-3194    

DOI:10.1002/mrm.1910200209

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe relative brightness of adult white matter inT1‐weighted MRI arises from myelin, but the mechanisms responsible remain to be clarified. Koeniget al. [Magn. Reson. Med.14, 482 (1990)] conjectured that the cholesterol of myelin (∼ 30% of its lipid) was responsible. We present 1/T1and magnetization transfer contrast imaging data [Wolff and Balaban,Magn. Reson. Med.10, 135 (1989)] on a model system— 50% lipid—50% water by weight, with the lipid one‐half phosphatidyl cholinc (PC) and one‐half cholesterol—and a control in which the lipid is all PC. The differences between the model and control samples mimic the myelin contribution to white matter in both experiments. © 1991 Acade

ISSN:0740-3194    

DOI:10.1002/mrm.1910200210

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn vivo1H spectroscopy using the STEAM sequence for localization has been applied to the human kidney in normal volunteers and subjects with succesful renal transplants. We show that, within the resolution of our measurements, trimethylamines are present in the spectra from some of the subjects and absent from others, the prominent peak seen at 5.8 ppm in the spectrum is identified as that from urea and not lipid, as previously suggested. © 1991 Academic Press, Inc

ISSN:0740-3194    

DOI:10.1002/mrm.1910200211

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

年代:1991

数据来源: WILEY