摘要:

AbstractNuclear magnetic relaxation measurements of water in gels made of crosslinked dextran or polyacrylamide (water content, 30‐60 wt%) were carried out using broad‐line proton‐pulsed NMR. BothT1andT2values showed inflection against pore size, i.e., the size of the compartment made by crosslinks of the polymer gels.T2(orT1) values obtained for gels with compartments smaller than the critical size remained low within the range of the water content used in this experiment. Those values of gels with larger compartments, on the other hand, became higher with increasing size. When the size of the compartment was larger than the critical size,T1andT2values also became higher with increasing water content. The inflection point can be considered to correspond to the critical compartment size below which the motion of compartmentalized water in gels is more or less restricted. When the compartment is small, however, not only the effect of the molecular motion of water but also that of the proton exchange between compartmentalized water and gel matrix or hydration water should be taken into consideration for the interpretation of the short relaxation times observed, especially byT2. The results obtained in this investigation might provide useful information in the explanation and evaluation of the relaxation values in tissue. © 1989 Academic Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910090102

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe effect of fructose loading on high‐energy phosphates in the jejunum, ileum, and large intestine of rats was studied using31P NMR. Following fructose loading, an increase in the intensity of the PME resonance was observed in the jejunum, indicating an accumulation of fructose‐1‐phosphate. There were no significant changes in ATP orPi. This demonstrates that the activity of fructokinase in the jejunum can be monitored by31P NMR. Fructose loading had no detectable effect on metabolite levels in the ileum and large intestine. Resolution of intestinal spectra was poor due to unusually large linewidths and the presence of broad underlying signals. To study the mechanism of line broadening, theT2's of the phosphorus resonances were measured using a solenoidal coil. TheT2's ofthe ATP orPi, PME. and PCr resonances were much longer than the T2's, suggesting that the linewidths of these resonances are primarily due to susceptibility gradients and/or compartmentation of metabolites. Other signals, particularly in the PDE region, were homogeneously broadened and had very shortT2's. Spin echoes obtained with evolution times of 1 to 4 ms suppressed these broad components, with little loss of intensity in the inhomogeneously broadened resonances; as a result, resolution was improved. © 1989 Academic Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910090103

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

年代:1989

数据来源: WILEY

摘要:

AbstractCurrently the accepted method for setting the correct rf power levels to achieve 90° and 180° rf pulses for MR imaging is to peak the echo amplitude of a rf spin‐echo sequence. The echo amplitude of this α‐2α pulse sequence is proportional to sin3(α) and has a relatively broad maximum. Recently another method for setting the rf flip angle by maximizing the ratio of the stimulated echo to the primary echo amplitudes (in a 3α sequence) demonstrated accuracy similar to that of the spin‐echo method using a shorter repetition time. We present a new, more sensitive, and more accurate method for setting the correct rf power levels for 90° and 180° rf pulses. In this method, based upon the stimulated echo pulse sequence, we are able to accurately set the rf power to within ±0.1 dB by minimizing the signal amplitude of the third spin echo. This null method works for both selective and nonselective rf pulses of flip angle 90° or 180°, allowing the user to accurately adjust the relative amplitudes of the four rf pulse types within a single pulse sequence. © 1989 Ac

ISSN:0740-3194    

DOI:10.1002/mrm.1910090104

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

年代:1989

数据来源: WILEY

摘要:

AbstractIn order to overcome the problems that arise from nonuniformB1, fields, there has been interest in developing pulses that are insensitive to large variations in RF power. Pulses derived from adiabatic passage principles that can execute spin inversion, excitation, and 90°and 180° plane rotations in the presence ofB1, inhomogeneities have recently been described. When driven with optimized modulation functions, these pulses can execute uniform excitation, refocusing, and slice‐selective inversion over a 10‐fold or greater variation inB1magnitude. This insensitivity toB1strength enables the execution ofT 1 −and/orT 2 −weighted spin‐echo imaging experiments using coils, such as the surface coil, with extremely inhomogeneousB1profiles. We have successfully acquired images with these pulses at 200 MHz using a single surface coil as the transmitter and receiver. Images of the slice definition, the region over which the excitation and refocusing pulses operate with a surface coil, and brain images obtained with slice planes perpendicular to the plane of the surface coil are presented. Results demonstrate that these pulses can be transmitted with a surface coil to yield high‐qualityT 1 −and/orT 2 −weighted images withoutB1, arti

ISSN:0740-3194    

DOI:10.1002/mrm.1910090105

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe1HNMR spectra of the lipid region of human plasma from healthy adults, neonates, and patients with malignant and nonmalignant tumors have been recorded on a JNM‐GX400 FT spectrometer operating at 399.6 MHz for protons. The chemical shifts of methylene and methyl groups of plasma lipids were measured with respect to the higher field component of the methyl proton resonance of the lactate molecule. The results show that there are changes in the chemical shifts of the methylene proton resonances among the plasma from healthy adults, adults with tumors, and neonates. The shifts observed in the case of cancer patients and neonates are in the direction opposite to the shift measured from the plasma of healthy adults. Thus, the observed changes cannot be explained by the activity in the cell proliferation of tissues which is high in the cases of both healthy neonates and patients with malignant tumors, but they most probably reflect the different lipoprotein compositions of neonates, healthy adults, and adults with tumors. © 1989 Academic Press, I

ISSN:0740-3194    

DOI:10.1002/mrm.1910090106

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

年代:1989

数据来源: WILEY

摘要:

Abstract31P nuclear magnetic resonance (NMR) saturation transfer has been used to measure enzymatic flux through the creatine phosphokinase reaction in the direction of ATP synthesis in the human forearm muscleflexor digitorum superficialis. Modification of the ratio method for measurement of spin‐lattice relaxation (R. Freeman, H. D. W. Hill, and R. Kaptein,J. Mags. Reson.7, 82 (1972) was tested and used to appreciably shorten the duration of the measurement. Under conditions of steady state work intracellular pH decreased slightly by 0.06 units and the spin‐lattice relaxation time of phosphocreatine in muscle was unchanged, while flux from phosphocreatine to ATP was 64 ± 10% of the resting value. This is contrary to the increase in flux of 155% predicted from previous saturation transfer studies carried outin vitroon rabbit skeletal muscle creatine phosphokinase using metabolite concentrations to mimic thosein vivo(E. A. Shoubridge, J. L. Bland, and G. K. Radda,Biochim. Biophys. Acta805, 72 (1984). This discrepancy could be accounted for by an underestimation of the ADP concentrations to which the enzyme is exposed due to inaccurate assumptions about the total metabolite concentrations, or possibly by compartmentation of creatine phosphokinase and its reactants. © 1989 Academic Press

ISSN:0740-3194    

DOI:10.1002/mrm.1910090107

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

年代:1989

数据来源: WILEY

摘要:

AbstractInsulin stimulates hexose transport, intermediary metabolism, and cell growth and development. These effects are well‐documented in skeletal but not smooth muscle.31P NMR spectroscopy was performed on rabbit urinary bladders (n=4) to characterize insulin's actions on smooth muscle. The bladder and its vasculature were surgically isolated from the animal and perfused with a PSS/red blood cell perfusate. After a control steady state was achieved (approx 1−2 h), insulin (0.100 mU/ml) was added to the perfusate. Relative levels of intracellular phosphorylated compounds, pH, and free Mg2+were measured and compared to control values. Also, extracellular pH and fractional volume were assessed using phenylphosphonate, a31P NMR extracellular pH and volume indicator. Insulin induced significant increases in PCr (16 ± 9%) at the expense ofPi, intracellular pH ( Δ 0.24 + 0.07 ), and fractional extracellular volume (49 ± 1%). Intracellular free Mg2+and extracellular pH did not change. These results indicate thatin situsmooth muscle is sensitive to physiological levels of insulin. In fact, insulin improves the energy state of smooth muscle cells and the overall tissue perfusion. © 1989 Academic Pre

ISSN:0740-3194    

DOI:10.1002/mrm.1910090108

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

年代:1989

数据来源: WILEY

摘要:

AbstractNuclear magnetic resonance (NMR) spectroscopy provides a unique view of ions through its noninvasive character and relaxation time measurements. Several previous studies have demonstrated that only approximately 20% of cardiac intracellular potassium is visible with current NMR techniques. This study investigates the NMR visible intracellular potassium in a perfused rat heart preparation. When shift reagents were used to separate the intra‐ and extracellular signals, an intracellularT1of 11.8 ± 0.6 ms, and an intracellularT2with two time constants of 1.3 ± 0.6 ms (33 ± 8%) and 10.1 ± 1.9 ms (67 ± 4%) were measured. Curve stripping techniques used to separate the intra‐ and extracellular components of a bulk relaxation decay yielded an intracellularT1of 8.4 ± 0.3 ms and an intracellularT2with two time constants of 1.1 ± 0.6 ms (38 ± 10%) and 8.0 ± 1.6 ms (62 ± 12%). These results demonstrate that there are at least two distinct pools of potassium within the cardiac cell in slow exchange with each other on the NMR time scale. Studies with an enriched41K perfusate demonstrated that the exchange rate for the visible intra‐ and extracellular potassium is on the order of 15 min. © 1989 Aca

ISSN:0740-3194    

DOI:10.1002/mrm.1910090109

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

年代:1989

数据来源: WILEY

摘要:

AbstractWater‐suppressed localized proton NMR spectroscopy using stimulated echoes has been successfully applied to detect metabolites in the human brainin vivo. The STEAM spectroscopy sequence allows single‐step localization by exciting three intersecting slices. Water suppression is achieved by preceding chemical‐shift‐selective (CHESS) rf pulses. High‐resolution (0.05 ppm) proton NMR spectra of healthy volunteers have been obtained on a conventional 1.5‐T whole‐body MRI system (Siemens Magnetom). Volumes‐of‐interest (VOI) of 64 ml(4 × 4 × 4 cm3) were localized in the occipital area of the brain and spectra were recorded within measuring times ranging from I s (single scan) to about 10 min. The experimental procedure is described in detail. Resonance assignments include acetate,N‐acetyl aspartate, γ‐amino butyrate, glutamine, glutamate, aspartate, creatine and phosphocreatine, choline‐containing compounds, taurine, and inositols. Cerebral lactate was found to be at a maximum concentration of 0.5 mMwhen assumingN‐acetyl aspartate in white matter to be 6 mM

ISSN:0740-3194    

DOI:10.1002/mrm.1910090110

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

年代:1989

数据来源: WILEY

摘要:

AbstractGd(DTPA)2−(diethylenetriaminepentaacetic acid) and the polyaza macrocyclic Gd(DOTA)−(1,4,7,10‐tetraazacyclododecane‐N,N′,N″,N′″) are paradigms of general purpose paramagnetic complexes useful for enhancing contrast in magnetic resonance imaging (MRI). It is of both fundamental and practical interest to determine how one might modify the chemical structure of these chelate complexes to improve their utility for MRI in specific circumstances. In the present work, we investigated polyaza methylene phosphonate complexes of Gd3+ions to compare their NMRD profiles with those of their carboxylate analogs and with Gd(DTPA)2−. We find that the numberqof exchangeable water molecules coordinated directly to the Gd3+ions tends to be smaller in the phosphonates, in principle reducing their utility in MRI. However, these phosphonates have a tendency to oligomerize, and the resulting decrease in rotational mobility of the paramagnetic oligomers increases their relaxivity at higher fields, offsetting the effect of decreases inq. In particular, Gd(DOTRP)3−(1,5,9‐triazacyclododecaneN,N′,N″,‐tris (methylenephosphonic acid) would be an increasingly effective contrast agent above ∼ 10 MHz if the oligomerization was stablein vivo(and the Gd3+ions were sufficiently well bound). At lower fields, the relaxivity of these small chelate complexes is dominated by τso, the relaxation time of the spin moments of the paramagnetic ions. We find this to be favorably long for complexes of Gd3+with the macrocyclic phosphonate ligands, as was found earlier by us for Gd( DOTA)−. This situation, ostensibly related to the relatively high symmetry and rigidity of the macrocyclic complexes, can increase the low‐field relaxivity of the phosphonates almost a factor of 2 beyond that of Gd(D

ISSN:0740-3194    

DOI:10.1002/mrm.1910090111

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

年代:1989

数据来源: WILEY