摘要:

AbstractA novel approach is presented for imaging macromolecule and metabolite signals in brain by proton magnetic resonance spectroscopic imaging. The method differentiates between metabolites and macromolecules by T1weighting using an inversion pulse followed by a variable inversion recovery time before localization and spectroscopic imaging. In healthy subjects, the major macromolecule resonances at 2.05 and 0.9 ppm were mapped at a nominal spatial resolution of 1 × 1 × 1.5 cm3and were demonstrated to be highly reproducible between subjects. In subacute stroke patients, a highly elevated macromolecule resonance at 1.3 ppm was mapped to infarcted brain regions, suggesting potential applications for studying pathological condition

ISSN:0740-3194    

DOI:10.1002/mrm.1910350502

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

年代:1996

数据来源: WILEY

摘要:

AbstractAlthough Ca2+transport regulation at subcellular organelles is of great interest, only limited methodology has been available for measuring organellar [Ca2+] levels. The present study employs the19F NMR resonance frequency of 4F‐BAPTA to measure free [Ca2+]. In 4F‐BAPTA loaded perfused rabbit hearts, two19F NMR resonances were clearly observed. The frequency of one was consistent with cytosolic [Ca2+] levels. Responses to agents that alter sarcoplasmic reticulum function identified the other resonance as originating from that organelle. The experiments demonstrate the utility of NMR shift indicator methodology in obtaining simultaneous multi‐compartment intracellular [Ca2+] measurements and in enabling organellar [Ca2+] measurements to be made from within intact living t

ISSN:0740-3194    

DOI:10.1002/mrm.1910350503

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

年代:1996

数据来源: WILEY

摘要:

AbstractA paramagnetic Yb(lll) complex that is the prototype of a novel class of probes for MRI and MRS has been developed. The complex displays highly shifted1H resonances that are characterized by short relaxation times and, as such, may prove to be a valuable alternative in applications that currently require fluorine‐containing probes. Selective excitation of the para‐magnetically shifted resonances allows the spatial distribution of the complex to be mapped. This communication reports the images that were obtained by selectively exciting the most intense methyl group (−14.2 ppm at 27°C) for complex concentrations ranging from 0.003−0.1M.Spectroscopically, the complex may be used as a temperature probe since the proton chemical shifts exhibit a strong temperature dependence. In human serum the chemical shift difference of a selected pair of proton resonances was observed to follow a gradient of −0.42 ± 0.01 ppm/°C. Furthermore, since the chemical shift of the methyl resonance displays a temperature coefficient of −0.04 ± 0.01 ppm/°C, it should be possible to use the image phase for

ISSN:0740-3194    

DOI:10.1002/mrm.1910350504

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

年代:1996

数据来源: WILEY

摘要:

AbstractAn adiabatic pulse has been developed to accomplish uniform slice‐selective excitation with a spatially inhomogeneousB1. This new pulse can generate a uniform, arbitrary flip angle that is determined by four adjustable phase shifts in the pulse. Self‐refocused slice selection is achieved by modulating a Bogradient in concert with the pulse frequency (or phase) modulation.B1‐compensated, self‐refocused slice selection is demonstrated in computer simulations and phantom experiments using a surface transmitter/receiver coil. This adiabatic pulse can provide optimal performance in multislice MRI and localized spectroscopy when transmitting with an inhomoge

ISSN:0740-3194    

DOI:10.1002/mrm.1910350505

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

年代:1996

数据来源: WILEY

摘要:

AbstractPhosphorus magnetic resonance spectroscopy (31P MRS) at 1.5 T was performed on nine polysubstance abusing men. All nine patients met DSM‐III‐R criteria for concurrent cocaine and heroin dependence, were neurologically normal, were negative for the human immunodeficiency virus, and had normal clinical brain MRI scans. Patients were scanned 2‐7 days after admission to a drug treatment unit. Eleven age‐matched control subjects also were studied. The ISIS localized phosphorus spectra were obtained from a 5‐cm thick axial brain slice and a 100‐cc white matter volume. In the brain slice, the phosphorus metabolite signal expressed as a percentage of total phosphorus signal was 15% higher for phosphomonoesters, 10% lower for nucleotide triphosphates (β‐NTP), and 7% lower for total nucleotide phosphates in polydrug abusers compared with those in controls. Phosphodiesters, inorganic phosphate, phosphocreatine, total phosphorus, pH, and free magnesium concentration were unchanged. None of these parameters correlated with the methadone dose or the number of days abstinence. Single photon emission computed tomographic imaging of a subgroup of the patients revealed abnormal cerebral perfusion in 80% of the patients scanned. These data suggest that cerebral high energy phosphate and phospholipid metabolite changes result from long term drug abuse and/or withdrawal and that these changes can be detected and stu

ISSN:0740-3194    

DOI:10.1002/mrm.1910350506

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

年代:1996

数据来源: WILEY

摘要:

AbstractWe have developed a method that can measure high‐energy phosphate metabolite concentrations in humans with 1D resolved surface‐coil NMR spectroscopy. The metabolites are measured by phosphorus (31P) NMR spectroscopy, and the tissue water proton (1H) resonance from the same volume serves as an internal concentration reference. The method requires only the additional acquisition of a1H data set, and a simple calibration, performed separately, to determine the ratio of the signal per proton to the signal per phosphorus nucleus. The quantification method is particularly useful for human cardiac spectroscopy, where it eliminates image‐based tissue volumetry and the corrections for signal sensitivity and phase nonuniformity necessary in prior approaches. Corrections are introduced to account for blood and fat contributions to the spectra. The method was validated on phantoms of phosphate of varying concentrations and on the human calf muscle. In calf, the adenosine triphosphate (ATP) and phosphocreatine (PCr) concentrations were 5.6 ± 1.6 (mean ± SD) and 26 ± 4 mmol/kg wet wt, respectively. In normal heart, [ATP] was 5.8 ± 1.6 and [PCr]was 10 ± 2 mmol/kg wet wt. These values are in excellent agreement with prior NMR studies and biopsy data. The protocol is easily accommodated within existing 1D cardiac patient protocols, and the same approach is advantageous for eliminating tissue volumetry and sensitivity corrections when measuring concentrations by 2D and 3D resolved sp

ISSN:0740-3194    

DOI:10.1002/mrm.1910350507

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

年代:1996

数据来源: WILEY

摘要:

AbstractA single‐shot diffusion MRI technique on a standard clinical 1.5T scanner is presented. The method incorporates the following elements: (a) an inversion RF pulse followed by a delay of 1.3 s to null cerebral spinal fluid (CSF) signal, (b) a stimulated echo sequence (TE=56 ms, TM=100 ms) to obtain strong diffusion weighting, (c) a single‐shot gradient‐ and spin‐echo (GRASE) sequence for imaging with a modifiedk‐space trajectory and Carr‐Purcell Meiboom‐Gill (CPMG)‐phase cycle. The trace of the diffusion coefficient obtained with this approach is in good agreement with values reported for animal brain, and for recent human studies. It is demonstrated that single‐shot diffusion imaging of human brain is feasible on an unmodified standard instrument without high‐gradient slew rate or extrem

ISSN:0740-3194    

DOI:10.1002/mrm.1910350508

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

年代:1996

数据来源: WILEY

摘要:

AbstractProton MR spectroscopic imaging (MRSI) of human cerebral cortex is complicated by the presence of an intense signal from subcutaneous lipids, which, if not suppressed before Fourier reconstruction, causes ringing and signal contamination throughout the metabolite images as a result of limited k‐space sampling. In this article, an improved reconstruction of the lipid region is obtained using the Papoulis‐Gerchberg algorithm. This procedure makes use of the narrow‐band‐limited nature of the subcutaneous lipid signal to extrapolate to higher k‐space values without alteration of the metabolite signal region. Using computer simulations andin vivoexperimental studies, the implementation and performance of this algorithm were examined. This method was found to permit MRSI brain spectra to be obtained without applying any lipid suppression during data acquisition, at echo times of 50 ms and longer. When applied together with optimized acquisition methods, this provides an effective procedure for imaging metabolite distributions in cerebral cortical surfac

ISSN:0740-3194    

DOI:10.1002/mrm.1910350509

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

年代:1996

数据来源: WILEY

摘要:

AbstractProton spin relaxation rate constants in normal and hyponatremic rat brain were measured to determine the sensitivity of metabolite relaxation properties to cytotoxic edema and to quantify metabolite concentration in normal and edematous brain. Relaxation rate constants for protons of water and spectral regions with dominant contributions from methyl protons of cholines (Cho), creatines (Cr), N‐acetylaspartate (NA), and lactate (Lac), and for methylene protons of glutamate (Glu) were measured at 7 T. Changes in metabolite relaxation properties associated with cytotoxic edema were a decrease in the Cr longitudinal rate constant, from 0.63 ± 0.02 s−1(mean ± SE) in controls to 0.50 ± 0.03 s−1in edematous brain, and an increase in the transverse rate constant of NA from 5.3 ± 0.2 s−1in controls to 6.6 ± 0.3 s−1in edematous brain. Four hours after induction of hyponatremia, there was a 14% reduction in summed metabolite concentrations of Cho, Cr, and NA, and a 200% increase in Lac signal intensity. It is concluded that changes in both metabolite spin relaxation and detectable spin concentration accompany the cerebral pathology of cytotoxic edema complicated with seco

ISSN:0740-3194    

DOI:10.1002/mrm.1910350510

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

年代:1996

数据来源: WILEY

摘要:

AbstractAt room temperature aqueous solutions of dextrans with concentrations>25% (w/w) exhibit a sol‐gel transition in the presence of>1.0Mpotassium chloride. In dextrans the gelation was unexpected due to missing anionic groups that usually provide the binding sites for cations. The quantitative investigation of the gel formation is based on changes of the diffusibility of water and dextran chains. The apparent diffusion coefficients of bulk water (in the order of 10−6cm2/s) and of water trapped in the junction zones as well as of polymer chains (in the order of 10−7to 10−8cm2/s) are determined by employing pulsed field gradient stimulated echo (PFGSTE) NMR. The restricted diffusion of bulk water in viscous sols and in soft and rigid gels has been quantitatively analyzed providing data for interbarrier distances (pore size), permeabilities of the diffusion barriers (density of junction zones) and interbarrier diffusion coefficients of water. Based on already published x‐ray structure data and in accordance with the diffusion data presented in this paper “potassium‐bonding” is assumed to be the most important interaction for the formation of a microstructure and for the stabilization of crosslinks. The ionic radius of the potassium ion perfectly fits to the cage established by six oxygen atoms of glucose units of three polymer chains. Other cations, such as Li+, Na+, Rb+and Cs+, according to their nonfitting ionic radii, do not provoke dextran gelation under these conditions. The mechanism of the transitions from sol to soft gel and further to rigid gel is discussed on the basis of restricted diffusion and x‐r

ISSN:0740-3194    

DOI:10.1002/mrm.1910350511

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

年代:1996

数据来源: WILEY