ISSN:0740-3194    

DOI:10.1002/mrm.1910300102

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

年代:1993

数据来源: WILEY

摘要:

Abstract31P NMR spatial localization and saturation transfer techniques were combined to enable the transmural measurement of the forward creatine kinase (CK) rate (ATP:creatineN‐phos‐photransferase, EC 2.7.3.2.) in thein vivocanine myocardium. Five epicardial towards endocardial regions of the left ventricle (LV) were simultaneously examined using spatially localized voxels. Although intralefl ventricular CP/ATP ratios were constant, the pseudo first order rate constant (K′) and the forward creatine kinase rate (Rt) displayed a 61% variation across the LV wall. Because CK levels and calculated [ADP], [CP]and pH are transmurally invariant in the normal left ventricle, the observed changes in the Rtcould not be explained by changes in the absolute levels of these substrates and of creatine kinase. In addition, because myocardial oxygen consumption rates are known to be higher in the endocardium, these results imply that forward creatine kinase rates are not directly related to oxidative phosphorylation

ISSN:0740-3194    

DOI:10.1002/mrm.1910300103

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe intracellular to extracellular sodium distribution is one of the primary determinants of action potentials necessary for the electrical function of organs such as brain, heart and skeletal muscle. The ability of shift reagent enhanced23Na MRS to directly measure the intracellular and extracellular sodium distribution in brain is controversial and centers on the relative contributions of bulk magnetic susceptibility and hyper‐fine interactions to the observed chemical shifts. In this study, infusion of dysprosium (111) triethylenetetraminehexacetate (Dy(TTHA)−3), resulted in a23Na MRS spectrum of dog brain with two well resolved peaks at 9 and 0.4 ppm. The 9 ppm peak corresponded to the resonance seen in aspirated blood. After disruption of the blood brain barrier, the single peak at 0.4 ppm split into two peaks at 3 and 0 ppm. The ability of Dy‐(lTHIA)−3enhanced23Na MRS to follow global changes in brain sodium distribution was tested during cardiac arrest. The expected rapid Na influx into the intracellular space produced a marked decrease in the 3 ppm signal and a parallel increase in the 0 ppm peak. This is consistent with the assignment of the 3 ppm peak as interstitial sodium and the 0 ppm peak as intracellular

ISSN:0740-3194    

DOI:10.1002/mrm.1910300104

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

年代:1993

数据来源: WILEY

摘要:

AbstractIn vivo1H MRS can be used to detect and quantify the lactate resonance at 1.3 ppm provided that overlapping lipid resonances are eliminated. A homonuclear spectral editing method was developed to acquire uncontaminated1H spectra of lactate with adiabatic pulses. An advantage of the adiabatic pulse sequence is the ability to induce uniform flip angles and to maximize sensitivity in applications employing surface coil transmitters which produce highly inhomogeneousB1. Glycolytic activity in an intracerebral C6 glioma in rats was monitored by using adiabatic editing sequences to observe [3‐13C]lactate produced from infused [1‐13C]glucose. Acute hyperglycemia (serum glucose>22 mM,n= 10) had no significant effect (P= 0.08) on the total ([12C]+ [13C]) tumor lactate signal intens

ISSN:0740-3194    

DOI:10.1002/mrm.1910300105

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe response of the myocardium to prolonged or chronic ischemia may differ from the well documented changes that occur acutely subsequent to the onset of hypoperfusion. Therefore, we have examined in an instrumented canine model and using spatially localized spectroscopy to achieve transmural differentiation, the myocardial HEP andPilevels as well as wall thickeningin situduring prolonged ischemia induced by sustained coronary artery stenosis. The results demonstrate that subtotal coronary artery occlusion causes immediate andtransmurallyinhomogeneous decreases in the myocardial HEP content and increase in thePi/CP ratio; however, during prolonged mild hypoperfusion, metabolic changes occur which lead to statistically significant recovery of CP (but not ATP) and disappearance ofPidespite the persistence of reduced blood flow and oxygen supply. Upon release of the occlusion, the previously ischemic muscle recovered blood flow, and some (but not all) of its preischemic contractile function without parallel changes in the HEP levels. It is concluded that normal HEP andPilevels cannot be equated with either the absence of underperfusion orinsensitivityof NMR spectroscopy to ischemia. Rather, it is imperative that bothfunctionalandspectroscopicmeasurements are performed simultaneously to distinguish between ischemic myocardium which is adapted versus unadapted to the hypoperfusion.

ISSN:0740-3194    

DOI:10.1002/mrm.1910300106

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe1H NMR spectrum of the macromolecule fraction of rat brain cytosol was investigated following centrifugation and dialysis to remove low molecular weight metabolites and peptides (<3500 daltons). At least seven well resolved resonances were detected between 0.9 and 3.0 ppm in the1H NMR spectrum of rat brain cytosol after dialysis, several of which cannot be observedin vivodue to overlap withN‐acetylaspartate, glutamate, glutamine, creatine, and yaminobutyric acid. Several cross‐peaks detected in 2D COSY spectra of the cytosolic macromolecule fraction coincided with those measured in a previous study of rat brain tissuein vitroandin situ(K. L. Behar, T. Ogino,Magn. Reson. Med.17, 285 (1991)). Treatment of the cytosolic macromolecule fraction with a nonspecific protease permitted partial assignments of resonances in the1H NMR spectrum to specific amino acids. Fractionation of the dialyzed cytosol of rat brain by gel filtration yielded qualitatively similar1H NMR spectra for elution volumes corresponding to molecular masses from 12.5 kDa to over 100 kDa. The results indicate that many of the background nonmetabolite resonances observed in the1H NMR spectrum of normal brain tissue arise from cytosolic prote

ISSN:0740-3194    

DOI:10.1002/mrm.1910300107

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe intrinsic phosphocreatine (PCr)T1values measured by time‐dependent magnetization transfer in isolated perfused rat, hamster, and turkey hearts were indistinguishable. The value of 3.5 ± 0.3 s for the rat heart is similar to values measured by other magnetization transfer methods. Irreversibly inhibiting the phosphoryl exchange between PCr and ATP in the rat heart using iodoacetamide changed the apparentT1values of the two exchanging species when measured by inversion recovery: The apparentT1of PCr increased from 1.92 ± 0.06 s to 3.55 ± 0.06 s, in excellent agreement with the intrinsicT1, measured by magnetization transfer. The apparentT1of [γ‐P]ATP decreased from 0.92 ± 0.07 s to 0.44 ± 0.03 s. The value for theT1of [γ‐P]ATP in hearts with inhibited phosphoryl exchange was similar toT1values for [α‐P]ATP and [β‐P]ATP, which remained unchanged. This illustrates that apparentT1values for PCr and [γ‐P]ATP measured by inversion recovery in the presence of exchange are averageT1values in between the intrinsic values. The large differences between the intrinsicT1measured by magnetization transfer and theT1measured by inversion recovery makes the use of the appropriate value in different applications qua

ISSN:0740-3194    

DOI:10.1002/mrm.1910300108

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

年代:1993

数据来源: WILEY

摘要:

AbstractPartial Fourier reconstruction algorithms exploit the redundancy in magnetic resonance data sets so that half of the data is calculated during image reconstruction rather than acquired. The conjugate synthesis, Margosian, homodyne detection, Cuppen and POCS algorithms are evaluated using spatial frequency domain analysis to show their characteristics and where limitations may occur. The phase correction used in partial Fourier reconstruction is equivalent to a convolution in the frequency domain and the importance of accurately implementing this convolution is demonstrated. New reconstruction approaches, based on passing the partial data through a phase correcting, finite impulse response (FIR), digital filter are suggested. These FIR and MoFIR algorithms have a speed near that of the Margosian and homodyne detection reconstructions, but with a lower error; close to that of the Cuppen/POCS iterative approaches. Quantitative analysis of the partial Fourier algorithms, tested with three phase estimation techniques, are provided by comparing artificial and clinical data reconstructed using full and partial Fourier techniques.

ISSN:0740-3194    

DOI:10.1002/mrm.1910300109

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

年代:1993

数据来源: WILEY

摘要:

AbstractFast spin‐echo imaging has been investigated with attention to the requirements and opportunities for high‐field MR microscopy. Two‐and three‐dimensional versions were implemented at 2.0 T, 7.1 T, and 9.4 T. At these fields, at least eight echoes were collectable with a 10 msTEfrom fixed tissue specimens and living animals, giving an eightfold improvement in imaging efficiency. To reduce the phase‐encoding gradient amplitude and its duty cycle, a modified pulse sequence with phase accumulation was developed. Images obtained using this pulse sequence exhibited comparable signal‐to‐noise (SNR) to those obtained from the conventional fast spin‐echo pulse sequences. Signal losses due to imperfections in RF pulses and lack of phase rewinders were offset in this sequence by reduced diffusion losses incurred with the gradients required for MR microscopy. Image SNR, contrast, edge effects and spatial resolution for threek‐space sampling schemes were studied experimentally and theoretically. One method of samplingk‐space, 4‐GROUP FSE, was found particularly useful in producing variedT2contrast at high field. Two‐dimensional images of tissue specimens were obtained in a total acquisition time of 1 to 2 min with in‐plane resolution between 30 to 70 μm, and 3D images with 2563arrays were acquired from fixed rat brain tissue (isotropic voxel = 70 μm) and a living rat (isotrop

ISSN:0740-3194    

DOI:10.1002/mrm.1910300110

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe principles of a fastT2*‐sensitized MR imaging method (Moonen et al.,Magn. Reson. Med.26, 184 (1992)) are extended to further increaseT2* sensitivity. It is shown that the period of T2*‐weighting can be lengthened bynTR‐periods by appropriate gradient schemes without RF refocusing resulting in progressively delayed gradient‐recalled echoes. This extension of the echo‐shifting concept thus introduces large flexibility in the choice ofT2*‐weighting without changing total imaging time. The coherence pathway formalism is used to evaluate and describe the selection of the desired echo and the attenuation of unwanted coherences. The new techniques are demonstrated for tracking a bolus of susceptibility contrast agent in cat brain. Relative blood‐volume maps are derived with expected contrast between white an

ISSN:0740-3194    

DOI:10.1002/mrm.1910300111

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

年代:1993

数据来源: WILEY