摘要:

AbstractMeasurement of the resonances of glucose between 3.2 and 3.9 ppm in1H NMR spectra from the human brain is difficult due to spectral overlap with peaks from more concentrated metabolites. The H1 resonance of α‐D‐glucose at 5.23 ppm is resolved from other metabolite peaks, but potentially overlaps with the intense water signal at 4.72 ppm. This paper demonstrates that the increased resolution at 4 Tesla permits to suppress the water signal sufficiently to reliably detect glucose directly at 5.23 ppm by1H MRS and the estimated peak intensity is consistent with previous13C NMR quantifica

ISSN:0740-3194    

DOI:10.1002/mrm.1910360102

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe authors report the development and implementation of a water‐suppressedJ‐refocused coherence transfer sequence to observe glutamate in human brain at 4.1 T. The sequence is modeled for I2S2and I2S2M spin systems analytically and plotted for a range of echo times. In this sequence, water suppression and refocusing ofJ‐coupled resonances are achieved through a brief multiple quantum step without significant loss of signal. Phantom data are shown. Human brain spectroscopic imaging of glutamate, acquired with a total echo of 36 ms, demonstrates the application of the sequence to observe gray and white matter differences in glutamate co

ISSN:0740-3194    

DOI:10.1002/mrm.1910360103

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe dependence of functional MRI contrast on the repetition rate (1.5–9 Hz) of a sensory stimulus was investigated with aT2*‐weighted gradient echo method during forepaw stimulation of α‐chloralose anesthetized rats (n= 5). An activation area was observed in the left or right somatosensory cortex dependent on the stimulation of the right or left forepaw, respectively. The activation intensity decreased for stimulation frequencies above 3 Hz, and was negligible at 9 Hz. The interpretation is that at low stimulation rates the neurons can respond to each stimulus, but at higher rates there is insufficient recovery time so that the response is progressively oc

ISSN:0740-3194    

DOI:10.1002/mrm.1910360104

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe purpose of this study was to examine the differential myocardial signal responses due to the blood oxygen level dependent (BOLD) effect in magnetic resonance imaging (MRI) under differing conditions of myocardial oxygen supply and demand. The signal response was measured when myocardial blood flow was increased in excess of oxygen demand or when flow was increased in response to increased myocardial oxygen demand. Normal volunteers were studied using a segmented, interleaved, double‐echo, gradient‐echo sequence at baseline conditions and during pharmacological stress with either dipyridamole (n = 5) or dobutamine (n= 6). Changes inT2* in the myocardium during stress were calculated. Peak coronary flow velocity was measured at rest and during stress using a breath‐hold phase contrast technique. Administration of dipyridamole induced a 124 ± 27% increase in coronary blood flow which resulted in a 46 ± 22% increase inT2*, consistent with a decrease in myocardial venous deoxyhemoglobin concentration as myocardial oxygen supply exceeds demand. In contrast, the administration of dobutamine resulted in a 41 ± 25% increase in coronary blood flow but no significant change inT2* (−5 ± 19%), consistent with a lack of change in myocardial venous deoxyhemoglobin concentration and balanced oxygen supply and demand. Thus, alterations in the relationship between myocardial oxygen supply and demand appear to be detectable usi

ISSN:0740-3194    

DOI:10.1002/mrm.1910360105

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

年代:1996

数据来源: WILEY

摘要:

AbstractMetabolic differences in the content ofN‐acetylaspartate (NAA), creatine (CR), and choline (CH) in cerebral gray and white matter can complicate the interpretation of1H spectroscopic images. To account for these variations, the gray‐and white‐matter content of each voxel must be known. To provide these data, aT1‐based image segmentation scheme was implemented at 4.1 T. The tissue composition of each voxel was determined using the point‐spread function of the spectroscopic imaging acquisition and the segmented anatomical image. Pure gray‐ and white‐matter values for CR/NAA and CH/NAA, and the content of CR, CH, and NAA, were determined using a linear‐regression analysis of 984 voxels acquired from 10 subjects using white‐matter CR as an internal standard. This information was used to establish means and confidence intervals for CR/NAA and CH/NAA from a voxel of arbitrary tissue composition. Using a single‐tailedttest, the extent and locations of the metabolic abnormalities (P<0.05) in a patient with multiple sclero

ISSN:0740-3194    

DOI:10.1002/mrm.1910360106

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

年代:1996

数据来源: WILEY

摘要:

AbstractIn1H NMR spectroscopic studies of fatiguing skeletal muscles, two peaks consistently arise near 1.3 ppm, typically 15–20 Hz apart at 300 MHz. From a variety of NMR and biochemical evidence, both peaks are identified as lactate. Both the CH3and CH protons of lactate experience the same shift in intact muscle; this rules out chemical bonding or complexation. The ratio of intensity of the two methyl peaks varies with muscle type and suggests a correlation with oxidative and glycolytic fiber populations. The shift can be accounted for by the presence of paramagnetic myoglobin in the oxidative fibers. Phantom studies, as well as oxygen, temperature, field, and orientation dependence of the muscle spectra are all consistent with an explanation based upon bulk magnetic susceptibility. It is concluded that the two lactate peaks represent separate contributions from glycolytic and oxidative muscle fiber

ISSN:0740-3194    

DOI:10.1002/mrm.1910360107

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

年代:1996

数据来源: WILEY

摘要:

AbstractIt has been suggested that the anistropy of the water‐diffusion coefficient measured in nerve and in white matter could arise from locally anisotropic background gradients induced by the static field,Bo. By utilizing 1) pulse sequences, which minimize the effects of background gradients, and 2) changes in sample orientation, which would maximize the change in the magnitude of these gradients if present, it is shown that in four excised nerves the background gradients do not play a measurable role in the anisotropy of the water‐diffusion coefficient at a field strength of 2.35 T. The excised nerves evaluated were the olfactory, trigeminal, and optic nerves of the garfish and the sciatic nerve of the f

ISSN:0740-3194    

DOI:10.1002/mrm.1910360108

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

年代:1996

数据来源: WILEY

摘要:

AbstractThis study is the first report on the multiexponentialT2relaxation of the13C‐1 carbon of glycogen. In contrast toT1relaxation, which does not display observable multiexponential decay behavior,T2relaxation is described by a continuous distribution ofT2times. Changes in molecular weight and sample viscosity, which affect the overall mobility of the glycogen particle have little influence onT1andT2relaxation times. This is in contradiction with earlier results thatT2is dominated by the overall motion of the glycogen particles [L.‐H. ZangBiochemistry29, 6815–6820 (1990)].T1depends strongly on the external fieldBoand is almost temperature independent in the range 23–37°C whereasT2is field independent and varies appreciably with temperature. The experimentalT1andT2relaxation data are shown to be consistent with existing theoretical models for relaxation, suitably modified to include a distribution of correlation times for the internal motions. The presence of fast decaying components (shortT2) in the FID implies broad line components in the frequency spectrum and the corresponding need to appropriately set the integration limits for the quantification of the glyco

ISSN:0740-3194    

DOI:10.1002/mrm.1910360109

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

年代:1996

数据来源: WILEY

摘要:

AbstractTo obtain a better understanding of the mechanisms underlying early changes in the brain water apparent diffusion coefficient (ADC) observed in cerebral ischemia, dynamic changes in the ADC of water and in the energy status were measured at postnatal day 8 or 9 in neonatal rat brains after cardiac arrest using1H MRS/MRI and31P MRS, respectively. The time courses of the MR parameters were compared with changes in the extracellular space (ECS) volume fraction (α) and tortuosity (λ), determined from concentration‐time profiles of tetramethylammonium applied by iontophoresis. The data show a decrease of the ADC of tissue water after induction of global ischemia of which the time course strongly correlates with the time course of the decrease in the ECS volume fraction and the increase in ECS tortuosity. This indicates that cell swelling is an important cause for the ADC decrease of wa

ISSN:0740-3194    

DOI:10.1002/mrm.1910360110

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

年代:1996

数据来源: WILEY

摘要:

AbstractProton magnetic relaxation timesT1andT2were measured at field strengths from 0.05 T to 1.5 T in solutions of ferritin with loading factors from 90 to 3600 iron atoms per molecule. 1/T2increased linearly with field strength, as previously observed, and the slope per unit iron was approximately the same in all samples. This latter finding indicates that the field dependence ofT2may be used as a measure of ferritin‐bound iron, regardless of loading factor. A possible explanation is presented, based on the presumed antiferromagnetic structure of the ferritin core and the linear dependence of 1/T2on core magnetization. A nonzero contribution to 1/T2in the limit of low field and a contribution to 1/T1were also found, both of which increase linearly with loading factor for constant protein concentration; these effects represent quantum mechanical dipole‐dipole relaxation of water protons either by iron atoms on the surface of the core or by the iron core itself. Finally, the extrapolated intercept at LF = 0 for both 1/T1and 1/T2indicates a contribution from a small number of iron ions bound to the protein shell. These results may help in the use of MRI to measure brain iron and possibly even ferritin loading fac

ISSN:0740-3194    

DOI:10.1002/mrm.1910360111

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

年代:1996

数据来源: WILEY